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Title 24 2016: LIGHTING (residential)

Title 24 2016: LIGHTING (residential)

The sun sets on Edison.


Do you care?  Yes, you do.

A quote I found on google that evokes the existential importance of Light in your work and Works.

“Light is of decisive importance in experiencing architecture. The same room can be made to give very different spacial impressions by the simple expedient of changing the size and location of its openings.”

– RASMUSSEN, S. E. (1962) Experiencing architecture (1)

Title 24 2016!!!?  Isn’t that gonna be in effect in…. like … 3 from now?!  Didn’t the 2013 code just come out?

Perhaps those are questions you didn’t ask, but I’ll answer them anyway.

Yes, it might feel a long way from now, but I think what’s currently drafted into the 2016 code will significantly change lighting as it’s designed and installed into new and renovated homes.  In a nutshell, what I’m seeing drafted is that at Final Inspection, there will be no ‘low-efficacy’ light installed in the house.  NONE.  No halogen MR16 halogens that constellate living room ceilings.  No incandescent lamps in art fixtures which render tessellated patterns on future Mondrian installations.  Not even a bedroom reading lamp.


The future will be lit with fluorescents and LEDs, at least in California.



Verschiedene_LEDs.jpg” by Afrank under CC BY-SA 2.0

For many of you in the practice, I suspect that this is fine.  You’re already deploying LEDs and fluorescents in most of your projects.  And you only use halogens and incandescents for specialty applications.  You’ll learn to find high-efficacy sources for those Specialty applications, and you’ll learn what works and what doesn’t along the way.

But perhaps some of you haven’t been totally satisfied with LED’s yet.  The inexpensive ones have decent specs (like color temperature), but they still seem like what would happen after 3 generations of photocopying an incandescent.  A jaundiced or weirdly bluish half-blooded lamp.  Pat Boone when you really wanted Fats Domino.

And then there’s cost– the decent ones cost an arm and a leg, and the really good ones seem to be priced at the level of a kidney or a liver.

Either way– new technology means new understandings and intuitions about achieving a consistent aesthetic outcome.  And new understands of cost vs. performance and that eternal question of what’s gonna be ‘good enough’ for that client in that specific application.

Well, now the writing on the wall is being drafted, and that wall will only be legible from permanently installed fixtures using high-efficacy sources in the 2016 code, according to the California Energy Commission.


Caveats and Context

Now that I’ve probably long belabored the point of why you actually should care, let me point out a few things early on for where this might or might not apply.

Might:  the Pen is more subjunctive than the sword?

While these changes are in draft form, they still could change.  The CEC is drafting these documents and will probably finalize them in June of this year (2015).  I would encourage any reader with an opinion to send your well-articulated arguments  to the CEC.  Send your e-missives here:  docket@energy.ca.gov

Your comments, both individually and collectively, may in fact carve out exceptions or other flexibilities in this draft language, if that’s what you desire.

Permanently installed lighting:

Note how I mentioned this qualifier a couple of times.  Well… the building code pertains to things that are permanently installed in the building, and would be present at the time of final inspection.  And ‘permanently installed’ is the general purview of Architects.  Portable fixtures that are installed after final CO are clearly not captured under these rules, as they are done by ‘occupants’ and not a part of the asset of the house.

So can your clients still bring in their plug-in halogen lamps and melt their faces with 1.00,000 lux of full-spectrum bliss in their Master Bath mirrors?  Yup…  If the homeowner lugs it in, they can plug it in, and may the circuit be unbroken.



Speaking of Mondegreens–I’ll mention one the most common, and one of my favorite.

In Creedence Clearwater Revival’s “Bad Moon Rising”, the chorus goes “There’s a bathroom on the right”.  I always thought that the title referred to those are less than callipygous



On to the draft language:

 Code language in underlined italics

  • 150.0(k)1 says

    • A. Luminaire Efficacy: All installed luminaires shall be high-efficacy in accordance with TABLE 150.0-A.

    • Table 150.0-A just says effectively defines (by reference) what they mean by “high-efficacy”

  • 150.0(k)1.Cv Recessed Luminaires in Ceiling…:

    • Shall not (emphasis mine) contain screw based lamps.

    • They seem to be trying to prevent homeowners installing any kind of screw-base incandescents later on.

  • G. Screw based luminaires. Screw based luminaires shall meet all of the following requirements:

    • i. The luminaires shall not be recessed luminaires; and
      ii. The luminaires shall contain lamps that comply with Reference Joint Appendix JA8; (in other words– high efficacy)

    • iii. The installed lamps shall be labeled as compliant with JA8.



I’ll reiterate what I led with in this article, but now with more nuance:

When the inspector comes out, she’s going to see only non-screw based lamps recessed into the ceiling, and any other light (sconce, pendant, whatever) could have a screw-based luminaire but will have a high-efficacy lamp installed.  What happens after the inspector signs off is up to (and always has been) to the homeowner/inhabitants.  So, if the homeowner wants to take on their own retrofit of all the high-efficacy lights and put in whatever toaster-oven filament lamp they want, then that’s their prerogative.  So, that might be your escape hatch as a Designer.  Spec the fixtures that keep options open for the homeowner down the road and do your best with finding attractive lamps that don’t have to be changed out.

Commission by Ommission:  Kitchen lighting wattage 50%

In case you didn’t notice, the 50% wattage rule that you may have now hard-wired into your brain since 2001 is now gone.  Given that all lights are supposed to high-efficacy, it’s obsolete. and so the Draft has completely struck all that language.

Implications for Design/Construction practice

It seems now that the Design/Construction world is being pushed into the future and into all the vagaries of high-efficacy lighting.  I’m sure you’ve heard many homeowners have emotional responses to the word “fluorescent,” and usually followed by ‘over my dead body.’  People don’t have that same emotional response to LED’s because they’re newer, but my personal experience has occasionally been worse than fluorescents in terms of quality of light.

In short, without incandescent lights, we don’t have a ‘safe’ choice to somehow integrate universally approved lighting.  Our new choices have problematic reputations– here are some that probably sound familiar to you.

— inferior color rendition (even for high CRI lamps)
— limited dimming capability: the lights just don’t work well on dimmers, and don’t change to warmer colors as they dim.  Most they just dim slightly and then cut out
— long warm-up times: CFL’s in closets take 1-2 minutes to achieve 100% light output.
— lifetimes don’t measure up:  lamps fail after just a few thousand hours.

Coalescing industry standards for quality

So now it’s up to you to specify a lighting system that won’t disappoint the homeowners.  Well… you’re gonna have some help from the Regulators.  The LED industry is a pretty new one, and it’s taken some time to figure out pertinent and meaningful standards to apply to the technology.  It still feels a bit like the Wild West out there, where you’re really not sure what to expect when you purchase a new fixture or lamp.

Fortunately, the CEC, Dept. of Energy, and industry tradegroups are actively trying to improve these standards of performance so that it’s not so hit-and-miss.

Here are some things they’ve included:


  • JA8.4.4 Color Temperature

    • The light source shall be capable of providing a nominal Correlated Color Temperature (CCT) that is 3000 Kelvin or less and within 0.0033 Duv of the black body locus in the 1976 CIE color space

  • JA8.4.5 Color Rendering

    • The light source shall provide a Color Rendering Index (CRI) of 90 or higher and color rendering R9 value of 50 or higher.


All high-efficacy lights (with a few exceptions of course), are required to be of good quality– 3000 K (“Warm White”), and CRI of 90+.  And how about that R9 value of 50 or higher?  It turns out that the original ratings of CRI only required adherence to some, and not all of the visible spectrum.  And manufacturers could exclude such subjectively important colors as Strong Red, and other saturated colors when they were paying for CRI ratings on their lamps.  These colors could also be described as the colors which make us look like a humans on full-complexioned on a bright sunny day.  Without these saturated colors, we might look pallid, wan, and more like where the sun doesn’t shine.


Table source: Wikipedia– http://en.wikipedia.org/wiki/Color_rendering_index


We love dimming, so the CEC has also included requirements to manufacturers that the lamps operate reasonably well when dimmed.  They’re supposed to not noticeably flicker when dimmed 90%, and also not emit a bunch of electromagnetic noise such that you can’t listen to your AM radio through the buzz and interference.


Lumen Maintenance

Neil Young– “It’s better to burn out, than to fade away”

Well… old LED’s lamps never die, they just grow dimmer.  You’ll see all that marketing language around LED lamps lasting 50,000 hours or whatever.  Some of that language has been ignorant, or perhaps even dissembling about how much of your lamp’s output will be left after 50,000 hours.  It’s one thing if it degrades to 90% of its original output, and another thing entirely if it degrades to 20%.  This gradual dimming effect is called “Lumen Maintenance”.

The CEC has therefore included performance requirements which are supposed to prevent some of the more egregious examples of this effect in LED’s.

There are bunch of other performance and labeling requirements that I don’t think y’all will find as interesting, but you can dig into the standards here:


Known unknowns

Will there be aesthetically attractive and low-cost lamps in the future?  Will the technical issues in User Experience of the New Lights be resolved?  Will the lighting manufacturing industry step up to provide us consumers of lamps with plentiful options?  In the long run, most prognosticators agree that we should be able to work out most of the kinks with these new technologies.  But, as John Meynard Keynes said “in the long run, we’re all dead.”

By legal fiat, we’re moving into the future of lighting, and it behooves us all to get comfortable with new technologies in our industry, regardless of the impetus.

Signing off.


PS–  If you think I’ve misinterpreted something, or missed something entirely, feel free to send me any comments/questions/non-spam to the following address:   luke (..at..) petemoffat.com
It took a long time to peruse the code, and it wouldn’t be surprising if I didn’t get it 100% right.

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Metal windows behind bars in Title 24 2013?


Skip this introduction if you:

  • Know that Title 24 2013 edition went into effect on July 1st, and the dust is still settling over this.
  • Have heard that there are new SUPER HARD requirements on windows and the California Energy Commission is painting V’s (for vendetta) on all those new metal windows.
  • Are freaking out because you think that the CEC wants to legislate us to live in Brutalist Boxes with tiny windows for state-mandated quotas of air and light

End Introduction (and all that John Birch Society-sounding nonsense).

Two sentence summary:

The new rules say that if you spec some mediocre windows that don’t meet the new minimum performance, you can only  to make up for them with GOOD windows that are a lot better than minimum performance.  So, if you want that window-wall system in the great room that’s all metal, then just expect that you’ll have to go with a really double or even triple glazed window in a good frame everywhere else.  What you CAN’T do anymore is think “ahhh well the radiant floor should make up for that aluminum and glass heat highway”.

ok– that was 3 sentences– crap, now 4.5 since this isn’t an actual sentence with a clear subject and predicate.

And I of all people should know about sentences:

The Meat

What the 2013 Energy Code ACTUALLY says about fenestration thermal performance is quoted below.  Note that it ONLY applies to Low-Rise Residential.  In all other project types, this mandatory minimum performance does not exist.


Title 24 part 6 Building Energy Efficiency Standards
Section 150.0 (q) of Fenestration Products. Fenestration separating conditioned space from unconditioned space or outdoors meet the requirements of either Item 1 or 2 below:
1. Fenestration, including skylight products, must have a maximum U-factor of 0.58.
2. The weighted average U-factor of all fenestration, including skylight products, shall not exceed 0.58.

EXCEPTION to Section 150.0(q)1: Up to 10 square feet of fenestration area or 0.5 percent of the Conditioned Floor Area, whichever is greater, is exempt from the maximum U-factor requirement.

*Reminder of U-factor:
U-factor is the measure of how easily heat flows through the window. The units are BTU/[hr-sq.ft.-degF].  Higher U-factors conduct more heat. The opposite of U-factor in the building industry is R-value. A U-factor of 0.58 is an R-value of 1 divided by 0.58, which is R-1.72.

What the CEC is mandating here is that windows must meet an overall minimum thermal performance. A U-factor of 0.58 is about what a mediocre wood window is. A double pane metal window might be upwards of 0.77 U-factor, which by itself wouldn’t comply. Those old single pane aluminum windows are upwards around U-factor of 1.00– in other words, pretty awful.

Note Item 2 says “Weighted Average”:
You can do whatever windows you’d like, but you have to prove that the weighted average U-factor is less than 0.58.  And that’s usually not as hard as you think.

That works like this:
It’s a brand new house, and you have 100 sq.ft. of old aluminum single-pane windows that you found at the junkyard. Let’s assume they’re U-factor of 1.00.
And then you have some really nice fiberglass triple-glazed windows that are Passivhaus certified in addition to NFRC-rated. Their U-factor is 0.15.
Those 200 sq.ft. of windows are all you have in the house.
Would these windows comply? Let’s find out…..

100 [ft^2] * 1.00 [U-factor]= 100 [UA]
100 [ft^2] * 0.15 [U-factor]= 15 [UA]
Now let’s add the [UA] Factors and divide by the total area of the windows
(100 [UA] + 15 [UA]) / 200 [ft^2]= 0.575

0.575 is less than 0.58, so the energy code allows you to use those old aluminum windows from the junkyard.  That doesn’t mean other sections of California code will, though.

If you redo the math with the high-performance windows at a U-factor of 0.20, then it doesn’t work anymore and you might have to rethink that junkyard purchase.

10 sq.ft. exception? huh?
Well the CEC and commentors threw in a little exception for 10 sq.ft. of whatever you want. That actually came from sidelites by the front door. Those often come in single pane, for whatever reason, so the CEC gave the tract home builders of California a way to keep their sidelites without incurring penalty. Or if you have a 10,000 sq.ft. house, you can use the 0.5% factor. That’ll give you 50 sq.ft. of ‘free’ window area, that you can do what you want with.
…It pays to have lobbyists.

Proving your case(ment)
If you have a house where you want to use ALL metal windows, then you can’t without proving that the overall performance is better than 0.58.
So how do you do you prove it.
Well, there are a couple of ways. But they all boil down to 4 letters: NFRC.

NFRC stands for the National Fenestration Rating Council, and their job is exclusively to evaluate the thermal performance of fenestrations (windows and doors with window and skylights and just about anything with glass in it).

Through software and hardware testing magic, they provide 3rd-party verification for manufacturers that windows perform to a specific level. If the window is tested through NFRC methods, then the CEC allows you to use whatever U-factor that NFRC comes up with. It doesn’t matter if the window is made out of wax and Plastic wrap, you can use the NFRC tested values to comply with the above section of code, though you may have other problems.

What if you don’t have NFRC numbers?
Well– then you’re at the mercy of

Here’s the table in the code:


You see all those numbers above 0.58?
Yeah…. that’s gonna be a problem if you’re building a new house with non-NFRC rated windows.


Back to the big picture:
Ok– so your windows are less than 0.58, everything;’s good right?
Well, no not necessarily. You still have to have your whole HOUSE pass title 24, and if you’re using mediocre windows, then you’re gonna have to make up for their performance with some other efficiency measures.

You see– the ‘standard’ window now in California takes its inspiration from some good-ol’ vinyl frames with decent glass. It’s somewhere around U-factor of 0.32. So, if you’re worse than that you’ll have to make up for it elsewhere in your house.

That’s a whole other blog post.

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Embodied Impact of Materials: Two rules of thumb

If you’ve been in the green building world for a while, you’ve probably wondered about the embodied environmental impact of all the materials and such that goes into our built environment.  And, in my research about the topic, I’ve found some things that might be more helpful than the in-depth analyses that we’re relegated to for our projects.  Given the cost of doing said analyses, we usually don’t do them.
The first challenge that we confront is about metrics.  Mostly we hear about ’embodied energy’, and I’ll stake out a polemical position here: Embodied Energy is a stupid metric.  I challenge any of you reading this to tell me how embodied energy is either relevant or even quantifiable as an environmental impact indicator.
I suspect many of you might say “but do you know how many barrels of oil went into that spray foam” or “how many tons of coal go into concrete?”
And with those suggestions, it’s not the energy content of energy source you’re worried about, it’s the environmental impacts with the extraction and combustion of said fuels.  At least you’ve cited materials that have quantifiable energy inputs– since that’s in the form of fossil fuels which we’re very good at quantifying since the stuff isn’t free.
So– let’s talk about some different metrics.
How about “embodied fossil fuel energy”
or–Embodied Emissions of Particulates of less than 2.5 microns
or–how about one that’s easy to get behind and global:  Embodied Greenhouse Gas emissions
For the rest of this, I will be talking about Greenhouse gas emissions, because that’s one that’s well understood, and hopefully going to be well regulated someday soon.
Rules of Thumb:
Alright, with metrics out of the way, let’s talk about some rules of thumb about how to think about embodied GHG emissions without spending a lot of money sifting through numbers that we’ll quickly be overwhelmed by.
First rule of thumb:
All other things being equal, more money=more environmental impact.  
This should seem sort of obvious– people don’t screw up the environment for free.  We’re paying them to do it so we can get our cars fueled up and our cell phones charged.
Of course, there are a whole host of caveats and distorting factors to this– government subsidies, differing environmental impacts of different industries and services.  But the basic notion still holds true.
This is why the per-capita environmental impact of people in the first-world is so much more than that of third-world countries.  People who spend only a little money (e.g. the world’s poor) have a small fraction of environmental impact relative to us here on the top.
Ok– so being cheap is a virtue, but we know that’s not sufficient.
This notion is formally captured in the following database, hosted by Carnegie Mellon– called Environmental Input-Output Life Cycle Assessment: Think of it as a sort of GDP country-wide assessment of environment impact.
Here’s a website where you can look through it for free– at Carnegie Mellon University.
This at least gives you the power to see what the environmental impact associated with generally with spending in certain parts of the economy.  For example– what are the environmental emissions involved with spending $100 in the “food/beverage/tobacco” industry?  You probably never asked that question, but you can get answers there!
Of course, the main challenge with a tool like this is that it isn’t product or sector specific enough to empower you to choose among different products/services within a defined sector.  And it will never be specific enough to get down to individual brands.
Second Rule of Thumb:  Less weight is better in construction
I did a non-academic study several years looking at a selection of 10 single-family residential projects that my firm had designed over the previous years, and specifically comparing it to our LEED-Platinum project.
In our research, we evaluated houses that ranged from 900 sq ft. to 9000 sq. ft.:
And we found something interesting (and don’t you dare take this out of context):
Our smallest house didn’t have the lowest embodied footprint, and neither did our largest house have the biggest footprint.  The highest embodied footprint went to our LEED-Platinum house, and the 3rd largest footprint went to a house with about half the square footage.
What?  How!
Well– to rephrase the “size doesn’t matter” phrase, let us now say SIZE ISN’T MATTER.  If we step back, it’s kind of patently ridiculous that we think that taking the area of the floor plane of conditioned space has anything but a very crude bearing on the embodied impact.  Such impact is simply not defined by space– since we all know that space is defined as the absence of stuff.  Rather, it’s the stuff that we use to define that space/volume that has the environmental impact.  It’s the sheetrock, the wood framing, the stucco, the metal lathe, the insulation, etc.  And all that stuff is MATTER.
Since it’s the stuff that matters, that’s how we found the stuff that has less matter has less environmental impact.  All of the houses with the highest footprints had a ton of concrete.  And by ‘ton’ of concrete, I mean actually 10’s and ‘100’s of metric tons of the stuff.  They were built like fortresses, and they’ll probably last for eons if even a modicum of maintenance is performed on them.
The houses with the lowest embodied footprint (I’m thinking of Greenhouse Gas emissions especially– just to remind you) were all light-framed construction.  They were all wood covered with wood cladding and a light layer of sheetrock.  The space/volume/floor area that they defined varied widely.
Durability: is it worth the gamble?
Many of our projects were built like fortresses in part for durability’s sake.  Heavier things tend to be more durable.  Brick as a siding material is much much more durable than cedar shakes.
But is it worth it to incur the environmental cost of brick (kilned with natural gas) than to go with a less durable siding.
The devil is in the details.  We found with our crude calculations (performed through the Athena Impact Estimator software) that the embodied GHG impact of clay roof tiles was worth 4-5 changes of cedar shakes.  In other words, if the clay tiles would pay back after about 80 years relative to the cedar shakes.  Is that worth it?  maybe…
I say– good look designing a building that lasts 80 years.  It’s not a question of durability of materials, but a durability of purpose– or a building that ‘learns’.  Of course, that’s a whole other subject that I’m not at all equipped to handle.
Summing up:  here’s a crude recipe for a low impact house:
Build it light
Build it cheap
(Operational Energy) Build it well insulated (insulation is mostly air and therefore isn’t heavy, and most insulation isn’t expensive).  A well insulated house shouldn’t need additional heating.
(Operational Energy) For every energy service your house provides (e.g. refrigeration, cooking, entertainment, lighting):  make it efficient and mostly turned off.
Contradictions, inconsistencies, fallacies?
If you’ve been following on and thinking carefully here, you’ll find a number of tensions, and apparent contradictions and all sorts of other problems.  I can say that at least for some of these questions, I’ve purposefully left them in here, since I’m approaching some complex systems with some crude findings.   Feel free to email me with anything that still seems really wrong (luke … at .. fgy-arch.com)
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07–Sleepless with Stack Effect

Sleepless with Stack Effect:
How natural cooling with stack effect failed me…

Hi all,
It’s the summer season and I thought I would spend a little bit of time on the cooling your house in the summer by cycling fresh outside air to cool your house.

During a heat wave recently, I discovered how natural v]]entilation was actually the most ineffective way to cool down my room and resulted in a number of sleepless nights.
In particular– there are a couple of points I’d like to make, and these will, of course, specific to the temperate mid-to-southern California climate.
— For our heat waves, we often hear that   just opening up your windows at night and closing them during the day will help cool your house.  That is most definitely true, but I’ve found in projects that I’ve worked on that such natural cooling strategies may not work as well as you would hope.  And it’s all in the specifics.

First– let’s look at possibilities:
The following “carpet” shows annual hourly temperatures.  The red’s are mostly in the summer (notably September which is around the equinox!), but it shows that even at night during those heat waves, there’s still some cooling that can be done if let in the outdoor air.

And this is just an indication of “stack effect” which uses the bouyancy of hot air inside the home to create pressure differences and effectively make.  We all know probably know how this should work.  Open up the windows up above and down below and you get a nice circulation of air.  Just like this:

Ok– Cool!  We’ve got a nice breeze induced in the house.  We could do fancy math and calculations and figure out how much effective cooling we’re doing , but in the meanwhile we’ll just lie in our bed (which I expect is upstairs) and feel the night breeze cool us, right?

Yeah– not so much, as I experienced.

No, in fact the house I was in induced a rather lethargic and hot breeze up in my bedroom.  I got no fresh air from the outside, and only stale warm air from the house.  I even smelled some of the leftover fish fry from earlier that night.   

Stack effect is my enemy! 

So why isn’t the air getting cold in my bedroom upstairs?

Well– I happened to be in a fairly massive house.  By massive, I don’t actually mean square footage– I actually mean MASS, as in heavy.  Heavy things tend to act as effective “thermal mass” which means they can soak up, retain, and bleed off a lot of heat.

What happened was that the hot air leaving out of the window in my room was resulting in a LOT of cold, fresh, comfortable outside air coming into the house.  It was just coming down into the windows on the 1st floor in the middle of the kitchen.  As it passed down the hallways, up the stairs, and back down another hallway toward my room at the end of the hall, it was effectively warmed up by the inside mass and so all I got was the mass-heated stale air from the 1st floor of the house.  Of course, what I really wanted was the reverse.  I wanted to bring the cold in up TOP (into my bedroom) and the warm air to go outside wherever.   And for that, I can’t really use stack effect.


What about wind effect?

Well– one thing you may notice about wind during heat waves is that you usually have a high pressure system thing going on (countercyclonic) and if you’re sitting right in the middle of that atmospheric phenomenon, there often isn’t nary of gnat’s fart of a breeze going on.
But if there were, then that would probably change things substantially, if intermittently.  If we had a reasonable breeze, it would probably overwhelm the stack effect pressure and reverse the flow well enough when it’s gusting.  And that would probably be good enough to get some outside air into my room.

But, no– no breeze was present.


Answer:  an artificial breeze

So– we want a breeze in my bedroom.  Great!  Provide some way of negatively pressurizing my room (or the whole house) and we can induce a breeze through my window.  And that’s called a whole house fan

Yes– I took a standard floor fan and put it up against a window at the other end if my hallway (far away so that I couldn’t hear it).  I then closed up all the windows except for the one in my bedroom and let ‘er rip.  Booyah!  Instant cold air in my bedroom where I wanted it.

Of course, I had to have a free air path between my window and the fan to make sure that air could freely move between my room and the fan– hence moving it way down the hall so there could be a reasonable amount of sound attenuation.

Challenge question:  Could I put the fan on the first floor instead?

Sure!!   This may strike some people as totally wrong, cuz doesn’t hot air rise?  Well that’s stack effect, and yes hot air will rise, but it will also convect any way we give it a reason to.  Stack effect bouyancy is pretty weak– on the order of 3-5 pascals.  Fans can do a bit more than that– even a small one could probably induce 10-20 Pascals pressure difference, and that’s enough to easily overwhelm the relatively weak stack effect.

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06– Exploring Stack Effect

I’ve been thinking a bit lately during our recent hot weather about Stack Effect.  And, I’ve been trying to get it to work the way I want it to in my house, and it’s been trickier than you might expect to get what we want out of it.

So, let’s start with the basics– we’ve all heard about the power of Stack Effect.  On a hot day, we hear how hot air rises and cold air comes in to takes it’s place.  It’s a nice little cycle, and it seems pretty straight forward, right?  Well, let’s talk about it a little more formally:

Stack effect generally relies on lots of factors, but in a building, we can simplify these factors to the following:

  • Temperature difference between inside and outside
  • Height of the building
  • Size of openings and air pathway between inlet and outlet
  • Stack effect in low-rise buildings is usually small, and often intermittent.   But it can be a useful way of exchanging air with the ambient environment.
  • Its intermittency makes it a poor choice for fresh air ventilation.
  • Many designers do not sufficiently explain to occupants for how to deploy stack effect usefully in low-rise residences, and therefore such strategies are poorly deployed or ignored altogether.

This diagram is an example of how many people understand stack effect.  The hot air rises outside of the 2nd floor, and then the cold air comes in to the 1st floor underneath.  In terms of building physics, this is expressed in terms of pressure differences.  The air on the 2nd floor is at a relatively higher pressure to the outside, and therefore finds itself ‘equilibriating’ preferentially to the outside.  In other words, the hot air upstairs gets pushed out of the open window (or some other hole in the building envelope) up there while the cold air pushes itself into the 1st floor (which finds itself under slightly negative pressure to the outside).

A couple of things to note here, which may seem obvious, but I’ve seen neglected:

  • The flow of cold air in below on hot air exhausting above depends on openings at both ends as well as an open pathway for air in between.  Having only one part open (high side or low side) without the other defeats the majority of any stack effect.  Also– if there is no clear pathway for air to travel (and it doesn’t have to be big), then you will mostly block this effect.
  •  The place that will get the least amount of cool outside air flow from this is the 2nd floor.  As the hot air rises out of the house and the house cools, then the flow will also reduce.  The most flow will happen when the 2nd floor is the hottest and that will occur at the 1st floor inlet.


Now– here are some findings about why stack effect often doesn’t work in houses that consider it at the design phase as a design strategy.

  • For any air to exit, there must be the same amount of air coming in somewhere else.  That means there must be two openings for a good exchange with the outside environment.
  • People need to focus on where they want the makeup air to come into, and not where the hot air is exhausting from.
  • Stack effect will tend to cool off the lowest floor first, and the highest floor last.
  • As air comes in below, it pushes the hot air up and out.  That means that the highest floor will get a breeze of hot air, which could in fact increasing warming near the exhaust openings of the top floor.
  • As the cold air circulates, through the house, this cycle will continue since the cool outside air coming in will be heated up by the warm mass inside the house and then rise up and out.  As the mass cools off, so will the stack effect thermal engine.
I’ll make these points in a different way with a slightly different question:
If I were to look at using Stack Effect to ‘naturally cool’ my house, how would I do it?

First– I’d make sure that there’s a temperature difference that’s favorable.  In other words, I would want it hotter than comfortable inside, and relatively cooler outside.  Ok– 1st condition is satisfied.

Next– I look at the space where I want the cool air to be delivered and I make sure I have a window to the outside that can reasonably communicate directly into, or indirectly into that space.

Then, I need to make sure I have another location that is HIGHER than that window in the house to open.  Maybe it’s a skylight, or maybe it’s a window on the next floor up.  If the room I want to bring cool air into is already on the highest floor of the house– well, I’d better think about whether or not I’ll get any useful stack effect cooling in that room.

Let’s assume I’ve got some other opening that’s higher–  ok.  Now we need to make sure that there’s some open corridors, stairwells, and passages for air to freely flow from the lower window to the higher one.  If there are doors or floors or other hard and opaque things in the way, then we’d better find a way to open them (and leave them open) for this whole thing to work well.  It really doesn’t matter how far away these openings are from each other… as long as there’s a way that I could imagine air flowing without having to open something that’s airtight (like a door) from one opening to the other.

If all these are true– then open it up and feel the breeze.

Another great blog about this is by a very smart acquaintance of mine named Allison Bailes.  And in his post, he’ll describe how heat doesn’t always rise with stack effect– it often falls.  I’ll let him explain though.



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05-Green Roofs, Tornados, and Heat Island Effect:

Here’s my question:

Is it true that green roofs reduce heat island effect in the California coastal climate?

We see it in pretty much all the green building certification systems– Green Roofs give you points for reducing the Heat Island Effect.  I can sort of understand why in some locations this might be true.  I’m just not sure I believe it for all locations.

Full-disclosure– why I avoid green roofs
Let me just get my biases out of the way.  I work mostly on low-rise buildings with some reasonable amount of landscaping around.  I love green roofs, and due to their cost, I always recommend to my projects that they avoid green roofs unless all other options are off the table.  At least, that’s my recommendation where function comes into play.  If you just want the ‘look’ of a green roof, then aesthetics aren’t really about cost-effectiveness, usually.

I’ll go further– there’s only one functional way for a Green Roof to be an environmentally-friendly feature for a house– ecology.

What do I mean by ecology?  Green Roofs should first and foremost be some sort of replacement of what local flora and ecology once occupied the footprint of the house, or some close variation thereof.   And that, there friends, is the only necessary and sufficient reason why one should want to pay for a green roof for environmental reasons.

That said– it’s fine to install a green roof that has an ecology separate from the surrounding area, it just won’t have add ‘environmentally-friendly’ attributes to the house below it.

A good example of an awesome green roof that satisfies the ecological criterion is the California Academy of Sciences in San Francisco.

But what about storm water management?
Well, it’s true that green roofs can effectively act like temporary swimming pools elevated 10-20 feet in the air (with all the structural engineering to support that).  I’d say why don’t you spend all the money you would be spending on designing a structurally sound swimming pool on top of your home and instead spend it on a good landscaping earthworks design that more directly gets the stormwater into the landscape and percolated into local aquifers.  That’s where we want it to end up anyway, right?

Believe me, it’s probably going to be a lot cheaper and more effective to deal with the stormwater on the ground than way up high in the air.  There are always exceptions, and I dare you to find them and tell me about them.

But what about the insulation value (R-value) of a green roof?

It is true that green roofs have some insulating value.  How much?  Well– it’s pretty hard to say, and it’ll vary all year according to soil moisture content, plants species, and a host of other factors.  If it’s winter-time and you’ve got really saturated soil on your roof, then I’d might even argue that the green roof is actually lowering the insulation level of your roof (relative to a standard roof).  There are a lot of details about this, and a lot of devils.

The point is– if you need more insulation on your roof, don’t expect a green roof to always perform for you.  If you’re getting a good idea of how it’s performance would vary over the course of the year (after paying for a lot of consultant time), then great.  Even then, I’d argue that a green roof is a really really expensive form of insulation.  Save the money and install some kind of insulation that you know will perform better, and for cheaper.

But what about Heat Island Effect?
This is the core of this post, and perhaps the most complicated question to answer.  Maybe that’s just to say that I don’t fully understand all the factors involved.  But here’s how I see it:

In order to reduce Heat Island Effect, we need to absorb less sun and reflect more sun.  Just like the following chart from the Lawrence Berkeley Labs.  






Absorb less, reflect more

Now look at the following pictures from Google Earth, and look at them as a proxy of what the Sun sees.  Then ask yourself which one will absorb the most and reflect the least.






It actually looks like the the Northern California forest is the darkest, which is probably some trick of the satellite photography.  The LA sprawl, Green Roof, and Forest all have fairly low “albedos,” which is a technical term for reflectivity.

The picture with the high albedo is the snowfield in Greenland.  This kind of reminds you of what Cool Roof looks like, right?  There’s a reason for that.

Riddle me this Batman, if forests have such low reflectivity, then why are they cool?

The answer to this lies in another term called evapotranspiration.  You might also think that since plants photosynthesize, they absorb a lot of sun to turn into sugar.  However, science tells us that the efficiency of photosynthesis is quite minimal– on the order of 1-3% at best.  A modern solar panel can make electricity many times more efficiently these days– roughly 15-20% efficient.

Here’s a little picture from Wikipedia:

Evapotranspiration (from Wikipedia)

Plants take water from the ground, and use the sun to evaporate it off into the air.  HVAC engineers would call this “latent heat”.  In effect, plants are using the energy from the sun to evaporate water instead of heating up air directly (and increasing “sensible” temperature).

So, forests are literally cooler, and they create lots of humidity, and that might even create clouds way down the road. Clouds are important– clouds reflect sunlight, but only if they form in the right way (wider and not taller).   Cloud formation downwind from a City isn’t likely to help the City itself.

So in a hot-dry climate like Los Angeles, if we encourage evapotranspiration we might be making the air a little less hot, but the tradeoff is that we’re making it more humid.  hmmm– hot and humid– sound comfortable doesn’t it?

Sensible and Latent heat are both “heat”

The point is that if we encourage evapotranspiration in a hot-dry climate, we’re just evaporating water we may not actually have in that environment, and relative to the albedo of the mediterranean grasslands that occupied the region before we built it up, we’re actually absorbing more sun and therefore making the city hotter and/or more humid.

If you want to cool the urban heat island out West here, install a cool roof.  Reflect on reflectivity, and then choose something white/off-white so that we can show the aliens out on Kepler 62-f can see (literally) that we understand physics.

Perhaps that made some sort of sense.

If you want to comment, don’t use the WordPress form here, but email at

luke – [at] – petemoffat.com

and tell me where I’m wrong here so I can correct or retract altogether.


PS.  So, where do tornados come in to play here?

If you want to see a great example of the energy involved in latent heat, then consider the formation of tornados over the midwest.  Where does the energy from a tornado come from?  LATENT HEAT (in part).

When you turn warm moist air into clouds, there is a massive release of heat.  This heat is called the Heat of Fusion, and it is the same amount of heat as it takes to evaporate water in the first place.  The Latent heat is now turned to  Sensible heat, and there are large pressure gradients formed when you get large updrafts of warm air rising.  Combine with downdraft of cool dry air, and a host of other things, you get a tornado.

I just wanted to point out that latent heat not only teaches humidity, but is quite a powerful reservoir of energy in our meteorology.  Consider that the next time a perfect calm and quiet day gets turns into chaos from some passing thunderstorm.





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04- Unvented Attics

This is an older post, but I think it’s still a good one to review– all about unvented attics and the California Building Code (and Residential Code).

Why Vent a Roof:

In the old days when we heated building but didn’t insulate it, we didn’t really need venting.  If you go back to Europe, or to older homes in the U.S., you can probably see a legacy of this.  But then venting of attics/roofs became required.  And now we can installed unvented attics, but only under certain circumstances.

What gives?

In general, there is good reason to vent a roof.  We have a situation where we have a warm house full people who cooking, burning stuff, metabolizing sugars (and exhaling water), and sweating.  And let’s not forget the moisture storage capacity of the house itself.  The absolute humidity of a building is going to be higher than the outside environment (until we dry it out with an air-conditioner).

 The chart to the right shows real data of interior and outside humidity conditions.  You’ll first notice that they bounce around quite a bit.  Secondly, you’ll notice that the Blue line is ALWAYS above the Green Line– showing the point previously made.

The lines are generally converging since the chart is showing winter to summer, and in the summer the house tends to be open a bit more and better at equalizing humidity levels.

Winter Outside– Wet Hot American Summer inside

SO– we’ve got hotter and wetter air inside the house much of the year.  Why is that a problem?

Well– let combine that with a roof that’s not only cold from the outside air temperature, but ESPECIALLY cold since it’s facing a cold, unfeeling universe.

Yes, I’m referring to night-sky radiation.  The basic explanation of this is that our roof is being heated by the house, but then losing a lot of that heat into space.  Somewhere out there, there’s an alien with a super-powerful telescope that might be able to pick out each roof in a neighborhood like 1000 points of (thermal infrared) light.  From afar, this looks like a twinkle of infrared in the Universe.

A great image from a great article

From the Roof’s perspective, this means that it’s getting even colder than the air temperature outside.  Well, we all know that hot air rises, and in a house, it tends to rise into the attic.  Now we have hot and relatively wet air leaking into the attic.

What happens when a warm, moist air hits a cold roof?  The water condenses, and forms drops that end up soaking the wood. Months later of having wet wood, it turns to mush and the roof fails.

So, the answer to why we introduce venting is to keep the roof from getting wet by allowing a faster way for moisture to exit the attic.

 Unvented attics

If we can deal with moisture in some clever way, we no longer need to vent.

  • Eliminate the moisture sources inside the house:
  • This is a tall order.  We’d most likely have to eliminate the people and some activities in the house.  That’s just not gonna work– NEXT
  • Prevent moisture from inside the house getting into the attic:
  • This means installing a perfect vapor retarder/barrier and air barrier at the ceiling level.  If it’s perfect, it’ll probably work.
  • This can be achieved in the form of spray-foam insulation– both open and closed cell varieties.  This can reasonably achieve the ‘perfect’ air and vapor barriers.
  • Keep the wood roof deck warm to prevent condensation
  • One stupid way to do this is the installation of strip heater wires along the roof deck to keep the roof from being cooled off by the night-sky radiation.  We’re effectively increasing the radiation to the night sky.
  • A smarter way to do this is to insulate with moisture-inert materials like rockwool or rigid foamboard ABOVE the roof deck.  This will keep the deck warm by insulating it from the night sky.  This is also specifically allowed in the code.


Here is a discussion of code references:

You code wonks on the email list here probably are already quite familiar with the IRC, which was essentially adopted into California.  So, this might be old hat, but you’ll hear it again anyway.
Code finally comes around–
Last comment before I get into the meat– it’s nice to finally see the code come around to the kinds of topics and discussions I was having in school 6 years ago.  This had been building science that’s been published for likely 10+ years.
Unvented attic assemblies:
Do you remember what it was like, up until today (I assume you can’t submit plans for permit tomorrow), when you had a project that wanted to include mechanical systems inside conditioned space, and you wanted go for an unvented attic insulation assembly.  And those silly AHJ’s always made it more painful than it was really worth by making you fill out a specific application so you could grovel and get them to approve you’re design?
HAH, no more!
R806.4 Unvented Attic Assemblies
R806.4 Unvented attic assemblies (spaces between the ceiling joists of the top Story and the roof
rafters) shall be permitled if all the following conditions are: met:
…It goes on.  Essentially it provides assemblies for foam insulation, for fiberglass/cellulose insulation, and for the combination of the two.
The interesting ones for me at this point are the latter two.
Unvented attic assemblies with cellulose or fiberglass can be achieved so long as you provide a minimum of R-4 (1″) of rigid insulation above the roof deck for condensation control.
Those details shouldn’t be so bad, right?!
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03– Car Charging: How density may no longer be our destiny (but they’re still anagrams)

How big of a charger do you need for an Electric Car?

This posting will be about electric cars, at some point, but first I’m going to talk about how amazingly powerful the cars we drive in are.   This will set the context of why it’s hard for electric cars, and the charging infrastructure to support them are difficult to make equivalent to fueling up our cars at gas stations.  I’ll also talk about a lecture I saw from Richard Muller at Berkeley, who talked about how the 9/11 terrorists and how they used planes to take down a couple of very large buildings.


So, first—Energy Density:  Density is our Destiny?


Above is a chart that I took from Wikipedia in its article on Energy Density.  I highlighted two areas of interest—one is the energy density of diesel and gas, and the other is the energy density of batteries.

Note that there are two axes here— they’re measuring different things.  One is a Volume based density, and the other is a Mass-based density.  You’ll note that Hydrogen is way out on the MJ/kg  (which is Megajoules of energy per kilogram), but really low on the MJ/L (Megajoules per Liter).   That makes sense, if you think about hydrogen gas—it’s the lightest gas around, and to have a kg of it, you’d need to fill a volume about the size of a hot air balloon (about 400 cubic feet).  In other words, it’s not practical, unless you can liquefy it or super-pressurize it and get it to about the volume that would fit into a car’s gas tank.  Even then, it’s tough.

And you’ll note it’s the stuff that’s kind of in the middle which tends to look familiar in terms of what we use.  They’re relatively efficient in both mass energy density and volume energy density.

And then you’ll see down on the lower left the energy density of a battery.  But—don’t let that alarm you—there are advantages to a battery system that can’t be readily taken advantage of by other energy sources, which is why we consider them for powering our vehicles.

A look at gasoline and diesel

We tend to use gasoline and diesel to fuel our planes, trains and automobiles.  It’s a liquid fuel, which means that it’s easy to transport and fill our tanks with it.  It’s relatively easy to contain (easier than unoxidized aluminum for sure!)—or at least, we’ve designed pretty good systems to make sure that the fuel doesn’t leak.  It also doesn’t spontaneously combust at standard temperatures and pressures.  Lastly—it’s readily available once you poke holes in the ground, extract crude, and purify the crude into nice clean hydrocarbons.  We have a nice whole economic system built around this that’s been evolving for 100 years.

So, yeah—gas and diesel seem like pretty good choices when it comes to a fuel choice, especially given its history.  Of course, if hydrocarbons weren’t so easily found in oil deposits around the world, we might easily be using a less dense fuel like ethanol.

Gas and diesel both hold around 135 Megajoules of energy per gallon.  That’s actually quite a bit of energy.  If we have a gas tank in our car of 20 gallons, it’s about the equivalent of a half a ton of TNT that we’re sitting on.  But, if we trickle that fuel out of our tank and into an internal combustion engine—it’s that same energy that allows us to hurl a large mass down the road at 70 mph for 300 miles without stopping to refill.

Put in another context though—it’s why the terrorists on 9/11 used a jetairliner to crash into the World Trade Center buildings.   The tank in a 777 is about 40,000 gallons of jet fuel, which when you do the math, is about the same as 1 kiloton of TNT.  What you have there is a big deliver vehicle to penetrate into the building, and then a huge amount of energy that’s sufficient to burn and melt almost everything around it.  It was only a matter of time for the structure of the Trade Center towers to liquefy and then pancake down to the ground.

Another comparison—if a 777 airliner is about 1 kiloton of TNT equivalent, the “Fat Boy” nuclear bomb was only 20 times larger than that in terms of energy payload.

Disregarding all the politics and good vs. evil of the 9/11 attacks—one way of seeing the problem of modern transportation is not that it’s been weaponized, but rather that it’s weaponizable.  The fact that we’re sitting in cars that are heavy metal objects that hold a half ton of TNT in energy is perhaps a problem in itself.  One conclusion could be that the more we make transportation lighter and more efficient, the less effective of a weapon it becomes.

Super dense fuel:  nuclear power?

Another digression—thinking about a super dense energy source like nuclear energy—why don’t we use THAT as a transportation fuel.

The answer is that we kinda do, but it turns out that the energy density of fuel is not the only consideration here.  For the bigger picture, we need to factor in the amount of equipment it takes to convert the fuel into useful work.  For a car and gasoline, it’s actually pretty lightweight.  But for a nuclear powered vehicle, we need huge boilers, heavy turbines, and really thick walls metal walls for radiation containment.  That all adds up to nuclear power only being practical for things like submarines and aircraft carriers.

There was experimentation on nuclear powered jet airplanes, but it turned out that in order to make the darn jet light enough to be practical, the pilots flying it would die from radiation poisoning.



The act of fueling

We’ve talked about energy density of transport fuels, which also implies that it takes a substantial amount of energy to move use and our stuff around.  We’re working toward setting expectations for what’s reasonable for an electric car charger to fill up our electric cars in the same amount of time as our gas cars.

If our cars hold half of a ton of TNT of energy in the tank, and we refill them in a couple of minutes, then the energy flow out of the gas pump must be enormous.  Let’s see just how big:

20 gallons of gas in 3 minutes = 6.66 gallons per minute or 875 MJ per minute or 243 kWh per minute.

Let’s focus on that last metric—243 kilowatt-hours per minute.  Kilowatt hours are how we usually measure electricity.  The flow of electricity (energy per time) is called Power, and in order to supply 243 kWh per minute, that’s the same as 14,500 kW.  The average consumption of a house is about 1 kW, so that’s the same amount of energy flow as would power 14,500 houses.

Geeez—that doesn’t sound practical does it?

Carnot efficiency =  Car  Not efficient

Electric cars take a while to charge, but they don’t take THAT long.  As an energy conversion technology (converting stored energy into moving a car down the road), electric cars are roughly 5-10 times more efficient than a gas engine.  This means that for traveling the same miles, they only need a fifth to a tenth of the energy storage.

In actual efficiency, the power train of a gas car is about 20% efficient, while an electric car is 90% efficient.  Yes—this means that for a gas car, 80% of the gas that you buy goes straight into waste heat, and doesn’t go into making you go forward.  That might seem stupid, but 100 years of engine development can’t really improve that much higher than 40% in lab conditions.  This is the limit of carnot efficiency.

Finally—what amperage do you need to charge an electric car?

Now that we’ve ascertained that electric cars are much more efficient than gasoline cars, it still doesn’t answer our original question—how big of a charger do you need to charge your car.

Well—the main points before I tell you:

  • It’s gonna be hard to fully charge your car in 5 minutes like you do your gas car.
  • The limitation is not your battery but the voltage and amperage of your electrical service, and also the electrical grid.
    • To fully charge a 100 kWh battery in 5 minutes, you’d need a 1.2 Megawatt power plant.  And at 240 Volts electrical service, you’d need an amperage 5000 Amps
    • You’d need a wire about the size of your leg in order to supply that amount of electricity.
  • Standard high-capacity chargers these days are 80 Amps at 240 Volts, which will charge your car in about 3-5 hours.

Here’s a spreadsheet to allow to play around with numbers, if you’d like




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02– LED’s: wonky metrics for a new technology


What follows is a somewhat technical exploration of some of my recent learnings about what makes a quality LED light.  LED’s have been around for a long long time, but mostly in the form of blinking red lights associated with electronics.  It’s been only in recent years that the solid-state lighting industry has starting combining blue LED’s with the right kind of phosphors to create a more full spectrum light source for general use.


Their strengths lie in their potential energy efficiency (thus far, not realized in a cost-effective manner) and their adaptability in form.  In laboratory tests, they have been shown to be much more efficient than fluorescent lamps, and that level of efficiency is slowly being realized in commercially available LED’s gradually.


What I’ve written below is some learnings I got from a recent presentation given by a Lucifer lighting representative.


Color Rendition Index:

The general assumption here is that for a light in residential applications, we want a reasonably full spectrum light.  This is why we tend to like things that provide light by burning really really hot.  The classic example of the sun, which by definition is light at 5900 Kelvin (notice how ‘cool’ full sunlight is!)

Incandescent lights give us the same thing, but generally at a lower temperature (and therefore warmer colors).  They’re full of reds and oranges which are nice for our ‘flesh tones’ which are generally favorable to showing hues in skin and such.


There is an invention of the “Color Rendition Index” which is how we compare light sources like fluorescent and LED to an incandescent.  Sometimes, it looks like fluorescents and LED’s don’t give off an entirely full spectrum of light, at least compared to their incandescent cousins, and this of course is actually, literally true.


Wikipedia has a lengthy article on this which includes this chart comparing the spectrum we get from incandescent to a fluorescent:


The invention of Color Rendition Index:

When we buy non-incandescent lamps, they usually come equipped with a Color Temperature, as well as a Color Rendition Index, which generally compares how close they are to an incandescent light source of the same rated temperature.  The higher the number, the better– thus we want to get close to 100.

CRI pitfalls

In most LED’s, however, we usually look for values of at least 85, if not 90+ in order to get the closest we can to something close to incandescent light.  But as a number, it isn’t all we expect it to be.  The test is officially to 8 colors, which you can see in this wikipedia article under “Test Color Samples” (and to the right).  The ones in Italicized Red are optional supplementary colors for the index.

The important one that Therese pointed out was “TCS09” which are the ‘flesh colors.’  These colors are really saturated, so if the light source doesn’t have that spectrum in it, then the color won’t look nearly as bright or vivid due to the lack of light from the source.


So– this means that even though a light has a high CRI doesn’t always mean it will be as good as an incandescent source– especially for really saturated colors.  It might be, but you can’t tell by the CRI number.


Macadam Steps and the aging of LED lamps:

Short-version:  Good quality LED’s will change less than 2 Macadem steps over their lives.  (what the heck does that mean though)

It is unfortunately not uncommon for LED lamps to age differently.  Age can do weird things to LED lamps, and not all in the same way.  Imagine if at the beginning of a project, the LED lights are perfect and all the right color.  Then a couple of years later, the LED’s start changing color, and you have a bunch of wall-washers on a white wall and so the home occupants can really start noticing it.  If only the darn lamps would change color in the same way that it wouldn’t be so noticeable.


Well, the metric for measuring the changes in the light color out of an LED is called a Macadem Step.

I won’t explain exactly what that is here, other than to say that it’s a measure the minimum change in color that is noticeable by human eyes.  An exceptional LED lamp will change less than 2 Macadem steps over reasonable portion of its life (say 20,000 hours).  There are often lamps out there that change more than 7 steps, and it becomes really, really, noticeable.  If the homeowner is picky about chromaticity in their lighting, then you can expect a premature Change-out of a bunch of not-too-cheap LED lamps.  And someone might ask about warranty, whether it’s the manufacturers, or yours.


As usual, wikipedia has a good article with more math and technical detail than you could shake a pencil at:  http://en.wikipedia.org/wiki/MacAdam_ellipse



Lumen Maintenance:

“It’s better to burn out, than to fade away”

Neil Young’s prophetic ode to Kurt Cobain is more apropos to incandescents than LED’s here.  But, it’s a nice way to segue.

LED’s tend not to burn out (unless there’s something really wrong with the Driver or thermal management).

They do, however, just get dimmer.


The rate at which LED’s dim is called Lumen Maintenance.  You’ll see lumen maintenance as a percentage– say 70%.

This means that the rated output of the lamp will decline by 30% over the life of the lamp.


If the rated life of the lamp is 50,000 hours, and the initial rated output is 1,000 lumens, and the Lumen Maintenance is 70%, then you would expect (1,000 lumens x 70%)= 700 lumens out of that lamp after 50,000 hours.



If you’re expecting LED’s to get down to below 10% power (which is essentially for very high dimming application), then be careful about the specifications on the LED drivers.  LED’s run on DC current, not AC. The driver’s job is to convert that AC to DC within very specific voltage parameters.  You reducing the light output of an LED by reducing the current to it from the driver.  But the driver electronics get tricky when your trying to do that too.  There are cheap ways to do it, but they usually result in a loss of efficiency, poor dimming capability, or really weird results from the lamp.

In a lab with expensive equipment, you can regulate amperage to the lamp very well, but when you’re trying to manufacture lots of commodity LED lamps with drivers at a reasonable price, some quality in dimming performance gets compromised.


Of course– if you asked me– I would say, “why the heck would you want to dim down to 1%?”  There are lots of other, cheaper ways to create mood lighting.

For example:

Step 1: put on Jimi Hendrix’s “Electric Ladyland”

Step 2: take a 12 gauge power cord, cut off the female plug side and plug each bare wire into opposite ends of a pickle.

Step 3: Plug in cord.  Welcome to “Electric PickleLand” (Totally suitable for work):  http://www.youtube.com/watch?v=tMhXCG6k6oA



Quality Control in industry:


Sophia’s takeaway here– In the DOE tests for industry LED’s, something like 44 out of 200 lamps actually lived up to their published values.  There are a lot of quality control issues in the industry, and if you get involved in specifying LED’s, then it’s a challenge of knowing what metrics of quality control to Specify, and how to set expectations for the client.

Specifications, and expectations.   Solid state lighting just behaves differently than our old incandescent lighting, which is currently the gold standard.  Proceed with caution, or hire a lighting consultant who can take the credit/blame.


Last point– Recessed Lights that are IC rated (insulation contact):

After everyone left, me and Patrick were  talking shop. And he mentioned something interesting.  Recessed lights are required to be rated as “IC” or “insulation contact”.  This is for fire as well as heat dispersion (which are essentially the same thing).

The insulation they had in mind was cellulose and fiberglass, and NOT closed-cell foam.  Patrick was saying that there were a few houses that he had been involved with with a lot of failures or issues with recessed LED lights in spray-foam ceilings, and the designers were installing them without air-spaces in the middle of insulation.  The LED’s got toooo  hot and started failing left and right since there was no way for them to disperse heat.  ‘

The builder and homeowners were claiming failed warranties, and the product rep responded that ‘insulation contact’ doesn’t mean rated for ALL insulations, just the most common ones, which pretty much consist of fiberglass and cellulose.





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#1 Statement of purpose

Hello readers,

This is an inaugural post in what hopes to be a somewhat well maintained blog.  And here is where I’ll write a little statement of purpose, just in case anyone who ever cares to read it will have some insight for my raison d’etre here.

Topics Covered

Generally, this blog will cover topics of building science, technology, and policy, especially as it pertains to the ever-evolving “green” space.  It is an ever-changing world, and it can be quite confusing to evaluate marketing claims and word-of-mouth testimony.  I will attempt to inform some of those decisions in this blog.

Understanding, not answers?:

One thing I will try hard not to do is make decisions for my readers.  Of course, that is easier said than done in many cases, but I simply don’t like being in a place where I pontificate to others’ what they should value.  I will, however, invevitably draw conclusions and make implicit recommendations as a matter of course.  In part, this is

Other blogs of similar topics/inspirations:

There are lots of blogs in the world of Green Building.  I read some of them, and they’re great.  Examples include:





My contribution to this space will be to try to curate some of the knowledge and understanding to the climate and clients I work with in my usual work.  That is– Coastal California, which is a mixed-dry climate.  We can experience some fairly cold conditions (design heating temperature is around 30 degrees F), and also some dry hot days in the summer.

In addition, I am also keen on providing numerically driven models and associated graphics to help drive some conceptual understanding.

As always, please feel free to email or post comments and I will try this an interactive, and actively monitored space.



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