Be a Controlling Building Enclosure Control Freak with Control Layers
Frank Lloyd Wright was a control freak. This was a guy who not only designed houses but also all of the trim details and even the furniture. No, you’re right. That’s not really enough evidence to convict him. The really damning part is that he also placed the furniture exactly where he wanted it in the homes he designed…and expected you to keep it there! If you owned one of his homes, you better hope he never visited and found the furniture out of place. If so, you’d get a good scolding. Then he’d put the furniture back where it was supposed to go. Control freak!
Sadly, his personal life was a mess, and his control didn’t extend to some areas where it would have helped more than in the placement of furniture, but let’s focus simply on the idea of control for now. If you design, build, inspect, rate, or verify buildings, I want you to be a control freak, too. Not about furniture—about control layers.
One of the biggest knowledge gaps I see in the world of building is the understanding of the properties and uses of the various materials used in building homes. For example, I ask this question a lot in our classes and when I speak:
What is the purpose of house wrap?
I usually get told that
it’s an air barrier or a vapor barrier. I rarely get told what it’s really for. It’s one material you can use as a really important control layer in the building enclosure. But what’s it supposed to control?
Become a control freak.
Here’s what you want to control in a building:
- Heat
- Air
- Liquid water
- Water vapor
Understand also that controlling doesn’t necessarily mean stopping. Let’s take a look at these and see what materials we can use as control layers for them.
Controlling heat
This one’s easy and obvious, right? You use insulation to control the flow of heat across the building enclosure. Yeah, that part’s easy, but there are a lot of choices for insulation materials. Some of them also qualify as air barriers or vapor retarders or both. It’s not a problem doubling up to control heat and air, but you’ve gotta be careful with vapor retarders.
The PassivHaus folks are the total control freaks in this area.
Controlling air
This one’s easy in theory, too. Seal up the house as tight as you can. The old myth that a house needs to breathe has been thoroughly debunked. Unfortunatley, not everyone has gotten the message. I’ve talked with home builders, even here in Georgia where they have to pass a Blower Door test, who still believe that you shouldn’t air-seal a house too much or you’ll make it ‘too tight.’ Sorry! Not true.
Be a total control freak here and get the air leakage as low as you can, as they did in this net-zero home in Tennessee.
Controlling liquid water
This is probably the most important control layer of all. Wait, no, it IS the most important control layer because if you screw this one up, your house fails, sometimes quicker than you 
might imagine. If you’re not absolutely maniacal about being a control freak here, it could well come back to bite you.
And this is what house wrap does. It’s a drainage plane behind your cladding (siding, brick, stucco…) that keeps water away from the more permeable materials behind it. It needs to have proper flashing at all openings for windows and doors, be layered in a shingling fashion so water doesn’t get funneled to the back side, and sealed at the seams.
Of course, house wrap is only one of many types of drainage plane. You can also use a product like Huber’s Zip Wall (shown at left), rigid foam board, or any number of other materials.
This is where Frank Lloyd Wright could’ve used some help in being a better control freak. Some of his spectacularly gorgeous buildings had some spectacular liquid water failures. It may be nice to work in a striking-looking building, but if I had to listen to that water dripping into the bucket by my desk all day, it’d drive me crazy. To be fair, though, he didn’t have the kinds of materials to work with that we have today.
Whatever you do here, be a total control freak with liquid water.
Controlling water vapor
This is probably the most confusing one. A lot of people think house wrap is a vapor barrier. Guess what? It’s not even close! It’s got a permeance well outside the range of even a Class III vapor retarder.
And speaking of permeance, be sure you understand the difference between permeance and permeability as well as the three classes of vapor retarders. Go now and read my article about water vapor if this is a mystery to you. Once you thoroughly understand this, it may be clear to you that you don’t even need a vapor barrier.
The thing about controlling water vapor is that you sometimes need to stop, and sometimes you need to let it flow. In a really cold climate, we stop it on the inside of a wall but not on the outside. In a mixed-humid climate, like Atlanta, you don’t want a vapor barrier on either the inside or outside.
The Perfect Wall
Joe Lstiburek likes to talk about what he calls the Perfect Wall. It’s got all the proper control layers and puts them in places where the assembly can work in any climate. Check it out. I combobulated the Perfect Wall a while back. (In case you’re wondering, I just got tired of seeing so much discombobulation in the world.)
Control the flows!
There you have it — a quick overview of your path to becoming a control freak.
Related Articles
You Don’t Need a Vapor Barrier (Probably)
Vapor Retarder? Vapor Barrier? Perms? What the Heck?!
Combobulating the Perfect Wall – The Basics of Control Layers
Myth: A House Needs to Breathe
5 Reasons House Wrap Is Not an Air Barrier
Photo of Frank Lloyd Wright from Wikimedia Commons, a freely licensed media file repository.
This Post Has 15 Comments
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Three cheers. I am a
Three cheers. I am a homeowner but have developed a neurotic fear of uncontrolled air infiltration. When people talk about air LOSS from air conditioning ducts leaking to the outdoors, I wish they would consider the equal amount of outside air sucked in through random holes in the structure. In a hot-humid city environment that cannot be good.
Of course water leaks are extremely important but people already understand that. You can see water.
One thing that you could
One thing that you could clarify (for me at least) is when the control layers can be combined in a single layer. Or if there are cases where they should not be.
For example, can the house wrap be an air barrier despite being vapor permeable (and with a vapor barrier in another layer)? If so presumably it has to be a certain type of wrap and taped just so?
And some taped, foil-faced insulations could act as all three? Or peal and seal membranes are both vapour barrier and air barrier in one, with insulation adjacent? And that is okay in a perfect wall that breathes in and out from a vapour barrier layer?
As usual I think I know the answers but my confidence on these points is not total (and often nowhere near).
Allison I need some advice.
Allison I need some advice. I’m working on a volunteer project in Santa Fe New Mexico called Horses for Heroes. We are building an 1100 square foot “bunkhouse” where wounded and PTSD comabat veterans can gather for counseling and group therapy. Our wall assembly is 2×6 construction with blown-in fiberglass, full OSB sheathing, Tyvek house wrap, two inch rigid bead board then roughsawn board and batten cladding. Interior finishes are drywall in some rooms but 1×6 horizontal T&G; applied directly on studs in the great room. The question is whether or not we should install an air barrier and/or vapor barrier behind the T&G.; I’m thinking yes but other “building scientists” on the project say no. What say you?
So glad you did not miss that
So glad you did not miss that Frank Lloyd Wright did…a building’s primary purpose is to give protection from the elements to the occupants. A really cool-looking building that leaks, and its architect indifferent to such leakage (see Wright’s famous response to S.C. Johnson when the latter’s brand new house leaked during a rainstorm – client complained it was dripping on his head, Wright told him to move away from the drip)is a failure as a building, regardless of coolness factor. It’s high time we refocused on what we construct buildings for…not merely to make an artistic or status symbol impression, but for shelter!
Good overview of the subject,
Good overview of the subject, but you left out one extremely important issue that almost always gets ignored by builders – sealing all mechanical penetrations to the weather barrier, not just the windows and doors. Among the builders that do a good job with their house wrap (and there are few that even do that), most still install siding or brick on the house before all the electrical, HVAC, and plumbing work is complete. So even if the house wrap is well installed, there are dozens of holes cut in it that are NEVER flashed properly, providing lots of places for moisture to work its way into the structure and insulation. I urge all my clients to not start any siding until all the pipes and wires are installed and fully flashed to the weather barrier. I also recommend installing some conduit, also flashed, insulated and capped off, so future equipment can be installed without causing moisture damage. If builders ran most of these pipes and wires through the foundation instead of the framed walls, it would be easier to seal them, but they don’t seem to be interested. Still some big gaps in knowledge on moisture management.
Hello..control freak here.
Hello..control freak here.
just a lowly energy rater here but I want to see felt over drip edge, all seams of foil/foam sheathing on exterior of walls taped, all penetrations sealed before cladding, ICAT can lights, air tight drywall
and calcs for hvac sizing,
duct sizing & design. and thats just the shor list.
In a perfect world architects would design with efficiency in mind. ducts in conditioned space, wide overhangs, etc.
tradespeople would know their jobs, seal their own holes and everyone would pass a blower door & duct leakage test.
until then..control freaks make good healthy houses.
imho.
another important issue that
another important issue that was not discussed within any of your points is workmanship. a material or wall construction is only as good as the installer- and, for that matter, the logical long-term performance of the installation. for example, rigid board works great as a drainage plane as long as the joints are all taped/sealed and there is absolutely no relative movement of the boards. but what happens if those seals are not completely continuous? or if a slight amount of settlement of the boards occurs (it will)? better have a continuous backup to keep water out…
Allison,
Allison,
I totally agree with all you’ve said here, especially the part about controlling liquid water.
However, I’m eternally fascinated by how both workmanship, and what is (or what is though to be) the proper way to build control layers has evolved over time, and has almost invariably been driven by cost considerations, more so than anything else.
Consider that, in the distant past, exterior wood siding and trim in a reasonably well-built house was carefully scribed to fit tightly together, keeping both air and water out. There was no need for a secondary drainage plane — the exterior was the drainage plane.
In time, of course, frames settled and boards shrank, and houses became drafty and prone to moisture infiltration. But that same draftiness usually (though not always) allowed a wet assembly to dry out quickly, and this observation is probably what led to trades persons of latter days cultivating the misconception that “buildings need to breath”, when that actually was never intended by earlier builders.
Of course, all that measuring and cutting and fitting together of the weather shield required a great deal of skill and time, so in the interests of reducing costs, we eventually abandoned it all in favor of mass produced and easily installed exterior siding and trim, and this necessitated the need for a new, secondary layer (likewise cheaply produced and reasonably straight-forward to install) that now takes on the function of a true weather shield.
Now, an earlier comment here, posted by Erika, states (to the effect), what happens when foam panels shift in time? Or tapes open up? What then?
Well, it’s interesting to note that the buildings of old that survived despite their leaky weather shields demonstrated a certain degree of “resiliency”, but that resiliency was never actually intended, nor designed for. It just came about by chance (and then again, only in the buildings that survived moisture infiltration; not all did).
So, I think a key lesson from the past is that control layers are nothing new, and that we should design them in such a manner that they’re not just effective when perfectly assembled, but also exhibit some degree of resilience or fault-tolerance, by intended design, in order to be considered ideal as control layers. Even if this means costlier production and installation.
Just as Wright was indifferent to water dripping in from his roofs, modern building scientists ought not be indifferent to resiliency as a fundamental design concept.
My $0.02, anyway 🙂
~John
@Kim Shanahan, <
@Kim Shanahan,
The nice thing is that you you already have the makings of an air barrier already and may already have one installed. What I mean is that the Tyvek building wrap is an air barrier already, but needs to be properly installed to be effective.
1. Every seam needs to be taped and properly lapped to shed water.
2. Every penetration (e.g. conduit, wire, pipe, dryer vent, HVAC penetration, etc.) has to be taped and sealed to the building wrap to seal the penetration.
Remember that air barrier have to go on all 6 sides of the building. Not have the ceiling or floor sealed for air infiltration greatly reduces the effectiveness of air sealing the walls.
Jeremiah
M. Johnson
M. Johnson: Yep, the hip bone’s connected to the thigh bone.
Paul P.: Great questions. Yes, housewrap CAN be an air barrier but I wouldn’t use it that way. I’d seal the sheathing. Yes, foil-faced foam board can control heat, air, liquid water, and water vapour. Not all peel-and-stick membranes are vapour barriers, though. Check their permeance. Also, I linked to my earlier article called Vapor Retarder? Vapor Barrier? Perms? What the Heck?! at the bottom of this article. If you click over, you’ll find a link to an article by Joe Lstiburek that has a lot of different assemblies that work and it tells you what climates they work in.
Kim S.: If you’ve got enough exterior insulation, the vapor barrier inside should not be necessary. If humid air gets into the wall cavity and finds the sheathing, it should be warm enough not to cause problems. Martin Holladay wrote an article about how much foam board you need at greenbuildingadvisor.com. You should be able to find it easily with a quick search.
Cameron T.: Hadn’t heard that story about the dripping yet. Thanks. Also, you may like this Venn diagram of those who know Joe and Frank.
Green Curmudgeon: Great point. Thanks for mentioning it here. I can’t put everything in my articles for 2 reasons: (i) I don’t always know everything, (ii) I like for smart, experienced readers like you to make the articles even more useful.
Debbie: Ah, yes…a perfect world! Until we get there, though, we need people like you to keep educating and doing the right things.
erika: Absolutely! Using the right materials and installing them properly is critical.
John P.: Good point. I don’t know of any building scientists who are indifferent to resiliency. We all want buildings to last when we put a lot of resources into them, and we can certainly learn from the old buildings that managed to survive. I’m sure there were plenty of older buildings that weren’t so resilient, though, and also, the conditions in our buildings now are much different with the high degree of conditioning we do in them. But resiliency is definitely a good thing.
Jeremiah E.: Well, house wrap MAY be an air barrier, if installed properly. See the article called 5 Reasons House Wrap Is Not an Air Barrier that I put in the Related Articles above.
Hey Allison, we’re in New
Hey Allison, we’re in New Mexico (Kim and me) and vapor barriers are not even in the code. Neither interior or exterior. Just like Joe Lstiburek recommends.
Allison, you are such a rock
Allison, you are such a rock star. Let’s hang out at the conferences in the spring. Keep writing the good stuff!
Hi Allison, Janet and I live
Hi Allison, Janet and I live in the Frank Lloyd Wright Boulter House designed in 1954 and built in 1956. We’ve registered the home for LEED Certification and are currently working on the Integrated Design Charette for the improvements. The home is a passive solar design tucked into the hillside. The home inspired me to get involved with the Green Building movement and we Certified our offices LEED Platinum last year. Learn more at our Green Building Division www(dot)Green-Cincinnati(dot)com.
M. Johnson – The need for
M. Johnson – The need for protecting from bulk water entry may be well understood, but unfortunately you actually can’t see the water until much later (after the warranty period has expired). For this reason more than any other, builders consistently get it wrong. We do moisture diagnostics many times where there is plenty of blame to go around. I have a phrase I often use: “We could argue about whose fault this is, but I know whose fault it’s not, and unfortunately that’s who is going to pay to fix it.”
Kim Shanahan – I agree with Allison about enough exterior insulation (controlling temperature so you don’t have a condensing surface in the wall). Notice that he didn’t say how much that would be! Which illustrates the point that you could easily get that wrong. Like Allison, I’m from the SE so you should take this with a couple grains of salt, but I think you’ll have lot’s of vapor pressure from inside to out in the winter, & not much coming in during the summer months because it’s such a dry climate. So I would think a class 1 vapor retarder (we’re not supposed to say vapor barrier any more y’all!) would be a good idea. Regarding the air barrier (air retarder?), you have exterior layers that should be able to be sealed so that you don’t need one inside. But then you also have to top & bottom plates to think about. I find that these areas are rarely sealed well enough to trust. Also, you end up relying on caulk, glue, tape, etc., that is outside which I also don’t trust over time. For these reasons we always install an air barrier under any T&G; type material inside. We use Tyvek because it serves that purpose & has a sky-high perm rating (~50) so we’re not putting a tight vapor retarder on the inside in our climate.
So if I know (or at least
So if I know (or at least study their writings) Joe Lstiburek and Frank Lloyd Wright, I’m set to make a great building? Yes! Art and Science as one. As Joe himself has said, when buildings are beautiful, people tend to take care of them.
Therefore make it durable, beautiful, and truly great shelter!