“Airtight Drywall:” Hoax, hack, or Help?
Sorry, gu8ys, but the recent FHB articla, and this site’s video series on, “airtight drywall” has my BS detector ringing. There are a few reasons for this.
First off, the author places his butt joints in free air, rather than on a framing member. This is contrary to all practice I’ve seen. Somehow decades of drywallers have been making invisible butt joints without needing to ‘float’ them in the air and pull them back with backerboards that bend the drywall in.
That leads to gripe #2: the author finds it necessary to put foam seal in all sorts of places that have been quite happily filled with ordinary mud and paint. Gaps between boards, and around windows? I’m having a real hard time remembering ever seeing those when the rockers were done.
Around electrical boxes? OK, maybe there’s an issue here …. far too often there is an opening larger than the 1/8″ allowed by the electrical code, and far too often the electrical boxes are set, or pushed, too far back. Alas, the solution isn’t to squirt gobs of flammable goop around the boxes … it’s to stop allowing the rockers to get away with using unskilled crews to slam / jam / push / hammer the panels into place as quickly as possible. Comprende “charge-back,” Amigo?
Maybe – just maybe- our Canadian cousins have been on to something the past decade or so, in being positively anal about sealing electrical boxes and maintaining the vapor barrier. I say ‘maybe,’ because I’m not convinced that a perfect seal is a good thing.
Why not? Well, I’m a firm believer in Murphy’s law, and I remember the Carter-era mania for sealing … and the mold issues that followed. The ‘indoor air quality’ discussions, and reports of ‘sick buildings.’
We also have a variety of other methods being used that severely limit air flow into and out of walls. Even ordinary paint often forms one heck of a vapor barrier – I have pictures of a layer of paint making a 2-gallon “bubble,’ holding water from a failing in the roof flashing like a rubber bucket. Add to that the caulking of everything outside the house, plus an interior vapor barrier, and you have a mold farm. Water WILL get in, in the form of the air present when you first close the walls in, if nothing else.
Look at an old home, and you find walls that are simply walls, and nothing else. That’s no longer the case. Walls are filled with all manner of things passing through – plumbing pipes, air conditioning tubing and ducts, electrical wires, computer cables, alarm leads, speaker wires, etc. We’re packing them with insulation, firestopping penetrations, adding shear panels and increasing bracing.
Perhaps worst of all, we’re conditioning the indoors much more than we did before. This leads to greater temperature, humidity, and pressure differences than we had in the past, between the inside of the house and the outside air. The greater the difference, the greater are the forces forcing moisture into the walls.
We don’t need to seal the walls; we need to give the moisture that does get in a way to get out. We also need to separate the ‘weather shield’ part of the wall from the ‘pipe and wire chase’ part. Naturally, this last part flies in the face of the current mania to stuff the walls with as much insulation as we can cram in.
What say you?
Replies
I haven't read the article yet, but I agree with your question about butt joints without a nailing surface.
Quite a few people (including some here) are big fans of off-stud butt joints (though usually using some sort of backer). (I personally avoid drywall work unless a (screw)gun is held to my head, but I understand the merits of the off-stud approach.)
The idea of installing drywall in an "airtight" fashion has been around for a dozen years at least. I can remember a TOH episode of that many years ago where the technique was demonstrated, using foil-backed drywall and sealants on the framing along the edges.
I can attest that standard rocking practices leave serious air leaks around windows, and of course electrical outlets have always been a problem. There are various ways to address these issues, but you've presented no evidence that the "airtight drywall" approach is inferior to any of the others.
You exhibit an utter lack of understanding of the dynamics of moisture in walls (Moisture trapped in the wall during assembly??? Really???) and you seem to be suggesting that we stop insulating walls, and go back to heating with wood stoves.
(Is that really you, Reno, or has someone hijacked your account? You're not usually this far over the edge.)
My reply is, unfortunately, "queued for moderation".
The account has not been hacked :)
One cannot avoid moisture from entering wall cavities during construction. Even in an arid climate (like Reno), there's plenty of moisture in th air itself. Trap the air, and you trap the moisture. There's also the little detail that many compounde release moisture as they cure. A slight change in temperature, and -voila!- you have condensation, soon to be followed by mildew. That's problem #1 with the 'airtight' approach.
No evidence? I point to an entire decade -the 80's- of evidence, as caulk-happy builders built fungus farms instead of houses. Now, we've upped the ante with multiple vapor barriers- despite code prohibitions against them. Spray foam IS a vapor barrier - and when you layer it with fiberglass, you have the fiberglass sandwiched between the paper barrier and the foam barrier. Hello mold!
Omit the paper? If the drywall itself is made airtight, you will still have that second vapor barrier. Too bad tht mold can't be made to pay rent!
Thanks for mentioning the foil-backed drywall. Yes, drywall itself has some permeability- so, no matter how you seal the edges, moisture will still pass right through.
Window leaks are window leaks, and not drywall problems.
I never said anything that could lead anyone to think I advocated eliminating insulation. That's a red herring.
I think you are juggling apples and bananas and complaining they don't throw the same way!
Is drywall vapor permiable - yes. Is foam and caulk a vapor barrier - also yes. But is isn't using them to make a vapor barrier, he is making an AIR barrier, says so in the first line of the article.
Yes, the various finishing compouns and paints will introduce water into the drywall - but not into the seams, as those have been sealed. Since the drywall is permiable, it will be able to get back out.
You mention condensation and those evil Carter era caulkers - great point! Because since then we've learned that the air sealing works as part of a system that includes proper insulation levels. Now there should be no condensation in the wall because it is properly insulated to begin with. Air sealing an old drafty house with poor insulation IS a path to ruin, because the air sealing works against the draftyness that allowed infiltrating moisture that could condense to easily evaporate back out again. Air sealing a new wall that is properly insulated reenforces the system and allows the insulation to do its job.
Butt joints off a framing member are a valid idea.
http://butthanger.com/ is one company that makes a product just for this. And their reasoning is sound. Makes a good, flat joint.
I don't think air sealing is a bad idea. But it has to be done as part of a system. Make the house tight enough and you might need some sort of air exchanger.
airtight drywall approach
I somewhat agree with your comments.
I build homes in the 60's and 70's without any problems
In the 80's we were forced to seal homes with plastic and caulking. This resulted in another code requirement: mechanical ventilation. Problem was that homeowners either neglected to service the ventilation equipment or totally ignored it (humming away in the basement). until it quit alltogether
Added insulation (from R7 to R 20) had definitely benefits but closing the home totally off from natural ventilation was not advisable. We closed the gaps around electrical outlets and around window and doorframes but left minor gaps unsealed where there was little chance to damage the wall system.
I believe in natural ventilation (open windows for fresh air in the morning and sometimes during the day); I do not wear plastic shirts or shoes.
I have build only one structure with the ADA system. So far I have not heard of any problem from the homeowner, that is not to say that there is absolutely no problem.
My home is not sealed airtight and a few dollars more spend on the gasbill is most likely offsetting the cost of repairs down the line
I can see how the mold explosion of the 80s and 90s would make builders nervous about tightening up houses. I too am remodeling a 60 year old home that never had an air barrier, vapor barrier, or even insulation in the walls. There’s evidence everywhere of the walls getting wet and yet nomold or rot, because everything was able to dry quickly.
But it’s 2012, energy is a lot more expensive than it was when my house was built and modern materials like housewrap and insulation are required by code. In my opinion, relying on leaky walls to breath and dry is poor practice.
“Built tight, ventilate right” is the mantra of today’s building scientists. Building tight, as tight as possible prevents energy loss and stops moisture laden air from entering walls. It does not mean that the walls can’t dry, however.
An air barrier is not necessarily a vapor barrier. Housewrap, drywall, and open cell foam can all be used as part of an air barrier for a house and all will let vapor diffuse and walls dry. Here’s a podcast with a leading building scientist that might shed some light on the subject: http://www.greenbuildingadvisor.com/blogs/dept/building-science/air-barrier-or-vapor-barrier-building-science-podcast
There a good article with another coming up in our next issue, as well.
renosteinke,
Myron has been butting seams between studs for a long time because it results in a better job. The guy lives breathes, and sleeps drywall. Airtight drywall, as stated in the article, is part of a larger air barrier system. This is different from a vapor barrier, and the distinction is important.
Plastic in walls is the reason for so many houses in the 80's couldn't dry and wound up rotting. Plastic worked its way into the building code in the 1930's even though the (then) current research indicated that it was air leaks carrying moisture and not diffusion that caused the most moisture problems. In extremely cold climates, it appears to make sense to use a plastic vapor barrier, because the vapor pressure caused by large temperature differences inside and outside (-10 degrees outside, 70 degrees inside) gets pretty big. In fact, it is off the psychrometric chart. According to most building scientists and forensic engineers, in the more moderate climate zones 1 - 5, a plastic vapor barrier is asking for trouble.
Retarder is the key word in the code, not barrier.
In the next issue (#230), we have an article called Air Leaks: How They Waste Energy and Rot Houses by John Straube, an engineer with Building Sciemnce Corporation. It should clear up misunderstandings between air leaks and rotted homes.
With tight houses comes lower energy bills and a mechanical ventilation strategy. It is better to specify where the air is coming from than to rely on random leaks that the plumber or framer left for you. For many reasons.
Thanks for commenting on the article,
Dan
D'OH! You're supposed to say Spoiler Alert before you give away major plot points... now I won't be surprised when I get my next issue.
Oh wait, I've got ADD... I'll forget anyway. Oh look, a chicken!
Wow! I certainly got everyone's attention!
I look forward to the follow-up article.
My point, my concern, is based on the assumption that water WILL get in. I see a need to allow the water to get out, rather than to sit in the walls and fester.
Now, I intend to foam the walls in my complete-gut remodel. I submit that making the wall faces 'airtight' is a mistake when the wall is foamed.
Somone said there was a difference between 'airtight' and vaportight.' I agree with the idea, but believe they got it backwards. Anything that blocks air will stop moisture - but there are plenty of things that will block moisture yet let air through. This is possible simply because oxygen is smaller then water. Indeed, Union Carbide used to run an ad where they had a canary singing under water, kept dry and happy by a thin slicone membrane- yet able to breathe.
"Saving energy" has a very nice sound to it ... but I fear that 'one for all,' extreme solutions will backfire. I'd hat for it to reach the point where the holiday candles poison everyone with CO, just because the house is 'airtight.' For all the concerns about air leaking out, there's been no emphasis on letting fresh air in .... or for getting moisture out.
On this topic alone, in our lifetimes, we have seen the 'experts' be very, very wrong already. So, forgive me if I'm not so willing to accept 'expert' advice at face value.
As for drywall techniques .... I'm no pro. Far from it. All I know is what I've seen. Your author may 'live and breathe' drywall, but he's not the only one out there who does. I've yet to meet a rocker who doesn't do everything he can to land all his seams on the framing. I note that specifications for fire resistant assemblies specify seams on the framing. Your guy may prove to be right, but from my perspective his opinion is unique.
Sit down and calculate how much water is in the air that could be "trapped" in the walls during construction. Then tell me how that amount of water could cause a problem.
Doesn't take much. Anyone, even desert dwellers, who truly pack things in sealed, airtight containers often find all manner of mildew when they re-open them in a few months.
"Anything that blocks air
"Anything that blocks air will stop moisture - but there are plenty of things that will block moisture yet let air through."
For Union Carbide, maybe. But not with common construction materials.
Brian had replied that "an
Brian had replied that "an air barrier is not necessarily a moisture barrier." The OP was rebutting this, by pointing out that such a statement simply cannot be true.
My jacket has a Gore-tex lining that is definitely 'waterproof,' yet breathes quite well. This makes sense, as air is smaller than water.
Brian was implying that there was something that would let water through, but not air. Not even Union Carbide can do that!
So you're saying the way to keep moisture out is to let air through??
airtight drywall
But joints in space are not worth the electrical energy it would take to think about them. Move along now please.
Yep, joints in space would be worthless. They need air to stay lit.
Water, air and water vapor. Relative size!
I am sorry to write that the scale of size is, water the largest, air comes in the middle and water vapor on the end being the smallest.
So called water vapor barriers, are barriers with holes small enough to keep out the rain, but with holes large enough for the water vapor to pass through. (Posh and expensive)
The way to understand this, is to think of a box full of footballs, each blob of air equals one football, there is a lot of space between the footballs (air) and it is in this space that the water molecules move about.
At a temperature of 30 degrees C and one hundred percent humidity the air holds as much water vapor as it can, about five teaspoons. 100%. In one cubic metre = about 32 cubic feet.
As the temperature drops, so the amount of water vapor held between the footballs drops.....to the point where at arround 7C the air holds one teaspoon of water vapor in one cubic metre, thats about one teaspoon in 32 cubic feet. Its to all intents dry air.
As the temperature drops further towards zero centigrade, the water vapor drops out first as condensation, then as frost and ice until the air is dry.
The water vapor molecules are so tiny they can move within the surface structure of most traditional building materials.
While there may not be much water vapor inside a cubic metre of air, the problem is, there is a hell of a lot of air with water vapor in it and this wet air is on the move the whole time.
Perry, a "vapor barrier" is
Perry, a "vapor barrier" is used to STOP water vapor passage and is blazingly cheap (plastic sheeting).
"Barriers with holes small enough to keep out the rain, but with holes large enough for the water vapor to pass through" describes Tyvek and it's kin. Not as cheap as plastic sheeting but certainly not "posh and expensive".
Your football analogy also sucks. (But then that's true of most football analogies.)
A couple of comments have been made that seem to show a positive genius for understanding things backwards.
Water (liquid) is obviously larger than air (gas.) Maybe it's not so obvious that water in it's gas form is also larger than air. It's pretty clear, when you think about it: two three atoms arranged in a triangle (water) has to require a larger hole to pass through than two atoms in single file (oxygen). So, one can make a barrier that will block the larger item. What one cannot do is make a barrier that will only let the big stuff pass.
That's only half the question. The other half is that there is no guarantee that water will remain in its' liquid form. Change the temperature or pressure just a bit, and that water vapor will condense out, as a liquid. Now you have a liquid trapped inside your barriers.
I advocate the practical approach of accepting the reality of Murphy's law. Water WILL get in. What is needed are construction practices that make sure the water also has a way OUT. This conclusion of mine is directly opposed to the basic assumptions of the 'airtight drywall' crowd.
My skepticism is encouraged by the disaster that followed our previous fad of making things 'airtight.' I'm a whisker away from deciding that every stud bay needs a drain (or 'weep hole').
Brian has promised a further article explaining the 'airtight' concept in greater detail, and I look forward to it.
You don't understand the chemistry very well
The hydrogen atom is considerably smaller than an Oxygen atom at the same conditions. Think tennis ball, versus Bowling ball.
Two tennis balls hooked on a bowling ball at 135-degrees seperation are not as large as two bowling balls hooked together.
Not sure where to begin
First, please try to use spell check before you hit send. It will make your argument more believable.
Second, all of your comments come across as being very negative, I think you may want to look into partnering with some other subcontractors. On our team, we all work together to make a better project. Once I explained the importance of creating a tighter “air barrier” by the use of the “Air Tight Drywall” approach my drywall installers got it and made it happen.
Here are just a few other bullet points –
Remember there is an “Air Barrier” and “Vapor Retarder” and not the other way around. I can stop the movement of air completely, but nothing stops the movement of moisture completely. In other words “Diffusion”. Picture a balloon filled with Helium and in a day or two it no longer stays afloat even though there are no holes = Diffusion. Now put a small pin hole in the balloon before you fill it with Helium and it will be flat in a couple of minutes, not days. It is the hole that matters, not diffusion.
There are thousands of self created holes in your exterior walls – electrical, window openings, the drywall gap all along the bottom of the walls, etc., etc. The “Air Tight Drywall Approach” seals up these holes to keep the warm moisture laden air from getting into my exterior walls. Then we seal all vertical penetrations and install carefully placed, custom sized batts of Cellulose Wall Spray insulation with non-directional fibers to avoid convective looping within the walls. On the outside, we use insulated sheathing to raise the temperature of the first condensing surface to avoid any air that does get into the walls from turning to water. Can you say belts & suspenders.
Then there is your argument about making your walls “too tight”. There is no such thing as “too tight”, just “half too tight”. Unless you can convince your customers to completely remove their insulation from their walls so they can dry out, you need to keep the moisture out. Perhaps you would have an easier time of telling your home owners they cannot have central air conditioning to make your walls more durable. Good luck with that.
In closing, I recommend my fellow builders think twice before giving up of making durable high efficient wall assemblies. We have been doing it for the last 25 years and I have yet to kill one of my customers. Don’t believe me, go to one of Joe Lstiburek http://www.joelstiburek.com/ seminars and expand your mind and your vocabulary.
Sincerely,
David Brooke Rush Builders
You got it right!
I know
I was trying to develop a nontechnical anaolagy that someone who hasn't had a few semesters of chemistry can visualize.