Image Credit: All photos: Matt Risinger Most of the wall sheathing on this house is OSB, except for a 2-foot-high course of pressure-treated plywood at the base of the walls. The gap between the top of the concrete foundation and the bottom of the wall sheathing was taped with a 12-inch-wide peel-and-stick product, Carlisle CCW 705. The Carlisle CCW 705 covers about 1 or 2 inches of the concrete slab to air seal the gap. The peel-and-stick tape also keeps water off the bottom of the wall sheathing. Notice that we apply a primer (which darkens the sheathing) before adhering the Carlisle CCW 705. Before installing the Siga Wigluv tape, make sure that you have the right primer (Dockskin primer), a tape dispenser, and a J-roller. We used Siga Wigluv 60, which is 2 1/4 inches wide. Before taping an OSB seam with Siga Wigluv, it's a good idea to install a coat of Dockskin primer with a mini-roller. Siga Wigluv covers the seam between the pressure-treated plywood and the lowest course of OSB wall sheathing. The wall sheathing is almost fully taped. After all of the wall sheathing seams were taped, a layer of Tyvek Commercial Drainwrap was installed over the OSB as a water-resistant barrier (WRB).
Every house needs four control layers. In order of importance, these layers need to provide:
- 1. Water control
- 2. Air control
- 3. Vapor control
- 4. Thermal control
The building codes have dictated the levels of thermal control and vapor control that builders must adhere to, and nearly every builder in the U.S. knows off the top of their head the R-value of the insulation in their walls and attics.
But until recently, the building codes haven’t addressed air control. The 2012 IRC now dictates that builders in my climate zone (Zone 2) need to achieve a blower-door test result of 5 ach50 or less, which is actually pretty tight. This new requirement will make quite a few builders need to research air-sealing methods in order to reach this level of airtightness.
Codes need to do a better job addressing water control
As an aside, it’s interesting that building codes barely touch on water control, which is of course the most important control layer on any house. What difference does it make what R-value your wall has if water is getting into that wall through a leaky window or a poorly sealed plumbing or HVAC penetration?
In my quest to build ever-tighter houses, I’ve decided that my goal is for every house I build to get as close to 1 ach50 as possible. Not every house I build will get to this standard, as I’m sometimes limited by the architecture or the weatherstripping of exterior doors. I’ve found that sliding glass doors, custom doors, “store front” doors, and other architecturally cool doors can really kill my blower-door test results.
Air sealing approaches
If you’ve followed my blog, you know that I’ve used a ton of different methods to air seal inside a house: spray foam, Owens Corning Energy Complete, caulk, etc. Using these methods, I’ve been able to get most of my houses below 2.5 ach50. But to reach my goal of 1 ach50, I’ve decided to take a page from the Passivhaus playbook and tape my exterior sheathing seams.
After reading Martin Holladay’s “Backyard Tape Test” article from the March 2013 issue of Fine Homebuilding, I thought that Siga Wigluv was the clear winner as the best tape for OSB sheathing seams. Martin’s article says that it’s best to use a primer, and I fully agree.
I bought my Siga tape (along with the necessary Siga accessories) online from Small Planet Workshop. I recommend using a J-roller to roll out the tape and ensure good adhesion. To see a step-by-step demonstration of the installation process, check out the video below, as well as the series of photos and photo captions.
Unfortunately, I’ve been waiting on the rear and front doors for this house, so I’ve not yet been able to perform the blower-door test. I’m expecting this house to get very close to my goal of 1 ach50.
I’ll post an update to this blog post once I get the blower-door results. Overall, I’m really happy with this Siga tape and I think this method of addressing air control is superior from a “best practice” standpoint.
Matt Risinger is a custom builder and whole-house remodeling contractor in Austin, Texas, specializing in architect-driven design and fine craftsmanship. His company, Risinger Homes, uses an in-house carpentry staff and the latest building science research to build dramatically more efficient, healthy, and durable homes. You can read more examples of Matt’s writing at Matt Risinger and the Green Building Blog.
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Could y'all be more specific about what "a primer" means? As in
paint, or something else that bonds hard to the OSB and leaves a
nice smooth surface for the Wigluv to adhere to? I'd almost
think solvent-based urethane to give really good penetration...
Boy, I *wish* the guys on my retrofit had used J-rollers on the
Weathermate tape. I don't think they even had such things in their
toolbags. You simply cannot get tape of almost any sort adequately
stuck down by rubbing a sweaty hand along it... fishmouth city.
Comparison of sealing methods
Matt, Martin or anyone. Could you comment on the comparative efficiency of using tape over caulking or acoustical sealant on sheathing seams?
Response to Hobbit
The primer comes from Siga, the same manufacturer that makes Wigluv tape. It's called Dockskin primer, and you can see a small can of the primer in Image #5.
It's applied like a paint, but it's sticky. Even when it's dry, the surface of the cured primer is somewhat sticky -- a little like rubber cement.
Response to Malcolm Taylor
Q. "Could you comment on the comparative efficiency of using tape over caulking or acoustical sealant on sheathing seams?"
A. I'm not sure what you mean by "efficiency." I think that it's faster to install tape than caulk. But remember, caulk won't work on horizontal sheathing seams -- since most horizontal joints aren't over framing.
If you wanted, you could use caulk or acoustical sealant for vertical seams, I suppose, but installing the caulk would really slow down the sheathing crew, who probably just want to slap up the OSB and use their nailing guns.
If you are asking about long-term effectiveness, I don't know if we have any answers. Clearly, though, the only way to go with horizontal seams is tape.
@Hobbit: In general if you want a peel and stick product to stick well it needs a primer. I used to think primers were optional, but I won't apply anything to concrete to wood without a primer. Nothing sticks well without a double adhesive bond. It's a lot like a laminate countertop install. Roll on the primer, wait for it to get "tacky" then when the two come together it's nearly impossible to peel the tape. Even in 110 heat of Austin, TX. I made another video when I first got the Wigluv tape and did a destructive test. You can find that here, this link fast forwards the video to the part where I try to rip off the tape.
Tape vs Caulk
@Malcolm: I've done a lot of interior caulking of framing prior to spray foam insulation in the past. I've found this method has limited success on the blower door test. I believe the tape is a much better overall strategy. I still do some caulking however. I find that the bottom wall plate to concrete slab connection is a bear to air seal. For years I thought the foam tape call "sill seal" would work magic, but I built a house a few years ago where the clients didn't install base molding at the floor till later and they felt drafts coming under that bottom plate. I now caulk that joint with a sausage tube of Tremco Dymonic along with sealing the outside with Carlisle CCW 705 AND sill sealer.
Air Barrier/drainage plane
One thing I'm not clear on is why the housewrap cannot function as both the liquid water control layer and the air barrier. If you wrap the framed structure and tape the seams of the housewrap, I don't understand why that air barrier would be inferior to Matt's method above.
I realize there may be a lot of tiny hoes caused by the staples in the housewrap. Well, those could be taped. The gap at the bottom plate is also a concern. Common sense tells us not to tape the bottom edge of the housewrap to the concrete foundation, because it could hold bulk water. SIGA says go ahead and tape that joint. The tapes and housewrap will allow it to evaporate, and none of the materials there are subject to damage by water. Plus, since you have done a good job of flashing above, there is very little water getting behind the water control layer.
I think it's an important question because it would save hundreds of dollars of SIGA tape.
Products and processes evolve depending on material cost, labor cost and performance. I think Matt is right on the leading edge of this evolution with OSB, SIGA tape, and housewrap. Great job, and thanks for all your helpful videos.
Response to Kevin Dickson
You're right; you can use housewrap as your air barrier. Contractors who try this approach have varying levels of success, depending on the quality of the housewrap they use and the efforts they make to seal tears, edges, and penetrations.
Almost all builders who have tried both approaches -- taped housewrap vs. taped sheathing -- report that they get lower blower-door numbers from the taped sheathing approach than they do from the taped housewrap approach.
Martin and Matt.
Thanks for the replies. Very helpful.
It's all in the results
For whatever it's worth, I've learned a lot since starting the "Siga air barrier odyssey". Using taped sheathing as the air barrier means that every penetration has at least 7/16" of depth to "self-seal" around a fastener. The only membrane that has that ability is a really good liquid applied product like Prosoco Fast Flash & Cat 5 (along with the other STP's now following in their footsteps).
If you consider drying, aging and movement from wind load stress, fabric membranes have a harder time dealing with these changes over time and it's bound to affect their performance. (It seems that this description fits my 50+ yr old frame equally as well)
The Small Planet Workshop is the Zehnder dealer for the NW corner of the US and Western Canada. When our regional Zehnder design engineer, Matt, started on his new house it was obvious that he was going to take the air barrier seriously since he knew his ventilation system performance is enhanced by a good air barrier.
Here is Matt late last year in mid-project. You can see the taped seams with Siga Wigluv. The joint to the foundation is also backed-up with Tremco Acoustical sealant. The Siga Majvest is not the air barrier and gets a layer of polyiso over it.
Matt called early this week after getting his blower door test done by the local portland "guru's" eager to see how well it was going to do.
0.25ACH 50 based on exterior volume. He estimated it to equate to 0.29ACH 50 on interior volume. Astoundingly good results!
These results will get him a long lasting air barrier AND a 6 pack of beer at this springs Passive House Northwest's PHnw 5 spring conference on March 29th in Portland Oregon. https://www.phnw.org/100/31/phnw-5.html
This is a call to any of you North-westerners going to the PHnw 5 conference who got a better than 0.6ach 50 result on a project in the last year. Send your result and name to [email protected] for FREE BEER at PHnw 5!!!
Btw… NOT a Passive House. He just built it that tight because he could.
Wigluv's awesome. Another good tape is PassivTape and their PassivPanels for cable/pipe penetrations. Should be available at power-house.ca
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