Ooops… where’s the air barrier?
Here in WA state we now have blower door testing required for new homes, and they have to meet a fairly lax standard. As expected, a lot of folks aren’t clear on what air leakage is and how to build tight. Got a call yesterday from a man with a new owner/builder home underway, insulation just installed, and he wants to know about testing. He intends to put T&G wood on all walls and ceilings. The building inspector advised him that he would need 4-mil poly as a VB if he wasn’t going to have drywall with VB primer.
I told him I was skeptical that this would provide much air sealing, and that he should really install and tape drywall even if he’s going to put paneling over it. Well, the windows are already installed and the jambs aren’t deep enough for the extra 1/2″. The cathedral ceilings may be able to get drywall, but he didn’t sound convinced.
I don’t know what else to suggest here. Air barrier material = rigid material, right? Will be benefit from a very carefully installed and taped poly layer? Tyvek or other housewrap on the interior? Something like Membrain?
Thanks for your thoughts.
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Replies
What type of insulation? Is siding installed?
David,
Probably Albert Rooks and Ken Levinson will post comments recommending a European membrane designed as a smart vapor retarder and interior air barrier. Several such products are available.
MemBrain is also being touted as an air barrier.
With all of these products, however, they only work if seams are carefully sealed, the perimeter is sealed to other air barrier materials, and all electrical boxes and other penetrations are airtight and sealed.
In the 1980s, a lot of Canadian builders used 6-mil poly as an air barrier. The routine required all seams to occur over framing lumber, and for all seams and edges to be sealed with lots of messy Tremco acoustical sealant. However, I don't recommend the use of 6-mil poly in your climate.
I bet this owner/builder thinks he's "saving money" by not hiring an experienced builder. I wonder what other surprises will come up as his adventure proceeds...
Apparently siding is not installed, so I did talk to him about taping sheathing.
Hi David, Haven't talked since the old Breaktime (remember I live just across from you on Vancouver Island)
Builders here still routinely use a sealed and taped 6 mil poly air barrier behind wood ceilings and walls. Combined with a porous exterior sheathing or well vented roof space it appears to work quite well.
Martin & David,
I hate to be so predictable... But yeah, he'll probably need a membrane on at least the lid I would guess. That combined with taped sheathing should get him to the WA state 5.9ACH requirement (which is really an SLA equivalent)
The current requirement is about what average construction yields anyway, so it seems like just replicating what the drywall would normally do should get him there. The reality is that if he fails, there is no current penalty. He can re-test and in the end just post the test result. It won't stop occupancy.
But, when we get to the 2012 IEC. Then it will be a different game in WA altogether...
Speaking as a DIYer, you could never convince me full level 2 drywall is an economical or time efficient air barrier. Or particularly green. ProClima's intello plus installs fast with inexperienced labor. An owner builder is likely to have a better outcome with tape and membrane than drywall IMHO. However, beware of spontaneous credit card combustion when buying these materials!