Air Barrier vs. Insulation

[John B]

Bill R
Concerning airtight ceilings...and ventilated Attics
are you seeing anyone (in your area)doing ADA (Airtight Drywall Approach)?
Or is "sealing of seams and penetrations" always done after drywall?

[Dancing Dan]

It's also very easy to bypass if your air barrier is the drywall at the ceiling but somewhere else (i.e. the exterior sheathing) on the walls. You need continuity at the top plates, perimeter of the ceiling plane, soffits, etc. You need to design and execute it carefully, and test.

One of the reasons I'm not crazy about ADA is that you can't test it until pretty late in the process. The nice thing about the shell being the air barrier is that you can test it at dry-in and have plenty of opportunities to fix it - until insulation.

[Allan Edwards]

The nice thing about the shell being the air barrier is that you can test it at dry-in and have plenty of opportunities to fix it - until insulation.

When you reference the shell being an air barrier, with regards to the attic I assume you mean a non-vented attic with Zip Roof?

[Dancing Dan]

Essentially, yes.

[Allan Edwards]

Essentially, yes.

Are you conditioning the attic at all with supply and return ducts when you don't vent the attic.

[Ted S.]

Pull-up covers over fg have been long proven to counter the effects of convective currents.

So I'll ask the question here, when it comes to air barriers and hockey I never question a Canadian.

What are pull-up covers?

[dgbldr]

What are pull-up covers?

Any air-impermeable material that is installed over the top of the insulation. Could be Tyvek, reflective film, plastic sheet, whatever, depending on whether you want a vapor barrier as well or not.

Anything that will stop convection.

[ThingOfBeauty]

Alan, around here we've found some "weatherization"/insulation retrofit companies who have a crew or two that do air sealing work, specializing in attics.
These crews go into existing houses, lift the insulation off the attic floor to expose the top plates and electrical boxes, and use spray foam or caulking to seal the drywall to the top plates and fill the holes.
They make covers for recessed lights, and use mastic and/or spray foam to seal ductwork.
At soffits, they use sheet goods to make a new "attic floor" that covers the whole soffit, carefully air sealed on all edges.
Knee walls are covered, usually with foam board, on the back side.
At the end you have a pretty continguous barrier.
There's no reason not to bring them in on a new build before the insulation is installed to do the same tasks. (We've been doing that on jobs with no spray foam crew.) Or you can train a worker or crew yourself.
It's probably easier to manage soffits during the construction process, and do what you can to keep ductwork below the drywall.

[Dancing Dan]

Are you conditioning the attic at all with supply and return ducts when you don't vent the attic.

We haven't built any houses with attics per se - they've all had hot roofs and finished space below.

[Allan Edwards]

With an attic above your 2nd floor, other than the drywall what are the options for an air barrier between your living area and the unconditioned attic. Walls and knee walls can have air barriers on the outside of the wall, but what is recommended for attics. Dan, what would you use if you had attics.

Also, why are R-value insulation requirements higher for ceilings than walls.

[greentree]

Alan, around here we've found some "weatherization"/insulation retrofit companies who have a crew or two that do air sealing work, specializing in attics.
These crews go into existing houses, lift the insulation off the attic floor to expose the top plates and electrical boxes, and use spray foam or caulking to seal the drywall to the top plates and fill the holes.
They make covers for recessed lights, and use mastic and/or spray foam to seal ductwork.
At soffits, they use sheet goods to make a new "attic floor" that covers the whole soffit, carefully air sealed on all edges.
Knee walls are covered, usually with foam board, on the back side.
At the end you have a pretty continguous barrier.
There's no reason not to bring them in on a new build before the insulation is installed to do the same tasks. (We've been doing that on jobs with no spray foam crew.) Or you can train a worker or crew yourself.
It's probably easier to manage soffits during the construction process, and do what you can to keep ductwork below the drywall.

I've recently gotten into this line of work (weatherization) as another business segment and we've had good results, the last 2 we have done resulting in a 50% and 42% reduction in air leakage (one early 1900's,the other 1960's, both typical w/ no major defects) focusing just on basement and attic and resulted in huge comfort improvements to the homeowners. We've discovered wall plate lines in the attic contribute substantially to the air leakage into the attic space and the overall CFM to the house. I've also had good success blower door testing before drywall in remods and additions and it has made some dramatic results in the air leakage numbers.

Some raters have seem surprised by our results, I'm beginning to think it's because alot of crews dont have the construction background to really understand how a house is put together and therefore will miss or spend too much time looking for leaks.

Speaking of airsealing, on the last major build I did I went through with 1 part gun foam and picture framed every stud bay, gap and crack. It worked great, didn't take that long and was way more cost effective than using caulk as far as material yield, just wondering thoughts on durability. Dont mean to hijack, just thought this was relevant.

[Albion]

Greentree were these insulated attics fiberglass? Are you going to such extremes with cellulose in attics?

Just read in a vented attic to have a best practice consider installing a baffle in every joist bay and foam or caulk it to the wall top plate. Because most homes leak at the soffits thus air wash results in the edge of the insulation... So if one installs baffles in every joist bay extending it 2' above the insulation does this not eliminate air washing of the insulation ? And is the air above the insulation below the baffel not creating its own air barrier?

[John B]

I have read thru this thread a couple of times.
As far as I can tell no one is suggesting ADA (Airtight Drywall Approach)

Is ANYONE building homes with vented attics and using Airtight Drywall Approach?

[worthy]

Moi. That's essentially the Building Code here.

Here's how with exterior insulation. I prefer to use a combination of exterior and interior insulation, i.e., XPS as sheathing or over sheathing with fg batts between the studs, cellulose in the attic and spf at rims, odd places, basement wall and over garages/entries with conditioned spaces above.

[ThingOfBeauty]

We're sort of using ADA--the drywall is the air barrier--but IMHO piecework drywall crews are not the right people to depend upon for air sealing details at top plates, and the drywall approach does nothing for the other penetrations--lights, funky soffits, penetrations at top of wall, flues...all of which are normal for weatherization crews.
Greentree, those are good numbers. 1/4 is considered good here, when I tell people I got my house down by 1/3 they usually seem surprised it's possible. Congrats. also I have the same impression about can spray foam yield (much better than caulk) which is why I used it in my attic.

Alan, my understanding is high r-values for attics/roofs are mainly based on the relative ease/inexpensiveness of the additional insulation.
Walls are expensive to add insulation to--attics are cheap