Another “help me design a wall” thread
I’ve read wall build articles here but I’m still ambiguous as to the placement of barriers. I’ve also watched Dana’s series titled, “Extreme 10 foot or less snowy knoll patch skiing”, but couldn’t find any relevant information there.
Zone 5. Inside to out: (sealed?) Drywall | 2X6 studs sealed with Ecoseal and filled with dense pack | either OSB or ZIP taped | 3″ poly foam taped | rain screen, vinyl siding.
From what I’ve learned here this wall will need to dry to the interior.
a few questions, if I may?
° Do I need any other thin barriers in this stack up anywhere such as Intelloplus behind the drywall or anything on the outside of the sheathing?
° Since I’m using exterior foam and I intend to Ecoseal in the stud bays and plates, will I benefit from installing drywall airtight using sealants?
° Would I benefit from airfoil electrical gang boxes or is that a waste at this point? I’m betting the answer to this will pivot on the above question’s response.
° Am I leaving anything out of this build, or adding unnecessary material?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Drew,
Q. "Do I need any other thin barriers in this stack up anywhere such as Intello Plus behind the drywall or anything on the outside of the sheathing?"
A. No, not from a building science perspective. But it never hurts to check with your local building department to see if you are in compliance with your local building code - especially if you live in Canada.
Q. "Since I'm using exterior foam and I intend to Ecoseal in the stud bays and plates, will I benefit from installing drywall airtight using sealants?"
A. I would say that in your case, the airtight drywall approach is probably overkill -- although we have plenty of GBA readers who believe in overkill. (This response is based on my assumption that "dense pack" is shorthand for "dense-packed cellulose.")
Q. "Would I benefit from Airfoil electrical gang boxes or is that a waste at this point? I'm betting the answer to this will pivot on the above question's response."
A. In my opinion, it always makes sense to try to limit air leakage through electrical boxes. If you choose not to purchase airtight electrical boxes, you may still want to squirt some caulk at the hole in the back of the box where the cable enters, and to caulk the crack between the drywall and the electrical box.
Q. "Am I leaving anything out of this build, or adding unnecessary material?"
A. If you plan to use taped Zip sheathing, then I don't know why you would bother with EcoSeal.
You need something that counts as a WRB. If you choose taped ZIP, that counts. A layer of Tyvek counts. Exterior foam may count, depending on what type you use.
Reid,
Good point.
I just built a house similar. Here is my advice and I ran calcs to determine the costs to come up with my game plan. 1/2" OSB with taped seams using 3M All Weather tape saved me about seven thousand dollars versus Zip. Of course I had $800 in DuPont Drainwrap go over that. As to the airtight drywall business, save your money and time. As to that tape, it works as window flashing tape as well and is perfect for taping the seams of your outsulation exterior foamboards, too. If you really want to keep air sneaking out through the gaps and cracks make your air barrier the outside wall. That is where the tape comes in. When I had my foam board up with the two and a half inch foam on the outside, and no cellulose inside as we were wiring, it was amazingly how warm the walls were on the inside. In an area where there was no foam yet, it was noticeably colder. But the fact that there were no howling drafts due to having things buttoned up tight was awesome. If you are really OCD like me, buy some good caulk and caulk your stud bays where the 2x6s meet up with the sheathing and anywhere you can see an inside seam on the OSB which isn't many places. I think it costs me $180 in caulk to do that and it was probably overkill. I also caulked where any framing members met like window jacks, plates, headers., etc. I think ecoseal might be wasteful in this case. ...as to electrical boxes Martin explained it well. Also once your rock is up and when you are doing your outlets and switches, that is a good time to caulk around the box opening where it meets the drywall, and do as Martin says as to placing a bit of duct sealing goop/caulk over the holes where the nail went through and where the wires come into the rear of the boxes. One of the important things here also is that it limits the amount of dust that the cellulose creates from entering the house. Believe me there will be some. Best wishes.
Most excellent gentlemen. Thank you for your input.
Joe, I like the way you caulked your plates and other components--I'm going to do the same.
Joe et al - is there any benefit of using low expansion foam vs. caulk in the stud bays?
Cons? ie; caulk: 3 sided adhesion. I'm assuming expanding foam may seal better but is more costly.
I'm probably just nit-picking at this point...
Joe,
Great discussion. Thanks for your feedback.
You stated, "1/2" OSB with taped seams using 3M All Weather tape saved me about seven thousand dollars versus Zip. Of course I had $800 in DuPont Drainwrap go over that."
$7k is considerable, but I don't see a significant difference when comparing 7/16 OSB vs. 7/16 ZIP on my design. Implementing 9' walls, I calculate 2074 ft^2 wall area total.
2074 ft^2 / 32 (4x8 sheet) = 65 sheets. I did not subtract window cutouts or the massive garage door areas which should reduce this number generously.
Using Lowe's advertised prices;
65 sheets 7/16 ZIP @ : $21.48 = $1396
65 sheets 7/16 OSB @ $10.35 = $672
----------
Delta = $724
I believe that I might find discount if purchasing mass from Lowe's and Zip currently offers a $3 / panel rebate ($65*3 = $195) reducing the delta to $529.
I realize I didn't consider the ZIP tape, but I also didn't consider 3M tape for OSB. Using ZIP, I will also save the cost of house wrap. The attractive benefit to me is that I will have a weatherproof shell stood up fairly quickly.
I'd really like to understand how using OSB saved you $7000. Maybe you have an entire envelope including the roof? I do plan to run the air barrier at the ceiling and not the roof, so I will not have a conditioned attic. But even if I did, I don't think my offset cost would still not save $7k.
I ask because I am wondering if I am missing something here or using incorrect pricing or products. Thanks Joe.
Sorry for late response, Drew. I had 150 sheets OSB including garage. Then I had the roof. I used 5/8 OSB there, as my roof is vented and covered in a mechanically seamed standing seam roof. My calcs were about seven thousand less. Perhaps there was a more striking price variation at the time plus I had a framing quote from a crew. Maybe they wanted more money to do ZIP. But that is what I recall. Oh, wait. Now I know! I was pricing ZIP R!!! The 1.5" stuff with the polyiso foam. THAT WAS WHY, I am sorry!! Funny how a busy life obscures some memories. Although the number of graduation parties I attended the weekend I graduated high school has not escaped me. That was 1983 and I went to exactly 18 parties. So yeah... aging...
Ok, so being serious again and remembering. The seven thousand was the difference between OSB 7/16 with 3M tape and Tyvek Drainwrap, and then 2.5" of reclaimed EPS foam VERSUS THE ZIP-R 1.5 polyiso. Ok, that was how I came up with the seven grand. I had 147 sheets but there were a few extras, plus I used treated ply wood along the bottom 2' of the house and garage. All and all I think if you use the ZIP plain sheathing you are fine, but do yourself a favor and look for some reclaimed foam. Also as to outlets, buy a foam gun and get the refills. Use the window sealing stuff that doesn't grow too big. Very carefully seal the entrances of the boxes where wire comes in with a touch of the foam. Don't fill the box or anything. Try to put as few outside wall electrical boxes as possible. When you plan a room you will be amazed how few you need on outside walls. Use your judgement as to where caulk would be better than foam and where foam might work better on your framing and stud bays and gaps. After a few hours of doing this you will intuitively know what will work better. But by all means get the fifty dollar gun and use the foam refill cans because the degree of CONTROL you will have over the foam coming out will mean your waste of foam will be exceptionally minimal. Cheers!
Some caulk work.
Thanks for the pic Joe, that looks great.
I called my dense pack cellulose installer, Jack, today. The price comes in at $1.05 / ft^2 of wall. I asked Jack to explain the procedure and he informed me that he installs at 6-7psi, and that the insulation will feel like the palm of one's hand after installation. I asked if the fabric that is tacked up to hold the insulation in would bulge out when finished and if the walls would be rolled flat if this happened. I was informed that they would be rolled if needed, but they will not bow outwards. Does this sound right? For whatever reason, I am under the impression that the retainment fabric would bulge out when properly installed.
Drew,
The usual metric for insulation density is pounds per cubic foot, not psi. The usual goal is 3.5 pounds per cubic foot, not 6-7 psi.
If the insulation is installed behind a membrane like InsulWeb, bulging is typical. The bulges are flattened with a roller after the blowing is complete.
For more information on these issues, see How to Install Cellulose Insulation.