air leakage question

[maxdog]

I recently built a cabin and used recycled 3.5" styrofoam for the ceiling/roof insulation. I need to seal the joints and small holes from the from the material before I install my finish ceiling material. I am torn between using spray foam or using a high end constuction tape for the sealent. can anyone give any real life experience or advice??

Thank you

[pearldog]

Max,
Air gaps should be filled with foam. Tape seal the joints is a good secondary action but probably not worth the time and effort as you are putting a tight roof membrane over it. Do not use duct tape type stuff, use a Tyvec type tape or some other kind of high quality tape- Protectowrap, Siga, 3M, etc.
Good your foam is used and "Pre-shrunk" as all sheet foam shrinks over time creating gaps at the seams after the job is done and covered.
.........terry


Terry Nordbye
The Practical House
CGBP- BPA
Inverness Ca.
415 669 1555

[gh100]

Your question doesn't have enough information. Is this a vented or unvented attic, or a cathedral ceiling? The short answer is foam would be the better sealant for these joints because of the open cell nature of the styrofoam installed, which incidently doesn't have nearly enough R-value for a ceiling assembly anywhere in California (if being green and saving energy is the concern).

[maxdog]

to answer the question, the ceiling is vented and cathedral. I am not in Calif. I live in PA. I am not overly concerned with the R value in the ceiling at this time. It is only a hunting/getaway cabin and will be only used a weekend a month(at best in the winter)

addtionally, I have decided to go withthe foam after little more research and friends at work..

Thanks for all the imput.

[AndyWahl]

Not a simple answer. Spray foam will help fill in the gaps in the foam
board and will seal until the foam shrinks. We know foam shrinks over time
as well as the daily movement of the building changing shape due to
temperature and moisture conditions can beak the foam away from the material
it is sticking to. Tape on the other hand can bridge gaps and can be more
flexible over time but will not insulate the gaps in the foam board.

So we need to ask, what is our thermal barrier and what is the air barrier?
If the foam is the air barrier as well as the thermal barrier then I would
use both the spray foam and tape. If the foam is only the thermal barrier
then just use spray foam to fill the gaps and voids. Another material such
as the sheetrock can be used as an air barrier.

When using spray foam consider getting a foam gun and canisters of the foam.
Be sure to read the installation instruction on the foam since most need to
be warm before installing. Practice and see how much it takes to fill the
opening, the foam will expand depending on what you get. Use a Japanese
pull saw to slice off the excess.

[JohnfromIPC]

There are some great responses here. I am going to say that you are probably going to cover the foam with sheetrock. Therefore, you would not need to tape the foam. I also agree that you need to make sure you select the right foam for your application. With that said, this is never going to be perfect as foam shrinks which will create some gaps going forward. Make sure you allow adequate time for the foam to adjust to the conditions of the house before sealing the joints. This will help eliminate future gaps.

[mikebonar]

Several air leaks and drafts are trouble-free to find because they are easy to feel like those approximately windows and doors. Holes may be hidden in attics, basements, and crawlspaces are usually bigger problems. You can find many useful suggestions by internet search for filling such kind of leaks or get help to any professional.