Which foam system to use in air-sealing the attic in an older home before adding cellulose?
I am getting two different recommendations from contractors and could use some guidance. We live in Portland, OR in a 1951 ranch-style house that was extensively remodeled in 2005. We started to significantly upgrade our attic insulation & air-seal and discovered that we have a vermiculite/asbestos remediation problem to solve first. Some of the abatement cost is covered by the ZAI Trust fund.
Result- all the existing insulation (vermiculite, old cellulose, blown-in fiberglass) is being removed first. Then, air seal and blow-in cellulose to R49.
This is a very well ventilated attic (remodel design) so all air-seal and insulation must go between the ceiling joists. I have received two different proposals:
Contractor A: seal leakage sites in attic prior to insulating including top plates, penetrations, bath fans, etc using a 1 part foam with blower-door direction. Then add blown post-consumer recycled 100% borate cellulose insulation to R49.
Contractor B: use 2 part foam to seal the entire ceiling; then add the cellulose. Not clear yet whether they’re recommending open cell or closed cell.
The ceiling joists are predominately 2×8. Couple of other data points: the house floor had fiberglass batts installed between all floor joists so we had that all encapsulated in foam during the 2005 remodel. Also most of the walls were taken down to studs and cavities (2×4) filled with foam. In areas of new construction (2×6) we added rock wool on top of the foam in order to fill the cavity. Also, 1″ polyiso board was added to the exterior walls before the siding or stucco was installed. In other words, the floor and walls are fairly well sealed and insulated. Focus is now on the attic. Just installed 10kW solar array so we really want to decrease our energy load.
I think my questions are: 1) should we go with A or B? 2) If B, should we use open cell or closed cell ?
Thank you very much for your time and thoughts.
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Replies
If the ceiling is sheet gypsum rather than crumbling plaster on lath there is no point to doing a flash-foam over the entire ceiling. Go with plan A.
R49 cellulose requires an initial installed depth of about 15", which you probably don't have the vertical space for near the eaves. With 2x8 rafters & joists you'd be looking at maybe 6" of depth over the top plates of the exterior walls after the code-required 1" minimum clearance between the insulation & roof deck, which is about R22.
What sort of foam and at what depth was installed in the wall cavities?
Yep, I agree with Dana. Contractor B is just looking for more money and his approach would also entail more potential risk to your home because of the 2 part nature of the foam. You could even do what Contractor A is suggesting with 1 part foam yourself. I did that on my home. But since you are already doing remediation of the vermiculite involving outside labor you may as well pay Contractor A to do it.
First off, thank you very much for such a prompt response!
The ceiling is gypsum board.
If it helps (or hurts), when we did the remodel in 04, they sprayed foam into the areas where rafters meet the ceiling joists; open cell.
Regarding the walls, the old area of the house is 2x4 and had 1950's style paper-backed fiberglass batts that were maybe R8 at best. All of that was removed and the cavity filled with open cell. I think we added firing strips onto the 2x4s but don't remember for sure. On the exterior of the wall, 1" polyiso board was added plus a rain screen for venting. Trying to get to at least R19 in those walls. New construction was 2x6 and cavities were filled with foam and rock wool, plus the polyiso board on the exterior.
Kent, If you are at all worried about any potential bad consequences of the previous 2 part open cell spray foam - I wouldn't be. You would have already noticed the consequences of a bad installation. I would think of the whole issue as being a statistical problem with a very bad result for the 1 in a 1000 or 1 in 10000 individuals that were unlucky enough to have an incompetent installer. The results of being unlucky is often so awful that it just isn't worth getting a ticket in that particular lottery. It seems you were a winner in that game of Russian roulette.
Open cell cavity fill is exactly the type of foam you want for the walls, especially with the inch of rigid foam on the exterior, otherwise it would severely restrict drying capacity.
In your climate (zone 4C) an inch of polyiso is plenty for dew point control at the sheathing for either 2x4 & 2x6 construction, so you don't need or want a low vapor retardency layer between the sheathing and the conditioned space- standard latex paint on wallboard is plenty.
At the attic floor joist/rafter interface, does the open cell foam contact the roof deck?
Yes, I believe the open cell foam may contact the roof deck. However, we added a 3/4" thermosiphon space between that first layer of OSB (which has the foam contact) and the next one on top, so there is good ventilation between the metal roof and the innermost roof deck.
Kent,
I'll modify Dana's advice and Eric's advice slightly. Eric assumes that Contractor B's bid is higher than Contractor A's bid, but that's an assumption -- you never wrote that.
If you're not making the decision on price, the most important factor is the reputation and skill of the contractor. Either approach to air sealing will work just fine. The quality of the air sealing job depends entirely on the skill and conscientiousness of the contractor, and both of the described methods can work.
Here is a link to an article with more information on this topic: Air Sealing an Attic.
If it's just a short section of roof deck over the exerior walls that has the foam contact and it's vented on the exterior it's unlikely to have a problem in your climate. The 3/4" space isn't much, but it's way better than nothing, and if the roof deck is vented on both sides higher up it'll be pretty dry overall.