Insulating a 1.5 story bungalow, climate zone 6A
Hi All. We recently purchased a 1914 bungalow in coastal Maine (climate zone 6A). We are wrapping our heads around the scope of our remodel (the last upgrade was in the 70s). We know we need to re-roof and we want to upgrade the attic insulation at the same time, but as with most bungalows and capes, there are challenges to insulating the attic when there is 2nd floor living space to contend with. Also the primary bedroom, which sits under a shed dormer, also partially extends out over an uninsulated, but fully enclosed south facing sunroom.
First:
We’ve been told that CCSF would be the easiest solution for insulating our attic, and after reading all the GBA articles on insulating capes and cathedral ceilings I can see why. The permanence of spray foam, and the fact that it can trap humidity or bulk water makes me nervous though, but I’m willing to accept that it might be the most practical and effective solution we can go with. If we go with spray foam against the attic sheathing do we need to add vapor control layers or is the drywall ceiling and walls on the 2nd floor enough? Also will we need to dehumidify the attic after spray foaming?
Second:
I thought poly iso over the roof deck and rockwool between the rafter might be a good option for us, but we only have 8” of headwall between the roof shingles and the bottom of our shed dormer windows. I don’t think that would allow the right ratio of insulation on the exterior of the roof deck correct? Would love some advice from folks who have done this in the past and wrestled with a dormer. (see attached picts) I assume this type of roof assembly is more expensive and detail oriented than spray foam?
Third:
How would you all go about detailing the underside of the bedroom that sits out over the uninsulated sunroom? It’s currently blown in cellulose.
Fourth
Currently the 2nd floor bathroom has no vent, and there are only a couple of canned lights in the 2nd floor ceiling. There are no obvious issue of mold in the attic. We plan to add an additional bathroom and a washer/dryer on the second floor, but are uncertain about where to vent these considering the different possibilities for insulating the attic. Any reasons we couldn’t just vent out the gable end wall and avoid the complications of going through the roof? I know this is a rudimentary question, I just wanted to ask in light of the the reinsulation question above
LMK what other details I need to provide. And many thanks for your time.
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Replies
I would spray foam. I seems like you may be getting some of the problems often associated with open cell spray foam and closed cell mixed up. I would not recommend open cell. Closed cell does not trap humidity (unless your framing is wet when you install. It can hid bulk water so if you see signs of old roof or moisture damage I would make sure this is fixed. I would also spray foam your bedroom over sunroom.
Generally I wouldn’t use spray foam and certainly not in a new build but I certain situation ( retrofit with a complicated roof structure) it is the best solution. Do some research into the exact type of foam they are spraying also. Make sure it is a hfo with a low GWP and also take a look at the fire retardant numbers. Some foams have exceptionally high concentration of these chemicals and these are the chemicals that have been shown to off gas. Do some research into before you go that route, but I think this is the direction I would go.
Thanks. That's two for spray foam. But I had not thought to ask installer about the make up of the foam they are using. Good thing to get educated one. Cheers.
Our rafters run from the inside out and beyond the envelope. I assume in this situation the space between the rafters at the top plate gets blocked up prior to being sprayed, leaving the tails of the rafters unsprayed. Is it OK that some of the framing is sprayed and some is not (in a cold climate)?