Q&A Forums

Spray foam for attic Post New Topic | Post Reply

Author Comments
Gregory Elukowich
Posted: Jan 05, 2012 11:37 PM
Spray foam for attic
Good evening. I gutted my entire house.Its a one story with a finished basement.The main floor has block outside walls with brick finish. The wall is about 10 inched thick.I reframed it using 2x4s.I tarred the inslide of the walls and was thinking of spray foam instead of fiberglass insulation. My friends think that is overkill. And instead sprayfoam the roof instead. The attaic is going to be used as a extra room since i am only having 2 bedrooms on the main floor. If i spray foam the roof, will the roof need to breath? I have no ridge vents. Just soffit vents.
steven argus
Posted: Jan 06, 2012 01:31 PM
steven argus
Posted: Jan 06, 2012 01:32 PM
Respectfully, your friends are wrong. What to do? A lot depends on your climate. Minumum, 2 inches of closed cell foam on the walls, hold the studs off the block wall. Minimum,3 inches of closed cell foam in the roof, unvented. The only reason your roof would need to "breath" is if you were using fiberglass or cellulose. They let through excess heat and moisture. Foam does not. You wont be sorry for using the foam.
Gregory Elukowich
Posted: Jan 06, 2012 08:01 PM
Thanks for the info. I live in New York City. So we get all four seasons of the year. I really dont think I can spray foam the whole house. Its 46'x26'. Due to the fact money is an issue. So I think it is more important to do the roof, since heat rises.
richard sucher II
Posted: Jan 07, 2012 12:09 PM
with all due respect to previous posters, given the choice between foaming sidewalls or attic in your particular case, I would advise you to foam the sidewalls and install cellulose in the attic. If you use conventional insulation in the attic, you would need to provide adequate ventilation. In order to deal with low R factor at roof/wall juncture, you could spray some foam up the roof line a few feet to increase R factor in that tight space; blow balance of attic area. You will get high R factor where space allows for it; foam at sidewalls will control indoor air quality/infiltration issues. Two (2) inches of closed cell foam would do nicely in the sidewalls. If money is no object, then have at it in the attic with foam but given that money is an issue I would recommend that you foam walls and do some foaming in attic up roof line but bulk of attic would be done conventionally. Just my opinion after spraying foam for over 33 years in the Midwest.
Paul Covert
Posted: Jan 08, 2012 01:34 PM
If you are converting attic space to living space, some, if not all, of the roof will be cathedralized. That is where you want the foam.
richard sucher II
Posted: Jan 08, 2012 02:43 PM
i misread your post. was thinking that you were in single story with no room for additional living space above. must be more like story and one half with dormers possibly. given this info, am thinking that it makes sense to spray walls and roof line of attic area with two inches on walls and at least three inches on entire roof line. furr out roof framing if necessary to get additional space for foam in roof. no need to vent at all. if you try to use conventional insulation to insulate this attic space, you will not be happy; you will cook or freeze up there without foam. My first home was like this and we foamed the attic room as outlined above.
as far as concrete walls are concerned, would consider minimal thickness of spray foam just to eliminate any infiltration issues. if budget does not allow, focus on attic foaming and go with batt on the main floor. good luck.
maurice richter
Posted: Jan 08, 2012 07:58 PM
Has anyone talked about amount of energy savings payback times? (I'm just a homeowner.) Gregnirene, what is the theory of tarring the walls? Did you tar before putting up the 2x4 interior? (Do I assume the 2x4 are inside?) I do know wind can work it's way thru brick and block. I also wonder about the tar being a vapor barrier on the wrong side of a possible fiberglass?
steven argus
Posted: Jan 09, 2012 11:24 AM
Lets be clear here... Heat seeks cold in all directions. Warm air rises. The main reason the R value in a roof is higher is because the roof is typically more square footage. Also, masonry loves to suck the heat out of a building. Basically, all your walls are a giant heat sink. Because of budget reasons, put the 2 inches of closed cell in the walls and change to open cell in the roof. With open cell, however, in your climate make sure you use a vapor retarding paint/ primer on the finished side of the wallboard. If you can't ventilate, do not use anything but foam.
Gregory Elukowich
Posted: Jan 09, 2012 08:51 PM
The house is not very large. About 1200 sq feet. So im making it two nice sized bedrooms. To get more liveable space I took out some joists above the living room, made it a catherdal ceiling. So there will be a railing in the attic over looking the livingroom. The attic space will be a play room for me and my son. Its only 6 and a half feet high in the middle of the roof line. The space will be used year round. Has to be comfortable in the heat and the cold times of the year. A small section in the attic will have the central air stuff. I put in a staircase to get up there. As for the tarring, I felt it was an easy and cheap way to seal the blocks from any air getting through the mortar joints. So i was thinking 3 inches of closed cell in the rafter bays. As for the walls, I framed them with 2x4s. So it leaves me with about 3 and a half inches of insulation space. R13 or R15 will work. R19 is to thick and i dont want to loss space moving the walls in.
Gregory Elukowich
Posted: Jan 09, 2012 09:15 PM
I thank you for the information. Quick question. Its January now, no heat up the on the main floor. Can they spray foam in these temperatures. Or do I need warmer temps like in the spring. Just like the info before I have contractors come and see what they say.
John Shockney
Posted: Jan 10, 2012 11:49 AM
Depending on the type and brand of foam you can spray some foam down below 30deg but warmer is always better, foam is formed by hot expanding gases and yield is better when spraying warm surfaces.

Which also brings up the fact that it takes more (10-20%) chemical to spray block than wood in any weather due to the fact that wood is an insulator and the block will suck the heat out of the foam.

I do agree that if you use fiberglass in the walls over the tar you will most likely have a moisture problem inside the wall when the warm moist air travels through the fiberglass and reaches the cold surface of the block/tar. If you use fiberglass in this application there needs to be a drain plain at the inside surface of the block to allow the water to drain out like the weep holes installed in brick today.

Personally I agree that 2 inches of closed cell is the best way to go on a block wall because it will seal out any water that comes through the porous block. But you have already sealed the block and 3inches of open cell will give you the same insulation for about half the cost and still solve the moisture issues.

As for your cathedral ceiling the only way to go is a none-vented roof with as much insulation as possible given the room provided and your budget get as close to R-40 as possible if you want true energy savings, but you can live with an R-19 or 6inches of open cell as a minimum.

I can send you some detail drawings if you email me at Airpro@gotsky.com

Hope this helps


You need to login to reply to this topic. Please click here to login.