spf attic and vaulted ceiling | Ask Mason Knowles - SPF Consultant | Spray Foam Technical Questions and Answers | SprayFoam Magazine Q&A Forums

Q&A Forums

Author	Comments
Pablo Illanes Posted: Jan 31, 2012 11:54 PM	spf attic and vaulted ceiling First post and before i go want to say this site is awesome and informative. Toronto Canada is where im spraying a one story bungalow with raised rafter ties. Wondering best suggested application. originally i was going to to spray the walls up to the rafter ties and use blow in for the attic space and vent it out. getting some drips of water from the shingle nails poking through so i wanted to spray the walls and rafter cavities to deal with any water issues and replace roof further down the road with some nice peel n stick. I have read that 1" is ok and to use batting for the rest of the r value needed. Is this valid. If not how think should i be spraying. Would it be ok to spray entire perimeter walls and attic roof (with whatever minimum recomended thickness) and still do the blow in insulation in the rafter ties. Rafter ties are deep. Rafter cavities would need to be deepend and would like to avoid the extra work.
mason Posted: Feb 01, 2012 08:28 PM	First thing first. Fix the roof. Then insulate. If you are doing a hybrid system (foam and fiberglass), spray a sufficient thickness of foam to eliminate the possibility of condensation. You may have to do some hygrothermal modeling to determine the thickness required. I would guess around 3 inches of closed cell foam but again do the calculations to specifically know. Next if you want to divide the attic into vented and unvented areas it is possible. I am doing that same thing on my house in Savannah, GA. But you have to completely separate the spaces with a dividing wall that is also insulated so that air from one space is not transfered into the other. Vent the vented space properly in accordance with your areas ventilation requirements.
John Shockney Posted: Feb 01, 2012 11:39 PM	?is the water from the roof leaking or condisation on the cold nails?? Airpro
Pablo Illanes Posted: Feb 02, 2012 06:12 AM	just want to seperate attic from main. condensation. house is gutted and heaters being used. if i vent attic do i still need 3" on top of the drywall if im goin to blow in.
mason Posted: Feb 02, 2012 10:08 PM	yes you still need a sufficient thickness of foam even more so if you vent the attic
mark moyer Posted: Feb 03, 2012 10:23 AM	not clear to me,,, one story bungalow,,,4/12,,,6/12 pitch??? bungalow,,,not to big im'a thinkin,,, not sure of the climate zone he's in either,,but to be redundant,,in zone 5 minimum r19 of an air impermiable insulation applied to the roof substrate in a cathedral/vault to prevent condensation,,,minimum,,, it should be noted that the word applied means ADHERED TO ,,,NO AIR SPACE FOR CONDENSATION TO LAY OUT ON BETWEEN THE INSULATION AND THE SUBSTRATE,,, why not spray 10-12" of open cell foam from the top plate to the peak of the roof for the best possible assembly? define the building envelope at the perimeter of the building...whoa,,what a concept,,,go figure,,, we like to "seal" our flat attic lids with open cell foam with about 3-4 inches...works good for us,,,gives us a good $$ to get in the attic,, gives them a good installation,,we then top over the foam with filterglass to get to the prescriptive energystar r49 kiss your heers raters booty number,,,to keep our r value blinders firmly in place so we dont offend any of the big players... god bless

Author

Comments

Pablo Illanes

Posted: Jan 31, 2012 11:54 PM

spf attic and vaulted ceiling

First post and before i go want to say this site is awesome and informative.

Toronto Canada is where im spraying a one story bungalow with raised rafter ties.

Wondering best suggested application.

originally i was going to to spray the walls up to the rafter ties and use blow in for the attic space and vent it out.

getting some drips of water from the shingle nails poking through so i wanted to spray the walls and rafter cavities to deal with any water issues and replace roof further down the road with some nice peel n stick.

I have read that 1" is ok and to use batting for the rest of the r value needed. Is this valid. If not how think should i be spraying.

Would it be ok to spray entire perimeter walls and attic roof (with whatever minimum recomended thickness) and still do the blow in insulation in the rafter ties. Rafter ties are deep. Rafter cavities would need to be deepend and would like to avoid the extra work.

mason

Posted: Feb 01, 2012 08:28 PM

First thing first. Fix the roof. Then insulate. If you are doing a hybrid system (foam and fiberglass), spray a sufficient thickness of foam to eliminate the possibility of condensation. You may have to do some hygrothermal modeling to determine the thickness required. I would guess around 3 inches of closed cell foam but again do the calculations to specifically know.

Next if you want to divide the attic into vented and unvented areas it is possible. I am doing that same thing on my house in Savannah, GA. But you have to completely separate the spaces with a dividing wall that is also insulated so that air from one space is not transfered into the other. Vent the vented space properly in accordance with your areas ventilation requirements.

John Shockney

Posted: Feb 01, 2012 11:39 PM

?is the water from the roof leaking or condisation on the cold nails??

Airpro

Pablo Illanes

Posted: Feb 02, 2012 06:12 AM

just want to seperate attic from main.

condensation. house is gutted and heaters being used. if i vent attic do i still need 3" on top of the drywall if im goin to blow in.

mason

Posted: Feb 02, 2012 10:08 PM

yes you still need a sufficient thickness of foam even more so if you vent the attic

mark moyer

Posted: Feb 03, 2012 10:23 AM

not clear to me,,,
one story bungalow,,,4/12,,,6/12 pitch???
bungalow,,,not to big im'a thinkin,,,
not sure of the climate zone he's in either,,but to be redundant,,in zone 5 minimum r19 of an air impermiable insulation applied to the roof substrate in a cathedral/vault to prevent condensation,,,minimum,,,

it should be noted that the word applied means ADHERED TO ,,,NO AIR SPACE FOR CONDENSATION TO LAY OUT ON BETWEEN THE INSULATION AND THE SUBSTRATE,,,

why not spray 10-12" of open cell foam from the top plate to the peak of the roof for the best possible assembly?

define the building envelope at the perimeter of the building...whoa,,what a concept,,,go figure,,,

we like to "seal" our flat attic lids with open cell foam with about 3-4 inches...works good for us,,,gives us a good $$ to get in the attic,,
gives them a good installation,,we then top over the foam with filterglass to get to the prescriptive energystar r49 kiss your heers raters booty number,,,to keep our r value blinders firmly in place so we dont offend any of the big players... god bless

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