[federer]

HI all

first just want to thank everyone for their comments and input in my other thread. i know i dragged you all through a whole lot of pictures and stupid questions and what not.

anwyays not getting any replies in the other section-so now that the new roof is in place, i am going to do spray foam insulation for the attic. what do you guys think about this?

thanks for all the input:thumbup:

 

[federer]

pic of decking

 

[seeyou]

i am going to do spray foam insulation for the attic. what do you guys think about this?

thanks for all the input:thumbup:

Open cell or closed cell?

 

[OldNBroken]

Federer! As annoying as you've been the last few months and that's the only picture you gonna give us of your final handiwork? Geez!!!! :whistling2::whistling2:

 

[federer]

Open cell or closed cell?

open cell. sorry didnt clarify before

 

[federer]

Federer! As annoying as you've been the last few months and that's the only picture you gonna give us of your final handiwork? Geez!!!! :whistling2::whistling2:

lol you are kidding right..i posted like 13 pics in my other thread...i know it was pretty annoying...i thought most people on here wanted pics though...

 

[OldNBroken]

My bad, guess I better head to the other thread. I missed that

 

[rodeo]

why do you want to sprayfoam the rafter bays?
is your new roof vented?

sprayfoam is considered "the best", I suppose,
but its not all roses and is best used in spot applications or
difficult situations. Sealing rim joists is one example.

 

[federer]

why do you want to sprayfoam the rafter bays?
is your new roof vented?

sprayfoam is considered "the best", I suppose,
but its not all roses and is best used in spot applications or
difficult situations. Sealing rim joists is one example.

not the rafters-the underneath of decking. i just used that pic as a reference. the reason is because i have a flat roof, so there is not a lot of space between decking and attic floor. so i cant use fiberglass because i can only get like R12 or something.

the roof is not vented-which is also why we are going with foam-otherwise we would need intake and ridge vents,etc.

i do need to seal rim joists too!

 

[rodeo]

Spraying the underside of the decking is the same thing as spraying the rafter bays. They mean the same thing.

Did you lay any rigid foamboard above the deck when the reroof was done?

 

[seeyou]

not the rafters-the underneath of decking. i just used that pic as a reference. the reason is because i have a flat roof, so there is not a lot of space between decking and attic floor. so i cant use fiberglass because i can only get like R12 or something.

the roof is not vented-which is also why we are going with foam-otherwise we would need intake and ridge vents,etc.

i do need to seal rim joists too!

Don't use open cell if there is no venting. If I understand correctly, moisture can permeate open cell, but not closed cell.

 

[federer]

Don't use open cell if there i no venting. If I understand correctly, moisture can permeate open cell, but not closed cell.

oh? isnt that why though? just in case there was a leak in the roof the water could come through-otherwise i would never find out until its too late (all teh wood would already rot away)

 

[seeyou]

oh? isnt that why though? just in case there was a leak in the roof the water could come through-otherwise i would never find out until its too late (all teh wood would already rot away)

It'll come through where the insulation meets wood or other material. But, if you trap condensation against the wood, it might not show up until serious damage has been done.

 

[federer]

so closed cell will prevent condesnsation?

 

[seeyou]

so closed cell will prevent condesnsation?

Not exactly prevent. But it keeps the water vapor inside from reaching the cool underside of the sheathing where condensation would occur. Open cell lets the vapor through.

Water coming the other way through the roof will find it's way in past either type foam.

 

[federer]

Not exactly prevent. But it keeps the water vapor inside from reaching the cool underside of the sheathing where condensation would occur. Open cell lets the vapor through.

Water coming the other way through the roof will find it's way in past either type foam.

ah i see what you are saying now...thanks for the input. what about if i drywall it up after installing the foam? that way the vapor will hit the ceiling/drywall and not travel through the foam

 

[Gary in WA]

Drywall can be an air barrier though never a vapor barrier. ADA the drywall: http://www.buildingscience.com/docu...rs/air-barriers2014airtight-drywall-approach/

Find your location: http://www.buildingscience.com/docu...sheet-310-vapor-control-layer-recommendations

“In Zones 1 through 3, open cell (vapor permeable) foam can be used successfully to enclose building spaces with moderate or dry interior humidities. In colder zones (Zone 4 and 5) open cell foam will require additional vapor control on the interior (in the form of spray applied vapor retarding paint). In cold zones (Zone 6 and higher) a closed cell foam is generally required. Dense cellulose can control convective loops, and provides significant amounts of safe storage capacity. However, in Zones 4 and higher, additional vapor diffusion and airleakage control (in the form of vapor retarding paint coatings and sealed drywall respectively) are required. In higher interior humidity spaces, closed cell foam or other roof designs are recommended.” http://www.buildingscience.com/documents/digests/bsd-115-wood-pitched-roof-construction?full_view=1

Gary

 

[johnk]

I thought it was best to use open cell under sheathing.I'm not a foamologist though:jester:

 

[federer]

Drywall can be an air barrier though never a vapor barrier. ADA the drywall: http://www.buildingscience.com/docu...rs/air-barriers2014airtight-drywall-approach/

Find your location: http://www.buildingscience.com/docu...sheet-310-vapor-control-layer-recommendations

“In Zones 1 through 3, open cell (vapor permeable) foam can be used successfully to enclose building spaces with moderate or dry interior humidities. In colder zones (Zone 4 and 5) open cell foam will require additional vapor control on the interior (in the form of spray applied vapor retarding paint). In cold zones (Zone 6 and higher) a closed cell foam is generally required. Dense cellulose can control convective loops, and provides significant amounts of safe storage capacity. However, in Zones 4 and higher, additional vapor diffusion and airleakage control (in the form of vapor retarding paint coatings and sealed drywall respectively) are required. In higher interior humidity spaces, closed cell foam or other roof designs are recommended.” http://www.buildingscience.com/documents/digests/bsd-115-wood-pitched-roof-construction?full_view=1

Gary

thanks for the link gary. so i do need more than the drywall. time to slap some more paint on!

 

[mem]

After Roof Project

In addition to the closed cell foam, I would also use 6 mil poly sheeting behind the drywall as an additional vapor barrier.