Spray On Foam Insulation ?

[Medix]

I have followed a number of the postings where they have used spray on insulation on the underside of the roofing. It does not appear that the attic area is vented at all. Is this correct and if so are there any issues in not venting the attic area?

 

[benjamming]

I used spray on foam but it was still vented.

 

[krooser]

The idea of venting the attic is to keep the roof underlayment cold so ice won't melt and sneak under the shingles to form an ice dam. That happens on one portion of my roof which causes water to leak into my porch.

I didn't have the problem until I installed a pellet stove in the porch/kitchen area of my home. That part of the house was always the coolest... now it's the warmest. There isn't sufficient venting in the attic space to cool the roof... a problem I plan on foxing next summer.

Spray foam, I think, would give a total thermal break between the attic and the roof keeping the roof cold and the ice dams away... it would still be best if you ventilated the attic.

 

[ilateapex]

I am currently working on a project for the Navy where Spray Foam was speced and they required the underside of the roof deck to be sprayed. The attic is not vented and actually has a HVAC register up there. The idea is that the HVAC duct is in conditioned space and not a non-controled attic. If you have duct in the attic this is a graet idea. We used closed cell foam, not sure of the weight maybe 1.7lb or so.

Things we ran into with this:
Not all shingles are warrantied on a non vented roof.
have to spray fire retarder on the foam as it is not covered with drywall

I always understood that venting the attic was to allow heat to escape. I don't remember anything about it for preventing snow to melt. I always look at houses where snow has melted off the roof and can tell about heat loss from the house.

Michael

 

[GSSFC]

The idea of venting the attic is to keep the roof underlayment cold so ice won't melt and sneak under the shingles to form an ice dam. That happens on one portion of my roof which causes water to leak into my porch.

I didn't have the problem until I installed a pellet stove in the porch/kitchen area of my home. That part of the house was always the coolest... now it's the warmest. There isn't sufficient venting in the attic space to cool the roof... a problem I plan on foxing next summer.

Spray foam, I think, would give a total thermal break between the attic and the roof keeping the roof cold and the ice dams away... it would still be best if you ventilated the attic.

Not exactly...

The SOLE purpose of venting is to overcome the performance limitations of convention insulation.

When using traditional insulation, the warm air is able to pass through the fiberglass or cellulose and is still warm when it contacts the cold roof surface. The difference in temperature will cause the warm air to condense when it hits the cold surface and moisture problems will begin. The idea of the venting is to have a constant flow of cold air to "wash" the warm moist air away before it has the opportunity to condense on the cold surfaces.

Venting is not to allow a building to "breathe" or to reduce attic temperatures.

Proper insulation and sound building practices are the key to building science.

Tim

 

[GSSFC]

I am currently working on a project for the Navy where Spray Foam was speced and they required the underside of the roof deck to be sprayed. The attic is not vented and actually has a HVAC register up there. The idea is that the HVAC duct is in conditioned space and not a non-controled attic. If you have duct in the attic this is a graet idea. We used closed cell foam, not sure of the weight maybe 1.7lb or so.

Things we ran into with this:
Not all shingles are warrantied on a non vented roof.
have to spray fire retarder on the foam as it is not covered with drywall

I always understood that venting the attic was to allow heat to escape. I don't remember anything about it for preventing snow to melt. I always look at houses where snow has melted off the roof and can tell about heat loss from the house.

Michael

There foams that are in the stages of ICC approval where addition thermal/ignition barriers will not be required. Currently, LaPolla has already passed the tests.

Most major manufactures will warranty a hot roof application. The key is the shingle installer needs to correctly install the roof. In our area of the country, New England, a roof won't last anywhere near the warranty period, regardless of installation, insulation, or venting!

Tim