My question is this, after the foam is sprayed into the rafters, won’t this system cook and curl the shingles because of lack of ventilation? I have a 1901 house(Victorian style) with 4 turtle back vents in the roof. The article was in the april issue titled”Remodeling for energy efficiency”and involved spray foam 6 inches deep with 2 inch foam board over that.
Lighting up an exterior isn't just about ambiance— it's also about code compliance. Here is what the code says about safety and efficiency when it comes to outdoor lighting.
"I have learned so much thanks to the searchable articles on the FHB website. I can confidently say that I expect to be a life-long subscriber." - M.K.
Dig into cutting-edge approaches and decades of proven solutions with total access to our experts and tradespeople.
Start Free Trial NowGet instant access to the latest developments in green building, research, and reports from the field.
Start Free Trial Now
Replies
Nah. No one's ever been able to prove that.
Forrest
If that is the case,Why is it recommended that vents, vented soffits, ridge vents,etc. be installed on new and existing homes? I thought all of the above was to extend shingle life and stop condensation between shinge and roof sheeting.
It's a big topic here and in building technology groups. The ideal now is to have a totally sealed house "envelope", including the attic, with the required air-changes regulated by active fan(s).
You might try the "advance search" option on the browser to the left - it doesn't work well, but may lead you to the VARIETY of opinions here on the subject.
Basically, while it can't be proven that a sealed attic hurts shingles, it CAN be proven that ventilaing an attic lowers the attic air pressure relative to the house, and sucks (not really, but it's a good description) conditioned air from the house; makeup air comes into the house from the normal gaps in a normal house.
Building codes finally allow this - but they require that the roof plane insulation be a vapor barrier as well - usually closed-cell spray foam is used.
In moderate climates, Like here around Atlanta, I and many others just blow dense-pack cellulose or loose 'glas behind mesh over the rafters, and add DW or the mylar sheeting for code-dictated fire retarder.
Forrest
Your right, advance search is rough.What I guess I'm searching for, and can't find is an answer to this. I live in northwest P.A. where it gets windy and cold in the winter and I want to finish the attic area(which is very large). If I use that rafter system that was highlighted in the mag. in april, would it be an effective insulator and not ruin my very expensive roof. (Ice dams,etc.)I plan on installing a small hvac system for the attic room,which would incorporate some outdoor air ventilation. With the spray foam system,should i cover the turtle back vents,gable vents, and remove the attic fan? The room itself will be insulated,with only 4ft. of the rafters incorperated into the room ceiling. The rest of the attic will be outside of the room, accessable by a small door.
Here's a really complete attic thread I did - near Atlanta; from bare rafters to moving in - really the definitive thread, IMHO!
http://forums.taunton.com/tp-breaktime/messages?msg=84041.1
Forrest
Edited 6/17/2008 2:43 pm ET by McDesign
Why is it recommended that vents, vented soffits, ridge vents,etc. be installed on new and existing homes? I thought all of the above was to extend shingle life and stop condensation between shinge and roof sheeting.
Although a lot is said about the life of shingles, the main reason ventilation has been used is that the deck under the shingles is subject to rot. Warm, moist air from the house rises and when it contacts the cool, underside of the roof deck, it condenses. This causes the deck to rot, as the attached pictures show.
The house in the photos I've attached had no vapor barrier in the ceiling and very little insulation. The owner was sold a roof by Sears and in the package the contractor covered the vents in the eaves with "maintenance-free" vinyl. When she asked me to fix her roof, I went up to the attic and the entire deck on the north side of her house was wet. The roof was fairly new but the deck rotted from underneath.
The prevailing wisdom in building science is that the moisture in the house can be sealed off from the roof deck. The problem is that, in the real world, many houses don't have a sufficient barrier to have an unvented roof.
I'm thinking you're right on.
Where are the pics of the inside of this ... that's where it's all happening!
Ventilation is for moisture .... which may affect shingles directly or indirectly.
Seal it up, no moisture, no problem ... I think that is the theory. Sealed ceiling can ensure no issues (but it has to be totally sealed).
check out these
http://www.buildingscience.com/documents/digests/bsd-149-unvented-roof-assemblies-for-all-climates
http://www.buildingscience.com/documents/digests/bsd-102-understanding-attic-ventilation
http://forums.taunton.com/tp-breaktime/messages?msg=94228.5
Great info., Thanks a lot!!