Icynene and Ridge Vents

[Rick Burkman]

Inspected a house today that had soffit vents, but no ridge, roof, or gable vents - no high ventilation of any kind. The owners indicated that it had approximately 10" - 12" of low-density soft foam insulation (Icynene) sprayed between the roof rafters. The Icynene website says that: "By its nature, Icynene® requires no ventilation space from soffit to ridge, which increases design freedom for both the exterior and interior of the house. Icynene® is intended to fill all of the gaps and crevices, thus eliminating the need to leave a path for air ventilation within the rafters."

My question is, isn't the roof ventilation supposed to help lower the temperature of the roof sheathing and consequently the asphalt shingles in the summer when the sun is beating down and heating that surface? Therefore, shouldn't ventilation be provided for, even when low-density soft foam insulation is used in the roof space?

[Bob Spermo]

Houses are now being built with unventilated attics where the rafters have foam insulation. The entire house now has a thermal boundry from the walls to the rafters. It allows air handlers and ducts to be in a partially conditioned space. The jury is still out on the question of premature aging of composition shingles. Houses built like this often require mechanical ventilation and the A/C units must be properly sized (i.e. not too big!) If you are going to insulate like this it does not make sense to have holes in the soffit.

[Brandon Whitmore]

The last roofing manufacturers installation instructions that I read stated that their warranty was reduced (I think cut by 50%) for un- ventilated systems. I can't remember who the manufacturer was (probably GAF or Certainteed).

[Rick Burkman]

Thanks for the answers. Here is a little extra info that I inadvertently left out of the original post. This house has cathedral ceilings, so basically drywall, rafters and insulation, roof deck, and asphalt shingles (going from underside to topside). It also has forced air heat but no a/c for warm season air conditioning.

[Jeffrey L. Mathis]

I think that whole cool the shingles thing has been pretty much debunked. A very wise man told me studies showed that good ventilation reduced the shingle temp. by like .001 degrees. What is does do is exhaust moisture.
Icyene is a pretty cool product, but you know how the building business is with new products. The industry's track record warrants a go slow and watch approach. That stuff is really installer driven. If it isn't done right or thick enough . . .

[Rick Burkman]

Jeffrey,

Do you know of any studies or references that I can access re: the shingle temperatures vs. ventilation? It sounds like good info to reference in cases like this.

Rick

[Jim Luttrall]

RR-9904: Unvented-cathedralized attics: Where we've been and where we're going — (http://www.buildingscience.com/documents/reports/rr-9904-unvented-cathedralized-attics-where-we-ve-been-and-where-we-re-going/view?searchterm=shingle%20temperature)
Check here at the Building Science site for this study as well as many others.

[Rick Burkman]

Jim,
This is great information! I wish they had a study done in the Severe-Cold region (defined in one of their hygro-thermal range maps), but this is still helpful - thanks for the link!

[Jim Luttrall]

I have not researched their site, but they may well have information more pertinent to your region. Dr. Joe has written books for most if not all of the climatic regions. Spend some time on their site, it is worth your time even if the site is hard to navigate. I have one of Dr. Joe's "Builder's Guide" for hot and mixed-dry climates and use it on a regular basis.

Try this
BSD-149: Unvented Roof Assemblies for All Climates — (http://www.buildingscience.com/documents/digests/bsd-149-unvented-roof-assemblies-for-all-climates?full_view=1)