Insulating Attic.

[Lisa Starr]

I can't speak to shingle life, as the homes we've done have had alternative roofing materials. 2 had metal roofing and 1 had synthetic slate (plastic). That said, all three had ice dam issues. 2 of the homes were cape style so even where the only insulation space is the remainder of the rafter cavities we found the system resolved all icing issues so I think it would work great with cathedral style ceilings.

[Warren Lake]

I can understand aspects of this say for the winter. How is this any better in the summer or not worse. The small air space on the underside of the roof. Would it not be alot hotter and increase shingle temp than unless it was open to the whole attic area?

[Jim Koepke]

Often the problem can be seen from the outside. Parts of the roof without snow accumulation is where the in house heat is getting through to the roof and melting the snow. The melted snow flows down the roof and refreezes, creating ice dams.

jtk

[Lisa Starr]

Warren,

I can't really tell you about summer. I do know that when we were working on one home is was 95 F outside and you could feel the air rushing up the cavities we had finished to the peak. The NFA (Net Free Area of the 3/4 x 13-1/2" space is 10 sq inches. Most Proper Vent type things, if not crushed by insulation, have around 9-10 NFA for 16" cavities and 18-19 for 24" cavities NFA. Additionally, the ventilation is spread over the whole cavity instead of only the center portion.

I'm not saying this system is the answer to every problem or the "perfect" vent system. Simply, my experiences show that the system will stop icing problems and creates good eave to peak flow under the roof decking. With a traditional attic space, insulating the first maybe 4' from the eaves to above the attic floor and associated insulation in the fashion I described may well be the best of both worlds. It would keep the air moving up past any restrictions due to insulation and provide a greater air space.

[Warren Lake]

I think my thoiught was a good thought, I can easiliy see that styro way being better in the winter but switch arount to when attic hit Some peak of maybe 150-170 F under dark shingles and I cant see it helping. Now when there is only 3/4 of air space between the styro and the roof I dont see the pull of air up from the soffit being enough to cool that. Just what came to mind

[Bill Dufour]

I can tell you that a 14" diameter hole in the roof on a calm spring day has plenty of thermal airflow. All the saw dust comes up into your face if you need to trim the hole a bit bigger. So I think the air chutes will have good thermal draft flow in summer when it gets hotter. But not enough to stop a screw from falling.
Bill D.