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steveny 10-15-2011 12:59 PM

smart vent in 1890's Victorian, outside NYC
About to replace my original slate roof ( :[ ) with Certainteed Carriage House. Roof deck seems OK.
Victorian with open ~18" eaves, no easy way to place vents in fascia at bottom of joist bays. Cathedral ceiling finished atticó finished 30+ years ago, not by me. No venting of joist bays or ridge, no baffles, but they only put in R-7 and tacked it close to the sheetrock so, far as I can tell from the few entry points of view I have, there seems to be space between the insulation and inside of roof deck. So far no evidence of wetness/rot/mold issues in joist spaces.
Pitch ~10/12. ~20' joists, 35' main ridge. ~11' dormer on one side of house almost at one end of main roof. Intersects main roof about 8-10' downslope of main ridge.
My present plan is to use SmartVent (SV) in mid-roof application just upslope of 3 foot ice shield. Contractor has no experience with SV. As yet undecided brand of ridge vent. Contractor would put in one of Cobra models if I don't tell him otherwise.
At present am not ready to spend the time and money to either have decking or wallboard removed to add insulation/baffles.

Have a bunch of questions regarding the SV install for any here with experience in that install and thought I'd ask a few at a time rather than drop the whole load at once.

Overall experience with the SV?

Preferred exhaust vent? (ridge only thing I'm considering at the moment and probably not SV as exhaust because I'm already doing some things a bit foreign to my contractor and that makes me nervous)

Any experience running the SV around dormer valleys? Seem to need to go up and around dormer to get ventilation to main roof bays above valleys.

Any experience using Carriage House or other double thickness shingles with SV: How's it look? Should I use a starter course on the vent if I'm using a thicker shingle?

Do I follow 50/50 rule for intake/exhaust or 60/40 or something else?

Got more but will add if ok.



shazapple 10-15-2011 06:19 PM

An alternative is to install a "ventilated nail base"
It is basically rigid foam, an airspace, and a new deck which is attached over your existing deck. More $$, but helps you insulate as well.

In the instructions for the SV it says to stop it 12" away from dormers, valleys, rakes, etc... which makes sense as those spots tend to gather quite a bit of water.

The ventilation split ideally would be 50/50, but it depends on your local code. Mine (Canada) calls for 1:300 vent to ceiling area, with a 25/75 split top/bottom and vice versa

steveny 10-15-2011 07:12 PM

tx, shazapple

interesting product. But, as I understand it, it will only handle the ventilation issue as far as keeping the shingles cool is concerned. Doesn't handle the problem of ventilating the joist spaces to prevent condensation. Have I got that right?


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