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Question DetailsAsked on 10/11/2017

Do I need a Deck Air Vent system (roofer suggestion), in addition to a Ridge Vent system being installed.?

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Your attic (assuming it is open to outside air, not part of the "conditioned space" heated and cooled by your A/C system), need ventilation to prevent excessive attic heating in the summer, and especially to ventilate moisture so it does not go moldy and mildewy or, in the worst cases, start fungal growth on the wood and on any organic insulation.

This means providing both exhaust openings (ridge vent usually best for this on a sloping/gabled roof), and at least equal intake airflow capacity low down on the roof. Screened eave vents (or screened soffit vents leading to open eaves) is the usual and generally most efficient way to provide this intake for outside airflow, but on roofs without significant roof overhang (what are they teaching architects these days, anyway, that they still design no-overhang roofs ?) or due to unusual framing system without the ability to install eave vents between the rafters or trusses, sometimes an in-roof intake vent system is needed, which may be your case.

You definitely need air intake or despiote the ridge vents you not only will not have air exchange through the attic, but will be increasing attic "theft" of air from the house itself, through any ceiling/wall penetrations into the attic.

That is what the Deck Air Vent system (and similar brand in-roof ventilation air intake systems) achieve - not my first choice as a solution but sometimes what you have to live with. It is necessary to be VERY careful about the water barrier under the shingles when installing this, so any water running down the roof on top of the water barrier does not go into the vent - generally you use seamless ice and water shield in the vent area to trap any water coming down the roof, taking the roof water barrier up OVER the vent to drain downslope of it, with separate ice and water shield UNDER the vent and surrounding it for a foot or two to trap any water and carry it to the roof edge.

Details vary by the product, but it should not be counted on to keep water out entirely - provide positive ice and water shield (which most roofs should have on the bottom 3-9 feet anyway, depending on ice damming potential, And in that light, generally putting the inlet edge at the roof edge (at the bottom of the first row of shingles) is usually best for avoiding that, rather than putting it further upslope, but sometimes on low-slope roofs that will not get the intake into a location where it can freely vent into the attic so sometimes you end up with the inlet a row or few up the roof.

Ditto to minimizing the risk of ice damming backing up and going into the vent - generally by putting the inlet where any damming cannot back up into it - sometimes involving a roofing extension over the inlet to protect it from water entry, so it lies under a shingle overhang (with support) at the downhill roof edges.

Answered 2 years ago by LCD

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