Ventilation problems under this snow covered roof (C) Daniel Friedman Roof Eave Venting on Roofs with no Overhang or Soffit

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How to add roof intake venting at the eaves:

How to Correct Inadequate Attic Venting to Stop Attic Condensation, Ice Dam Leaks, Attic Mold, & Roof Structure Damage.

This article describes alternatives for venting attics and cathedral ceilings by providing air intake openings at the lower edge or eaves of roofs that have no building overhang or soffit or eaves.

Our page top photo shows a cape Cod home in Poughkeepsie New York.

This building was constructed with no roof overhang, making roof intake venting tricky to obtain, and risking extra damage from ice dams or gutter overflow leaks.

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Our photo at page top shows a modern synthetic mesh type ridge vent (with modest airflow capacity) and our photo at left shows a typical installation of continuous soffit or eaves intake venting at the lower roof edges of a building.

Problems With Roofs Lacking Any Overhang - No Soffit?

Don't give up on providing roof intake ventilation openings just because your building was constructed with no roof overhangs. In fact, providing exit venting (at a roof ridge or at gable end vents) on a building with no intake venting at the building eaves will increase the building heating costs and can also add to attic or under-roof condensation, moisture, and mold problems.

buildings such as the cape Cod shown at page top may be constructed with no roof overhang whatsoever. While this design offers the advantage of more light entry at the building windows (not shaded by a soffit), owners of buildings built with this design need to watch out for several problems:

Venting Solutions for Roofs with No Overhang or Soffit

Photo of a home with no roof eaves
Roof fascia vent or eaves vent (C) Daniel Friedman Soffit vent construction detail (C)Daniel Friedman

Reader Question: do little air gaps in my DIY foamed roof deck built atop an existing roof lead to any issues?

Bob's DIY vented SIP roof design - Note: this is not a CODE-Approved design - at InspectApedia.com2017/10/26 Bob said:

I have 1 room. Between garage and house. The roof is connected but independent. It has catherdial ceiling with fiberglass between the tounge and groove (interior) and roof sheathing. I want to make it a hot roof to prevent condensation.

I will tear off shingles at foamboard. Frame with 2×4s and spray foam cavitys and cover with plywood and re shingle.

I will be able to airtight the interior suppifficently. My concern is after spray foam and applying new plywood.

If there is small air gaps between foam and roof deck will that lead to any issues? Help is appreciated thanks.

[Click to enlarge any image]

Watch out: the roof design shown above is a sketch provided by the reader, is incomplete in that it does not show the details of the cathedral ceiling, and may require additional measures for fire safety and to meet building codes.

Reply: Possibly yes, both fire safety & design: a vented hot roof design may contain contradictions

I don't think foam gaps that do not communicate over any distance more than a few inches would be an issue as long as you are taking steps to be sure no indoor air/moisture leak into the enclosed roof cavity. You do that with a vapor barrier on the warm interior side and/or by using closed cell foam and taking care to seal around ceiling penetrations.

But I'm a bit worried about your design combining venting and multiple layers of roof structure that may be constructing a concealed space that is a fire concern.

Please see our detailed discussion of your question and our original reply, now found at CONCEALED SPACE FIRE CODES.

To be accurate, I don't have a clear understanding of your structure. Be sure you're not building multiple layers of roof framing & sheathing in one roof - concealed spaces can be fire hazard and probably a code violation unless special fireproof measures are taken.

There are, of course, ventilated SIPs, as we illustrate just above and as we describe at CATHEDRAL CEILING INSULATION.



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