Solutions for Hard-to-Vent Roofs & Ceilings
Building roofs or ceilings where ventilation is difficult, not feasible, not wanted
HOT ROOF DESIGNS: UN-VENTED ROOF SOLUTIONS - CONTENTS: Un-Vented Roof Solutions: how to avoid condensation, leaks, attic mold, insulation mold, & structural damage to roof framing when roof venting is not possible. Hot roof designs: suggestions for un-vented or hard-to-vent building roof cavities. How to detect roof venting deficiencies, attic insulation defects, and attic condensation problems
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Solutions for roofs or ceilings that are hard to vent: hot roof designs, aka dense-packed insulated sloped roofs:
Data & design suggestions for hot roof designs or for providing roof and ceiling ventilation, and we describe roof & roof insulation or venting system inspection methods and clues to detect roof venting deficiencies, insulation defects, and attic condensation, mold, or structural damage problems in buildings covered by an un-vented or hot roof or hard-to-vent roof design.
In cathedral ceiling configurations where it is difficult to
provide ventilation, some builders have eliminated the
vent space, relying instead on careful sealing of the ceiling
plane to prevent moisture problems. While experts concede
that this should work in theory, most caution that it is
difficult to build a truly airtight ceiling assembly.
cathedral ceilings are slow to dry out if moisture problems
do occur, whether from condensation or roofing leaks. If a
hot roof is the only option for a section of roof, take the
Do not use recessed lights or other details that penetrate
the ceiling plane.
Carefully seal all penetrations in the ceiling assembly,
including top plates of partitions, with durable
materials. See the air leak articles beginning
at AIR BYPASS LEAKS
Use a non fibrous insulation, such as plastic foam,
and install it without voids where moisture could
collect. Insulation choices are listed
at INSULATION INSPECTION & IMPROVEMENT.
While fiberglass insulation is an excellent and effective product for insulating most building cavities, in areas where there is extra risk of trapping moisture (and thus rot or mold infections) such as crawl spaces and cathedral ceilings where roof venting may be absent or minimal, we prefer to use closed-cell foam insulation products or spray-in icynene foam insulation: these products can seal the cavity against drafts and they do not as readily pick up moisture nor do they readily form hidden mold reservoirs.
Ice and Water Shield: On roofs that are too difficult to vent, a second-best solution is to remove the shingles (or slates) from the lower 3 feet
of those slopes where leaks and ice dams have been recurrent, install a waterproof but nail-able membrane such as WR Grace's Ice and Water Shield (other product names from other manufacturers) which will prevent any ice dam
backup leaks from entering the building.
This is basically a sticky membrane that is applied to the roof decking and through which shingle or slate nails can be nailed back onto the roof; the membrane seals around the nails so
that those penetrations do not form leaks during a water or ice backup.
While we prefer to avoid ice dam leaks by good building design and good under-roof ventilation, where conditions require stopping ice dam leaks on an existing structure, proper installation of heating cables may be the fastest and cheapest solution.
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