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I am considering a skylight for my vaulted ceiling. The A-frame roof has 24″ on center trusses and the fiberglass insulation has the vent channels installed to provide the 1″+ air gap between the sheathing and the insulation. Question: If I install the standard 21.5″ wide skylight, won’t the framework essentially block off any air vent flow between those trusses? The vent channel is unable to continue up to the attic. I have read lots of statements on the importance of this vent channel (shingle life, ice dams, etc.) Just wondering if I am missing something or if anyone has a work-around? Thanks.
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The vent channels are not important at all. What is important is making sure that your ceiling is airtight so that hot air doesn't leak right through and hit your roof.
Skylights are notorious prformance problems because they are not supported in conventional roof venting wisdom. Some guys drill holes, or nothch rafters, or box out the skylight with thinner material. The end result is that there wasn't a whole lot of airflow through there to begin with and ANYTHING in a clear vent channel makes it worse. The tricks don't help get the air through.
So... Make the roof airtight, which includes the boxout for the skylight, and caulk the drywall to the skylight jamb or extension. MAKE THIS ASSEMBLY AIRTIGHT! No tongue and groove boards in this area, unless airtight drywall is under them.
Recessed lights and electric boxes are also other big leakers of hot air into the roof assembly.
-Rob
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I am considering a skylight for my vaulted ceiling. The A-frame roof has 24" on center trusses and the fiberglass insulation has the vent channels installed to provide the 1"+ air gap between the sheathing and the insulation. Question: If I install the standard 21.5" wide skylight, won't the framework essentially block off any air vent flow between those trusses? The vent channel is unable to continue up to the attic. I have read lots of statements on the importance of this vent channel (shingle life, ice dams, etc.) Just wondering if I am missing something or if anyone has a work-around? Thanks.