Shed Roof Venting
Posted on 18. May, 2009 by Ken Chipman in Building Envelopes
Five years ago renovations to a garage/shed for an art gallery in New England was completed. In the process the building’s envelope was “buttoned-up” using a spray foam insulation in the walls and roof areas. Recent exterior repairs to the clapboard siding reveal significant rot in both the walls studs and roof rafters.
Unlike the garage portion, the shed roof was not properly vented and the spray insulation did not allow air and water to move through the structure. Tight buildings save energy by retaining the heat but moisture will always find its way into a structure — the design should provide a way for it to get out.
So if you are insulating the shed portion of a building, venting at the eaves and the point where the shed roof contacts the vertical wall, and providing an air space above the insulation and below the roof sheathing, is critical.
The shed walls should also have a vapor barrier to prevent moisture from penetrating and condensing in the insulation. Finally, weeps holes, found in typical masonry construction details, can also help eliminate moisture when it gets into the wall cavity.
About the authorKenneth Chipman is an architect licensed in Maine and Washington states with over twenty five years of residential, commercial and institutional experience -- including schematic design, construction documents, project management and construction observation. Ken has an M Arch from the University of Washington and an ENVD from the University of Colorado. He can be reached at ken_chipman[at]yahoo[dot]com
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