Rain screen at soffit detail
Bbrown3381
| Posted in GBA Pro Help on
CMU house in zone 2.. Hot/humid. Unvented conditioned attic, Rigid foam around rafter tails to underside of roof decking. Cedar shingle sidewall. Verticle and horizontal furring for rainscreen.
Here’s the question: There is a plate at top of the wall but due to the slope of the roof the horizontal soffit line falls below the plate line. For added support I would like to run the verticle furring up to and attach to the top wall plate. This means the top of the rain screen will terminate in the unvented soffit.
Do I need…and how do I accomplish ….the top rainscreen vent. Thanks
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Replies
Robert,
Most builders fasten vertical furring for a rainscreen with long screws to the studs. The furring strips don't have to be attached to the top plate of your framed wall.
Attached is an illustration showing one way of venting rainscreen gaps at the top of a wall.
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Robert,
Even here in the wet PNW hardly anyone vents the top of rain screen cavities. It does increase the drying capacity of the wall, but no where near as significantly as including the bottom vented rain screen over a wall that doesn't have one.
In addition the wall already has a good drying capacity by being clad in cedar shingles, as opposed to more impermeable siding like cement board or metal.
Venting the top of a rain screen into the roof space is contrary to our code, as it provides a concealed space for fire to spread into the soffits and roof. I would block between the furring to close off the top of the cavity below the soffit.
The reason for the question is...there are no studs. The wall is concrete block and I thought attaching to the top Plate would provide a very secure wood to wood connection. Malcolm had an interesting point of fire danger and building code. Better safe than sorry so...thanks Malcolm!