- Q.I plan to install clapboard
siding using the rain screen method. The siding will be
fastened to 3/4-inch vertical battens, nailed over each
stud. At the top, I plan to ventilate the rain screen
into the soffit area. What is the best detail to
ventilate the bottom of the rain screen, while still
excluding insects?
A.Luis De Miguel, senior
researcher at the Canada Mortgage and Housing
Corporation, responds: Venting the top of rain
screen cavities is not recommended. Research has
shown that when wind pressurizes one side of a
house and depressurizes the opposite side, vents at
the top of a rain screen or curtain wall can allow
moisture to be sucked into the cavity. Vents at the
top of a rain screen do not contribute appreciably
to helping the cavities dry out. If the cavities
are closed at the top, quicker pressure
equalization is possible, and less water will enter
the cavity.
The bottom of the rain screen cavities can be
screened with insect screen or thin aluminum soffit
vent, bent into a U-shape. The screen should be
stapled to the sheathing prior to installing the
vertical battens, and then later folded over the
battens and stapled again.
For more information on rain screen details, see
the Canada Mortgage and Housing
Corporation’s Best Practice Guide:
Wood Frame Envelopes, available for $89
Canadian or about $60 U.S. (613/748-2003;
www.cmhc-schl.gc.ca).