Screen Porch Underlayment


Old 03-30-05, 12:25 PM
Daniel Clawson
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Question Screen Porch Underlayment

I have a 2nd floor screened porch over a patio. The underlayment is 5/8 inch exterior plywood layed over spaced 1by 3 redwood boards on 16" joists. The porch exterior side is supported by 4" x 4" redwood posts set to the patio.
The overlay is outdoor carpet.

The underlayment is deteriorating, and needs replaced. It lasted approximately 15 years, but rain and winter snow eventually weakened the plywood bond.

I propose to replace the plywood with 1/2" Cement Board. Anyone have experience with using cement board for this type purpose? Any cautions or recommendations?
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Old 04-26-05, 03:55 PM
Join Date: May 2004
Posts: 341
I would replace with plywood. The cement board is not designed to be underlayment and would be structurally unsound unless the 1/3 redwood would carry the load. If you sealed the ply it should hold up much better in weather. I would lay a coat of fiberglass on it before putting outdoor carpet on. Or you deck it with 2by6 leaving a nice gap (I like 1/2") and the ventilation would keep it from dry rot, etc. over the patio.

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