Enclosing the space under a deck
I have an interesting situation I’m trying to resolve. The home is in southern NY & my client had a deck built about 5 years ago which is fully enclosed below with concrete block walls & stone veneer. The space underneath the deck is unfinished & has at least 8′-9′ of headroom & is just used for storage of outdoor furniture in the off season. The space has a few inches of gravel over earth.
Decking is mahogany…..not T & G, so water drains through the deck. The space suffers from high moisture levels & is wreaking havoc with the deck framing, as some have rotted & need to be replaced. Inside face of the concrete block walls are wet as well.
My proposed solution is to:
Remove the decking (saving for reinstallation. Is possible since hidden fasteners were used).
Install EPDM membrane or a deck drainage system that laps over the top of all joist & beams.
Pitch membrane to a gutter, tying into a leader which would extend to daylight outside the space.
Install a concrete slab over gravel & 10 mil poly VB to eliminate moisture from below.
Reinstall decking from above with screws.
This should keep the space dry, but my question is should we consider an exhaust fan that’s on a humidistat to exhaust moist air? I think we should not be considering any type of passive vents (like those used in a crawl space), as those seem to do more harm than good. Any suggestions or recommendations are welcome…
Brad DeMotte, RA
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