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Question DetailsAsked on 6/23/2017

Can outdoor carpet be laid over roofing paper on a flat deck

I have a second story deck 3/4 around my house. It has deck boards and plywood and previously had carpet on it. The plywood rotted. The deck serves as a carport over my car as well as we use it to entertain on. Can we lay roofing paper over the plywood and under the carpet to keep water from coming through and leaking down on our car.

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If you want it to rot to heck and still leak, sure - roofing paper/roofwrap is NOT waterproof, it is watershedding only and designed for use on sloping roofs as a backup layer under the roofing, not as a primary water barrier like you are talking about - so on a flat roof will accumulate water and leak very badly at seams. Any water barrier under the deck boards (unless metal) will rot them out in short order - plus accumulate dirt and leaves and seeds and such so generally cause problems.

For a garage-top deck, your choices are built-up roofing (tar roof), or a traditional membrane roof (very heavy plastic sheet) - both of which would need a wood decking or such over them because they are not made to be walked on. But a wood decking like that can cause leaks at the contact point, and also accumulate dirt underneath which accelerates the weathering of the waterproof surface.

For a walk-on surface the normal solution would be an IRMA roof - where pavers or stone/gravel bed are put over insulation board over a padding over a membrane waterproof roofing material, but the weight of that is likely more than your deck is designed for.

So - for your case - best solution is probably a walk-on granulated roofing membrane - a very thick plastic membrane (probably seamless for a carport sized area) which is designed for light walking (note - VERY sensitive to barbecue hot grease or coals) and has granules on it like shingles - but spike type heels would have to be banned at a minimum.

Another solution though you would have to check with manufacturers because I don't think any would warranty this, would be heavy membrane roofing with outdoor carpet over it.

Roofing is clearly the Search the List category for this type of work - but you might best talk to an Architect/Engineer firm or at least roofing system manufacturer about the design and selection of the materials.


Another totally different approach - go with exposed plank decking (ground contact treated or metal lasts longest) and let the water go through, then trap it underneath (assuming you have some headroom) - either with a heavy membrane or underdeck product (or for shorter life a heavy plastic tarp) under the deck and angled down to the front enough to drain, or with a deck drainage product like Underdeck, DrySpace, Tuftex, or DryDeck as described in this article -

though it requires taking up the deck boards for the catch-all types like in the first photo in the article. Note the full coverage types like that first photo have problem with accumulating debris from trees and such, and some do not slope to the front enough so back up and put water against the house, so there are plusses and minuses to each option.

For a one car carport (as opposed to a garage or such), depending on your sense of aesthetics and neighborhood standards, I think I would just put lag screw eye hooks into the joists with maybe an intermediate rope or two if needed for added support, and hang a sloping heavy duty plastic tarp under there, sloping down maybe 1/4" per foot (from wall to front) to drain - easy to hose off, or if it really starts accumulating debris then just take down and hose off. Be sure it keeps the water below the joists, not in contact with them except at the connection points at the grommets.

Answered 3 years ago by LCD

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