Build a Composite Deck on Existing Joists

Get tips on how to build composite decking on existing joists. Learn why you shouldn’t put composite decking over existing wood, and why you should remove the old decking first.

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LESLIE: James in Wyoming is calling in with a decking question. What can we do for you?

JAMES: We are at the tri-annual point of refinishing our deck. And so we were wondering the feasibility of overlaying the existing deck, using that as a base and putting a composite decking over the top of it. Is that feasible to do?

TOM: Oh, absolutely.

LESLIE: But I wouldn’t put it over the existing planks. I would take those planks off and use the existing framework and then put the composite where the old wood decking itself was.

TOM: (overlapping voices) Right. Yeah, exactly. You would strip off the decking and you would install new composite decking on top of that. You would not want to layer it over the old decking.

JAMES: OK.

LESLIE: Well no, because eventually that wood is going to fail, decay, decompose. You’re going to have to get rid of it eventually, so just do it now. Don’t sort of sandwich that there.

JAMES: OK, I was told that the tensile strength of the composite may require additional stringers to be put underneath of it so that it would have less distance between the joists. Is that correct?

TOM: No, no.

LESLIE: No.

TOM: I mean some of the composites are really floppy but if you have a good-quality product like Fiberon decking, that’s actually a product that Leslie and I have both worked with and it’s very, very resilient. And it’s got an encapsulation process on the outside called Perma-Tech that seals everything in so there’s no real organic piece of the composite that’s at the surface so you never get a mildew or mold kind of growth on it; very easy to clean and it doesn’t fade. That board itself, very, very stiff board. You won’t have any problems with telegraphing.

LESLIE: And maybe I’m wrong but I mean at our summer home where we used it, we just took off the existing wood decking and put it right on top of the existing joists. You know, everything stayed …

TOM: Oh, so you did the exact same project.

LESLIE: Yeah, everything stayed as is. I mean we did have to sister a couple of joists here and there just due to aging of the deck itself but nothing else changed.

JAMES: OK. Alrighty, well thank you for the advice.

TOM: You’re very welcome. Thanks so much for calling us at 1-888-MONEY-PIT.