Under-Deck Roof The Family Handyman

Inexpensive roof panels keep it dry down below

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The design

Round up the materials

Rune bought corrugated fiberglass panels at a home center to use for his under-deck roof. The panels he used are 26 in. wide and 12 ft. long. He attached the panels with special roofing screws that have hex heads and neoprene washers for sealing. You’ll find these screws where steel or fiberglass roofing is sold. You could also use galvanized steel or plastic roofing panels and install them the same way. Rune screwed treated 2×4 purlins to spacer blocks to support the panels and provide the necessary slope (Figure A).

Gutters aren’t required, especially if the water drains onto your lawn. But if the water falls onto the patio, gutters can prevent splashing. Rune chose PVC gutters because they’re inexpensive and easy to cut and install. If you decide to install gutters, you’ll need lengths of gutter, gutter straps, end caps, a downspout outlet, downspouts and special glue to join the sections.

Attach the purlins

Photo 1: Hang the purlins

Rune screwed the 2×4 purlins to spacer blocks. The blocks are incrementally thicker as they approach the outside edge of the deck so the new roof will drain toward the outside.

" class="step3enlargePic enlargePic" href="http://hostedmedia.reimanpub.com/TFH/Step-By-Step/FH14MAY_RFDECK_03.JPG"> Photo 1: Hang the purlins

Rune screwed the 2×4 purlins to spacer blocks. The blocks are incrementally thicker as they approach the outside edge of the deck so the new roof will drain toward the outside.

" class="step3enlargeButton enlargeButton" href="http://hostedmedia.reimanpub.com/TFH/Step-By-Step/FH14MAY_RFDECK_03.JPG">

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Photo 1: Hang the purlins

Rune screwed the 2×4 purlins to spacer blocks. The blocks are incrementally thicker as they approach the outside edge of the deck so the new roof will drain toward the outside.

Plan to space the 2×4 purlins parallel to the house and 3 ft. on center. To provide drainage, the panels should slope toward the outside edge of the deck about 1/4 in. per foot. If the span under your deck is 12 ft. for example, the purlin at the outer end of the deck should be 3 in. lower than the purlin along the house (12 x 1/4 = 3).

First, mark all the purlin locations on the deck joists. Install the purlin along the house and the outer purlin. Then stretch a string between them. Measure down from the deck joists to the string at the other purlin locations. Those measurements (minus the thickness of the purlins) will give you the widths of the spacer blocks.

Cut the spacer blocks and screw them to the bottom of the joists at the marks. Then attach the remaining 2×4 purlins by screwing them to the spacers (Photo 1).

Screw the panels to the purlins

Photo 2: Attach the fiberglass panels

Attach the fberglass panels with special screws that have a neoprene washer under the head to seal the holes. The panels overlap at the seams.

" class="step4enlargePic enlargePic" href="http://hostedmedia.reimanpub.com/TFH/Step-By-Step/FH14MAY_RFDECK_04.JPG"> Photo 2: Attach the fiberglass panels

Attach the fberglass panels with special screws that have a neoprene washer under the head to seal the holes. The panels overlap at the seams.

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Under-Deck Roof The Family Handyman

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Photo 2: Attach the fiberglass panels

Attach the fberglass panels with special screws that have a neoprene washer under the head to seal the holes. The panels overlap at the seams.

Starting at one end, attach the first fiberglass panel to the purlin with the roofing screws (Photo 2). Place the screws in every other valley. Snug the screws enough to compress the washer slightly. Overlap the next panel onto the one you just installed and attach it the same way. When you get to the end, the last panel may be too long. You can just overlap it a bit more or cut it to fit. It’s simple to cut panels to length or width with a circular saw and a carbide blade.

Install gutters and downspouts

Photo 3: Finish up with a gutter

To keep rainwater from splashing onto the floor, Rune installed gutters along the beams. The gutters slope to a downspout at the end.

" class="step5enlargePic enlargePic" href="http://hostedmedia.reimanpub.com/TFH/Step-By-Step/FH14MAY_RFDECK_05.JPG"> Photo 3: Finish up with a gutter

To keep rainwater from splashing onto the floor, Rune installed gutters along the beams. The gutters slope to a downspout at the end.

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Photo 3: Finish up with a gutter

To keep rainwater from splashing onto the floor, Rune installed gutters along the beams. The gutters slope to a downspout at the end.


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