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Solid color stained raised deck with shed area underneath.
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How to Add a Waterproof Ceiling Under A Deck

Free up some extra space in the garage or expand your outdoor living space with this inexpensive project to make a waterproof ceiling under a deck. We added a shed under the deck this way.
Active Time1 day
Total Time1 day 2 hours
Yield: 1 deck
Author: Rachel
Cost: $200

Equipment

Materials

Instructions

  • First, to the underside, add spacer blocks to every joist if spaced 12 or more inches apart. Blocks or shims are cut from a treated 2x4 and spaced every 2 feet on a joist. Each block is ½ thicker than the last as it runs down the joist. This creates enough slope to direct the water down to the edge and into a gutter.
    Where to add a waterproof ceiling from under a deck looking at the joists.
  • Starting at one end, attach the fiberglass panels to the spacers with non-rusting roofing screws or deck screws and rubber washers. Screw into the valleys, not the water channels. Overlap edges of panels and seal with caulk or flex seal, if desired.
    Screw placement in hills of pvc corrugated board.
  • Adding gutters does make an under deck ceiling more aesthetically pleasing as well as functional. Plan ahead and attach the panels so that there is space for the water to properly flow into them and for you to be able to clean them out if necessary.
    Cross section of a deck with an attached ceiling design shown.

Notes

  • Screw through the highest point of the corrugation, rather than through the channels the water will flow.
  • We pressure wash our deck every 1-2 years and use this time to also wash out the panels and clean the gutters. Even small debris can build over time like algae, dog hair, caked dust, and pieces of grass. We use a plant safe house wash like this one.
  • Panels can be cut to length with a circular saw, carbide blade, or shears.