How do I Build a Waterproof Ceiling Under a Deck?

A deck is a great addition to any home; it adds usable square footage and provides an outdoor entertaining area. Many homeowners who have a second-story deck increase the versatility of their decks by making use of the area underneath it. Lower-level patios and sitting areas are popular and keeping rain from coming through the deck above is important. A drainage and gutter system can be installed to keep your under-deck space clean and dry. Many systems are available.

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Installing a rain drainage system increases the useful space underneath your deck.

Step 1

Install the rain diverters between joists. Tuck the diverters underneath the existing ledger board flashing and nail it to the ledger board. Caulk the seams with silicone caulk.

Step 2

Measure a starting point according to the manufacturer's instructions and snap a chalk line down the side of each joist. The line should have a downward slope with the high side closest to the house.

Step 3

Install the joist rails to the sides of the joists following the chalk line you marked in Step 2. Mount the joist rails with galvanized nails, then caulk along the top seams. The manufacturer's instructions specify how to cut the joist rails to allow for expansion. Apply tar tape to seal along the top surface of the joist rails to seal them.

Step 4

Install the joist collector panels. The directions on how to cut and install them are outlined in your installation manual. Seal all seams of the collector panels with silicone caulk.

Step 5

Install the joist gutters length-wise along the bottom of each joist.

Step 6

Install the rim joist gutter. This gutter mounts perpendicular to the joist gutters and collects water from them. The gutter should have a slight pitch to properly channel water away.

Step 7

Install the downspout to the low side of the rim joist gutter. Caulk all the seams for a water tight seal. Install a downspout kick-out elbow if necessary to channel water away from the house.