3 Ways to Create Waterproof Dry Space Under a Deck

The spaces between decking boards on outdoor decks are meant to serve an important function—namely, drainage. They help to prevent puddles from forming and enable the surface to dry more quickly after rain and snowstorms.

deck waterproofing systemBest Deck Storage Idea | SpreadRadio.com

Recover useful storage or utility space beneath a deck by utilizing a deck waterproofing system. Photo: SpreadRadio

Along with routine waterproofing application, spacing between boards helps to prolong the useful life of the decking material. But if you want to use the space beneath a deck for additional outdoor living or storage space, it’s better to install a barrier that prevents water from draining to the surface directly below.

 

 

Deck Membranes and Downspouts

The dominant solution for waterproofing areas below decks is to drape plastic membranes within joist spaces below decking to form troughs. The Trex RainEscape deck waterproofing system, shown below, is an example of a membrane-and-downspout system.

deck waterproofing systemHome Depot

The Trex RainEscape membrane, which comes in rolls, is fastened loosely to the top edge of deck joists. The downspouts can be oriented to fit between joists spaced 12 or 16 inches on center. Decking boards are then installed over the top. Butyl tape is applied to seal all seams. The only tools needed for installation are a utility knife and a stapler or hammer tacker.

Trex RainEscape deck waterproofingHome Depot

Wood or synthetic decking is fastened to the deck frame over the drainage assembly, and soffit or ceiling systems can be fastened to the bottom of deck joists for a finished appearance from below.

The Trex RainEscape troughs divert runoff to downspouts positioned near the joist header. A length of gutter is attached to the structure just below the downspouts to collect water and lead it away from the protected area.

Under-Deck Ceilings

A number of recently introduced under-deck ceiling systems use corrugated aluminum or plastic panels designed to catch water that drains through decking and channel it away from the area below. Among the newest is the RainTight system, introduced at Deck Expo 2014.

RainTight panels are made of heavy-gauge aluminum. The seamless panels are custom-fabricated, based on the size of the deck. They lock together along their long edges to form leak-proof joints.

raintight deck waterproofingRainTight

RainTight panels, made of aluminum, lock together to create waterproof joints.

A perimeter frame and graduated spacer-nailers are fastened beneath the deck joists so that the plane of the ceiling slopes slightly (at least 1/4 inch per foot) away from the house toward the joist header. A system-compatible aluminum trough is fastened below the joist header to carry runoff to one or more downspouts that drain to the ground outside the protected area.

Under-deck ceiling systems provide an all-in-one drainage and ceiling finish that is particularly suitable for areas beneath a deck that are high enough off the ground to provide a sheltered outdoor living space below. Special framing and moisture-protection measures can provide mounting points for overhead light fixtures and ceiling fans.

Waterproofing Decking Flanges

Simpler than membrane and ceiling systems, waterproof decking flanges offer an effective means of diverting water that would otherwise drain through conventionally spaced deck boards. Dexedry flanges are designed to act as spacers between boards and also as mini-gutters to channel water toward deck edges. The rubber flanges are pounded into decking edges with a rubber mallet.

dexedry deck waterproofingMichael Chotiner | HomeTips

Dexedry rubber flanges fit into flanges grooved into the edges of decking boards.

Dexedry flanges are available in a number of sizes that match the edge grooves found on major synthetic decking brands. The edges of wood decking boards can be milled with a dado blade, shaper or router to accommodate the flanges.

Whether you use gutters, flanges or an under-deck ceiling, creating additional patio or storage space under your deck can add to your enjoyment and to the functionality of your home.

 

Michael Chotiner is a home-improvement expert who has owned his own construction business and who is also a master carpenter. Michael writes on homeowner DIY projects and how-tos for Home Depot. For a selection of tools you might use if you are planning to install waterproofing on an outdoor structure, you can visit the Home Depot website.

 


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