Basic Components of Waterproof Decking

Waterproofing a deck relies on several things to help keep things dry and water tight.

When building a deck to be waterproof, the deck framing must be sloped to allow drainage away from the building-1/4" of slope per foot. So if a deck was 8' wide, it would be 2" lower at the outside edge from the building.

After a deck is properly framed and sheeted with exterior grade plywood, sheet metal flashings are installed at the perimeter of the deck. L metal flashing (also called deck to wall) is installed at the building to deck detail, and drip edge (or fascia) flashing, is installed on the outside edge to let water run off.

Drains and scuppers are often used to allow water to drain out without having the water just run off the edge. These items are incorporated into the deck before any waterproofing is put down.

Door pans are installed at all door openings (sliding doors or a swinging doors) to keep water from entering under the door in windy conditions or when/if the deck is plugged up with debris and the water backs up.

Finally, when all drains, scuppers, door pans and flashings are installed, and the deck is properly sloped, only then is the waterproofing deck coating installed.

As you can see, waterproofing a deck is not something that should be attempted by a complete amateur. These basic elements of materials to use and the procedures to install them are essential if you want your deck to remain waterproof for years to come.

This article on was written by Bill Leys of Central Coast Waterproofing