How to Install an Under-Deck Drainage System

The space below elevated decks offers plenty of storage and expanded living space, but it’s useless during rain.

Installing an under-deck drainage system can solve this problem.

The Trex RainEscape system is designed to be installed between deck joists spaced on 16-inch centers.

Before installation, prepare the components. Roll out the plastic troughs so you can crease them in the center and along the marks where they will overlap with the joists.

Next, take out the collection basins, or downspouts, and cut out the marked arc on one side. These basins will be installed at the end of the joist bay, which the water will travel toward.

Apply sealant to the top of the joists and place the basin between the joists with the cut-out section facing the open joist bay.

Then, stretch a plastic trough over the space. One end is scored to overlap the joists and it will be positioned on the opposite end from the basin.

With the score mark positioned on the joist, drive one or two staples to secure that end while you stretch the plastic over the length of the joist bay.

At the other end, cut off the excess trough about an inch from the back of the basin.

All along one side of the trough, there is a score mark parallel with the edge, about an inch and a half in. Align this mark with the edge of the joist on that side and staple the trough to the joist so it is stretched tight from end to end.

The other side of the trough has a tapered score mark, which is aligned with the joist edge on that side before it is stapled in place.

If all the score marks are properly aligned and the wrinkles are pulled out, you should be able to pour water in on the high side and have it run all the way to basin and out to the ground.

Now seal over the joists and staples with flashing tape.

To collect water from the basins, install a section of rain gutter under them so it runs downhill to move the water to one end.

At that end, connect a downspout to carry the water away from the deck.

Watch the video to see how it’s done!

Further Reading


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