How to Build a Deck Drainage System


A deck drainage system can be a relatively easy and inexpensive way to keep the area below your elevated deck dry and enjoyable. Instead of losing the space under your deck, you can extend your outdoor entertaining area and enjoy it no matter what the weather. Learn how to install this helpful and straightforward addition while building your deck so that you may enjoy the many benefits the extra space has to offer. Read on to learn more.

Things You'll Need

  • Scissors or knife
  • Staple gun
  • Caulk gun
  • Caulk
  • Purchase your drainage system materials, either in a bundle kit from a manufacturer or home improvement store or in individual pieces. You will need enough downspouts to cover the entire underside of your deck, a trough and at least one gutter.

  • Prep your deck for drainage system installation by placing a mid-span nailer on the underside of the joists on your deck. This nailer will keep your joists straight while you staple the downspouts to the deck and will be removed when you finish this home improvement project.

  • Cut the downspout to fit your deck either along the 16 inch o.c. side or the 12 inch o.c. side. Your downspout will extend 1 inch into the gutter, so cut or extend the downspout as needed to cover the length of your deck plus 1 inch. If necessary, install a gutter below downspouts. Read the caulking instructions before installing the downspout, so you are prepared for specific instructions with regards to downspout placement and when to apply caulk.

  • Caulk the perimeter of the deck and install the downspouts at the end of each deck bay. Make the cupped end of each downspout is face the deck so it will catch and funnel the rain water.

  • Add caulk to the deck joists. Then, beginning at the house with 3 inches of trough under the siding, unroll the drainage trough toward the downspout at the end of the joist. As you unroll the trough, do so only 6 to 8 inches at a time, stapling along the score marks and into the inside of the deck joists. Your trough creases will overlap those of other troughs and rest on the deck joists. Place a dot of caulk between overlapping troughs. Continue lining up the score marks with the deck joists and stapling every 6 to 8 inches until you reach the downspout.

  • Extend the trough over the near edge of the downspout at least 3 inches. If you have enough, extend the trough to within a 1/2 inch from the back wall of the downspout. Then cut the excess.

  • Lay down your decking and fasten it atop the drainage system.

Tips & Warnings

  • If you are having electrical wires running below your deck, install any wiring before setting up your deck drainage system.

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