Would you like to have usable space under your second-story deck? Believe it or not, it is possible with under-deck drainage systems! In this post, I will describe how to create dry space under your deck by installing an under-deck drainage system.

This post is all about how to install an under-deck drainage system

One of the most exciting parts of our current project is the outdoor living space we are creating. Before our renovations, our second-story deck was the only outdoor space that could genuinely be considered outdoor living space. We have an exterior concrete patio on the basement level; however, when it rains, the concrete patio becomes unusable because it is directly under the deck.

One of our top priorities was to create usable, dry space under the deck. We researched and found that the best way to solve our drainage issue was to take up the old deck boards and install an under-deck drainage system.

Trex RainEscape

We decided to go with the Trex RainEscape gutter system, which is considered to be one of the best under deck gutter systems. I am sure they are all very similar, but this system has a 25-year warranty and excellent reviews. Like a few others, the Trex RainEscape system is installed above the deck joists and under the deck boards.

One of the most attractive benefits of this system is the fact that aside from the gutter, the system, which is made up of a network of troughs, fits between the joists and does not extend below the joists. This allows you to install a finished ceiling giving underdeck areas a more polished look. Another benefit of this type of system is that it prevents wood rot because you do not have the moisture penetration that exists with a standard deck installation.

The Trex RainEscape above-joist system comes with easy installation, requires minimal tools, and can be installed in a few hours. Although I cover Trex RainEscape installation , reviewing the manufacturer’s installation instructions is always a good idea if you have a special case that may not be covered in my post!

Main Components

• Downspouts
• Trough material
• RainEscape Caulk
• Butyl Tape

Additional Components

• Gutter and downspout

Tools Required

• Staple gun
• Caulk gun
• Regular staples (3/8″ or larger)
• Utility knife

Considerations Before Installation

• Where will the gutter be installed?
• What kind of railing will you use?
• Will you use a picture frame or a divider board?
• Will there be any double or triple joists?

Depending on your answers to these questions, you may have to make modifications to the installation. I recommend reviewing the videos provided in this link for all special cases and modifications.

Prep Work

Make sure to let the material acclimate for a few days to the environment in which it will be installed. You can also fold a crease down the center of the material to make installation easier. If you plan to install blocking, make sure it is installed lower than the height of the trough.

First Step – Install the Downspouts

You will install one downspout in each space between joists. The height of the downspouts is designed for 2″ x 10″ joists. If your deck has 2″ x 12″ joists, you can extend the downspout by adding a small downspout piece. Alternatively, if your deck has 2″ x 8″ joists, the downspout can be cut down to accommodate the shorter height. Before anchoring the downspouts in place, you will use a utility knife to cut the downspouts as indicated by the marks.

Install the downspouts along the ledger board using a staple gun. Make sure the cut side is facing away from the ledger board.

Second Step – Install the Plastic Troughs

You can purchase material for 16″ OC spacing or 12″ OC spacing. Be sure you have ordered the correct material for your deck. When installing the troughs, be sure to install the trough with the shiny side facing up. Slide the trough material under the flashing of the house and staple the plastic trough material to the top of the ledger board.

As you unroll the material, be sure the 1-1/2″ mark is on the left as you move toward the downspout. The 1-1/2″ mark will be your guide as you install the trough material. Install your first staple at the ledger board on the 1-1/2″ mark. Fasten the material to the joist using a few staples. Once anchored, you can add staples every 8″ – 10″ in a zig-zag manner to secure it adequately.

When you get to the downspout with the material, make sure it reaches halfway across the downspout. Ensure the 1-1/2″ score mark is under the material for the second trough. Be sure that there isn’t any portion of the joist showing. Once you have completed the installation of the troughs, make sure to test your slope using water. There should be 1/4″ of fall per linear foot. Pour water starting at the ledger board end and make sure it runs out through the downspout.

Third Step – Apply Caulk

Once each trough is installed, you will add a bead of caulk at the ledger board and between the trough material and flashing. This is one instance where I deviate from the manufacturer’s recommendations. I tried using the butyl caulk as recommended and found that it never fully cured, so I removed it and elected to go with silicone instead. You will have to use your best judgment on the type of caulk you want to use.

Once you have added the caulk, apply tape over the location where the flashing meets the trough. For installations where flashing is absent, you will push 3″ of the plastic trough material under the siding and add a bead of caulk at the ledger board.

For flashing with brick or stucco, Trex advises you to cut into the mortar joint and caulk “z” flashing into mortar. You will then install the trough under the flashing and tape over the flashing to the top of the plastic trough material. If you do not need the seal to be watertight, add a bead of caulk where the trough meets the house and where the top of the ledger board meets the house.

If you need flashing for your project, you might want to check out the Trex RainEscape Wall Flash.

Fourth Step – Apply the Tape

Before applying any tape, trim off any excess material at the stapled seams. Be sure you maintain the overlap of the trough material over the joist. Apply the butyl tape to the top of the joist, over the overlapping trough material seams, to seal them. You will then cut a 1′” x 3/4″ tab at the end of the trough material where it meets the downspout and fold the tab down to prevent water from leaking from the downspout.

Final Step – Install the Gutter

You will need to install a standard 5″ gutter for the outflow from the downspouts. We actually used a 6″ gutter to avoid having a space between the house and the gutter, which worked perfectly.

Summary

In this post, I explained how to install an under-deck drainage system. With proper drainage of the water from the deck, you can have a usable covered patio with an attractive ceiling! Above-joist drainage systems are the easiest way to waterproof the underside of the deck and a great excuse to get a new deck! We installed an IPE deck on top of the under deck drainage system and couldn’t be happier! If you are intrigued by IPE, I recommend you check out my post, Pros and Cons of an IPE Deck.