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Installing a DIY Under Deck Drainage System

If your deck is elevated or on a second story level, you’ll want to consider installing a DIY under-deck drainage system, which diverts water away from the deck and into gutters so the area beneath the deck is dry and useable.

After installing an under deck drainage system, you’re free to use the space below the deck for a patio giving you a lovely retreat during inclement weather. You can also use the space to create a waterproof under deck storage.

Trex RainEscape by Trex Company, named among the 2019 Remodeler's Choice 100 by Qualified Remodeler Magazine, is simple to install and affordably priced. Trex RainEscape is installed before you lay the deck boards. It is an over-the-joist deck drainage system. This type of deck drainage system allows you to finish the underside of the deck (which is the ceiling of the patio below) with utilities for electricity, lights, ceiling fans, entertainment components and more.

Decks Ceiling of Outdoor Patio

Tools & Materials Needed for a DIY Under Deck Drainage System

  • Utility knife or scissors
  • Staple Gun
  • Caulk Gun
  • Trex RainEscape Downspouts
  • Trex RainEscape Trough
  • Trex RainEscape Butyl tape
  • Trex RainEscape Butyl caulk
  • Optional:  Trex RainEscape Soffit Lights, ceiling fan, TVs or other elements

How To Waterproof Under Your Deck with a DIY Deck Drainage System

This article shows the installation basics for waterproofing the space under your deck using troughs that run between joists and empty into the system’s downspouts. If your deck has unusual angles, oddly-spaced joists, railing posts inside the framing or other special cases, you will may need to modify the troughs and downspouts to fit the space but the approach is pretty much the same: Install downspouts and trough so that water flows to the gutter, then completely cover all seams with butyl tape.

This video provides instructions on how to install an under deck drainage system on a second story deck.

A deck drainage system is designed to direct water away from your deck and into a gutter system below the deck. In this video, we're installing Trex® RainEscape®, which is an over-the-joist system. This type of deck drainage system covers and protects the entire wooden substructure. It can be installed on a new composite or wood deck during construction.

The Trex® RainEscape® deck drainage system includes four main components: downspouts, 12-foot or 16-foot trough material, 4-inch butyl tape, and caulk. The tools you'll need to install the system are: a staple gun and regular staples, a caulk gun, and a utility knife.

Before you begin, there are four important factors to consider before you frame your deck:

  1. Where do you want the gutter line located?
  2. What type of railing will you use?
  3. Will you use a double, or single picture frame, or a divider board?
  4. Will the deck have any double or triple beams?

Your answers to these questions will determine how the Trex® RainEscape® system is installed.

The first step in installing an under-deck drainage system is to install the downspouts. The downspout is designed for 12-inch or 16-inch joist spacing. Each bay has one downspout. The downspout is 10 inches tall and the perfect height for a 2x10 joist. To install a downspout, cut the pre-scored marked guideline on the downspout with a utility knife. Install the downspout along the rim joist (or the ledger board), making sure the cut side is facing the deck bay. Staple the downspout into place.

The downspout funnels water into a standard 5-inch gutter below the deck. The funnel nozzle of the downspout hangs at least one inch into the gutter line. The funnel can also be extended down for 2x12 LVL or I-joist. The downspout can also be trimmed to fit a smaller size joist such as a 2x6 or 2x8.

Now that the downspouts are installed, it's time to install the trough material. If you're installing the Trex® RainEscape® system in a climate with fluctuating temperatures, the trough should be acclimated before installation. This is especially important when using the black trough.

There are two methods to acclimate the material. The first is to fold a soft crease lengthwise down the center of the trough. This relaxes the trough material and creates a "V" down the middle so that the trough is easier to install. The second method is to simply unroll the trough material and let it sit for a while to acclimate to the outdoor temperature.

If you plan on blocking between the joists, use blocking that is shorter than the joist height. The Trex® RainEscape® system hangs down a maximum of 4 inches, so at the mid-span, the trough will hang down 2 inches; which allows the blocking underneath.

If you're installing the system 12 inches on center, measure and cut 4 inches off the width of the trough roll on the side that has the 1 and 1/2 inch score mark. Align the left edge of the trough with the outside of the joist. The smooth, shiny side is always installed facing upwards. To install, slide the trough underneath the flashing, and make sure the trough edge sits on top of the ledger board. Staple the trough at the ledger board on the 1 and 1/2 inch score mark side. Unroll the trough halfway down the joist, and put a second staple on the same side. If possible, have a second person hold taut the loose corner of the trough. Unroll the trough down the rest of the way, and add a third staple on the same side.

Trim the trough making sure it's about midway across the funnel. Push the trough down into the opening of the funnel. Align the opposite side score mark to the inside of the joist and staple. With the second person still holding the loose corner of the trough, work your way back to the starting point by stapling on both joists in a zig-zag pattern.

After installing the first trough, continue to the left and install the next. The 1 and 1/2 inch score mark side of the trough should be underneath the adjacent trough material. The trough material must cover all of the exposed wood of the deck frame.

After the trough panels are installed test to ensure the slope is correct. Pour water on the material at the ledger board the water should run down to the downspout.

Now, seal the troughs. Trim excess trough material at the seams, but keep the overlap of the trough material. Use the Trex® RainEscape® butyl tape to seal the trough seams on top of the joists. Peel the non-stick backing off the tape, and apply the tape on top of the joists. The tape does two things: it covers the overlapping trough layers, preventing wicking, and also seals around the screws used to fasten the decking.

The butyl tape should never be put directly on wood. Apply it only on top of the trough material. Use a utility knife to cut a small 1in. x 3/4in. tab where the trough meets the downspout. Fold this tab straight down. The tab prevents water from waking up underneath the trough and leaking outside the funnel. The trough should be smooth and with minimal wrinkling. If you find the water does not release properly, use a screened spline roller to create a V-shape. The V-shape will help to properly drain the water.

The benefit of installing an over-the-joist deck drainage system, like Trex® RainEscape®, is that the area below the deck is dry and usable. With drainage taken care of, you can finish the space below the deck by adding an under-deck ceiling and utilities for soffit lights, ceiling fans, outdoor cooking, relaxing, or gathering your friends to watch the big game on your outdoor TV. You can also use the space for much needed storage. Whatever you choose to do, installing a deck drainage system on your elevated deck is the first step in creating an outdoor oasis you'll enjoy for years to come.

Trex RainEscape is installed over the joists before the decking boards are installed, ensuring no water touches the joists. Protecting the deck foundation from water is essential for preserving the longevity of the deck.

Some homeowners ask how to waterproof under an existing deck. This is not recommended, as it would require a system installed under the joists. An under-the joist deck drainage system allows water to run through the deck boards over the joists and into gutters under the deck. Repeatedly exposing the joists to water will result in wood rot and decay.

Cut your downspouts and install them along one rim joists and/or the ledger board

Cut your downspouts and lay them out

1. First, install the downspouts. These are made to fit between joists spaced 16 inches on center if positioned in one direction. If your joists are 12 inches on center, simply face the downspouts in the other direction. Check that the downspouts’ funnels will extend down at least 1 inch into the gutter you will install.

The downspouts are 10 inches tall, so they fit well with 2x10 joists. If your joists are smaller, cut the funnels as needed, so they extend. If you have 2x12 joists, use extenders. Cut out a panel along the perforation using a utility knife or simply tear by hand. Position a downspout in each framing bay at the end where you will put the gutter, and staple them in place.

Tuck the trough under the flashing to the wall

2. Unroll a trough panel and fold it in half lengthwise, pressing to create a crease. This will help create a trough for the water to travel along. Slip the panel under your ledger flashing as far as possible, and staple it in place.

Roll out the trough. Staple and cut to length.

Roll out the trough. Staple and cut to length.

3. Unroll the trough panel and staple it on one side with its edge flush with the edge of one joist. Pull the trough taut as you work. When you reach the downspout, tightly reverse-roll the trough to remove its roll “memory.” Then, cut it to length so its end falls near the center of the downspout hole.

Staple and roll out more trough

Staple and roll out more trough

4. taple the other side of the trough. Follow the guideline on the panel. This will automatically create a slight slope for water to run down. Continue installing trough panels.

Fill in the small areas at the angles

5. At an angle or another place where the downspout is not at the end of the framing, cut and staple short trough pieces. They should be sloped in their centers and cut so that water flows down onto the longer trough piece.

In some difficult-to-tape places, you may choose to use butyl caulk instead of, or in addition to, the tape. You'll need to carefully apply a continuous bead between two trough panels, or between the flashing and a panel.

Apply the tape at the seems and joints

Apply the tape at the seams and joints

6. Use a utility knife or scissors to cut any excess overlapping trough material. Starting at the house and working toward the downspouts, apply the butyl tape provided with the system by removing the paper backing as you unroll it. Work carefully to keep the tape from wrinkling, and press it firmly in place so it forms a tight seal at all points.

Then, apply the tape along the other end of the system, on the other side of the downspouts. Make any slits needed to help keep the tape flat. Press all the pieces smooth and tight. If you are unsure of a joint, apply more tape on top.

Nice and dry!

7. If you plan to install Trex RainEscape Soffit lights, a fan or other ceiling elements, you can do so now. Since this is an over-the-joist deck drainage system the space below the deck is dry.

Install your gutters

8. Install gutters for under deck - any type is fine - so that all the downspouts empty into the gutter. It should be slightly sloped for water runoff and connected to gutter downspouts, as with any gutter installation.

Install your decking

9. You can install decking using face screws or most types of hidden fasteners. The Trex RainEscape butyl tape forms a watertight seal around screws that penetrate the tape.

You can learn more about waterproofing your deck in this article. With a deck drainage system, you’ll easily learn how to keep the area under the deck dry. Additionally, here is a reputable place to buy Trex RainEscape.

 


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Water Drainage Systems

Installing a DIY Under Deck Drainage System

If your deck is elevated or on a second story level, you’ll want to consider installing a DIY under-deck drainage system, which diverts water away from the deck and into gutters so the area beneath the deck is dry and useable.

After installing an under deck drainage system, you’re free to use the space below the deck for a patio giving you a lovely retreat during inclement weather. You can also use the space to create a waterproof under deck storage.

Trex RainEscape by Trex Company, named among the 2019 Remodeler's Choice 100 by Qualified Remodeler Magazine, is simple to install and affordably priced. Trex RainEscape is installed before you lay the deck boards. It is an over-the-joist deck drainage system. This type of deck drainage system allows you to finish the underside of the deck (which is the ceiling of the patio below) with utilities for electricity, lights, ceiling fans, entertainment components and more.

Decks Ceiling of Outdoor Patio

Tools & Materials Needed for a DIY Under Deck Drainage System

  • Utility knife or scissors
  • Staple Gun
  • Caulk Gun
  • Trex RainEscape Downspouts
  • Trex RainEscape Trough
  • Trex RainEscape Butyl tape
  • Trex RainEscape Butyl caulk
  • Optional:  Trex RainEscape Soffit Lights, ceiling fan, TVs or other elements

How To Waterproof Under Your Deck with a DIY Deck Drainage System

This article shows the installation basics for waterproofing the space under your deck using troughs that run between joists and empty into the system’s downspouts. If your deck has unusual angles, oddly-spaced joists, railing posts inside the framing or other special cases, you will may need to modify the troughs and downspouts to fit the space but the approach is pretty much the same: Install downspouts and trough so that water flows to the gutter, then completely cover all seams with butyl tape.

This video provides instructions on how to install an under deck drainage system on a second story deck.

A deck drainage system is designed to direct water away from your deck and into a gutter system below the deck. In this video, we're installing Trex® RainEscape®, which is an over-the-joist system. This type of deck drainage system covers and protects the entire wooden substructure. It can be installed on a new composite or wood deck during construction.

The Trex® RainEscape® deck drainage system includes four main components: downspouts, 12-foot or 16-foot trough material, 4-inch butyl tape, and caulk. The tools you'll need to install the system are: a staple gun and regular staples, a caulk gun, and a utility knife.

Before you begin, there are four important factors to consider before you frame your deck:

  1. Where do you want the gutter line located?
  2. What type of railing will you use?
  3. Will you use a double, or single picture frame, or a divider board?
  4. Will the deck have any double or triple beams?

Your answers to these questions will determine how the Trex® RainEscape® system is installed.

The first step in installing an under-deck drainage system is to install the downspouts. The downspout is designed for 12-inch or 16-inch joist spacing. Each bay has one downspout. The downspout is 10 inches tall and the perfect height for a 2x10 joist. To install a downspout, cut the pre-scored marked guideline on the downspout with a utility knife. Install the downspout along the rim joist (or the ledger board), making sure the cut side is facing the deck bay. Staple the downspout into place.

The downspout funnels water into a standard 5-inch gutter below the deck. The funnel nozzle of the downspout hangs at least one inch into the gutter line. The funnel can also be extended down for 2x12 LVL or I-joist. The downspout can also be trimmed to fit a smaller size joist such as a 2x6 or 2x8.

Now that the downspouts are installed, it's time to install the trough material. If you're installing the Trex® RainEscape® system in a climate with fluctuating temperatures, the trough should be acclimated before installation. This is especially important when using the black trough.

There are two methods to acclimate the material. The first is to fold a soft crease lengthwise down the center of the trough. This relaxes the trough material and creates a "V" down the middle so that the trough is easier to install. The second method is to simply unroll the trough material and let it sit for a while to acclimate to the outdoor temperature.

If you plan on blocking between the joists, use blocking that is shorter than the joist height. The Trex® RainEscape® system hangs down a maximum of 4 inches, so at the mid-span, the trough will hang down 2 inches; which allows the blocking underneath.

If you're installing the system 12 inches on center, measure and cut 4 inches off the width of the trough roll on the side that has the 1 and 1/2 inch score mark. Align the left edge of the trough with the outside of the joist. The smooth, shiny side is always installed facing upwards. To install, slide the trough underneath the flashing, and make sure the trough edge sits on top of the ledger board. Staple the trough at the ledger board on the 1 and 1/2 inch score mark side. Unroll the trough halfway down the joist, and put a second staple on the same side. If possible, have a second person hold taut the loose corner of the trough. Unroll the trough down the rest of the way, and add a third staple on the same side.

Trim the trough making sure it's about midway across the funnel. Push the trough down into the opening of the funnel. Align the opposite side score mark to the inside of the joist and staple. With the second person still holding the loose corner of the trough, work your way back to the starting point by stapling on both joists in a zig-zag pattern.

After installing the first trough, continue to the left and install the next. The 1 and 1/2 inch score mark side of the trough should be underneath the adjacent trough material. The trough material must cover all of the exposed wood of the deck frame.

After the trough panels are installed test to ensure the slope is correct. Pour water on the material at the ledger board the water should run down to the downspout.

Now, seal the troughs. Trim excess trough material at the seams, but keep the overlap of the trough material. Use the Trex® RainEscape® butyl tape to seal the trough seams on top of the joists. Peel the non-stick backing off the tape, and apply the tape on top of the joists. The tape does two things: it covers the overlapping trough layers, preventing wicking, and also seals around the screws used to fasten the decking.

The butyl tape should never be put directly on wood. Apply it only on top of the trough material. Use a utility knife to cut a small 1in. x 3/4in. tab where the trough meets the downspout. Fold this tab straight down. The tab prevents water from waking up underneath the trough and leaking outside the funnel. The trough should be smooth and with minimal wrinkling. If you find the water does not release properly, use a screened spline roller to create a V-shape. The V-shape will help to properly drain the water.

The benefit of installing an over-the-joist deck drainage system, like Trex® RainEscape®, is that the area below the deck is dry and usable. With drainage taken care of, you can finish the space below the deck by adding an under-deck ceiling and utilities for soffit lights, ceiling fans, outdoor cooking, relaxing, or gathering your friends to watch the big game on your outdoor TV. You can also use the space for much needed storage. Whatever you choose to do, installing a deck drainage system on your elevated deck is the first step in creating an outdoor oasis you'll enjoy for years to come.

Trex RainEscape is installed over the joists before the decking boards are installed, ensuring no water touches the joists. Protecting the deck foundation from water is essential for preserving the longevity of the deck.

Some homeowners ask how to waterproof under an existing deck. This is not recommended, as it would require a system installed under the joists. An under-the joist deck drainage system allows water to run through the deck boards over the joists and into gutters under the deck. Repeatedly exposing the joists to water will result in wood rot and decay.

Cut your downspouts and install them along one rim joists and/or the ledger board

Cut your downspouts and lay them out

1. First, install the downspouts. These are made to fit between joists spaced 16 inches on center if positioned in one direction. If your joists are 12 inches on center, simply face the downspouts in the other direction. Check that the downspouts’ funnels will extend down at least 1 inch into the gutter you will install.

The downspouts are 10 inches tall, so they fit well with 2x10 joists. If your joists are smaller, cut the funnels as needed, so they extend. If you have 2x12 joists, use extenders. Cut out a panel along the perforation using a utility knife or simply tear by hand. Position a downspout in each framing bay at the end where you will put the gutter, and staple them in place.

Tuck the trough under the flashing to the wall

2. Unroll a trough panel and fold it in half lengthwise, pressing to create a crease. This will help create a trough for the water to travel along. Slip the panel under your ledger flashing as far as possible, and staple it in place.

Roll out the trough. Staple and cut to length.

Roll out the trough. Staple and cut to length.

3. Unroll the trough panel and staple it on one side with its edge flush with the edge of one joist. Pull the trough taut as you work. When you reach the downspout, tightly reverse-roll the trough to remove its roll “memory.” Then, cut it to length so its end falls near the center of the downspout hole.

Staple and roll out more trough

Staple and roll out more trough

4. taple the other side of the trough. Follow the guideline on the panel. This will automatically create a slight slope for water to run down. Continue installing trough panels.

Fill in the small areas at the angles

5. At an angle or another place where the downspout is not at the end of the framing, cut and staple short trough pieces. They should be sloped in their centers and cut so that water flows down onto the longer trough piece.

In some difficult-to-tape places, you may choose to use butyl caulk instead of, or in addition to, the tape. You'll need to carefully apply a continuous bead between two trough panels, or between the flashing and a panel.

Apply the tape at the seems and joints

Apply the tape at the seams and joints

6. Use a utility knife or scissors to cut any excess overlapping trough material. Starting at the house and working toward the downspouts, apply the butyl tape provided with the system by removing the paper backing as you unroll it. Work carefully to keep the tape from wrinkling, and press it firmly in place so it forms a tight seal at all points.

Then, apply the tape along the other end of the system, on the other side of the downspouts. Make any slits needed to help keep the tape flat. Press all the pieces smooth and tight. If you are unsure of a joint, apply more tape on top.

Nice and dry!

7. If you plan to install Trex RainEscape Soffit lights, a fan or other ceiling elements, you can do so now. Since this is an over-the-joist deck drainage system the space below the deck is dry.

Install your gutters

8. Install gutters for under deck - any type is fine - so that all the downspouts empty into the gutter. It should be slightly sloped for water runoff and connected to gutter downspouts, as with any gutter installation.

Install your decking

9. You can install decking using face screws or most types of hidden fasteners. The Trex RainEscape butyl tape forms a watertight seal around screws that penetrate the tape.

You can learn more about waterproofing your deck in this article. With a deck drainage system, you’ll easily learn how to keep the area under the deck dry. Additionally, here is a reputable place to buy Trex RainEscape.

 


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