One of our readers, Rune Eriksen*, sent
us photos of his design for a home-built
deck drainage system, and we were
impressed enough to check it out. His low-cost,
easy-to-build system catches the water
that drips through the deck boards and redirects
it to the outside of the deck. Now Rune
can use the area under the deck as a covered
patio, where he can enjoy warm
summer rainstorms without getting wet.
Several commercial systems are available
to create a dry space under a deck, but Rune's seems to be just as effective.
And it's inexpensive and easy to build
using materials found at any home center.
Here are the details in case you'd like to
build your own version. Thanks, Rune!
(*Rune Eriksen is a retired electrician
who has spent the past 20
years building his dream lakeshore
cabin, garage and shop.)
Figure A: Roof Details
Attach 2x4 pressure-treated purlins to spacer blocks sized to create a slope from front to back. Then screw the panels to the purlins.
Round up the materials
Rune bought corrugated fiberglass panels at
a home center to use for his under-deck roof.
The panels he used are 26 in. wide and 12 ft.
long. He attached
the panels with special roofing screws that
have hex heads and neoprene washers for
sealing. You'll find these screws where steel
or fiberglass roofing is sold. You could also
use galvanized steel or plastic roofing panels
and install them the same way. Rune
screwed treated 2x4 purlins to spacer blocks
to support the panels and provide the necessary
slope (Figure A).
Gutters aren't required, especially if the
water drains onto your lawn. But if the
water falls onto the patio, gutters can prevent
splashing. Rune chose PVC gutters
because they're inexpensive and easy to cut
and install. If you decide to install gutters,
you'll need lengths of gutter, gutter straps,
end caps, a downspout outlet, downspouts
and special glue to join the sections.
Attach the purlins
Plan to space the 2x4 purlins parallel
to the house and 3 ft. on center. To
provide drainage, the panels should
slope toward the outside edge of the
deck about 1/4 in. per foot. If the span
under your deck is 12 ft., for example,
the purlin at the outer end of the deck
should be 3 in. lower than the purlin
along the house (12 x 1/4 = 3).
First, mark all the purlin locations
on the deck joists. Install the purlin
along the house and the outer purlin.
Then stretch a string between them.
Measure down from the deck joists to
the string at the other purlin locations.
Those measurements (minus the
thickness of the purlins) will give you
the widths of the spacer blocks.
Cut the spacer blocks and screw
them to the bottom of the joists at the
marks. Then attach the remaining 2x4
purlins by screwing them to the spacers
Screw the panels to the purlins
Starting at one end, attach the first
fiberglass panel to the purlin with the
roofing screws (Photo 2). Place the
screws in every other valley. Snug the
screws enough to compress the
washer slightly. Overlap the next panel
onto the one you just installed and
attach it the same way. When you get
to the end, the last panel may be too
long. You can just overlap it a bit more
or cut it to fit. It's simple to cut panels
to length or width with a circular saw
and a carbide blade.
Back to Top
Install gutters and downspouts
If you want to install gutters, plan
ahead and leave space for them. You
may have to get creative to come up
with an attachment method, depending
on how your deck is built. Since the
in-stock 12-ft. panels didn't quite
reach the beams on Rune's deck, he
nailed vertical 2x4s to every other joist
to provide an attachment point for the
gutters. Then he screwed the gutter
hangers to the 2x4s. Slope the gutters
toward the downspout for drainage.
Photo courtesy of TimberTechUnder-deck waterproofing system
3 Ways to keep dry under your deck
If you want to buy a manufactured system rather than build your own as we show here, you have a lot of choices.
1. One option is to cover the deck boards with a
watertight membrane. DeckRite makes a deck floor
covering that has the added advantage of creating a
dry space below the deck. For more information, visit
2. If you're building a new deck or replacing your deck
boards, you can use a system like Trex RainEscape,
which installs in the joist spaces before you install
the decking. The advantage of this system is that it
allows you to easily add lighting or other wiring in
the joists, and cover the bottom of the joists with
bead board or any attractive ceiling finish you
choose. Learn more at trexrainescape.com
3. If your deck is already built, you can cover
the bottom of the joists with a system like
TimberTech's DrySpace. One advantage
these systems have over simply screwing roof panels to the bottom of the joists is
that you can remove a section to gain access to the joists if necessary.
To learn more, visit timbertech.com
These are just a few examples of what's available. Search online or visit your
local lumberyard or home center to find other options.