Double your clients’ outdoor living space by keeping the
area below their deck dry
Building a deck creates two distinct spaces. Topside, gleaming deck
boards and guardrails invite customers to enjoy the outdoors. But
if a deck is far enough above the ground, beneath all the pomp and
pizzazz exists another, nearly accidental, outdoor living space.
And while its creation may have been unintended, it can be awesome
real estate if you trick it out.
Under-deck drainage enables all kinds of upgrades by shielding the
area below a deck from rain and snow and diverting the water into a
gutter and downspout. All the systems discussed in this article
offer a warranty against leaks. Installation methods differ,
however, and it’s important to consider how they affect not
just the underside of the deck but its entire design.
The nationally available systems can be divided into three basic
categories: waterproof sheets that fit over the joists before the
decking goes down, systems that affix to furring strips below the
joists, and between-joist systems.
Dek Drain and RainEscape are examples of sheet systems. Both
companies claim their products are entirely waterproof.
The two products work on the same principle. After flashing against
the house, you roll a membrane across the tops of two joists to
create a long trough that’s pitched to drain at the front of
the deck into a gutter and downspout system. Adjacent rolls of
membrane lap at the tops of the joists and are capped with more
membrane or peel-and-stick tape. Deck boards are screwed to the
joists through the membrane, which self-seals around the
Because sheet systems are typically only 4 inches or so in depth,
you can run wire and junction boxes underneath the troughs. Then
you can add a ceiling of your choosing — beadboard, for
example. Another benefit to using this method is that the framing
is protected from decay, as the systems keep everything below the
deck boards dry.
Still, before selecting this type of drainage system, you should
keep a few things in mind. Mid-span blocking has to be installed so
that the troughs run above it. You can’t use blind fasteners
that install from the bottom of the deck. And deck boards
can’t be straightened by driving a chisel into the joist as a
lever or by using a BoWrench.
Dek Drain is made from black rubber that the company says remains
stable during temperature changes and isn’t affected by leaf
acid, acid rain, or salt spray in coastal applications. Direct
sunlight (not that much will reach under the deck boards) is no
problem, according to the company.
Installation requires no caulk, which feature most deck builders
will welcome. Post penetrations are flashed with peel-and-stick
membrane or butyl tape.
Dek Drain ships nationally and comes with a transferable, albeit
limited, lifetime warranty.
Dek Drain is made from a chemical- and sunlight-resistant rubber;
the system drains into standard K-style gutters.
RainEscape differs from Dek Drain in three main ways. For one,
RainEscape is made from high-density polyethylene rather than
rubber. Also, it’s brown instead of black, making it less
noticeable from below should there be no ceiling installed under
the deck. And it drains into RainEscape’s preformed scuppers
that send the water straight down into a gutter.
The company’s Web site shows caulk being used to seal the
laps and caps, but RainEscape’s butyl peel-and-stick tape is
less messy and goes in faster. You can use it for wrapping posts or
other penetrations (say there’s a gas line plumbed through a
joist bay for an outdoor kitchen assembly) so they drain into the
RainEscape’s brown polyethylene fabric drains into a
proprietary gutter system.
The panels of ceiling systems hang from vinyl rails or 2-by
sleepers that are attached to the bottom of the deck. They create a
finished ceiling at the same time they waterproof the space
underneath. It’s a one-shot deal, but you have to like the
look of the ceiling.
Unlike sheet systems, ceiling systems don’t keep the framing
dry. This is something to consider if you want to add overhead
electrical devices — say, lights or fans.
The key to the DrySnap installation is properly laying out and
installing the DrySnap joist brackets and pitch spacers on the
underside of the deck joists. It takes a little bit of layout math
to evenly space the joist brackets along the joists. As you move
out from the house, you create a pitch by adding spacers to the
joist brackets. Once those are installed, you mount the ceiling
panels on the bracket system. The result is a flat, slightly
pitched vinyl ceiling with a beadboard appearance.
DrySnap’s name is apropos because the whole ceiling pretty
much snaps together. The ceiling panel layout begins with a starter
strip and finishes with an end cap. You need a rubber mallet to tap
the panels into place and make sure they lock down, but
that’s the only tool you need that you don’t already
have in the truck.
DrySnap’s installation instructions call for the ledger-board
flashing to extend 8 inches out from the house — easy if
you’re building a new deck. For retrofits, the company
suggests using a peel-and-stick membrane detail on the ledger to
direct water into the system and guard against back-splashing.
Because vinyl is stiff when cold, DrySnap recommends storing the
panels in a warm place prior to installation.
Air flow is good and wood stays dry with the DrySnap system,
according to the company. Nothing actually touches the joists, so
no spots are created where water can accumulate.
The company offers regional classes and installation
certifications. The product doesn’t look hard to install, but
if you plan to install a lot of it, a couple of hours in a class
tweaking the process might turbocharge your production
If a beadboard look is what you’re after, DrySnap’s
vinyl panel system may be the solution.
The manufacturer describes American Dry Deck as a “watertight
drop ceiling.” Made of vinyl, this snap-lock system is
installed level below the joists on 2-by sleepers. It can be
installed running in any direction, a trait unique to American Dry
Deck. Unlike a typical drop ceiling, however, the panels run the
length of the joists and are arched to direct water down into
channels that in turn feed into a gutter and downspout.
Two gutters, one at the house and one at the front of the deck,
collect water. Because the system is level, water moves by piling
up in the channels until it reaches the ends where it drains into
the gutters. Having two gutters provides good air flow, and since
there’s no water actually in contact with the deck, the
framing dries, according to the company.
American Dry Deck is installed by attaching 2-by sleepers to the
bottoms of the joists and then attaching stringers perpendicular to
the sleepers. The arched ceiling panels are flexed and fitted into
the sleepers; to finish up, the bottom locking cap is tapped into
place with a dead-blow hammer.
The only drainage system to be installed level, American Dry Deck
panels can be oriented in any direction.
The Zip-Up system is a pitched, paintable PVC product that creates
a flat, water-diverting surface under the joists. The ceiling hangs
on furring-strip spacers installed under the joists at a
1/8-inch-per-foot slope. Zip-Up rails are screwed in place
perpendicular to the sleepers.
The main structural element of the system is the rails. The only
other parts are wall trim, seam trim, and the panels themselves.
Simple. The whole thing is held together with screws and washers
snugged just so to prevent deforming the PVC rails.
To lay it out, you begin by centering the field such that the left
and right end pieces will be ripped to the same width, much like
you would with a tile floor or a suspended ceiling. It requires a
little line snapping. The company doesn’t recommend
installing its product in temperatures lower than 50 degrees,
though you can be sure builders will store it inside to get it nice
and warm before bringing it outside and installing it in the cold
anyway. The panels are available in 8-, 12-, and 16-foot lengths
and in white and black (with beige coming soon). The system looks
like it goes in fairly quickly, using minimal parts.
Zip-Up is distributed only in certain regions at the time of this
writing, though the company plans to go national. The product can
also be ordered directly from the manufacturer.
Zip-Up UnderDeck uses paintable vinyl panels for the drainage plane
and the finished ceiling.
Between-joist systems use the edges of the deck’s joists
themselves as a fastening point for the system’s hardware.
The hardware then guides the water into a V-panel (DrySpace) or
into a below-joist gutter (UnderDeck).
As with ceiling systems, the spaces between the joists are exposed
to the elements, which your electrician needs to keep in
The anchor point to the deck frame for DrySpace’s extruded
vinyl under-deck system is a series of brackets. Ledger Brackets
fasten to the ledger, and U-shaped Combo Brackets wrap the bottom
of the joists. Both of these brackets are fastened like vinyl
siding, with nails or screws driven loosely through slots in a
nailing flange to allow the vinyl to expand and contract during
temperature changes. The tops of the brackets are sealed to the
framing with a butyl peel-and-stick tape. A V-shaped channel hangs
from the brackets to collect and drain the water into a
For oddball joist spacing, you can combine the 12-inch and 14-inch
DrySpace panels with 2-by filler strips to make the system work.
TimberTech notes that this variation may leak a little.
The end joists have an odd trim detail. The company doesn’t
have a purpose-made piece; instead, TimberTech says to cut the
outside flange from a Combo Bracket with a utility knife. I can
imagine wanting to add a trim board above that piece for high-end
DrySpace’s V-shaped vinyl panels hang from ledgers that are
fastened and taped to the sides of the joists.
Like DrySpace, UnderDeck uses the sides of the joists as the anchor
point for brackets, which are called joist rails. But rather than
draining to a trough in the joist bays, water drains into sub-joist
troughs from vinyl panels arched into place between the joists.
These troughs clip to the joist rails, capping the bottoms of the
joists and draining into a gutter at the front of the deck.
A water diverter, essentially a piece of vinyl flashing, is
installed at the ledger in each joist bay prior to closing the
system in with the arched panels. You can tuck the diverters (they
look like little diving boards) up under the existing flashing,
fastening and caulking them in place. The diverters drain into the
UnderDeck provides some helpful installation details. For oddball
joist spacing, the company advises you to rip a panel to fit such
that you can maintain a consistent arch on all the panels. And if
the pieces oil-can or ripple due to joists running off layout, the
company suggests running a pair of snips down the edge to trim the
piece, like scribing a cabinet filler but significantly less
exacting. I appreciate not having to figure that out on site.
A sheet-metal brake would be a handy tool to have when installing
this system, for two reasons. UnderDeck describes bending one of
its diverter pieces to create an end cap, a nice detail that can
easily be made with a brake. And while you can cut pieces to length
and width with a utility knife, who has that kind of time or
forearm strength? Snapping the vinyl panels into the jaws of a
brake would speed things up.
UnderDeck’s vinyl panels arch between the joists and drain to
troughs that run the length of the joists into a gutter.
Mark Clement is a member of the DeckExpo
live-demonstration team and builds decks in Ambler, Pa.