If practice makes perfect, then based on what we see these days,
there needs to be a lot more practice when it comes to installing
weather barriers. This is doubly true in coastal areas, where
wind-driven rain and short drying cycles mean that any exterior
cladding — be it wood, brick, vinyl, or fiber cement —
is especially prone to leaking.
I am a licensed general contractor in northern California, but
these days my livelihood is in training builders to meet the ASTM
E-2112-07 window and door installation standard through
Installation Masters, a certification program developed by the
American Architectural Manufacturers Association (www.installationmastersusa.com). That means my work
centers on best practices for stopping water and air penetrations
through building enclosures, and I get an opportunity to talk to a
lot of builders about what works and what doesn't work when it
comes to sealing out air and water.
I believe we're going through a renaissance of sorts in this
country when it comes to weather protection. There's increasing
emphasis in building codes on reducing water damage, and it's only
going to get more intense as current best practices become
standardized and these standards bring more detailed requirements
into the codes.
Cap nails are as easy to install as narrow crown staples but
provide much more holding power. This holding power is not trivial.
It's needed to keep the weather barrier intact before the cladding
gets installed, particularly where persistent ocean breezes provide
a constant risk of ripping housewrap to shreds.
The current code is a bare minimum, in my opinion. To put it
bluntly, it's the worst we can do. Like getting a "D" in math,
there is room for improvement. And in coastal conditions, where the
exposure to frequent high winds increases the risk of water
intrusion, there's no question: we have to do better.
The latest version of the International Residential Code calls for
weather barriers (officially called water-resistive barriers, or
WRBs) behind all exterior claddings, including brick and stucco.
The code specifies a 2-inch horizontal overlap and 6-inch vertical
overlap between successive courses. And most important of all, the
materials that make up this plane must be organized to keep bulk
water from entering the wall cavity while allowing water vapor to
All overlaps in a building wrap must overlap 6 inches where two
pieces join vertically, and 2 inches at horizontal seams. The first
course should begin around a corner a minimum 12 inches (or to the
first stud) and overlap the sill plate 1 to 2
To accomplish this, courses must be overlapped the same way you
install roofing materials — the lower course goes under the
upper course. And the material must be permeable; that is, it must
allow water to evaporate through it and not accumulate.
Defeating the wind. The basic code does not specify a
fastening schedule, but it does require builders to follow
manufacturer's installation instructions, and each manufacturer of
weather barriers has its own requirements. These specs are not
trivial, nor are they simply designed just to sell you accessories
like tape and cap nails. Fasteners are critical for protecting the
exterior in that time between the installation of the weather
barrier and the completion of the cladding. Like roofing
underlayment, it's part of drying-in the home. But it's also very
vulnerable to the wind before the cladding gets installed. I wish
had a dollar for all the times I've driven by homes under
construction that have large pieces of underfastened housewrap
flapping in the breeze.
Temporary help. Hammer tackers work to
position the housewrap, but they should never be relied on as a
secure fastener. The installation should be immediately followed by
a helper nailing the housewrap off with cap nails.
Fastener spacing is generally 6 to 18 inches along vertical framing
and 16 to 24 inches horizontally. The vertical spacing depends on
local weather conditions and exposure time. More exposure to wind
requires closer spacing.
You can expect to use some sort of cap fastener — a plastic
cap held in place by a staple or nail. It's true that 1-inch-crown
staples are also allowed in most cases, but this is more of a
concession to what has always been done rather than best
Staples just don't have enough surface area to pin down the wrap
when the home is subjected to a stiff breeze. Think about the
contact area of a 1-inch-crown staple compared with a
1-inch-diameter cap: the cap is going to hold in a much higher
wind. Also, the profile of the cap is less likely to allow water to
enter the building than is the staple. (An obvious exception here
is a stucco and cultured stone exterior, which typically needs the
metal lath to be stapled in place.) Small hammer tackers are out
entirely. Just how much holding power do you think these tiny
staples really have? It's certainly not enough to hold a sheet from
getting ripped off by the wind.
An all-too-common mistake: Not covering the
gable end with housewrap shows a fundamental disconnect in
understanding what the housewrap is for. It's first and foremost a
water barrier, and should be continuous across every wall surface
that will see rain, wind, and sun.
Production method. One way to streamline the
installation of housewrap on a gable-end truss is to install it on
the ground before the trusses are erected.
Tape is not required but is a good way to deny the wind a toehold
at the edges. Taping all vertical joints is especially recommended
for keeping out water that might get behind the siding from finding
its way under the weather barrier as it drips down a wall.
The weather barrier should be pulled tight and cover all exterior
faces of the building — everything that sees rain, wind, and
sun. Take note: Even the unconditioned spaces, such as attics and
crawlspaces, must be covered. Too often, installers feel it's
unnecessary to wrap gable ends, but in my mind this practice shows
a fundamental disconnect in understanding what a building wrap is
for. True to its accepted industry name, a WRB (water-resistive
barrier) is first and foremost intended to keep out water, and
gable ends see just as much wind-driven rain as any other part of
the wall. The fact that the space beyond the wall is unconditioned
has nothing to do with the water-resistive performance of the wrap.
Leaving gable ends uncovered presents an opportunity for water that
gets behind the cladding in the gable area to soak the wall and run
underneath the building wrap below.
Think again. While this looks like an
efficient way to run the roll in a gable end, it doesn't work with
a drainable housewrap. StuccoWrap and other drainable wraps should
be installed with the drain channels running vertically (that is,
with the edges of the roll running horizontally).
Also, be sure to "modify" door and window openings right way before
wind pressure has a chance to undo your work. "Modification
details" are the industry term for cutting the wrap at the opening
and securing the edges to the perimeter of the rough opening in
preparation for window and door installation.
Trigger happy. While 1-inch-crown staples are
allowed as fasteners for housewrap, they don't have the holding
power of cap nails. In an effort to secure the head of this opening
against the wind, it has been riddled with staples, which might
keep it in place but will make it extremely difficult to tuck the
window head flashing underneath once the windows have been
So far I've detailed only the basics, the minimum. This gives us a
D, if you will. But in the extreme conditions we see in coastal
regions, we're still likely to fail the big test.
Beyond the basic codes and manufacturer's guidelines there are
several application details that have been used successfully by
builders on both coasts.
Two layers. A two-layer weather barrier provides
redundancy. If water gets through one layer, or one layer is
compromised by exposure to the elements, the second provides
Coastal climates prone to high wind pressures and driving rain
demand more than current codes require. The detail shown here,
which results in a double-coverage weather barrier, provides a
level of redundancy that will reduce the chances of rain getting
drawn into the wall by wind pressures and capillary action. A
positive separation between the cladding and the drain plane
created by battens affords further protection.
There's another reason for considering this level of redundancy:
surfactants that leach through the cladding can compromise any
weather barrier. Surfactants are compounds that reduce the surface
tension of water and allow it to slip right through most
housewraps. Soap is a surfactant, which is why it works to break
down grease and dirt when we wash our hands, and why you don't want
a trade contractor adding soap to a stucco mix to improve the
workability of the mix. Other examples of surfactants include the
water-soluble extractives that leach out of wet cedar and redwood,
or additives sometimes found in synthetic stucco and cultured stone
base layers. The soap used when pressure washing an exterior can
also break down the weather barrier's ability to hold out
Half-lap coverage. Before housewraps, the primary weather
barriers were asphalt-treated building papers and roofing
underlayments, and in some parts of the country this is still the
only weather protection provided. In severe coastal conditions, a
half-lap or double-coverage detail using these traditional
materials works well (see illustration, previous page).
Rain screens. We have been using rain-screen technology
for many years in brick-veneer walls. The code-minimum 1-inch gap
allows any water soaking through the brick (and there is plenty of
that) to drain away before it contacts the structure.
The ideal rain screen creates a disconnect — a gap —
between the exterior cladding and the weather barrier. Bulk water
must be allowed to drain down and out of the wall cavity, so the
system needs a clear way to exit. In addition, ventilation from top
to bottom will promote drying and protect the weather barrier from
Bond breaker. Under stucco, a drainable
housewrap must have an intervening layer of building paper to
prevent the stucco from filling up the drain channels. Otherwise,
water penetrating the stucco is likely to seep right through the
There are several ways to create this drainage and drying space.
The easiest (but least proven) method is to install a drainable
housewrap — one with crinkles or dimples intended to allow
water to drain behind. Bear in mind, however, there's not a lot of
research verifying how well these products perform, and the drying
capacity is certainly limited.
Behind stucco, drainable wraps have added limitations: stucco will
simply fill up the drainage channels, and moisture is at risk of
seeping through the WRB. It's critical that any drainable weather
barrier include a "bond break" layer between the drainable layer
and the stucco.
As exposure to higher wind pressures and wetter climates increases,
the need for a positive separation between the cladding and the
weather barrier increases. This separation can be created with some
sort of strapping. The traditional strapping was made from 1-by
material, usually something decay resistant like cedar or redwood.
Strips cut from CDX exposure-1 plywood have seen good service and,
of course, pressure-treated plywood is a good option (for more
information about implementing such a rain screen, see
"Best-Practice Wall Shingles," March/April 2007; www.coastalcontractor.net).
There are now plastic corrugated materials available that can be
applied either horizontally or vertically with no fear of creating
a water dam we might find in the traditional solid strapping.
Coroplast is one material that can be ripped into strips
(coroplast.cat-x.net), and plastic battens (www.battensplus.com) come ready to apply. Cor-a-vent,
a product derived from the roof ventilation industry (www.coravent.com),
provides a 3/8-inch-thick alternative that can also be ripped into
To complete the rain-screen detail, there needs to be ventilation
at the top and bottom. Be sure to include fiberglass screen to keep
the bugs out while allowing airflow.~
Bill Robinson a licensed general trainer based
in of San Luis Obispo, Calif., and a trainer for AAMA's
Installation Masters Certification Program (www.installationmastersusa.com). All photos by the
author, except where noted.