Renovation 4th Edition
Page 36
3
Overlap 6 in.
Sill
Flashing strips
or tape
1
Sill flashing
overlaps WRB
Window sill
Step 1
Fold the top edge of the sill flashing over the bottom of the rough opening. Split each end of the sill flashing: fold the upper “ears” up onto the sides of the opening, and extend the lower ears out about 8 in. beyond the opening, onto the sheathing. Leave the lower edge of the sill flashing unattached for now.
Steps 2 and 3
Fold jamb flashing around both sides of the rough opening and over the ends of the sill flashing. Lap jamb flashing over the ends of the sill flashing but leave the bottom edges unattached so they can overlap the WRB (building paper or house wrap). Once the WRB is installed, overlap and attach the bottom edges of the sill flashing and the jamb flashing to the WRB.
Step 4
Install rigid cap head (cap) flashing first so that it weather-seals the gap between the top of the window frame and the sheathing. The ends of the head flashing overlap jamb flashing on both sides. Next, install self-adhesive flashing tape over the top of the head flashing to further ensure the seal. Last, install the WRB layer over the head flashing and the flashing tape.
Exteriors
155
or housewrap as long as it’s correctly installed
and conforms to local building codes. Often,
building codes will specify which barrier to use
with which siding. For example, beneath stucco,
many building codes require a double layer of
Grade D kraft paper or a fortified paper such as
Fortifiber’s Super Jumbo Tex® 60 Minute.
In new construction, water-resistive barriers
are usually installed before windows and doors
have been inserted into rough openings. Often,
builders just cover the whole expanse of a wall
with housewrap—including rough openings.
Then, using a utility knife, they slit the house-
wrap within each opening (like a giant X), fold it
into the sides of the opening, and staple it.
Precased windows and doors are then installed
and their perimeters weatherproofed with self-
adhering flashing tape or flashing strips. As
shown in the drawing on p. 155, the WRB course
above the window overlays cap flashing. Cap
flashing, also called head flashing, redirects
water that might otherwise dam up behind door
When installing traditional
or window head casing, leading to stains and
membranes such as felt paper
mold on interior surfaces, swollen sashes, peeling
or red rosin paper, overlap
As with other building systems, maintenance
horizontal courses by 6 in. The
paint, and rot. All flashing is important, but
is crucial. Each autumn after the leaves have
overlap for housewrap is similar,
flashing the head of a window or door is the criti-
fallen and each spring, clean gutters and down-
but you must also tape seams with
cal detail to get right.
a compatible tape.
spouts; if needed, do this more often to keep
them flowing freely. Every year, survey and
recaulk building seams as needed. Paint or stain
wood siding periodically. Trim trees and shrubs
so they don’t retain moisture next to the siding or
restrict air circulation. Slope the soil away from
the foundation to help direct water away. Adjust
lawn sprinklers so they don’t spray siding and
you’ll also conserve water.
P R O T I P
Water-Resistive Barriers
No matter how well siding or trim is installed,
Plastic housewrap is slippery,
sooner or later water will work its way behind it.
so don’t lean unsecured ladders
Typically, this happens when storms drive rain
against it. Secure the ladder or,
into building seams or gaps around doors or win-
better yet, use scaffolding if
dows. Water can also be drawn inward and even
you’re installing housewrap and
upward by capillary action. For these reasons,
siding to a second story. Always
builders cover exterior sheathing with a water-
install housewrap with its printed
resistive barrier (WRB). In older houses, the most
side facing out: It’s engineered
to allow migration of water vapor
common WRB is 15-lb. asphalt-impregnated
in one direction only.
building paper—also called felt paper—and in
newer houses, plastic housewraps such as Tyvek®
or R-Wrap®.
Both building paper and plastic housewrap
do a good job of reducing air infiltration. That
is, both are permeable enough to allow excessive
moisture behind the siding to escape, yet both
are sufficiently water-resistive to protect sheath-
Be attentive when removing flashing tape’s protective
ing from wind-driven rain. Bottom line: It
paper backing because its self-adhesive side will stick
doesn’t matter whether you use building paper
aggressively to whatever it comes in contact with.
156 Chapter 7
Of course, renovation is rarely as straightfor-
courses should always overlay those below so
ward as new construction. If you’re replacing the any water that gets behind the siding is directed
siding around an opening and installing new
down and out. Building paper also should over-
WRB, then sliding the top leg of cap flashing
lay cap flashing at doors and windows.
underneath is easy. But what if the siding is in
Seal building-paper seams, tears, and punc-
great shape and slipping cap flashing underneath tures with seam tape; smooth down the tape to
would require removing siding nails and, in the
make sure it adheres well. If you’re installing
process, destroying the siding? Or what if long-
housewrap such as Tyvek, use a seam tape rec-
ago builders installed the exterior trim over the
ommended by the manufacturer. Last, install sid-
siding, as they often did on Victorian houses?
ing as soon as possible after installing the build-
There, the cure of installing cap flashing by the
ing paper because wind can lift and stretch it,
book might be worse than the disease.
especially housewraps.
Consequently, builders trying to keep a job on
Corners. Take special pains with corners.
time and on budget may bend the rules.
Although a 4-in. overlap is often adequate for
Occasionally, with the help of a generous bead of
corners, you’ll be safer to overlap outside corners
55-year caulk, they will even surface-mount cap
by 1 ft. In addition, many builders reinforce cor-
flashing, as shown on p. 143. Especially if a large ners with flashing tape to keep water out of gaps
overhang protects a window, this solution works
between corner boards and siding. To prevent the
just fine.
building paper from bunching in inside corners,
use a straight board to press the paper into the
InStAllIng BuIlDIng PAPER
corner before stapling it.
Installation techniques for housewrap and build-
ing paper are much the same. In this chapter,
FlAShIng tAPES AnD StRIPS
To weatherproof windowsills, fold
both materials are often referred to generically as As building science improved its understanding
flashing paper strips into the rough
building paper.
of air and moisture infiltration, many codes
opening, staple the paper down, and
Before starting, survey the sheathing and
specified additional measures to seal building
apply caulk. When the window is
knock down protruding nail heads and wood sliv- joints and exterior openings such as windows,
installed, the sill will compress the
ers that could puncture the paper.
caulk, creating a seal. Preformed
doors, vents, outside lights, and electrical boxes.
Installation is a two-person job, especially if
corner pieces, such as Moistop Corner
Rigid cap flashing over windows and doors had
Shield, also are available. Tuck
you’re working with 9-ft.-wide rolls of Tyvek. As
been used for a long time, of course, to direct
building paper or housewrap under
one person unrolls the material, the other aligns
water away from these potential dams. But a
sill flashing.
and staples it. Start at the bottom of the wall,
new category of flexible flashings developed
overhanging the bottom edge of the sheathing by whose primary intent is to seal gaps where air
about 1 in. Position the building paper, tack an
and moisture might get in.
upper corner in place, roll out about 8 ft., and
raise or lower the roll until the edge of the build-
ing paper is roughly parallel to the bottom edge
of the sheathing. When it’s in position, staple
Every Person’s guide to
the paper every 16 in. along the edges and every
Flashing lingo
24 in. in the field; use 1⁄4-in. or 5⁄16-in. staples. You
can also use tabbed nails to attach building
there are hundreds of flashing products to choose from, and reading the labels
paper, although they are more expensive and
isn’t always enlightening. here’s a sampler of terms from flashing labels, and what
slower to install than staples. Thereafter, roll out
they’re really saying:
3 ft. to 4 ft. at a time, stapling as you go. Trim the
1-in. overhang later.
Self-adhesive,self-adhering,self-adhered: Flashing with sticky stuff on
As you roll out the building paper, make sure
the back; also known as flashing tape.
it lies flat. Puckered paper can elevate the siding
Flashing strips:nonsticky-backed, precut flashing pieces.
or trim and compromise its weathertightness.
Mechanicallyattachflashingsolution: Staple it.
Typically, the person holding the roll maintains a
Flexibleflashing:not metal.
slight tension on the building paper to prevent
Rigidflashing:Metal or, less often, plastic.
puckers. Also, take care not to tear the mem-
Elastomeric:Rubber based or rubberlike.
brane while handling and stapling it—more of
Water-resistant,weather-resistant,moisture-resistant:Our lawyers
a problem with paper than with housewrap,
won’t let us say waterproof.
which stretches.
Through-wallpenetrations:holes in walls, which need to be flashed.
Overlapping and taping seams. Overlap verti-
Compatiblewithmostsealantsandcaulks:Read the fine print.
cal end seams by 4 in. to 6 in.; overlap horizontal
seams 6 in. to 8 in. As you work up the wall, upper
Exteriors
157
gEnERAl PREPARAtIOn
Exterior trim can be applied in many different
ways, depending on the design of the house and
the type of siding. For wood shingles or clap-
boards, use trim boards that are thicker than the
siding, and apply trim to the sheathing before
putting up the siding. For flat shiplap and board-
and-batten sidings, apply trim boards over the
siding. In general, try to use the same materials
and installation methods that were used on the
house originally.
Solid-wood exterior trim should be a rot-
resistant species such as redwood, cedar, or hard
pine and sufficiently dry to avoid shrinkage, cup-
ping, and checking. For those reasons, avoid
sugar pine, knotty pine, hemlock, fir, and the
like. If you’ll be painting the trim, you may find
it cost-effective to use finger-jointed trim stock
fabricated from shorter lengths of high-grade
wood. It’s widely available and can be durable if
you keep it sealed with paint. For best results,
To retrofit French doors, it was
specify vertical-grain heartwood because it
necessary to cut back stucco roughly
1 ft. around the new opening so the
Flexible flashing takes predominantly two
resists decay, holds paint well, and is the most
unit could be correctly flashed. Gaps
forms: Precut flashing strips, reinforced with a
stable dimensionally. Caution: If this trim is
along both sides were covered with
polymer to resist tearing, are stapled to rough
allowed to absorb moisture, finger joints may
flashing strips stapled to the
openings or sheathing, and are often used in tan-
separate.
sheathing and caulked to the jamb
dem with a sealant or caulk. The second group,
edges; the gap above the frame head
self-adhering flashing tapes, are typically butyl
BACk-PRIMIng AnD PAIntIng
was flashed with foil flashing tape,
based; some are foil-faced as well. Because flash-
which is self-adhesive. These
Apply primer to all faces and edges of exterior
flashings will, in turn, be covered by
ing tapes adhere and seal aggressively, they usu-
wood (and engineered wood) siding and trim,
fortified building paper tucked under ally aren’t used with caulks or sealants. Self-
including the back faces. Back-priming is criti-
the stucco. Three coats of stucco will
adhesive flashing tapes seal so well that they are
cally important because wood will cup (edges
then be applied to lath nailed over
by far the favorite with builders.
the building paper.
Both flashing tapes and flashing strips are
available in rolls 4 in., 6 in., 9 in., and 12 in. wide
and are used for essentially the same tasks.
Their differences are subtle but telling. Because
flashing strips are thinner than flashing tapes,
zzzzzz Eaves trim
P R O T I P
Rake trim
for example, strips are often specified when
trim on older buildings is
sealing the perimeter of an uncased window (see
Fascia
rarely level or parallel. thus new
pp. 131–132), where the flashing is sandwiched
trim may look
better if it’s
installed slightly out of level so
between jamb edges and casing. On the other
that it aligns with what’s already
hand, the greater thickness (20 mil to 45 mil) and
there. For example, when stretch-
adhesion of butyl-based flashing tapes enable
ing a chalkline to indicate the
them to seal around nail shanks, thus preventing
bottom of the water table, start
leaks. Installing (and retrofitting) flashing
level and then raise or lower the
around door and window openings is discussed
line until it looks right in relation
at length in chapter 6.
to nearby windowsills and the
like. Once the chalkline looks
more or less parallel to existing
Exterior Trim
Soffit
trim, snap it on the building
However ornate or complex it may be, exterior
Frieze
paper, and extend it to corner
trim’s basic function is to cover critical building
boards.
seams, keeping weather out and reducing air
Corner
infiltration.
boards
Fascia, soffit, and frieze boards are
collectively called the eaves trim.
158 Chapter 7
Engineered trim: A Primer
Just as engineered lumber revolutionized structural materials, there’s
Fiber-cementtrim is wood pulp mixed with portland cement
now engineered trim rated for exteriors. Many of them are perfectly
and sand, and it’s virtually indestructible. Few people would mistake it
straight, flat, and factory primed on all six sides. If you’re accustomed
for wood, but it’s strong, lightweight, stable, and resistant to rot,
to working with wood, engineered trim will take some getting used to,
insects, and fire. hardietrim® is available in thicknesses from 7⁄16 in. to
and the jury is still out on its long-term stability and durability, espe-
1 in.; in widths of 4 in., 6 in., 8 in., and 12 in.; and in lengths of 10 ft.
cially that of hardboard. here’s an overview of types:
and 12 ft. See p. 171 for working with fiber-cement siding and trim.
Laminatedveneerlumber (lVl) is made from thin wood
CellularPVCplasticsare a rapidly growing category of
veneers glued so the grain runs in the same direction, faced on one
exterior trim, shaped molding, and sheet materials that can be worked
side with a medium-density overlay (MDO) of resin-impregnated paper.
using regular woodworking tools. At this writing, two ways to process