Renovation 4th Edition
Page 37
lVl trim is available in 1-in. and 11⁄4-in. (5/4) thicknesses and in stan-
cellular PVC yield slightly different physical attributes: free-form cooling
dard widths from 4 in. to 12 in., in 2-in. increments. Standard lengths
PVC is uniform throughout, and veteran carpenters report that its
are 16 ft. and 20 ft. It’s easy to cut, drill, nail, and handle, and its MDO density, weight, and workability are virtually identical to that of pine, face paints wonderfully. however, lVl is expensive. Clear lam® is one
whereas celuka-processed PVC has a somewhat harder and more brittle
well-known brand.
outer layer that tends to chip. For optimal results, use sharp, carbide-
Hardboard,fiberboard,orwood-fibercomposite is fash-
tipped sawblades and drill bits when working either type. the top-
ioned from wood chips that are steamed, pressed, and glued. there are
selling cellular PVC trim, Azek®, is a free-form type, as are Fypon®,
many brands in this category, including MiratEC®, Choicetrim®, and
kleer®, and Certainteed. In some respects, PVC trim is easier to work
Protrim®, and product features vary greatly. Composites tend to be
than wood. You can screw or nail close to the edges and ends of stock
available in 1-in. and 11⁄4-in. thicknesses, in standard widths of 4 in.
and not worry about splitting it because, unlike wood, PVC has no
to 12 in., and in 16-ft. standard lengths. Some are primed on all sides,
grain. It also lacks knots and won’t cup or warp. there are, however,
some not; some have MDO-like paper facing, some not—so check with
several critical differences when working with PVC: (1) It tends to
your distributor. hardboard sidings have had widespread problems with expand and contract along its length, so when joining long boards, moisture retention, swelling, and degradation, so hardboard-trim mak-bevel-cut their ends so they overlap. (2) Join trim with PVC cement,
ers have worked hard to improve their products. that noted, however,
which joins them chemically rather than mechanically, as is the case
take pains to prime all sides and the cut edges. Drive corrosion-resis-
with wood joints. (3) PVC doesn’t absorb moisture, so paint takes
tant nails just flush to the trim surface; nails driven deeper may need
longer to dry than with wood.
caulk to keep out moisture. gap butt joints 1⁄8 in. to allow expansion,
then caulk and paint the trim ASAP.
warping up) when the sun dries out the exposed
Prime all faces and edges of exterior
front face if the back retains moisture. The great-
trim and siding, including the back.
er the moisture differential between front and
Back-priming is especially important
back faces, the more likely the cupping.
because moisture trapped between
back faces and sheathing can lead to
While cutting trim or siding, keep a can of
paint or sealer failure, cupping, or—in
primer and a cheap brush nearby to seal the ends
extreme cases—rot. After cutting trim
after every cut; unprimed end grain can absorb a
or siding, be sure to prime the cut
lot of moisture. (It’s especially easy to forget to
edges as well.
prime cut edges when you’re using preprimed
trim.) Ideally, apply at least two topcoats of acryl-
ic latex paint after priming to seal trim and sid-
ing. If you want stained or clear-finished trim or
siding, use cedar or heart redwood.
AttAChIng tRIM
As a rule, for best attachment secure exterior
trim to framing. In those rare instances where
you have only sheathing to nail to, angle the nail
so that it will be less likely to pull out.
Exteriors
159
a 16-ft. corner board in place while balancing on
a ladder will appreciate this tool. Nailers also
ExtEriOr trim tiPs
drive nails quickly and accurately, reducing splits
TiP1.Jointrimboardsontheground,
and eliminating errant hammer blows that mar
especiallyinthesesituations:Thejointsare
trim. After setting the trim with finish nails, you
can always go back and hand-nail with headed
complex,theheightsaredaunting,thehouse
nails to secure the trim further. Or you can use
framingisoutofsquare,and/ortheboardsare
headed siding nails in the nail gun.
longandunwieldy.Todothismosteasily,place
thetrimstockonsawhorsestoshape,assemble,
Nailing schedules. To face-nail nominal 1-in.
andprimeit.Theresultingjoinedpieceswillbe
trim (actual thickness, 3⁄4 in.), use 8d box nails
alittleheavierthansinglepieces,butthe
spaced every 16 in. Nail both edges of the trim
board to prevent cupping, placing nails no closer
assemblywillbestraightandcrisp,evenifthe
than 1⁄2 in. to the edge. If the trim goes over sid-
framingisn’t.Useanexteriorgluesuchas
ing, say, at corners, use 8d to 10d box nails. To
GorillaGlueand6dgalvanizedboxnailstodraw
create a tight joint between corner boards, use
theboardstight.
6d nails spaced every 12 in., and drive them in
TiP2.ifyourtrimrunislongerthan
a slight angle. If you’ll be painting the trim, also
individualboards,jointheboardswithbevel
caulk this joint or glue it using an exterior ure-
joints,whichwon’tshowwoodshrinkageas
thane glue, such as Gorilla Glue or Titebond
obviouslyasbuttjoints.Whenusingbeveled
III (which is less expensive and won’t stain
jointsonverticalboards—say,cornerboards—
your hands).
makethetopbevelslantdown,awayfromthe
About nail heads. Taking the time to line up nail
building,sowaterwon’trunintothejoint.
heads makes the job look neater. For example,
Staggertrimjointsbyatleast32in.sothey’ll
when nailing up jamb casing, use a combination
belessobvious.
square to align nail pairs. If you’re putting up a
long piece of trim that runs perpendicular to
studs, snap chalklines onto the building paper
beforehand so that you’ll know stud positions for
Choosing fasteners. Pick a nail meant for exte-
nailing. If the trim will be painted, take the time
riors. If you’ll be using a transparent finish, mak-
to set the nail heads slightly below the surface,
ing nail heads visible, stainless-steel nails are the
using a flathead punch. Then use exterior wood
premier choice; though expensive, they won’t
filler to fill the holes. If you don’t set the heads
rust. Aluminum nails won’t stain but are some-
slightly, they may later protrude as the wood
what brittle and more likely to bend. Galvanized
shrinks, compromising the paint membrane and
nails are the most popular because they’re eco-
admitting water. On larger jobs, carpenters are
P R O T I P
nomical, stain minimally, and grip well. Many
usually expected to set nail heads. Painters fill
nail types (including stainless steel) also come in
; and paint them.
If trim paint is a different color
colors matched to different wood types—cedar,
than the siding, paint the trim
redwood, and so on. Ring-shank nails hold best.
EAVES tRIM
edges—especially hard-to-reach
For stained exteriors, some contractors prefer Because eaves trim is often complex and can
eaves and rake trim—before
galvanized finish or casing nails because their
impact framing, roofing, ventilation, and the
installing the siding. using a
heads are smaller and less visible. Box nails are a house’s aesthetic integrity, draw a cross section of
minimal number of staples, tack-
good compromise. Their larger heads hold better it as early as possible.
staple a 4-in.-wide strip of plas-
than finish nails, yet their shanks are smaller
There is no single correct way to construct the
tic to the painted trim edges,
than those of common nails, making box nails
then install and paint the siding.
eaves, but the boxed eaves on the facing page are
less likely to split wood. There are also “splitless”
Finally, rip the plastic out, and—
a good place to start. First, a fascia board that
siding nails that come with preblunted points to
voilá—perfect edges! Even if you
overhangs a soffit by 3⁄8 in. to 1⁄2 in. enables you to
minimize splits. (The blunt point smashes through
forego the plastic and need to
hide rafter irregularities—rafters are rarely per-
wood fibers, rather than wedging them apart.)
touch up trim edges, you’ll save
fectly straight or cut equally long. Second, that
Where you want maximum grip, use stainless-
tons of time.
overhang accommodates a rabbeted fascia–soffit
steel trim-head screws instead of nails.
joint, which protects the outer soffit edge, even if
Pneumatic nailers. Most pros use pneumatic
the wood shrinks slightly. Third, if you rabbet the
nailers to attach exterior trim. Using a finish nail- back edge of a frieze board or build it out using
er with galvanized nails allows you to tack up
blocks, the frieze will conceal the top edge of the
trim exactly where you want it. Anyone who has
siding. A frieze also creates an inconspicuous
spent time trying to simultaneously hold and nail space to install an eave vent.
160 Chapter 7
Ventilation channels at eaves allow air to flow
up under the roof and exit at ridge or gable-end
vents. This airflow is beneficial because it lowers
attic temperatures and helps remove excess mois-
ture from the house, thus mitigating mold, ice
dams, and a host of other problems. To keep
insects out, soffits need screening. In a wide sof-
fit, there’s plenty of room for screened vents in
the middle. In a narrower soffit, you may need to
leave a 3⁄4-in. space at the front of the soffit or at
the back hidden behind a built-out frieze board.
If the house has exposed rafter tails rather
than soffits, you have fewer ventilation options
that will look good. Consider leaving the eaves
sealed and adding rooftop intake vents, as
described on pp. 90–91.
WAtER tABlE
Water-table trim often
finishes off the bottom of a
A water table is horizontal trim running around
wall and provides a level
the base of a building below the siding. Not all
base for the first course of
houses have it. Depending mostly on regional
siding. To forestall rot, cap
preferences, the water table takes several forms.
the water table with metal
In the West, it typically looks like windowsill ears
or vinyl flashing before
installing the siding.
(the beveled parts that stick out) and is often
zzzzzz Boxed Eave: Detail 1
zzzzzz Boxed Eave: Detail 2
Insulation
Air rising
baffle
Rafter
Insulation
baffle
Rabbeted
fascia
Rafter
Fascia
Insulation
Insulation
Air rising
Soffit
Spacer blocks
Screened
Soffit
16 in. o.c.
soffit vent
Rabbeted
frieze
Frieze
Screen or
corrugated
vent strip
Siding
Siding
A strip of continuous screen in the soffit allows
air to circulate into the attic. The rabbeted frieze
You can create ventilation channels behind the frieze by
conceals and protects the top of the siding.
spacing it out 3/4 in., using blocks spaced every 16 in. on center.
This also conceals the top of the siding.
Exteriors
161
used to separate different types of siding materi-
CORnER BOARDS
als, such as shiplap siding from wood shingles
Corner boards are usually 1-in. boards butted
above. Typically, 11⁄2 in. by 11⁄2 in., this type of
together. Siding is then butted against them,
water table runs continuously around the build-
making an attractive and weathertight corner.
ing and is mitered at the corners. It often has a
Not all buildings have horizontal trim below
rabbeted heel, which fits over the top of the wood the bottom of the siding. For example, the first
siding below, and a beveled top, which is overlain (bottom) course of shingles is often doubled and
with shingles or clapboards.
overhangs the sheathing slightly. In that case, run
In the East, water tables are also called splash- corner boards 2 in. to 3 in. below the bottom
boards; they usually are 1-in. boards 8 in. to
edge of the sheathing; then, after you nail up the
12 in. wide and may be capped to shed water.
first course of shingles, trim the corner-board
Splashboards are most common in wet regions,
ends level to the shingles’ butts. If the house has
where roof runoff often splashes back along the
a water table or splashboard, measure from its
base of a house. (Some primal carpenter may
top edge up to the underside of the soffit to deter-
have reasoned it would be easier to replace a sin-
mine the length of the corner boards.
gle rotted board than to disturb several courses
If you’re installing shingles, whose overlap-
of siding, or that a thicker board would simply
ping courses have a higher profile than clap-
last longer.)
boards, use 5/4 corner boards, which are a full
Whatever the shape of the water table, flash
1 in. thick. To give the illusion that corner
the top with a metal drip-edge that extends at
boards are the same width at each side, rip down
least 1⁄2 in. beyond the face of the board. The sec-
the overlapped board by the thickness of the
/> tion where corner boards sit atop the water table
stock. And for a crisp, straight corner, preassem-
is especially prone to rot. Prime and paint the
ble corner boards before installing them, as
boards thoroughly.
shown in the photo below.
Occasionally, corner boards are nailed over
siding. This can be a problem because nails driv-
en through the trim may split the siding under-
neath. Besides, corner boards can’t seal well if
zzzzzz Corners
5/4 square stock
1x4
INSIDE CORNER
1x4 ripped down
OUTSIDE CORNER
Butt siding to the corner boards to avoid complex miter cuts. In
Preassemble corner boards, soffit and fascia boards, and
outside corners, rip down the overlapped board by the thickness
other exterior trim on the ground whenever possible. The
of the stock, and both boards will look equally wide.
joined pieces will be tight and square, even if the framing
and sheathing behind them isn’t.
162 Chapter 7
P R O T I P
Epoxy filler can be applied
with a putty knife. But the filler
is easier to shape to match exist-
ing contours by hand—hands
protected by latex gloves, that
is. Restorationist tom O’Brien
suggests donning three or four
pairs of disposable latex gloves
at the start of the job and peel-
After wire-brushing away loose material, inject liquid
Use a taping knife to compress and smooth the filler. The
ing them off as they become
consolidant into the wood until saturated. After allowing
galvanized metal tacked to the sill keeps the filler in place
gunked up.
the consolidant to set, apply the pastelike filler to build up until it dries and doubles as a screed strip to which you the damaged area.
can level the filler.
nailed over an irregular surface. It’s an awkward
original trim. To join the new section to the old,
way to resolve a corner, but this method was
use a biscuit joiner (see p. 480) to cut a biscuit
commonly used on Victorian homes with flat,
slot in both board ends. Dry-fit everything, prime
shiplap siding. Careful nailing and liberal doses
all surfaces with epoxy primer, and allow the
of caulk will help ensure a weathertight seal. To
primer to dry well. Then epoxy the pieces togeth-
minimize splits, predrill the board nails.
er. Hold the boards in place with a piece of scrap