Span rating
(rafters/studs)
Veneer grades. Veneer grades range from A to
D, with letters appearing in pairs to indicate the
front and back veneers of the panel. “A/B
exposure rating
Exterior,” for example, has a grade A front
veneer, a grade B back veneer, and grade C inner
plies. When you buy CDX (C/D exterior grade),
Mill number
it’s advisable to place the grade C side toward the
weather—or up, if used as subflooring.
Most roof and wall sheathing and subflooring is
CDX. If a panel is also stamped PTS, its imperfec-
Plywood grade stamps.
tions have been plugged and touch sanded. Lower
veneer grades have more plugs and bigger knots.
Grade D is the lowest grade of interior ply-
wood panels; it should not be exposed to weather.
Species grade or span rating. Plywood’s
strength may be indicated by two marks. One is a
reduced-Formaldehyde and species group number (1–5). Group 1 is the
FormaLdehyde-Free PaneLS
strongest and often contains Douglas fir or
southern yellow pine.
Composite panels such as plywood, oSB, and MDF have long been bonded with urea-
The second mark, a span rating, is more com-
formaldehyde (uF) resins, which outgas (give off) noxious gases. Volatile organic
mon. The two-digit rating looks like a fraction,
compounds (VoCs) are a problem for homeowners with chemical sensitivities, espe-
but it’s not. Rather, a rating of 24/16 indicates
cially as houses become more airtight. also, formaldehyde is classified as a probable
that a panel can sheath rafters spaced 24 in. on
human carcinogen by the epa, which, while alarming to homeowners, could prove fatal
center and studs spaced 16 in. on center. Span
to installers.
ratings assume that the panel’s long axis runs
in response, manufacturers investigated less-toxic resins. to date, they have been
perpendicular to framing members.
able to greatly replace uF resins in structural panels such as CDX plywood, primarily
Another common stamp is Struc I, which
by switching to phenol formaldehyde resins (pFs), which are less toxic than uFs.
stands for Structural I sheathing, a five-ply CDX
typically, these panels will be stamped NauF (no added urea-formaldehyde). it is
that’s tested and guaranteed for a given shear
hoped that manufacturers will replace all formaldehyde resins in structural panels
value. If an engineer specifies Struc I, it must be
someday, but presently there are no alternatives with the same bonding strength and
used. Plywood used for structural sheathing must
resistance to the elements.
have a minimum of five plies. Avoid three-ply,
1
Fortunately, there are formaldehyde-free options for the sheet materials used
⁄2-in. CDX: Although it is widely available and
cheaper than five-ply, it’s vastly inferior.
inside a house—as molding and paneling, as well as cabinet frames, doors, and
shelves. these low-VoC materials greatly help the quality of indoor air. Medite® ii‚
Thickness and length. Panels rated for Struc I
Medex®‚ and Sierrapine® are three of the better-known brands of MDF; visit the
wall sheathing, roof sheathing, and subflooring
internet or consult your local lumberyard for more choices.
range from 3⁄8 in. to 23⁄32 in. thick. Although 4x8
panels are the most common, 4x9 or 4x10 sheets
enable you to run panels vertically from mudsills
to the rim joists atop the first floor, thereby
reducing the shear-wall blocking you might need
behind panel edges and greatly improving the
shear strength of the wall. ( Shear walls are spe-
cially engineered walls that brace a building
66
chapter 4
against lateral seismic and wind forces.)
naiLing structuraL paneLs
P R O T I P
Although the square-foot prices of 4x9 and 4x10
Your local building code will have the final say
panels are higher than that of 4x8s, the larger
on sizing structural panels. To accommodate
just one fragment from a nail
panels speed up the job.
heavy loads, choose a panel rated for a higher
head can blind you. so buy a
exposure durability. How much weather and
span. A span rating of 32/16 indicates that the
pair of impact-resistant safety
moisture a wood-based panel can take is largely a panel is strong enough to sheath rafters spaced
glasses that are comfortable—
function of the glues used. Exterior-grade panels
and wear them.
32 in. on center and studs 16 in. on center and,
can be exposed repeatedly to moisture or used in
therefore, can support far greater live loads than
damp climates because their plies are bonded
a 24/16-rated panel, even though a 32/16 panel is
with waterproof adhesives. Exposure 1 is suitable only 1⁄32 in. thicker.
if there’s limited exposure to moisture—say, if
Nailing schedules for different uses of ply-
construction gets delayed and the house doesn’t
wood are the same: Nail every 6 in. around the
get closed in for three to six months. Exposure 2
perimeter, not closer than 3⁄8 in. to the edge; else-
panels are suitable for protected applications and where, nail every 12 in. For subflooring, annular
brief construction delays. Interior-grade panels
ring or spiral nails hold best; use hot-dipped gal-
will deteriorate if they get wet; use them only in
vanized nails for all exterior purposes. An 8d nail
dry, protected applications.
is sufficient for 1⁄2-in. to 3⁄4-in. plywood. For struc-
tural shear walls, follow the engineer’s specifica-
osb paneLs
tions for nailing. Shear walls often require tighter
OSB and plywood have almost exactly the same
nailing around the edges of the panel—and,
strength, stiffness, and span ratings. Both are
sometimes, thicker nails.
fabricated in layers and weigh roughly the same.
If a panel stamp says “sized for spacing,” leave
Both can sheath roofs, walls, and floors. Their
an expansion gap of 1⁄8 in. between sheets—or
installation is almost identical, down to the
whatever the stamp specifies. (Tongue-and-
blocking behind subfloor edges and the need for
groove panels may not need gaps.) For greatest
H-clips between the unsupported edges of roof
strength, run the long axes of panels perpendicu-
sheathing. Exposure ratings and grade stamps
lar to structural members and stagger butt ends.
are also similar.
In the intervals between joists, support plywood
In some respects, OSB is superior to plywood. edges with solid blocking; on roofs, place block-
It rarely delaminates, it holds screws and nails
ing clips (also called ply-clips or H-clips) beneath
better, and it has roughly twice the shear values.
th
e panel edges unsupported by solid wood.
(That’s why I-joists have OSB webs.) So given
Pneumatic nailers are widely used to nail
OSB’s lower cost (10% to 15% cheaper, on aver-
down plywood, and they save a lot of time. But
age), it’s not surprising that OSB grabs an
one thing a nailer won’t do is “suck up” a piece of
increasing market share every year.
plywood to framing. This is worth noting because
But OSB has one persistent and irreversible
almost all plywood is warped to some degree. So
shortcoming: Its edges swell when they get wet
after you nail down plywood with a pneumatic
and appear as raised lines (ghost lines) through
nailer, go back over the surface and give each nail
roofing. To mitigate this swelling, OSB makers
an additional rap with a framing hammer. The
Bamboo plywood has beautifully
seal the panel edges. However, when builders saw hammerhead, being larger than the striker of the figured faces and edges and is a great panels, the new (unsealed) edges swell when wet. nailer, will help drive the plywood down as well.
favorite of many cabinetmakers. A
Buildings under construction get rained on, so
As important, don’t drive a nail too deeply. If a durable, sustainably produced
edge swelling is a real problem. Swollen edges can pneumatic nailer’s pressure is set too high, the
hardwood, bamboo is as green as
also raise hell in OSB subflooring or underlay-
nail may be driven through the face ply, dimin-
green gets.
ment if it absorbs moisture, as commonly occurs ishing the shear value and holding capacity of the
over unfinished basements and uncovered crawl-
nail. Set the nailer’s pneumatic pressure a little
spaces. Thus, many tile and resilient-flooring
lower than would be needed to drive the nail
manufacturers insist on plywood underlayment.
flush. Then finish each nail with a hammer blow.
Given the huge market for OSB, however,
HardWood pLYWood
count on solutions before long. At this writing,
J.M. Huber AdvanTech®, Louisiana-Pacific
Hardwood plywood is not intended to be struc-
TopNotch®, and Weyerhaeuser Structurwood®
tural, but because you may need some during
are all tongue-and-groove–edged OSB panels
renovation, here’s a brief overview. As with soft-
purported to lie flat, install fast, and have mini-
wood plywood, there’s a great variety, classified
mal “edge swell.” Stay tuned.
by species, face plies (appearance), core mate-
rial (medium-density fiberboard [MDF], LVL,
particleboard), and glues. The range of uses is
building materials
67
suggested by the many thicknesses—from 1⁄16-in.
laid together in sequence) that allow
aircraft plywood to 2-in. door stock.
repetitions of face grain for visual effect.
Most hardwood plywood is used indoors, so
Premium (A). Grain patterns and colors
appearance grading and careful handling are cru- are matched precisely.
cial. Be sure to specify the grade of both faces,
Good (No. 1). Colors of matched veneers
and check the stock carefully for damage.
on a face do not vary greatly, but patterns are
Because this plywood is extremely expensive,
less closely matched than premium grade.
sheets are often used right up to the edges. Make
Sound (No. 2). Although colors and
sure edges aren’t damaged or frayed. Here’s a list
patterns are not matched, there are no
of hardwood grades:
open flaws.
Specialty. You can special-order closely
Utility (No. 3). These may have small
matched flitches (veneer surfaces that can be
flaws, tight knotholes, discoloring, and splits
that can be filled but no rot.
nail names
Backing (No. 4). Defects are allowed
as long as they don’t weaken the sheet or
Common: the workhorse of construction. basic uncoated nail; flat head.
prevent its use; the backing side may be from
Spike: a common nail “on steroids,” 40d or 60d. rarely used these days.
a different tree species than that of the
Box: same length and head size as a common nail but with a thinner shank.
exposed face.
Sinker: shank about the same size as a box nail; flat head, countersunk.
usually cement coated.
Metal Connectors
Cooler: a sinker with a bigger head.
Finish: same length as a box nail but with a thinner shank. brad head (not
If wood is the universal building stock, metal is
the universal connector. Nails of many types,
much wider than shank).
bolts, and screws are discussed in this section—
Casing: similar to a finish nail, but shank is thicker and head is slightly
notably, structural screws, whose use has
larger; countersunk.
increased dramatically in renovation. Specialty
Duplex: double-headed nail for temporary nailing to depth of first head,
plates that reinforce structural members also are
which holds wood down. protruding top head is easily gripped for removal.
described. Later in this chapter is a review of
construction adhesives, which, some say, are des-
tined to supplant metal connectors.
nail sizes
NaiL LeNGtH (in.) peNNy Size (d)
1
2
11⁄2
4
2
6
21⁄2
8
3
10
31⁄4
12
31⁄2
16
4
20
41⁄2
30
Nail types. Top row, from left: 60d galvanized spike, 40d common, 20d common, 16d galvanized,
5
40
16d common, 12d vinyl-coated sinker, 12d galvanized box, 10d galvanized common, 8d
galvanized box, and 4d galvanized siding. Bottom row, from left: concrete nail and six joist-
6
60
hanger and metal-connector nails (also called Teco® nails). Longer nails may be required when
sheathing covers framing.
68
chapter 4
naiLs
As they’re driven in, nail points wedge apart
recommended nailing schedule*
wood fibers. The ensuing pressure of the fibers
on the nail shank creates friction, which holds
appLiCatioN
FaSteNer
the joint together. Nails also transmit shear loads
between the building elements they join. Where
joist to sill or girder (toenail)
3-8d
nails join major structural elements, such as raf-
ters and wall plates, the loads can be tremen-
Ledger strip
&n
bsp; 3-16d at each joist
dous; where nails attach finish elements, such as
16 subfloor or less to each joist (face-nail)
2-8d (or two 13⁄
trim, loads are usually negligible.
4-in. staples)
There are hundreds of different nails, which
Wider than 16 subfloor to each joist (face-nail) 3-8d
vary in length, head size, shank shape, point,
composition, and purpose.
2-in. subfloor to joist or girder (blind- and face-nail) 2-16d
Length. Length is reckoned in penny sizes, abbre-
sole plate to joist or blocking (face-nail)
16d at 16 in. o.c.
viated as d. The larger the nail is, the greater the
penny rating. Nails 20d or longer are called spikes.
top plate to stud (end-nail)
2-16d
heads. The shape of a nail’s head depends on
stud to sole plate (toenail)
4-8d
whether that nail will be exposed or concealed
and what type of material it’s designed to hold
sole plate to joists or blocking
3-16d at 16 in. o.c.
down. Small heads, such as those on casing, fin-
doubled studs (face-nail)
10d at 24 in. o.c.
ish, and some kinds of flooring nails, can easily be
sunk below the wood surface. Large heads, such
doubled top plates (face-nail)
16d at 16 in. o.c.
as those used to secure roofing paper or asphalt
shingles, are needed to resist pull-through.
doubled top plates, lap spliced (face-nail)
8-16d
Shanks. Nail shanks are typically straight, and
continuous header, two pieces
16d at 16 in. o.c., along each edge
patterned shanks usually have greater holding
strength than smooth ones. For example, spiral
rim joist to top plate (toenail)
8d at 6 in. o.c.
flooring nails (with screw shanks) resist popping,
ceiling joists to plate (toenail)
3-8d
as do ring-shank nails. (By the way, it takes more
force to drive spiral nails.) Spiral and ring-shank
continuous header to stud (toenail)
4-8d
nails are well suited to decks and siding because
changes in wood moisture can reduce the friction
ceiling joists, laps over partitions (face-nail)
3-16d
between wood fibers and straight shanks.
ceiling joists to parallel rafters (face-nail)
3-16d
Points. Nails usually have a tapered four-sided
point, but there are a few variations. For exam-
rafter to plate (toenail)
Renovation 4th Edition Page 16