the cost of new.
exposed to rain, it will absorb water like a sponge and rot before you know it.
However, make sure all materials are structur-
ally sound. Use a pocketknife or an awl to test
lumber for rot or insects.
building materials
61
lumber quality became less reliable—much to the need for deep-dimensioned traditional roof raf-
dismay of builders.
ters and complex job-site cutting.
In response, the lumber industry combined
Advantages: Trusses can be prefabricated
wood fiber and strong glues to create engineered
for almost any roof contour, trucked to the job
lumber (EL), including I-joists, engineered
site, and erected in a few days. In addition, you
beams, plywood, and particleboard. EL spans
can route ducts, pipes, and wiring through
greater distances and carries heavier loads than
openings in the webbing—a great advantage in
standard lumber of comparable dimensions. In
renovation work.
addition, EL won’t shrink and remains straight,
Disadvantages: Other than specialized
stable, strong, and—above all—predictable.
attic trusses, roof trusses leave little living
Still, EL has two main drawbacks: It’s heavy,
space or storage space in the attic. Adding
so dense that it must often be predrilled, and it
kneewalls on the sides will gain some height,
costs considerably more than sawn lumber. Even but your design options will be limited. Roof
so, EL is here to stay.
trusses should be engineered and factory built
and never modified, unless an engineer
trusses
approves the changes; otherwise, unbalanced
loads could cause the trusses—and the roof—
The most common truss is the prefabricated roof to fail.
truss, which is a large triangular wood frame-
work that serves as the roof’s support structure.
Floor trusses, on the other hand, are often
Its short, weblike members are fastened together
open webs spaced 24 in. on center. Although they
with steel truss plates. Trusses are lightweight,
can span roughly the same distance as I-joists
inexpensive, quick to install, and strong relative
of comparable depth, it’s much easier to run
to the distances they span. They eliminate the
ducts, vents, wiring, and plumbing through open-
web trusses.
i-joists
I-joists are commonly called TrusJoists® after a
zzzzzz alternatives to solid-Wood joists
popular brand (a subsidiary of Weyerhaeuser®).
I-JOIST
Typically, I-joists are plywood or oriented strand
Stiff flanges
board (OSB) webs bolstered by stiff lumber
add strength.
flanges top and bottom, which add strength and
prevent lateral bending.
Although I-joists look flimsy, they are stronger
than solid-lumber joists of comparable dimen-
Plywood or
sions. Whereas solid joists are spaced 16 in. on
OSB web
center, I-joists can be laid out on 191⁄2-in. or
24-in. centers. They also are lightweight, straight,
and stable. Floors and ceilings constructed with
Follow manufacturer’s specs
I-joists stay flat because there’s virtually no
for sizing and locating holes.
shrinkage; hence, there are almost no drywall
cracks, nail pops, or floor squeaks.
Installing I-joists is not much different from
installing 2x lumber, but blocking between I-joists
is critical. (They must be perfectly perpendicular
OPEN-WEB FLOOR TRUSS
to bear loads.) You can drill larger holes in I-joist
webs than you can in solid lumber, but religiously
follow manufacturer guidance on hole size and
placement. And never cut into the flanges.
Manufacturers continue to develop more
economical I-joist components. Webs may be
plywood, particleboard, or laminated veneer
lumber (LVL). Flanges have been fabricated from
LVL, OSB, or—back to the future!—solid lumber
Lots of space to run
pipes and ducts
(2x3s or 2x4s) finger-jointed and glued together.
I-joists with wider flanges are less likely to flop
2x3 or 2x4 chords
and fall over during installation. Plus they offer
more surface area to glue and nail subflooring to.
Truss plate
62
chapter 4
engineered beams
The most daunting part of using engineered
beams may be the wide selection. Fortunately,
lumberyard staff can usually explain the merits
of each type and help you determine correct size.
Glulams, or glue-laminated timbers, are the
granddaddy of engineered beams. They’ve been
used in Europe since the early 1900s. In North
America, they’re fabricated from relatively short
pieces of dimension lumber (often Douglas
fir or southern pine), which are overlapped or
finger-jointed, glued, and pressure clamped.
Glulams come in stock widths of 31⁄8 in. to 63⁄4 in.,
but you can obtain them in almost any size or
shape, including curves and arches, as well as
pressure treated.
Glulams are expensive, but their stability and
strength make them suitable for high loads in
clear spans as great as 60 ft. Obviously, you’d
need a crane to move such a behemoth.
LVL (Microllam®) is fashioned from thin layers of
wood veneer glued together—much like plywood,
except the wood grain in all LVL layers runs par-
allel. It’s stronger than sawn lumber or laminated
strand lumber of comparable size, although it’s
roughly twice the cost of sawn lumber.
LVL is usually milled as planks 13⁄4 in. wide, so
it’s typically used as rim joists, cantilever joists,
or in-floor headers and beams. It’s a good choice
for medium-span beams up to 16 ft., and because
individual beams are easy to handle, a small
crew can join LVL planks on site to create a built-
up girder. LVL is available in other widths, from
31⁄2 in. to 51⁄2 in. Depths range up to 20 in.
A drawback of LVL is that it can’t be pressure
treated and shouldn’t be used on exteriors. If it
This engineered beam is a 4-in. by 14-in. Parallam girder secured with a Simpson CCQ column cap.
gets wet, it will cup. For this reason, keep it cov-
ered until you’re ready to use it.
PSL (parallel strand lumber, Parallam®) is created
from wood fiber strands 2 ft. to 8 ft. long, run-
Heavy STeeL FraminG
ning parallel to each other, and glued together
under tremendous pressure. PSL is the strongest
Load-bearing steel framing is heavier (14 gauge
and most expensive of any structural composite
to 20 gauge) and costs much more than lumber.
lumber; on many projects, PSL is the material
plus, it requires specializ
ed tools and techniques.
of choice.
Metal conducts cold, so insulating steel walls
Standard PSL sizes are 7 in. to 11 in. wide, up
can be a challenge. For exterior and load-bearing
to 20 in. deep, and they can be fabricated to vir-
walls, you’re better off with wood framing.
tually any length—66 ft. is not uncommon.
Because they’re stronger than glulams, PSLs are
built without camber (a curve built in to antici-
pate deflection under load), so they’re easier to
align during installation.
PSL beams can be pressure treated and thus
can be used outside.
LSL (laminated strand lumber, TimberStrand®)
is fabricated from 12-in. wood strands from fast-
building materials
63
growing (but weaker) trees, such as aspen and
Framing with Steel
poplar, and then glued together in a random
The use of steel framing in residential renovation
manner. Consequently, LSL carries less load than is increasing, but it’s still relatively rare, limited
the beams noted previously, and it costs less.
to applications where the greater weight or size
Still, it is stronger than sawn lumber, although
of wood framing would be a problem—such as
more expensive.
furring down a ceiling (see p. 203), building sof-
LSL is available in 13⁄4-in. to 31⁄2-in. widths
fits, or framing out chases in which to run pipes,
and in depths up to 18 in., but it’s most often
ducts, or electrical wiring. Metal studs may also
used as short lengths in undemanding locations,
be specified in residential situations where fire is
such as door or window headers, wall plates,
a concern.
studs, and rim joists.
LSL headers are stable, so they’ll probably
LigHt steeL Framing
reduce nail pops and drywall cracks around doors
and windows. But for small openings of 10 ft. or
Light steel framing consists primarily of
less and average loads, sawn-lumber headers are
C-shaped metal studs set into U-shaped top and
usually more cost-effective.
bottom plates, joined with self-drilling pan-head
screws. Fast and relatively inexpensive to install,
light steel framing (20 gauge to 25 gauge) is most
often used to create nonload-bearing interior par-
titions in commercial work. With drywall
attached, metal studs become rigid, so, in effect,
drywall panels become structural agents.
Advocates argue that more residential con-
tractors would use light steel framing if they were
familiar with it. In fact, light steel framing is
less expensive than lumber; it can be assembled
with common tools, such as aviation snips, screw
guns, and locking pliers; and it’s far lighter and
easier to lug than dimension lumber. To attach
drywall, use type S drywall screws instead of
the type W screws specified for wood. One big
plus: Because metal-stud walls are assembled
with screws, they can be disassembled easily and
recycled completely.
If you want to hide a masonry wall, light steel
framing is ideal. Masonry walls are often irregu-
lar, but if you use 15⁄8-in. metal framing to create
a wall within a wall, you’ll have a flat surface to
drywall that’s stable and doesn’t eat up much space.
That said, light steel is quirky. You must align
prepunched holes for plumbing and wiring before
cutting studs, and, for that reason, you must
measure and cut metal studs from the same end.
If you forget that rule, your studs become scrap.
Further, if you want to shim and attach door
jambs and casings properly, you need to reinforce
steel-framed door openings with wood. And
finally, safety glasses, hearing protection, and
sturdy work gloves are essential when working
with light steel framing—edges can be razor sharp.
FLitcH pLates
Flitch plates are steel plates sandwiched between
Steel I-beams span greater distances and support heavier loads than any other bearing material of
dimension lumber and through–bolted to
equivalent depth. But installing steel is best left to pros who have the know-how and the right
equipment. Here, a worker uses two 2-ton-rated chain falls to lift a 10-in. by 10-in. I-beam
increase span and load-carrying capacity. Flitch
weighing 1,600 lb.
plates are most often used in renovation where
64
chapter 4
existing beams or joists are undersize. (You insert
plates after jacking sagging beams.)
sorting out panel names
Ideally, a structural engineer should size the
flitch plate assembly, including the size and
structural panels:
placement of bolts. Steel plates are typically 3⁄8 in.
plywood is a sandwich of thin veneers sliced from logs, with veneers stacked
to 1⁄2 in. thick; the carriage bolts, 1⁄2 in. to 5⁄8 in. in
perpendicularly to one another (cross-grain) in alternating layers and glued. each
diameter. Stagger bolts, top to bottom, 16 in.
layer is a ply. alternating wood grain direction adds stiffness, dimensional stability,
apart, keeping them back at least 2 in. from beam
and strength.
edges. Put four bolts at each beam end. To ease
installation, drill bolt holes
oSB (oriented strand board) is made from logs shredded into long strands.
1⁄16 in. larger than the
bolt diameters.
the strands are oriented in the same direction, mixed with resins, and pressed into
Flitch plates run the length of the wood mem-
thin sheets. as with plywood, strands in alternating layers run perpendicularly.
bers. The wood sandwich keeps the steel plate on
nonstructural panels:
edge and prevents lateral buckling. Bolt holes
should be predrilled or punched—never cut with
particleboard (also known as chipboard) is fabricated from mill waste,
an acetylene torch. That’s because loads are
mixed with resins, and hot pressed. because of its stability and uniform consistency,
transferred partly through the friction between
particleboard is an excellent core material for veneered cabinets, laminated counter-
the steel and wood faces, and the raised debris
tops, and bookcases.
around acetylene torch holes would reduce steel-
MDF (medium-density fiberboard) is a mixture of fine, randomly oriented
to-wood contact.
wood fibers and resins, hot pressed for a smooth surface. it is used as interior trim
and cabinetry stock.
steeL i-beams
Hardboard (such as masonite) is a high-density fiberboard created by
Although lately eclipsed by engineered-wood
steaming wood chips and then hot pressing them into sheets. the hard, smooth
beams, steel I-beams, for the same given depth,
surface is well suited for underlayment, interior trim, and paneling. Hardboard used
are stronger
. Consequently, steel I-beams may be
as exterior siding has been plagued by warping, delamination, and other moisture-
the best choice if you need to hide a beam in a
related problems.
relatively shallow floor system—say, among 2x6s
or 2x8s—or if clearance is an issue.
Wide-flange I-beams are the steel beams most
commonly used in houses, where they typically
range from 41⁄8 in. to 10 in. deep and 4 in. to
10 in. wide. Standard lengths are 20 ft. and 40 ft.,
yeT more panel STamPS
although some suppliers stock intermediate
sizes. Weight depends on the length of the beam
t&G: tongue and groove
and the thickness of the steel. That is, a 20-ft.
G2S: good two sides
8x4 I-beam that’s 0.245 in. thick weighs roughly
300 lb., whereas a 20-ft. 8x8H I-beam with a web
G1S: good one side
that’s 0.458 in. thick weighs 800 lb. If you order a
prp 000: performance-rated panel (number
nonstandard size, expect to pay a premium.
follows)
Before selecting steel I-beams, consult with a
SeL tF: select tight face
structural engineer. For installation, use an expe-
SeLeCt: uniform surface, acceptable for
rienced contractor. Access to the site greatly
underlayment
affects installation costs, especially if there’s a
crane involved.
Structural and
Nonstructural Panels
Plywood and OSB are the structural panels most
often specified to sheath wood framing and
increase its shear strength. For example, a 20-ft.
wall sheathed with 7⁄16-in. plywood can withstand
more than a ton of lateral force pushing against
the top of the wall.
building materials
65
pLYWood
Structural plywood is made by laminating soft-
wood plies. Each panel is stamped to indicate
veneer grade, species group or span rating, thick-
ness, exposure durability, mill number, and certi-
Veneer grade
fying agency. The Engineered Wood Association,
which oversees about two-thirds of structural
panels in North America, also has stamps that
Certifying agency
specify a panel’s intended use, such as “rated
sheathing,” or installation details, such as “sized
thickness
for spacing,” to remind carpenters to leave 1⁄8-in.
expansion gaps between panels.
Renovation 4th Edition Page 15