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Renovation 4th Edition

Page 15

by Michael Litchfield


  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.

 

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