Renovation 4th Edition

by Michael Litchfield

  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

  16 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 16 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)