From the Ground Up: Framing
Tom Silva's best practices for building a strong and solid skeleton
A frame is the skeleton of a house. If the frame is strong, it provides the necessary support for everything that follows. But if it's weak, no amount of expensive finishes will hide the flaws: Those perfectly plastered walls will begin to crack every time a door slams, the granite countertops will gradually fall out of level, and the quartersawn oak floors will bounce and squeak like a rusty spring. "Shortcuts in framing are the biggest mistake you can make," says Tom Silva, This Old House general contractor, "although it may take four or five years before the sagging, the bouncing, and the movement start to show up."
While the basics of modern stud-wall framing haven't changed much in the past 25 years, the tools and materials certainly have. Pneumatic nail guns, which were novelties until the mid 1970s, have speeded up the assembly process; engineered lumber is steadily supplanting sawn boards, and metal connectors are now routinely used to enhance stiffness and sturdiness.
But Tom warns that tools and materials by themselves don't guarantee a strong house frame. They need to be in the hands of a skilled carpentry crew who know how to use them. "They'll build it right the first time," Tom says, "so you won't be sorry later on." To see how Tom frames a house, read on.
Building It Right
House frames can be made out of thick posts and beams (the oldest framing method) or extra-long studs (the balloon grames of the Victorian era). But Tom Silva typically frames in one-story "platforms" consisting of 8-or-9-foot-high stud walls resting on a plywood-sheathed subfloor. Each story is framed atop the previous one, until it's time to put on the roof.
- Use the right-size nails. Codes specify length, girth, and number of nails in critical joints.
- Don't overdrive. A nail head sunk too deep into the wood can't pull its full weight.
- Space consistently. Placing joists, studs, and rafters exactly 16 inches apart gives solid support to panel ends.
- Use dry wood. Lumber stamped "S-dry" or "KD" (kiln dried) is less likely to warp and twist.
- Keep wood dry.Block stacks off the ground and cover them with tarps.
- Use plywood clips on roof and wall panels. The 1/8-in. gap they create between each sheet prevents buckling.
- Lay sheets perpendicular to framing. Increases overall strength and stiffness.
- Glue and fasten. Adhesives can improve bond strength by a third.
As Seen on TV: Great Framing Ideas from TOH Project Houses
Metal Hangers and Ties
Concern about the weakness of nailed joints, particularly in earthquake and hurricane prone regions, has made metal straps and ties a fixture in codebooks and on today's job sites, even where such natural disasters seldom occur. There are hundreds of different types of galvanized-steel fittings, from joist hangers to hurricane straps, with new ones coming on the market almost every month. Each connector uses more nails than an "old-fashioned" joint because every hole in the connector needs to be filled. But with the right nail gun there's almost no reduction in installation speed. Note: Use only nails specified by the manufacturer—no substitutions!
An I-joist consists of a "web" of high-grade OSB (oriented strand board) glued between two horizontal "flanges" of conventional lumber or LVL (laminated veneer lumber). It's just as strong as a sawn 2x of the same width but only half the weight, and it's made in lengths of up to 60 feet. Best of all, holes for plumbing and ductwork can be cut through the web (at specified sizes and intervals) without compromising structural integrity. TOH first used I-joists at the 1989 barn project in Concord, Mass., and Tom has been using them ever since.
LVL beams are composed of wood veneers glued together under heat and pressure. All the veneers are oriented precisely in the same lengthwise direction, making LVLs nearly 20 percent stiffer than ordinary sawn lumber. While LVLs are commonly used as ridge beams and headers above windows and doorways, Tom has also used them as joists, rafters, and stair stringers—anywhere he needs maximum performance in minimum space. They're heavy, but Tom likes them because they're as strong as steel, yet he can cut them with an ordinary saw.
On the Horizon: New Technologies for the Future of Framing
New foam-based adhesives use the superior sticking power of polyurethane and are easily dispensed with just a finger on the trigger. Even better, one can of foam contains the equivalent of 15 tubes of old-style adhesive.
The Sheather-Plus sheathing nail resists uplift forces twice as well as standard smooth-shanked nails, thanks to a ringed shank, an oversize head, and a cement coating that acts like a lubricant to speed the nail home, then bonds to the wood.
Laminated strand lumber — flakes of wood that are pressure-glued to the size of a standard 2x4 or 2x6 (inset) — is free of defects, won't warp or bow, and can run as long as 22 feet, a dimension unthinkable in a sawn stud nowadays.
Where to Find It
Wood I-Beam joists, G-P Lam LVL beams
Georgia Pacific Corp.
Cordless framing nailer:
Metal hangers and ties:
Simpson Strong-tie Co.
Todal Products, Inc.