Wood Frame Construction: Platform, Balloon and Timber

Wood frame construction is a way of building in which a skeleton of many small, standard-size lumber members - studs, joists and rafters - carries the loads, and panels of plywood or oriented strand board sheathe it. Wikipedia describes light-frame construction as using more numerous and smaller supports than heavy framing, and calls it the dominant construction method in North America and Australia. The heavier alternative, timber framing, uses fewer and much larger timbers.

The numbers back up 'dominant'. The US Census Bureau's 2025 Characteristics of New Housing reports that 96% of owner-built single-family homes completed that year had wood framing and 2% concrete, and that 84% of multifamily buildings built for rent were wood framed against 6% steel.

• Sill plate - the treated wood member that lies directly on the foundation (Procore).
• Bottom and top plates - horizontal members at the base and top of each wall, 1-1/2 in. thick lumber (Wikipedia).
• Studs - the vertical wall members, typically 1-1/2 x 3-1/2 in. (a 2x4) or 1-1/2 x 5-1/2 in. (a 2x6), spaced 16 in. on center, or 12 or 24 in. depending on the load.
• Headers - horizontal members over doors and windows that carry the load around the opening.
• Cripples - short studs between the bottom plate and a window sill, or between a header and the top plate.
• Joists - horizontal members that carry floors and ceilings.
• Rafters - sloped members that carry the roof.
• Sheathing - plywood or OSB panels nailed to the outside; see our types of plywood guide for span ratings and bond classes.

The lumber itself is almost always softwood. The USDA Wood Handbook says retail yards stock dimension lumber in Select Structural, No. 1, No. 2 and No. 3 grades, frequently in only one or two general-purpose construction woods such as pine, fir, hemlock or spruce, and that 2x4s may also come in Construction, Standard, Utility and Stud grades. Lumber stamped S-DRY was surfaced at 19% moisture content or less.

Those are the two main types of light wood framing plus the heavy one, and together they answer most questions about 'types of framing'.

• Platform framing - each floor is framed as a separate platform, and the walls of the next storey stand on it. Wikipedia dates it from the 1940s to the present; it is the predominant method today. Codes traditionally limited it to four floors, and some jurisdictions now allow six.
• Balloon framing - long studs run continuously from the sill of the first storey to the top plate of the roof. Its first clearly documented use was a Chicago warehouse built in 1832, and it faded as tall trees were exhausted in the 1920s. Its weakness is fire: with no fire blocking in the connected stud cavities, Wikipedia notes a fire can spread from basement to attic in minutes.
• Timber framing (post and beam) - squared, carefully fitted heavy timbers, commonly 6 to 12 in., joined with mortise and tenon or more complex joints fastened with wooden pegs, where light framing uses members of about 2 to 10 in. The earliest surviving French half-timbered buildings date from the 12th century. Our mortise and tenon joint page explains the joint.

If a list asks for five types, one sensible way to reach five is to add half-timbering - a timber frame with the spaces between members filled in, the style of those 12th-century French buildings - and light-gauge steel framing, in which steel studs are joined with pan-head framing screws or bolts.

WoodWorks, the wood industry's design-support program, states that light-frame wood construction is permitted for Type III and Type V buildings up to six stories, and that podium projects can place up to six stories of wood framing over another construction type, typically Type I-A concrete - the '6-over-2' mixed-use building with shops or parking below and apartments above. Platform framing on its own was traditionally held to four floors, with some jurisdictions now permitting six (Wikipedia). Your local building department decides what applies to a specific lot.

• Cost - Procore's construction library says wood framing is generally priced lower than its counterparts, steel and concrete, and can be worked with basic tools. For a live market marker, NAHB reported the framing lumber composite at $515.93 per 1,000 board feet on 18 September 2026, up 8.4% year over year, citing Madison's Lumber Price Index.
• Carbon - the USDA Wood Handbook's Table 1-1, from CORRIM life-cycle research, compares wood and non-wood house designs: in Minneapolis the wood design's global warming impact was 26% lower than a steel-frame design, and in Atlanta 31% lower than a concrete-frame design, with embodied energy 17% and 16% lower.
• Market share - wood framed 96% of owner-built single-family homes completed in 2025, concrete 2% (Census Bureau).

Above the six-story limit WoodWorks describes for light-frame Type III and V buildings, other construction types take over, which is why the podium building pairs a concrete base with wood floors above.

• Moisture and decay - the Wood Handbook says decay fungi can be prevented in lumber by drying it to 20% moisture content or less and keeping it dry. Leaks, poor flashing and condensation are what let rot start.
• Termites - the handbook's advice is to deny hidden access: foundations of concrete, pressure-treated wood or other impenetrable material; in crawl spaces, keep wood floor joists at least 18 in. and girders 12 in. above the soil, with a polyethylene vapour barrier over exposed ground; and remove form stakes, stumps and scrap wood from the site.
• Fire - wood burns, and balloon framing's open stud cavities were the classic path for fire to climb a house; platform framing builds each floor as a separate platform, so wall cavities do not run through from one storey to the next.
• Lumber quality and shrinkage - Procore notes that fast-grown new-growth lumber is less dense and lighter, which can mean more shrinkage and weakness, and that disorganised sites generate a lot of scrap.

For older houses, the framing can also tell you the building's age: continuous studs through the floor line point to balloon framing, typically before the 1950s.

Framing species behave differently. From the Wood Handbook's Table 5-3b at 12% moisture, bending strength (modulus of rupture) is 12,400 psi for coast Douglas-fir, 12,800 psi for loblolly pine, 14,500 psi for longleaf pine and 10,200 psi for Sitka spruce, and stiffness (modulus of elasticity) is 1.95 million psi for coast Douglas-fir against 1.57 million psi for Sitka spruce. When you open a wall in a renovation and no grade stamp is visible, the end grain, colour and resin smell still help separate pine from Douglas-fir and spruce. WoodLens can name the likely species from a photo of the cut end, and our Douglas-fir and southern yellow pine pages list the identification points.

Wood stud wall framing follows the same sequence in almost every platform-framed house, as Wikipedia's framing article describes it:

• Lay out the plates. Cut a bottom (sole) plate and a top plate the length of the wall from lumber the same width as the studs, and mark stud positions on both at once, usually 16 inches on center.
• Mark the openings. At each door and window mark a king stud (full height), a jack or trimmer stud that carries the header, and cripples - short studs below the sill and above the header.
• Assemble flat on the subfloor. Nail studs between the plates, build the headers (typically two 2x pieces with a spacer to make up the stud width) and fit them on the jacks.
• Sheathe if the plan calls for it. Plywood or OSB is often applied while the wall is still flat; it braces the wall against racking.
• Raise, brace and fasten. Stand the wall, add temporary braces, and nail the bottom plate through the subfloor.
• Add the second top plate. A double top plate ties walls together; its joints must be offset at least one stud space from the joints below.

Local building codes set the allowed stud size, spacing and height for load-bearing walls, so check them, and have an engineer size anything unusually tall or heavily loaded.

Wikipedia's framing and wall stud articles give the standard: studs of 1 1/2 by 3 1/2 inch lumber (a 2x4) spaced 16 inches (410 mm) on center, changed to 12 or 24 inches (300 or 610 mm) depending on the load. 2x6 studs (1 1/2 by 5 1/2 inches) make a deeper wall.

"On center" means measured from the middle of one stud to the middle of the next, so the clear gap between two 2x4s at 16 inches on center is 14 1/2 inches. When you look for studs behind drywall, expect them at 16-inch intervals from a corner, with extra studs beside every door and window.

The studs themselves are softwood. See our types of plywood guide for the sheathing and our hardwood vs softwood page for why framing lumber is softwood.