Once the foundation, or substructure, of a home is set up, the next step is to create the superstructure: floors, walls and roof. Among all of the available building materials, wood is the most commonly utilized in North America, so that is where we’ll start.
Why Wood?
Wood is a top building material for several reasons. One is heritage: Historically, North America was inhabited, and old-growth forests were abundant throughout the united states. Wood is also easily processed into posts, beams, floor joists, roof rafters and other elements of a house’s construction. Furthermore, while a skilled carpenter can work wonders with wood, it’s possible for a beginner to build a small house of wood.
The great innovation in wood framing came about from the early 19th century with the industrialization of North America. Harvesting trees became more efficient, as did processing the trees into dimensional lumber that could be used for framing. Sawmills big and small sprouted up wherever there was a woods and a way to transport the felled trees, such as a waterway.
Together with the mass production of framing timber was the development of mass-produced nails. No longer hand forged onsite or nearby, nails became common and inexpensive. Between the mass production of dimensional lumber and nails, the wood-frame construction became ubiquitous, and the legendary magician with a hammer in hand, tool belt filled with nails and possibly one in his mouth, became the symbol of American home building.
Here are the basics of how carpenters build the first stage of a home’s aboveground construction: the floor.
AIA, Bud Dietrich
Elements of a Wood-Framed Floor
Start degree, true and square. After the concrete foundation is complete and has cured (dried and hardened nicely), a builder can start the floor construction. This starts with applying a sill sealer to the peak of the foundation. The sill sealer is a thin, compressible material that gives an air barrier between the wood frame and the concrete foundation.
The sill sealer helps create an energy-efficient building by closing the gaps between both rough and uneven concrete foundation and a wood sill plate — typically a 2-by-6 pressure treated to resist bugs, moisture and damage caused by the elements.
It is important that the sill plate be treated this way, as its proximity to the ground makes it particularly vulnerable to rust. In fact, in most older houses the sill plate has rotted away, causing the actual exterior walls to settle in order that cracks show up from the interior finishes. The sill plate could be replaced, but that is not a cheap operation.
The sill plate is tied down to the foundation with anchor bolts. These bolts become inserted into the concrete foundation wall and have threaded ends. Once the sill plate is put and leveled, nuts have been screwed to the anchor bolts, and all is locked down.
AIA, Bud Dietrich
Floor joists and open programs. Once the sill plate is down, you are able to install the floor joists. These are ordinarily 2-by-6, 2-by-8, 2-by-10 or 2-by-12 pieces of timber. The dimensions used will depend on the span (how far between supports) that the joist should travel. A commonly used size is 2-by-10, which may span about 15 feet.
An alternate to “2-by” (dimensional lumber) floor joists is truss joists. These are particularly helpful for spans of 18 feet or more.
Always check with the local building department prior to doing any dwelling construction, as the code changes by area. By way of example, some building departments require that homes built with long span joists have a fire suppression system installed. That’s something that you’ll absolutely need to understand prior to budgeting your project.
AIA, Bud Dietrich
A platform built to last. Next a plywood subfloor is laid atop the joists.
Usually 3/4 inch thick and in sheets that measure 4 by 8 feet, a plywood subfloor should be glued and screwed to the underlying joists. This can not be stressed too much, as there are many squeaky floors and tiled floors that develop cracks brought on by a subfloor that was not securely fastened to the joists. In fact, the squeaky floors that exist in older houses are the consequence of subfloors generated from 1-inch boards that have come loose in the joists, making them squeak when stress is put on.
Now’s plywood subfloor material includes a tongue and groove arrangement. The constant membrane shaped by installing the tongue of a single sheet into the groove of the adjacent sheet assists from the overall structural performance and wearability of these subfloors.
A well-installed subfloor will make a big difference over the long run, as the actual floor finish — be it wood, tile or something else — will develop fewer flaws.
More in Know Your Own House: What Makes Up a Home’s Foundation