Structural Systems

From: The Grassroots Newsletter, June 2005

The structure is the most fundamental system to a house's primary purpose (to provide shelter). Foundations (also called footings), framing for floors, walls, and roofs provide support for all other layers. You should not take a shortcut when dealing with the foundation of a home. Climate dictates how deep the foundation must go. In parts of the country that are frost free, footings are placed only a few feet into the ground, where in cold climates, a full foundation typically extends 4 to 8 feet into the ground. The most important thing about footings is the consistency of the concrete. Too much water will weaken the concrete. Not enough water will make it hard to pour. Remember, curing too quickly will also weaken the concrete. To keep moisture from penetrating a new foundation, the walls must be waterproofed. Make sure you use a waterproofing system, not a damp proofing system. Some contractors will not build a foundation without a French drain.

Platform, brace, balloon, and post and beam are the four methods of wood framing. Platform, where the floor and walls for each level of a multistory home are framed one at a time, is the most common. Joints in framing should be tight. When cut and nailed property, 2 pieces of wood should join fully where they meet.

A good habit to start is to not follow the building code; always opt for far more stringent requirements. This will keep a floor from bouncing when walked on, among other things. Another good habit is to use stacked framing. This is where the rafter and joist layout coincides with studs of the wall below and the studs on different floors line up with each other. This is to transfer the load of the house straight down, to reduce settling and any cracks it might cause in the walls. It also simplifies the task of running plumbing and ductwork between floors.

For a sturdier wall frame, to reduce sound better and accommodate more insulation, frame walls with 2 by 6's. You must provide a flat, plumb surface with wall framing so drywall or plaster is applied, the wall with be flat and true. You must assure that you anchor the house to foundation at each part of the frame to the next with metal connector from foundation to roof and make sure walls are braced against lateral movement in earthquake, hurricane and tornado zones.

For floor framing, the sizes of joists and beams are governed by the length of the span and the loads placed on them. Joists are doubled around stairways or other openings in the floor. You should caulk along the top edges of floor joists, along with nailing to prevent squeaking.

Insulation is imperative for an effective barrier against outside air temperature and humidity. You must make sure every part of a wall is insulated. Insulation should not be tightly squeezed in place, as it relies on tiny air cells to retard air movement. You should use expanding spray foam around windows and door frames. Don't forget the water impermeable vapor barrier, which always goes on the warm side. In new homes, exterior walls studs are usually covered with plywood sheathing, which is then covered with builder's felt, rosin paper, or house wrap. The kind of insulation you will use depends on, among other things, access to the cavities or surfaces being insulated, the required R-value, cost, and the need for an integral vapor barrier. There are many types of insulation including fiberglass blankets, spray in foam, foam board and wet spray cellulose. You must decide which one will suit your needs best for each individual project.

Darren
www.contractorexam.com