In wood frame design many times strong woods are used such as Douglas Fir, Larch, Southern Pipe and Oak. However, due to the decrease in supply of large diameter, old-grown trees, there has been in increase in the use of engineered wood materials, which is made from laminated strand lumber (LSL). LSL processes young, more abundant, small diameter trees such as aspen and poplar and processes them into small wood stands up to 12 inches longs. This wood is then coated with adhesive and compresses into large billets that are sawn into lumber dimensions such as panels, boards and framing materials. This wood can be used instead of traditional 2 x 4 and 2 x 6 dimensional lumber and installed with the same process, tools and fasteners. Below is a link to many common types of woods.
Since the wood frame design was broken down into the foundation, studs, sheathing, joists and rafters, the different materials and their normal sizes used is divided in a similar manner below.
As earlier described, there are three main foundation types, the basement, slab-on grade and crawlspace. For these three types, there are 5 main construction systems used: permanent wood foundation, cast-in-place concrete, concrete or masonry blocks, insulting concrete forms and pre-cast concrete.
Normally strong woods such as Douglas Fir, Larch, Southern Pin and Oak are used, but engineered wood materials can be used as well. Normally for studs supporting a roof only either 2x4 @ 24"o.c. or 2x6 @ 24"o.c are used. For studs supporting one floor and roof, normally 2x4 @ 16"o.c or 2x6 @ 24"o.c. When studs are used to support two floors and a roof, 2x6@16"o.c. are used. If studs are used to to support three floors and roof the normal size used is 2x8@ 16"o.c.
Sheathing is a rough covering over the framing of a building, either roof or wall, which is not exposed when a finish material is applied. Normally plywood or oriented strandboard (OSB) panels are used by nailing them to the studs with the long directions of the panels being oriented perpendicular to the joist. Plywood panels are made by bonding veneers together under heat and pressure. Normally the grain is at right angles to each other and symmetrical about the center ply. A veneer is a thin sheet of wood rotary cut, sliced or sawn from a log or flitch. Oriented strandboard (OSB) is a non-veneered wood panel product made by bonding three or five layers of long, thin wood strands under heat and pressure using a waterproof adhesive. The surface strands are aligned parallel to the long axis of the panel which makes the panel stronger along its length.
Normally strong woods such as Douglas Fir, Larch, Southern Pin and Oak are used, but Engineered wood materials can be used as well. Normal woods can also be used as long if there is a smaller span is used joists. Therefore, the type of wood affects the span of the joists. Below is a chart of the different wood floor joists with residential floor loads. If larger loads are needed, the joist size should be increased by one size.
The Architect's Studio Companion
Normally strong woods such as Douglas Fir, Larch, Southern Pin and Oak are used, but engineered wood materials can be used as well. Normal woods can also be used as long if there is a smaller span of used joists. As a result, the type of wood affects the spacing of the rafters. This difference between normal and strong wood can be seen in the chart below which is for wood rafters with a pitch of at least 3:12 and no finish ceiling attached to the underside of the rafters. Spans should be decreased by 1 to 2 feet for rafters with lower slopes and the rafter size should be increased by one size for unusually heavy loads.
The Architect's Studio Companion
While there are many ways to join wood members, the use of nails, screws, glue and gussets are the most practical for wood frame design. These methods are very simple and economical, with nails, screw and glue being normal things most people have used in their life. A gusset is a flat wood, plywood, metal plate or similar type member used to provide a connection at intersection of wood member. The gussets are fastened by nails, screws or adhesives. Many other methods to connect wood members are not practical. For example, a connection such as a mortise and tenon, could be used, but do to the amount of connections needed in a wood frame design, it would be too time consuming and unpractical. In this connection, a member is cut to insert into a hole in another member and the connection is often held in place by a peg.
This site was last updated 04/18/05