How To – Understanding species type when selecting lumber for framing

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    There are a variety of different tree species types used in home construction.  Although from their visual appearance you may not consider framing grade lumber to be hardwood it is.

    Most consumers consider woods such as oak, walnut or mahogany when they are thinking of hardwood however pine, spruce, Douglas fir and other woods are considered hardwood and used in the framing process.

    When selecting hardwood for framing and using structural span charts it is important two always match the species of wood to the span chart.  Cross selection could mean an underrated beam is used.

    Within each species type there are grades applied to the lumber that describe the quality of the material.

    Grading numbers are normally between one and three.  A grade maybe suggested in a span chart as number two or better which means any grade of lumber that is marked one or two may be used.

    The species of wood that may be available in your location may not be available commonly in other parts of the country.  Hemlock and fir are commonly found on the west coast of the united states while pine is more common on the East Coast.

    Where suggested by your architect you may use number three grade studs in walls and partitions.  The lumber commonly has a large number of defects such as knots and bark along the edges.  This will not effect it’s load bearing qualities but it means it cannot be used in an exposed area.

    In some instances exterior siding is used as a primary sheathing.  Often the siding when used unbraced must be installed diagonally to retain its structural rating.  This may be in conflict with the homeowners desired style as a contractor this important that you maintain structural aspect that the engineer or architect specified.

    If you’re working on an older home you may find that the subflooring is not plywood.  Subfloor made out of boards may not be of the same thickness as plywood he would use to replace it.  For this reason is important that you maintain the structural aspect of the design and install shims where possible or build up your floor joists.

    Plywood is not normally available in a number of different species.  However the outer surface of the plywood may be sheathed with a cabinet grade plywood made out of a hardwood.

    Like framing lumber plywood is also available in pressure treated grade material.

    Final Note

    So when selecting lumber for framing it is important to match the species type to the span charts.

    Different species of wood will provide different structural qualities.

    A span chart that suggests a number  2 grade  southern yellow pine product may require a #1 Grade Fir or other species in the same location.

     

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