Keep in mind the span table above shows just the allowable spans for Douglas fir or larch, there are different tables for all the construction lumber species. The narrow double lines show the floor joist themselves.įrom a three-dimensional perspective, the floor joist framing would look like this: The outer gray walls are the concrete foundation walls which support the floor joists. The picture below shows a plan view, that means looking straight down from above the house. So our house would look like the picture below (with all floor joists 2" X 8"). Reading the table, you'll see that 2 X 8s installed 16" apart on center can span 12'4". Since the example house we are designing for is 12 feet wide, we need to find, in the floor joist span table, a joist size and centering that can span 12' or wider. See the image below for an example of joists spaced 16" on center (16" o.c.). The floor joist spacing is the distance between the centers of any two installed joists. Looking at this table you will see there is a choice in the size of floor joist (2 X 6, 2 X 8, 2 X 10 or 2 X 12) and there is a choice in the joist spacing (12", 16" or 14"). The table excerpt above is simply a sample and may not be valid for your region. The table below shows the maximum span for a floor joist with the following designations: The house will have a gable roof and will be framed with wood studs. Let's start with a simple, very small house 12 feet wide by 13 feet long.
#LVL SPAN TABLE CALCULATOR HOW TO#
Now we'll look at how to read these tables. These designations and numbers will become important when you are reading your structural tables since the strength of a wood depends on its designations. Common lumber grade designations include: The stamp shown above indicates the lumber grade is standard or better (STAND & BTR) this is the same as number 3 or stud. Species (red cedar, certain pines, balsam and poplars) The stamp above indicates in the triangle that the wood is Douglas Fir (D FIR). The mill identificationindicated by name or mill number.How the wood was seasoned - this will give an indication of the moisture content.The wood association of which the lumber manufacturer is a member.The wood grade - could be a number or description.The information displayed varies between wood associations. The stamp displays several types of information. In general, all lumber is stamped near the end of the lumber piece by the manufacturer. You will however, need to become familiar with reading your local floor joist span tables for floor beams, floor joists, window and door lintels, ceiling joists, roof joists, roof rafters, and roof ridge beams, as well as the sizing and spacing of wood studs tables.īefore jumping into the span tables, let's first consider wood species and wood grades. Continuing on from Part 1: Residential Structural Design Vertical Structural Forces, we were about to start learning about floor joist span tables.ĭon't worry, you won't need to do a lot of calculations in determining the size and placement of the structural framing within your house design.
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