![]() ![]() ![]() 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. 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. Proper joist sizing and spacing prevent problems and guarantee your floor will be strong, stable, and durable.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. Use the span table for safe spans under normal conditions. Joist spacing - Closer spacing shortens spans compared to wider spacing.įollow local building codes for minimum joist sizes and spans.Load – Heavier loads need shorter spans than lighter loads.Joist dimensions - Wider joists can span further than narrower ones.Wood species/grade - Denser woods like Southern pine allow longer spans than lighter types.So, How Do You Determine Proper Floor Joist Spans?Ĭalculate maximum spans between supports to prevent sagging, bouncing, and related issues. Foundation and Framing for Back Porch Addition (video).Err on the side of caution rather than trying to push the envelope. Don’t use smaller lumber, wider spacing, or longer spans. When in doubt, always use bigger lumber, closer spacing, or smaller spans. Consult an engineer for unusual situations or nonstandard floor plans.īelow is a table of minimum joist sizes for 16′′ and 24′′ on-center spacing using #2 lumber with 10 psf dead load and 40 psf live load. Increase joist size or reduce spans for heavy loads like pianos or crowded decks.Ĭonsidering all the factors, we can give the minimum joist sizes needed for various wood types, grades, sizes, spacing, and floor loads.Ĭheck local building codes before construction. It ranges from 30+ pounds per square foot, with 40 pounds typical for residential rooms and decks. The live load includes furnishings like bookshelves and beds, people, and other items that you may place on the floor. Calculate it by adding material weights and dividing by the square footage covered. The floor’s load also affects the joist size and span length you need.ĭead load is the weight of building materials (joists, subfloor, etc.) and is commonly 10 pounds per square foot. Doubling width increases span 80–100%, even with the same linear footage of lumber. Knots near edges should also face up so they compress rather than stress.Ī board’s width plays a much larger role than thickness in determining joist span distances.ĭoubling joist thickness or number increases span by about 25%. Position joists with any crook facing up so weight will straighten it. Best Lawn Care Service for Service Dogs.Lighted Magnifying Glass That Stays Put. ![]()
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