How to Calculate Floor Joist Span How to Calculate Floor Joist Span

What You'll Need
Measuring tape
Calculator

Coming up with the floor joist span can be really difficult, but as long as you know what to measure, you’ll be able to solve the riddle.

Step 1 – Choosing the Wood

You need to look up the kind of wood that you will be using for your floor joists before you can come up with an accurate measurement of the floor span. You need such information because your contractor or hardware shop attendant will need to take that into account when you’re installing the floor joists.

Step 2 – Measure the Joist Span Length

After you have picked out the species of wood that you’ll be using, come up with the joist span length measurement by getting the distance between the supports.

Step 3 – Determining the Deflection Limit

The deflection limit is characterized as the ability of your floor joist to bow. To come up with the deflection limit, divide the joist span length with a number. Most of the time, the length is divided by 360 inches. The optimum deflection limit on your floor joist is an inch for every 360 inches.

Step 4 – Determining the Live Load

The live load will depend according to the floor. The main floor should have 40 psf, bedrooms should have 30 psf and attics should have 15 psf.

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