Span Distance of Deck Joist Framing

by Brett
(Vancouver, Canada)

How far out from the house can your deck joist extend before you need a post support under it? I am using 2x10 joists.

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Feb 18, 2010
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starstarstarstarstar 		Not too far
by: Dennis

If your using 2x10 treated pine or DF for a deck off the ground.

Standard rule is never follow code.

For some reason code allows this distance to go too far in most cases.

16' out should be the max span for wood species like Cedar, Redwood or AC2, with a cantilever beam 2' back.

Now here is what I think if you were to use composite decking 14' out.

The reason for that is you don't notice it right away, but after 2-3 years the whole deck tends to bow. And with decks costing anywhere from $1,000 to $75,000 you hate to see it look like crap in just a couple years.

It also tends to be very bouncy at code distances.
May 24, 2008
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starstarstar 		How Far Can Deck Joists Span
by: Editor - Rich Bergman

This is a great question. How far the joists on your deck can span before you need a beam to support them depends on three factors:

1. The dimensions of the joists
2. The spacing of the joists
3. The species of wood

It is impossible for me to provide a blanket answer for everyones backyard deck but let's try to help Brett as he embarks on his building project.

It also depends on what the total load is that you are designing for. In this response, we will assume a 50 lb./sf. load (40 lb./sf. live load for people and furniture, 10 lb./sf. dead load for weight of deck structure).

The numbers I am going to quote will change if you want a stronger deck.

He is using 2x10 joists.

With Fir or Yellow Pine at 12 inch on center (o.c.) they can span 17ft 4in. At 16 in.o.c. they can span 15 ft 7 in.

With Redwood or Cedar at 12 in.o.c. they can span 14ft 9in, 16 in.o.c. spans 12ft 9in.

So Brett, if you use pine the most you should span is 17ft 4 in. with 2x10 joists at 12 in.o.c. If you span say 12 feet then the load capacity of your deck will go up beyond 50 lb./sf.

Hope this helps you and other visitors contemplating the same question about joist spacing.

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