Sistering deck joists

Jul 07, 2003 4 Replies

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Andrew Duane USG 23 years ago

As part of some renovations I'm doing, I'm going to strip the top off of my 16x16 deck. The foundation and structure is VERY solid, but the decking and railings are in terrible shape, so they are going away.

The deck is set on 12 sonotubes that are plenty deep, holding up doubled 2x10 beams. All good so far. The floor joists are 2x6, 16" OC. This is OK, but marginal if I ever wanted to do something more with the deck like enclose a patio room on it.

Since I'm taking off the decking, now is the time to beef up those

2x6 joists. My question is: is it better to double up the 2x6s, either by sistering them to the old ones or by adding in the middle (making them 8" OC), or just get rid of them and go to 2x8 or 2x10s?

The cost of either solution is reasonable for me, as is the labor. Just want to know which is the "better" way.

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donald girod 23 years ago

If the room amounts to an addition to the house, you are going to need a building permit and the construction will have to meet code. 16' with

2x6's is way too big a span even for a deck, unless there is a beam down the middle--is there? I'm visualizing your doubled 2x10's as the rim of the deck.

But if there's a beam down the middle, then you should be ok as things are. An 8 foot span is pretty much the limit for 2x6's. If no beam, then even

2x10's is not really enough, you would need 2x12's.

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Larry Caldwell 23 years ago

You didn't say how far the 2x6 joists were spanning. Just about any kind of wood should be good for an 8' span, and really premium lumber is good for a 40 lb. live load at an 11'-6" span. You really have to go to tables to specify the maximum allowable span for your type of wood, but don't automatically assume that 2x6 is inadequate.

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