What Dimension of Beams and Joists Should I Use?

by Colin

I have a space constraint in that there is only 15" between the door into the house and the grade where the proposed deck would go. What dimension of beams and joists would you recommend?

If I use 2x8 beams and 2x8 joists will there be a step up from the house onto the deck as opposed to down to it or having the deck even with the door.

Also, what type of design would you recommend? Inset joists? Joists on beams?

The deck is a 32x12 rectangle.

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Apr 27, 2009
Choosing Beam and Joist Sizes
by: Editor - Rich Bergman

If you only have 15" of space from the grade to the door sill and you want to have a deck structure there are several options for you.

I will suggest one option and perhaps other visitors can offer you their suggestions as well.

You could use 2x6 for your beams. Laminate 3-2x6s to make each beam. Use 2x6 joists. You should probably have your beams set no farther apart then about 4-5 feet. Each beam should have a support post or pier every 4-5 feet.

Your joists should probably be set at 12" on center and they would be spanning the 4-5 foot gaps between the beams.

Your deck boards would be 5/4" thick. So together the beams, joists and decking add up to 12-1/4".

The only challenge is that if your beams have to be supported by a post or sit directly on a concrete pier, the piers can not be above grade by more than say 2" if you want everything safely below the door sill.

Probably the best idea would be to pour each pier so they are about 1-2" above grade as mentioned. Set some kind of anchor bracket in the cement to secure the beam to it and to prevent direct wood contact with the concrete or it will rot prematurely.

Overall the beams are still quite close to the ground but this would work. If anyone else has any other experience or good ideas please share.

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