Deck Design/Planning

[bigballer]

I am in the process of designing a deck I am going to build off the front of the house. The deck will be 24'Lx20'D. The area is sloped so the far edge (opposite the house) will be roughly 30"H and the edge near the house will be 12"H. I plan to use 4X4 attached to Simpson brackets on top of 8" round forms (24" deep). Also plan to use 2X8's (sandwiching the posts) as the beams and will use 2x6's for the joists (16" OC). All material will be PT.

I plugged these dimensions into Lowes online deck design tool and another from TimberTech to help determine post spacing. While both "appear" to use the backend software they come up with different results. The Lowes results show 4 rows of posts while the other only shows 3. On the 3 row design (running parallel to the house) there are 4 posts on the end rows and 6 posts down the middle. The 4 row design shows 4 posts in each row. In the end, the difference is 2 posts but not having any real engineering experience for load etc, my question is which will be stronger and work better at preventing sway, etc? One thing to mention is the 3 row design shows a live load of 60 PSF where the 4 row design shows only 56 PSF. What gives? Also I plan to have a 2' cantilever and the design tool defaults to a 6" cantilever. The other thing is the front door is in the corner and there are concrete steps I would rather not have to move. I would like to be able to just lay the decking right on top of them (this would be the correct height in terms of the rest of the deck) in this corner but not sure of considerations I should be making here. Any insight is appreciated on both the post layout as well as the concrete steps.

cheers,
bigballer

 

[UPRAISER]

I noticed you used Timbertech, be careful of some of the Timbertech material. I had planned on using the T&G material with the look of 1x4. I found out that it is not very stable and that Timbertech will not stand behind the problem.

I spoke to a local builder who is replacing 4 decks surfaced with this material, out of his pocket and the lumber yards.

I sent $7,000 of the stuff back to the supplier.

Curt

 

[bigballer]

Thanks for the headsup on the timbertech, I found them via a google search and saw they had an online program for determining dimensions. I actually had no intention of using their products and will most definately steer clear now.

cheers,
bigballer

 

[DOUBLEG]

Your strength would be a combination of the number of posts and the size of the beams. Perhaps you should check to make sure that the beams are the same in each estimate.

The summer I rebuilt my 14x20 deck, long overdue. Everyone recommended 2x6 joists and 2x8 two ply beam. I went with 2x8 joists and 2x10 two ply beam. The deck is real solid and the price difference was only a couple of hundred dollars.

Over build rather than under build.

 

[MarkV]

I would look into using 2x8 joists if it were me. I think if you run those programs again with a 2x8 joist material you will find that you require less beams and the price will work out about the same with a stiffer deck. Also a 2x8 is not going to allow for a greater cantilever although I am not sure you will be able to go 2’.

MarkV