How do I know what size steel to use?

[Spot the welders dog]

Thanks HM,

Yes, getting bit away from Welding now ain't I.....

Thanks again

 

[shenion]

Wow, two posts and I was still typing.....

I was going to raise the issue of how many posts would your diagram take shenion, but I was trying to digest what was proposed previously. Does your idea use all steel for the frame or wooden underpants & a steel dress?

Thanks for your input all

I assumed you were going to have a wood floor. Steel would be nice, but then you have to transition to the wood somehow. Also you would have rust issues.

I have seen it done in wood, usually 2x10"s for both the joists and the support beam (usually doubled to prevent warpage.) The hardest part with wood is it shrinks considerably (as far as pine). Strength is usually not a problem unless you get cheap. Here most decks fail because they are not properly attached to the side of a house and as the wood shrinks it pulls away.

Mine was that way, 16x10' deck nailed to the siding with Styrofoam behind it and 2 lag bolts. I added a bunch of 8" lag bolts though to the floor joist in the house. Deck had slowly pulled away from the house.

My deck is 10' above ground and has 3 posts for support along the far 16' side. I filled it in with lattice work in 4x8' panels.

A lot depends on the step and the wall. If you can firmly anchor a diagonal support to them, then you would need no footings/posts.

A lot also depends on what you have available. Small decks like this are usually fab'ed up before hand and then bolted in place. That requires you have a bunch of guys available to hoist them. The stairs, landings etc on my neighbors decks were done that way.

Another fly in the ointment is which way to run the floor planking. You want the joists 90 deg to the floor:

at 7', there would probably be more than 4 vert/horiz joists, but it shows the idea. Using 12" centers will make it real strong and increase the joists used for cantilevering.

As shown with a double center diagonal, it can be pre-fab'ed in 2 halves. Either the red diagonal support and no footings/posts or one post along the double diagonal, probably a foot or so back to hide it.

The red diagonal support could be steel to make it smaller and be almost hidden from view. Would make deck look floating.

Personally, i like filling underneath with lattice to keep animals and leaves from collecting underneath.

The deck boards could be done diagonally as shown in green. Or run parallel to the wall and step with a miter in the middle.

My deck has a 100'+ red oak tree growing right through the middle of it. I have had to widen the hole twice. The second time I had to cut the 2 joists and add 2 more farther out. Took me a while to figure out what the banging noise was on the house. Tree was frozen to deck and would break loose and refreeze where it rubbed and moved in the wind.

 

[Spot the welders dog]

Thankyou shenion,

Plenty of food for thought there....I really appreciate your input.

I think your (& Si's) idea of incorperating a cantilever into the design helps alot.
I did wonder if using a brace along the wall & step with a brace across the diagonal would work and negate the issue of where to drop the posts.

What i shall do now is to return to the site and do some better calculations, and try to figure a plan with this further knowledge.

not so paul