How to build deck framing over concrete and soil?

[at_water]

I'm looking at building a deck that covers a concrete slab and extends over the edge by about 500mm. The slab is a bit of a step down rom the door frame, so the deck will be flush with the door. Around two sides of the deck will be a step.

Here I've marked out about where the edge of the deck will be. The grass slopes away from the slab, so at the three steaks in the photo wil be about 380mm from the top of the deck to the grass.

This is roughly what the finished deck will look like.

This is the framing plan I've come up with. The joists are 90x45mm and will be attached directly to the slab offset by plastic packers or pedistal feet to keep it level, as the slab slopes away from the house. Where the joists extend from the deck they will be supported by a bearer attached to posts. On the left of the plan that extends off the slab, will this be enough support fo the joists running horizontally? For the posts, should the be set in holes with cement, or is sitting them on concrete footings/pavers OK? The decking will be running left to right.

Any help or advice would be greatly appreciated.

[MitchellMc · Accepted solution]

Welcome to the Bunnings Workshop community @at_water. It's wonderful to have you join us, and many thanks for your question about constructing a deck.

Great plan, and you are certainly on the right track. You'll need to indicate on your plan where you intend the joists to be supported in order for me to answer your question. If the last joist on the left is only supported at its ends, then no, it is not sufficiently supported as those noggins do not transfer the weight it will be holding to the outside frame sufficiently. I'll mark where supports should be placed on your image below. Adjustable pedestal feet are fantastic for this if plastic packers are not suitable. You can also use angle brackets.

Although the 90 x 45mm can span much further than what I've marked, keeping it to 1000-1200mm is the best practice as it results in a solid deck with little to no sponginess and bounce.

It would be best to have your outside frame posts concreted into a footer and, as per the image below, increase their count so the spans are minimised.

Please let me know if you have any questions.

Mitchell
 

[at_water]

Thanks @MitchellMc!

I forgot to add on the plan where I was going to attach to the slab using pedistal feet where I can, and brackets with plastic packers where the pedistals won't fit. Thank's for indicating where I should add supports and additional posts.

If using angle brackets, would these be sufficient? And what screws/bolts would be best to attach to both the concrete and the joist?

[EricL]

Hello @at_water 

The Dunnings 60 x 100 x 35mm M10 Galvanised Angle Bracket should be ok, I suggest using a Zenith M12 x 75mm Hot Dipped Galvanised Cup Head Bolt And Nut assembly with corresponding washer. My best advice is to get the angle bracket and walking over to the bolt and nut assembly in the store to make sure that the bolt is not too small for the bracket.

If you have any other questions we can help with, please let us know.

Eric