Very low deck over concrete

Hi Guys & Girls

Firstly I just want to say what a fantastic forum.

I want to lay a small deck (5 x 3) however there are a few road blocks I am faced with at the moment.

Firstly there is currently concrete laid where I want the deck to go with about a 70mm clearance to the top of the step into the house at the lowest point. The question is whether this is enough clearance to lay a deck in the first place? I would assume that it is if I was to use the concrete slab but there lies my second problem.

The second problem is that it looks like this particular section of concrete was put over the sewerage piping a little too soon after filling the trenches in so the slab has moves away from the house a little and has sunk slightly in places where the ground has compacted. This means that the slab is a little un even and has a considerable slop away from the house. This all means that I am a bit reluctant to just lay joist straight onto the slab because I am not confident that it won’t move in the future and the slop is a bit too steep to be comfortable with.

My current idea is to fix a bearer to the house with dynabolts and a bearer on posts just past the end of the concrete and then attach joists (I guess they will have to be about 45 or 50 mm) between the two using joist hangers. The question is though how do I support the joists on the slab? Do I just pack under the joists and not fix them to the slab incase it moves, if so with what? Or do I pack and bolt them to the slab? Someone suggested using threaded rod with a pad on the bottom so the height can be adjusted.

Any help with these issues would be great.

Thanks in advance and keep up the fantastic work. :2tsup:


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