Decking frame help needed

[damiantaylor]

Hi guys,
DIYer here looking to build my first deck and desperately need some advice!....

I have a concrete patio that I want to deck over.
The problem is, the concrete, while sound and stable, is only 135mm below the patio door sill, so I don't have enough room to use 6x2 joists.
I thought I could use 4x2 joists (actually 97mm x 45mm) and 28mm deck boards and pack the joists up off the concrete 10mm to allow water to drain.
I'd fasten the joists to the concrete using either 7.5 x 150mm concrete screws going straight through the joist, or attaching some angle brackets to each side of the joist and screwing to the floor that way.
Is this a good idea? Call me lazy, but I really don't fancy ripping up the patio so I can use 6x2s

If using 4x2s in this situation is ok, how often would I need to pack the joist up to prevent bowing and bouncing? Every 300mm or can I get away with wider gaps?

Thnaks for your help
Damian

 

[r896neo]

Every 600mm would be fine for a shim.

Personally I would forget about the concrete screws. Screw the ledger to the house and maybe use a conc screw in each of the outer corners to keep it square but screwing the lot down is unnecessary.

 

[Tigercubrider]

No experience in decking but have built many theatre type sets where lightish units are bolted together

Once the deck is built, it shouldn't move due to it's weight. So long as you can hold the frames in position while building, it should stay still. Even sealed bags of sand laid over the timbers shouLd hold hold them still.