We're planning to build a simple deck over an existing covered concrete slab 3.4m x 6.6m in size. There is only about 80mm height available between the slab and where the finished level of the deck needs to be. Please see the photo below. I'd really appreciate any help with the following questions regarding construction and termite safety.
I plan to use 90x45mm joists laid flat for 45mm height, with shorter-than-usual spans between anchors to compensate for the reduced strength of having them flat. Joists would be anchored directly into the concrete with a spacer between joist and concrete.
- Is it best to use something like Dynabolts to anchor the joists to the slab, or can I simply screw them straight in with pre-drilled holes and concrete screws? And would you use a bracket or go straight through the joist? Is there an obvious or better option here that I'm missing?
- I'm planning to use PVC or similar as spacers to leave a small gap between joists and the concrete slab for drainage and air circulation. What would be the minimum required gap to leave? (bearing in mind the limited height available)
- We live next to the bush and are concerned about termites. QBCC suggests a gap of 40mm between deck and existing dwelling for termite inspection. Does that seem correct? We would certainly prefer a more seamless look, e.g. a 10-20mm gap, but don't want to compromise on termite safety either.
- We are leaning towards H5 treated pine for the joists, as suggested by the QBCC for termite prevention. Is there anything more termite resistant that we should consider instead?
- The top of the deck would be above our Kordon termite barrier. I'm having trouble finding if this is compliant and/or if there are extra steps we need to take due to this?
- I'm assuming the deck should be at least 5mm or so lower than the adjacent floor inside the house, for cases where heavy rain could pool and potentially flow into the house, however unlikely that may be since it is covered. Is that correct? Is there a standard step down people normally have? (bearing in mind our limited height available).
Lots of questions here and I'm probably only scratching the surface, but thanks very much in advance for any help and advice.