Floating Deck - Plan

[cwhaley]

After slabbing an area at the bottom of my garden, this area has been vastly improved. The recent week of non-stop rain would have flooded the area in the past, but with the new patio and drainage with soakaway there isn't so much as a puddle.

Unfortunately there's an area of about 14 ft by 11ft deep which is serving no purpose. I'd like to deck it and build a covered corrugated gazebo over the top of it so we have more usable space. My actual proposed dimensions of the floating deck would be 11ft wide by 9ft deep. I'd be using scaffolding boards as I have access to these.

The floating deck would sit on concrete blocks turned on their side, with a membrane laid down underneath. Plan is to tamp the ground under each block, compact with hardcore and dry sand/cement, then a wet bed of mortar about 50-75mm thick. This is the plan:

Questions

- The largest unsupported span for the joists going across (left to right) would be ~5'6". If using 6x2 joists I'm presuming that span is acceptable? Do I need 3 extra concrete blocks for rigidity?

- Have I used enough joists? The largest unsupported span for the boards to be fixed to would be 2'9"

 

[scbk]

Will the gazebo/roof be attached to the decking? I'd be worried about it taking off

If it was me I'd think about setting the posts for the roof in the ground first, then build the deck off that

 

[cwhaley]

For anyone interested, I finished the decking this weekend. I bought 9"x2" joists and build the frame as seen above. I then attached 5"x4" posts to it and then for the flooring used the joists. 18mm ply on the top with felt on top of that. It's probably over-engineered but it is rock solid and I'm happy with it. The frame sits on concrete blocks which keep it about 10" off the ground.



All the timber I bought was un-treated, reclaimed material though. I coated the base with linseed oil, the decking boards with an oil and stain and the posts 3 coats of paint.

Worried about the base though. Is Linseed oil the best thing to be using -- should I be using something better? It's off the ground, but the edges of the deck will have contact with driving rain.