Ideas for more space.

From the pic below you see just how little space we actually have, the house used to be a corner shop, hence the lack of space between us and the pavemnet. The only real change from the pic is the area between the garage and the house, I raised the level of the hard standing for the car and added a raised border on two sides of it, this is now also full of plants.



The 20' X 9' garage roof leaks so needs attention, my thoughts were running to boarding over the existing corrugated roof, followed by roofing felt.
Now though I have an idea to replace the roofing felt with heavyweight pond liner grade plastic then add decking over most of it with a raised bed all round front and sides, and steps up to it at the rear.
The raised bed probably about 3' high and 2' wide.
with trellis most if not all the way round the front and sides.
Has anybody tried this? The garage is precast reinforced concrete, should it be able to stand the weight?

 

Pond liner sounds a very cheap method of making the roof waterproof. You cannot of course nail or screw anything through it as you will lose the waterproof integrity, but the sheer weight of decking on top will keep the liner in place. But I would add bits that overhung the edge downwards to keep it in place - I don't know how slipery pond liner is. If it ever shifted, say in a storm, you could never move it back without removing the decking.

I am very concerned about the weight. Two beds of 2' by 3' by 20' is 240 cu feet or 6.8 cubic metres. Soil has a density of about 1.25 so that is 8.5 tons. Thats a lot of weight. The concrete walls may be able to support that weight if it was perfectly vertical, but if a strong wind pushed it slightly out of the vertical I can see it all coming down.

I recently re-roofed my garage of similar size. In fact I raised the roof about 6 inches, by laying two lots of 4" by 2" on top of the concrete panels (attached with coach bolts) and then cross beams of 4" by 2" on top of that. (�£100+ for wood and fittings). Then boarded the roof and clad the insides with sterling board (�£200) then covered it all with 20 foot continuous sheets of corrugated plastic coated steel (�£350). I am very pleased with the result. It will never leak, it will last for decades (unlike felt), and as its totally boarded out it is a very pleasant environment to use (its my potting shed now).