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I'd like to add a decking to my garden, dimensions are 5m width x 3m depth. Am planning to have 3m joists laid vertically (about 50cm apart) and 5m decking boards horizontally As the soil is not very stable I was wondering whether about 10 C16 joists (2 inches x 5 inches), with bearers on both ends (3m apart), would work, could anyone confirm?
Thanks
Are you asking whether a 2x5" joist will span 15 feet (3m)? No. It'll be a trampoline. (Or yes, but it'll be a trampoline.) Here are your options as I see them:
Go with your original plan and lay it on the soil. Then you'll have critical intermediate support even with loose soil. Worst-case scenario it settles into the soil and ends up lower then it started, or becomes uneven in the case of non-uniform soil.
Lay a sleeper at the midpoint to cut the joist span in half. In this case I'd remove 4-6" of soil under each of the three sleepers and replace with crushed rock.
(Preferred method): Remove 4-6" of soil and replace it with crushed rock laid over heavy landscape fabric. Then set your joists right on the rock.
it would be wise to pour either one contiguous slab of concrete or individual pads of concrete under the supports (leveled, of course). This will eliminate the worry of soil type
