Decking over sloped tarmac

12 Dec 2009
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United Kingdom
I'm planning a decked area which is to sit over some sloped Tarmac. I want the finshed floor level of the deck to be roughly the same as the Tarmac at the point the decking starts and to then be level as the Tarmac slopes away underneath.
I was thinking of digging out trenches for 4x2 joists to sit in, placing dpm in the trench to protect the timber and use some cement/concrete to assist in making the joists level until they make it out of the ground to then be supported in the normal way.
Either that or trimming the 4x2 joists down to the approximate slope of the Tarmac and sitting them directly on the Tarmac for support.
I can't decide which one of these I'd like to do less! Any suggestions or other ideas?

Thanks in advance.
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I guess I'd still have to dig out a trench for each joist with these.
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As there is a 5mm (ish) gap between the underside of the deck and the Tarmac at the highest point of the Tarmac.
You can't avoid a step at the top of the slope, if you bury timber it will rot, dpc around it will just hold in the moisture and it will still rot.

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