Permeable granite patio - Permeable granite patio install

[m-organ]

Apologies in advance if this has already been covered elsewhere, but here goes:

I have an area of ~60m sq (roughly 15m wide x 4m at the back of the house) which was part patio and part conservatory and am looking to lay granite slabs (600x600 or 600x900) over the entire area with an oak sleeper surround so was wondering if it is possible to do this without putting a fall away from the house i.e. setting the the slabs with some sort of permeable mix on a permeable sub-base with permeable jointing compound?
The reason that i ask is that the shape of the patio may make the sleepers a pain in the ass to get fall right and if the permeable solution is possible, we would look to use the same materials & method around the side paths and small patio at the front (grand total of about 120m sq)

I've done a little bit of research and come across the SteinTec tuffbed bedding mortar which i assume could be laid on a Type 3/permeable sub-base, but how deep? We have taken the old patio up, the slab & footings for the old conservatory will be coming up next week with the whole area being excavated to ~350mm below the DPC (200mm below 2-courses under the DPC).

The area of the old patio seems fairly free draining, at no point since the slabs have come up (they were laid on sand, a lot of sand) have we seen any rainwater pooling on it.

Any advice welcome.

Thanks

[Tony McC]

What you propose is possible but it's a lot more effort, and far more costly, than it would be to set the sleepers with a fall.

The required depth of a Type 3 sub-base is determined by the size of the area being drained and the permeability of the sub-grade beneath, but as a standard 'minimum' we look for 250mm.