Slopes and permeable paving - driveways

[DenisG]

This query concerns the replacement of a concrete driveway (construction c.1965) from the garage to the main road. The house is above the main road and the main road itself is a steep hill. The drive is approx 7m x 2.5m (i.e.c.18 sq m) and has a fall from the garage to the road of approx 1 in 4.5 and and a fall across the drive from right to left at the bottom edge of c.1 in 7.

According to the guidance on the 'Planning portal' issued by the EA, a replacement drive must either be permeable or provide sufficient drainage of rainwater to allow it to drain naturally.

My question is whether a permeable driveway is to be considered as a possibility given the physical facts. My concerns are:

(1) Given the slopes (both down to the road and, at the lower end, across the width), would not most of the rainwater run off over the surface anyway?; and
(2) To the extent that any water does manage to seep below the paving blocks, would this not cause a gradual 'slippage' of the laying base and/or sub-base towards the bottom of the drive?

If permeable paving is an impractical solution, then the only alternative appears to be an impermeable drive plus drainage to a soakaway at the bottom - True or is there another choice?

NB: If this latter solution is followed then should I also provide details to the planning authorities and request a certificate of Proposed Lawfullness? (to avoid awkward questions by any solicitor in the event of selling the house).

Thank you.
DG

[lutonlagerlout]

what you need denis is a linear drain where the drive meets the road connected to a suitable soakaway
no need to apply for anything and its unlikely anyone will ask
cheers LLL

[DenisG]

Thanks LLL.

I still have to think about the actual construction of the driveway - in particular whether the degree of the slopes down and across makes ANY block paving an impractical proposition because of any gradual (but inevitable?) movement of the lower layers due to water ingress? Obviously a concrete drive should be safe (the last one lasted 40 years) and, as I understand from your comment, a permeable construction is a no-go. Would an ordinary concrete block construction still be feasible - even though it might (initially at least) allow some water through?

Thanks again
DenisG

[Tony McC]

Concrete Block Permeable Paving (CBPP) works perfectly well on gradients as long as they are not too excessive. The definition of 'too excessive' varies from specifier to specifier, but I'd say anything up to about 1 in 4 is do-able.

As LLL has pointed out, though, you could rely on a threshold interceptor channel drain discharging to a soakaway and that would meet the ridiculous requirements of the comedy legislation, and all for a lost less than CBPP

[DenisG]

Thanks to Tony McC (and LLL) for clarifying this. DenisG

[lemoncurd1702]

If you want to go down the permeable route you need to install baffles into the sub-base, or basically speaking dams with an opening in the centre. This slows down the rate at which the water flows downhill through the sub-base thus giving it opportunity to filter into the sub-grade.
Personally though I would take the totally irresponsible route and use non permeable and put a linear drain at bottom for show.
Building a soakaway into your drive would be a pain given how steep your drive is I.E. the soakaway needs to be below the level of the drain.
If your subsoil is predominantly clay or your house is old with no discernible foundations you should not have a problem with planning consent.