The Brew Cabin

I understand there is a "requirement" for paths, patios etc to be 150mm below DPC. Is this an ABSOLUTE requirement or just a wise precaution? What about steps out of a doorway; can these be at/near DPC level? What about an attached car port?
Is it essential to have a dampproof membrane under the car port (plan is to have a concrete base with paviors, car port open both ends)?

Thanks, alan

The 150mm below dpc rule is a very, very strong recommendation, but isn't a ruke for diy'ers working on their own property. Contractors are expected to work to this rule, and all new properties are built to this standard, and or good reason. It dramatically reduces the incidence of problems with damp.

For diy'ers, a problem may arise if they come to sell their property, as it's the sort of thing spotted by the buyers' surveyor, and you're faced with having remedial work done or reducing your asking price.

Steps from a doorway can be brought up to internal floor level (as in the relatively new Document M of the Building regs) but a threshold drain or cavity of some form is required to 'isolate' the outside from the inside, or vice versa.

I'm not sure what you mean about the car port -a dpm beneath the car port? Do you mean a membrane laid beneath the planned paving? And does your 'concrete base with paviors' mean you're planning to use rigid paving?

Yes, I am planning to use rigid paving. The proposed car port is immediately adjacent to the house wall with a fall of about 1:40 both along and away from the wall.
I plan the paving to be a sub base of hardcore - mainly broken brick, blinded with sand, then a DPM (if required) with 3-inch of concrete and paviors on top. The total slab is quite large (approx 3m x 4m) so am wondering how to accomodate expansion. Should I use reinforcing steel?
Thanks again.

Sorry, brain out of gear. Area of slab is 6m x 8m NOT 3x4!

Why rigid paving? It's far more labour intensive than flexible, as well as costlier, not just for the special rigid paving bricks, but for the concrete, the mortar and all the other bits and pieces!

If I was going to all the trouble of using rigid paving, I wouldn't skimp by using broken brick as a sub-base - I'd play safe and use a 'proper' sub-base material, preferably DTp1, and you definitely need a dpm - all concrete slabs should have one.

At 8x6m, I'd say you ought to use reinforcing mesh, a simple 6 or 7mm mesh would be sufficient, but a 75mm thick slab doesn't provide adequate cover - you need at least 100mm thick to give the minimum required 50mm cover all round. You could consider using fibres instead, if you stick with a 75mm thick slab.

I'd split the area into two slabs, each 4x6m, with a movement joint between the two. You definitely need an expansion joint where the slab abuts the house wall.

I can't help feeling you're making this job far more complicated than it need be. Why do you feel you need rigid paving?

Hmm.
You're likely to help me save money!
I'm reconsidering the whole idea of rigid versus flexible.
I'm going to get a couple of quotes.

I'm so glad this website has prevented me from going into this blind!
Tony, thanks.

Alan

Let me know what you decide to do, Alan. :)

This thread was of interest to me also. I am just about to build new steps from patio to underside of existing door threshold. What form should the 'isolate' be? Would a strip of dpc sandwiched vertically between the new step and the existing house wall be sufficient? You assistance would be appreciated. Thanks, David H

Yep that would be fine, David, or you could just leave a 12mm gap, depending on the exact construction. The purpose is to prevent a 'bridge' that would allow damp to work its way above the dpc.