Patio Advice Please, drainage gully alongside house?

Question

Hello and thanks for looking.

We cannot build our patio below the dpc so we need a drainage gully alongside the house.

How wide should it be and is it ok to fill it with some kind of nice looking shingle?

Thanks,

Stu

Answer 1

Just run some damp proof felt along the wall where you want to lay the slabs, then trim off any excess after you have laid the slabs.

Answer 2

What you seem to be proposing is a french drain, which effectively keeps the water away from the wall, allowing it to percolate down and drain away slowly. They do work but not as well as a gully.

If you want to put in a drainage gully, then the link below was useful last year when I was installing a patio.

Answer 3

The purpose of the 150mm gap between the ground level and the DPC is to prevent splash-back from rainwater, the theory being that the rain will not splash up to 150mm.

150mm, as said above is 2 courses of brickwork.

Raising the path level above the DPC will cause "bridging", effectively allowing moisture from the ground to by-pass the dpc and rise up in the wall. This has major implications in a solid brick wall (generally older houses), but far less impact (if any) in a cavity wall, provided the cavity isn't blocked. Ok a bit technical I know.

The problem you may face with the 150mm rule, is that if you raise the level of the patio too high, and you have a finished level within the drainage channel 150mm below the DPC, you may end up with a ravine between your house and the patio which could be a dangerous trip hazard. As a surveyor who previously owned a damp-proofing company I know this from personal experience.

My advice would be to create a drainage channel as discussed above. I needn't be 300mm wide (a little excessive and may again cause a trip hazard), 150mm should suffice. dig down (2-3 bricks depth) and re-fill with coarse gravel. The finished level should be at least a few inches below the DPC.

NOW - heres the IMPORTANT bit - before you fill the gulley with the gravel, apply a water-resistant coating to the surface of the wall from below the DPC level, to at least 150mm above DPC level. That will prevent any rain splash-back. Don't scrimp on the "raincheck" product either. Get some decent stuff.

Finally with regard to selling the home, and any potential problems a surveyor may have with the specfication - take loads of photos and label them if necessary. That way a surveyor can see what you have done.

Answer 4

you should never build any type of patio or path close to house unless its at least 2 course below damp ..if your ground level is high ..then you must start 300mm (a foot )away from house ..BUT you must remove the soil in between the patio and house to a depth of 3 bricks ..then put in pea gravel to leave 2 course clear ...if you don't do this you will have problems possibly with damp but definitely with surveyor when you come to sell