The Brew Cabin

I have had a patio put in by a local guy who was recommended by a friend. Some months after completion my neighbour noticed his garage was waterlogged- puddles against half the length of the wall.

The area affected can be best described as.....
1. Widening of existing path between my house and his garage
2. His garage is single skin brick
3. The paving runs up to his garage wall in places
4. Where the paving doesn't run up to the wall I have put down stone chips to make up the last 30-40mm level.
5. The level is up to 150 mm above the neighbours dpc for most of the wall with a concrete ramp that is up to 190mm above at its top
there is a drain on one end of the garage where some water will fall away and a run beneath the patio into it.
6. The contractor assured me that putting a membrane against the wall and running the water away from this wall with the slab levels would prevent any problems- well thats not been the case.

I've had the contractor back- who has since retired and closed down his business for health reasons. Bad back- not uncommon in his line of work I believe.
He says obviously he can't do the work but advised that there must be a break in the dpc membrane he put down and that digging out the areas and patching/ replacing this would be simple and sufficient.

My neighbour is a good guy and is being pretty patient so far. I don't want to depend on his good nature for too much longer.

I am not convinced by my contractors advice and would like some other advice- will his recommendation work.

What type of Damp proof Membrane was used? From what you say, it sounds as though it was a polythene sheet (Visqueen PIFA 1200 or similar) when a proper asphalt tanking or drainage composite should have been used.

To be honest, I don't think a rip in the DPM is the problem - the whole thing is wrong. The paving should not be higher than the neighbpour's dpc and it is this that is the cause of the problem.

There are a couple of repair options - either a proper tanked membrane is applied to your neighbour's wall (with their permission, of course) or the level of the paving is reduced to below the dpc. Any other strategy is a "sticking plaster" approach, as far as I can see.

Thanks Tony,

It looked to be a polythene sheet, blue if that means something to you.

Forgive my ignorance- what do you mean by tanking? and how would it typically be fixed in place?

This is an awkward side area of the house. Reducing the level of the whole area isn't really practical- it would have to be a drainage channel as you have shown elsewhere on your site. A trip hazard for my daughter. Would it need to be 200 mm in width as you show on one of your pages?
Is this the building regs standard?
Would 100mm be sufficient?

Sorry to bombard you with questions I want to get this right second time and not third!

If the drainage channel is is the more robust/ dependable of the two options then I would prefer to do this.

Thanks again for your help,

Edwin

Blue polythene is usually a Visqueen membrane. This is aan adequate DPM beneath concrete, but not for vertical applications, such as against a wall, which brings us to tanking.

Tanking is a coating of asphalt applied to a wall or other structure to render it completely waterproof. It's normally applied in 2 or 3 stages - I'm not sure as it's a long, long time since I last did it - gradually building up the thickness of the bitumen/asphalt. Tanking is most commonly used with relatively deep underground structures, such as cellar and basements. There are also bitumen-based coatings than can be used in situations where the pressure from groundwater is not likely to be too severe, and I would hazard a guess that your scenario would fall into this category. The tanking medoium, whichever is used, is painted onto the wall and brought to a base, thereby shedding water away from the structure. Your local BM will be able to tell you which products they have available, and how they are best applied.

If you decide to go with a dry channel arrangement, the channell need be only 100mm wide, if that's better suited to your property. Such an arrangement is not covered by building regs, as the existence of the dry channel of any width is deemed to be compliant, and so there is no specific ruling on what the minimum width should be, but most BCOs would accept a 100mm wide channel in awkward situations, such as you describe.