Damp Proof Course

squire1

Does anyone know if there are any regulations regarding what level below DPC external finished ground levels should be at?

The problem is, a friend is having some paving done in the back garden and the contractor is insisting that he can have the finished paving level 15mm below DPC. I would have thought that this was too little. He is also creating a fall towards the building to use existing rainwater gullys as drainage so this would add to the problem if gullys ever became overwhelmed.

I have done a bit of paving (DIY) in my time and would always ensure that at least 100mm gap between the top of the paving and the DPC level to prevent damp from rain splash and moderate flooding from entering the building above the DPC line.

I've spoken to this contractor about the concerns and he assures me that 15mm is plenty and this is the way it has always been done. He has being doing it for six years apparently :eek: If it was me I would have got rid of hm straight away but he is a friend of a friend so the customer is reluctant to rock the boat until I can prove my point.

Am I deluded or does anyone have a source for professional guidelines on this matter? Is what he is doing common practice?

Maybe this is better suited to DIY but I'll let the mods decide.

smashey

Try 150mm.

squire1

Yes 150mm, Sorry, mistype.

Yeah, that's what I understood the "Best Practice" to be but I cannot find anything "official" that states it. It's on a few paving websites and I'm fairly sure it's in the British building regs. Is it in the Irish Building regs?

The problem I have is that the guy is trying to convince both myself and my mate that I am wrong. He's quoted for this work assuming he would not be doing any digging out but if he does it "my" way, he'll have to dig out 9m3 of soil, so obviously, he is trying to avoid that.

smashey

Technical Guidance Document C (TGD C) states 150mm minimum.

squire1

Problem sorted, my mate came to his senses and told the guy to sling his hook. Jeez, I hate cowboy contractors. :mad:

Thanks smashey

paulmallon

you surely mean 15 centimetres?

squire1

Nope, 1.5cm below DPC. I kid you not.

I've since had two different experienced builders tell me that it is fairly common practice with a lot of paving contractors. I also rang a major paving contractor and asked how they do it and they said that once it is below DPC it dosen't matter. When TGD C (as sourced by smashey) was pointed out to them they said "ah sure, that's just for builders, it dosen't apply to us"

So be aware.

galwaytt

yes, but you need to bear in mind that paving or cobble lock is permeable, not impermeable, so it is not the same as having a concrete path 15mm down from your DPC, as no water will sit on it anyway.

Under the Part M guidelines, 15mm is the size mentioned for the max size of step at door threshold..............is that why your guy has this figure in his head, from doing previous door thresholds???

So, technically, at door thresholds, Part M goes against the advice of Part C.
Why doesn't something like this surprise me...........?

smashey

galwaytt wrote:

yes, but you need to bear in mind that paving or cobble lock is permeable, not impermeable, so it is not the same as having a concrete path 15mm down from your DPC, as no water will sit on it anyway.

Under the Part M guidelines, 15mm is the size mentioned for the max size of step at door threshold..............is that why your guy has this figure in his head, from doing previous door thresholds???

So, technically, at door thresholds, Part M goes against the advice of Part C.
Why doesn't something like this surprise me...........?

muffler

galwaytt wrote:

yes, but you need to bear in mind that paving or cobble lock is permeable, not impermeable, so it is not the same as having a concrete path 15mm down from your DPC, as no water will sit on it anyway.

Under the Part M guidelines, 15mm is the size mentioned for the max size of step at door threshold..............is that why your guy has this figure in his head, from doing previous door thresholds???

So, technically, at door thresholds, Part M goes against the advice of Part C.
Why doesn't something like this surprise me...........?

Threshold detailing is completely different from wall DPC detailing

squire1

No he insisted that the paving would be 15mm below the DPC along the 15m interface between paving and building with no slope/ramp up to the double patio doors.

The paving is permeable to a cetrain extent but that is assuming there is natural drainage in the ground. Like anything else if it becomes saturated......if the gullies are blocked.......where would the water from 60M2 of paving falling towards the building go?