re-paving side return, is it too high for the dpc?

[pxs871]

Hi,

I'm re-paving a side return outside my kitchen. A damp firm did a survey and said I need to put in a french drain because the paving level was too high (a couple cm below the dpc) and up against the side of the building.

I started by taking up the paving slabs, with the intention of digging down 30cm and relaying the paving, adding a french drain at the edge next to the kitchen wall (15cm for clearance below dpc, plus 15cm depth for the hardcore base and to re-lay paving). However I hit a problem because there is a concrete base under the slabs which is only 6cm below the dpc.

do I need to break out the concrete base (prob 5cm thick so not too difficult...)? Is there any alternative? The base is a bit bumpy but I could level it off and put paving ontop. However I think this would make it worse, because then I'd need to cut away a channel next to the building for clearance below the dpc, and then the channel would be lower than the patio and draw all the water..! There's no slope on the concrete base, so buy the time I added one, I'd probably be as high as the dpc (even if set away from it)

I've taken a photo (after heavy rain) at //www.diynot.com/network/pxs871/albums/

any advice appreciated!!

Peter

 

[r896neo]

its probably a mortar bed if its only 50mm thick.

No easy answer i'm afraid, get out the sledge hammer.

The 'cut a channel' method is a work around for lazy people or unusual situations where there is no option and is not a great idea anyway escpecially on older houses with shallow footings.

Seeing as its a side return there can;t be that much anyway.

 

[pxs871]

brilliant thanks. I thought this might be the case. bought an angle grinder for a smooth cut against the wall and I'll bash out the rest.

so I dig down far enough so the new top paving slabs will be at least 15 cm below the dpc. I can then lay the new pavers to butt up against the wall (so long as there is a fall that runs away from the house). I've got 2 more questions:

1. if the side return is only 1.5m wide hopefully it shouldn't collect too much rain water. for drainage then, can I just put in a slight fall away from the house into gravel/ over earth on the far side? e.g. house wall/ then 120cm wide paving with a fall away from the house/ into 30cm wide of gravel/ pebbles over earth. After the gravel is a fence and then the neighbours patio, so I wouldn't be causing damp but might not be popular if this would flood.. or do I need to think about something more complicated like a perforated pipe that runs under the gravel longways, through into the garden at the end (would be more complicated because the ground at that end steps up)?

2. I've also got a square area to pave in a different area that is 3m sq. Can I run this off into a flower bed at one end that is 40cm wide (i.e. 3m * 40 cm) and after this is a retaining wall?

I guess both questions are similar i.e. how much drainage do you need to allow for when paving smallish areas but only have very small areas of flowerbed/ ground to run them off into? does the ground usually soak up a fair bit or liable to cause flooding if you don't plan these things properly.

thanks for the help. maybe I'm being too cautious and there is nothing to worry about!

Peter

 

[r896neo]

for very small areas like that running off will suffice assuming you can allowing a drop of an inch or so off the paving into the gravel/flowerbed.

No need to grind anything, the concrete is not part of the wall so should just break away.

And as a tip, a heavy sledge hammer and pickaxe to lever bits up is far quicker than a breaker of any kind. But obviously harder work.

 

[pxs871]

that's really helpful thanks a lot!

going to try it with a lump hammer, chisel and crowbar as that's what I've got, it doesn't look too big an area although I'm sure a few metres in it'll start to feel a bigger job..

Thanks for the advice!

Peter

 

[pxs871]

right.. I've spent the day breaking out the concrete side return. I'm going to feel this tomorrow!

I've dug down a bit too, so the level outside is now 20cm below the dpc. at this level, next to the house wall I've exposed a brick that juts out (assume this is a brick footing for the foundation) and can already see a second one beneath it.

Assuming I don't dig below these bricks (I'll dig outwards rather than underneath), is there a risk if I dig down a further few inches so that I have enough depth to re-lay paving, that I'll cause structural damage by weakening the foundations? Is there anything to worry about by exposing the brick foundations? How low is too low when lowering the outside ground level to fix damp?