Posted: Sat May 10, 2008 3:49 pm
Hi,
Sorry for the long post...
I have a rainwater downpipe on the corner at the front of my house that serves an area of roof of approx 35 sqm. It feeds into an open gully that is set into a concrete path that leads from the front door to the boundary of the property.
The gully has been blocked for a while and, on investigation, I found that it has tree roots growing out of it.
I cleared it enough to find the likely direction of the outflow pipe and dug down in an area of the driveway where the pipe should emerge from beneath the concrete path.
I think I've found the original soakaway. The pipe ends in a rubble-filled (and totally silted) area that's partially beneath the path and partially beneath the gravel driveway that runs parallel to the path. It's 3m from the house.
I can see that tree roots are entering the pipe where it terminates in the old soakaway, but without digging up the rest of the path (and an access ramp into the front door), I can't comment on the condition of the rest of the old glazed clay pipework. Given that it's protected by the concrete of the path, it should be OK, but who knows?
I did break up a bit of the concrete around the gully to inspect the pipe at that end. There's no evidence of damage or tree root invasion, so it's possible that the remainder of the pipe is undamaged... but equally it might be broken elsewhere... It's almost certainly been there since the house was built in 1936.
My first thought was to get a drain clearance outfit in to clear the roots and internally inspect the pipe, but then I got an idea of the cost! Given that it would be wasted expenditure if it turned out that there is further damage to the pipe, it seems better to just go ahead, rip up the path and ramp and lay a new drain.
However, if I do that I then have a decision to make regarding the location of the soakaway....
I could dig out the original, but that would mean it would be partially in the driveway and, presumably, prone to subsiding - especially when the occasional skip delivery lorry drives onto it! I also thought that digging out the original location would be hard work because it's mostly broken bricks, whereas digging a new location would be comparatively easy because, once down 300mm it's like digging on a sandy beach.
So, I could put it in the front garden where I wouldn't have to be concerned about structural stability. However there are a couple of trees in the area which means I'll inevitably have to cut through a few roots. The other issue is that there isn't enough space to be able to comply with the 5m from building and 2.5m from boundary rule. The best I could achieve would be 4m from the building and 1m from the boundary fence (on the other side of which is a public asphalt-covered pavement, a grass verge and then a road).
My understanding of the regs is that I can dig out and renew the existing location (despite the fact that it's only 3m from the house) without involving Building Control, but a 'new' soakaway would technically require their involvement.
Is that right? If so, how do they normally deal with areas where it just isn't possible to be both 5m from any building and 2.5m from the boundary? Would you expect them to allow a compromise as I've suggested?
The subsoil here is pure sand. When installing a soakaway in my back garden years ago as part of building an extension I went down nearly 2m and there was never any sign of water. Same for the extension footings.
From the 'how big' section on soakaways on this site, there doesn't appear to be anything in the formulae that takes account of the range of difference in soil absorption rates that could be encountered. I'd expected to find that I could get away with a slightly smaller soakaway given that I'm on such dry sandy soil. Assuming I locate the pit in the front garden, rather than in the driveway, I'd planned to use the 'milk crate' system to get the maximum useful volume for the minimum sized hole. But the formula says that for my 35 sqm area of roof I still need a soakaway that's about 0.6 cubic metres in usable volume. No allowance is made for that fact that it's in sand as opposed to less absorbent soils.
Is that right, or have I missed something?
So, given the choices, what would you do?
Use the original location that's partly in the driveway - and, presumably therefore have to dig a bigger hole then fill it with chippings or rubble to give it sufficient structural integrity for a driveway location?
Relocate it into the garden area, put up with having to chop through quite a few tree roots and use the milk crate construction to reduce the size of the hole to be dug?
Involve Building Control or just get on and do it?
Finally, what's the best root-proof geotextile membrane? I've looked at the Terram site, but I'm not sure which is the best product to use. If I'm going to do this I want to make a decent job of it and ensure that roots don't cause the same problem again in a few years time.
Thanks,
Mike
Sorry for the long post...
I have a rainwater downpipe on the corner at the front of my house that serves an area of roof of approx 35 sqm. It feeds into an open gully that is set into a concrete path that leads from the front door to the boundary of the property.
The gully has been blocked for a while and, on investigation, I found that it has tree roots growing out of it.
I cleared it enough to find the likely direction of the outflow pipe and dug down in an area of the driveway where the pipe should emerge from beneath the concrete path.
I think I've found the original soakaway. The pipe ends in a rubble-filled (and totally silted) area that's partially beneath the path and partially beneath the gravel driveway that runs parallel to the path. It's 3m from the house.
I can see that tree roots are entering the pipe where it terminates in the old soakaway, but without digging up the rest of the path (and an access ramp into the front door), I can't comment on the condition of the rest of the old glazed clay pipework. Given that it's protected by the concrete of the path, it should be OK, but who knows?
I did break up a bit of the concrete around the gully to inspect the pipe at that end. There's no evidence of damage or tree root invasion, so it's possible that the remainder of the pipe is undamaged... but equally it might be broken elsewhere... It's almost certainly been there since the house was built in 1936.
My first thought was to get a drain clearance outfit in to clear the roots and internally inspect the pipe, but then I got an idea of the cost! Given that it would be wasted expenditure if it turned out that there is further damage to the pipe, it seems better to just go ahead, rip up the path and ramp and lay a new drain.
However, if I do that I then have a decision to make regarding the location of the soakaway....
I could dig out the original, but that would mean it would be partially in the driveway and, presumably, prone to subsiding - especially when the occasional skip delivery lorry drives onto it! I also thought that digging out the original location would be hard work because it's mostly broken bricks, whereas digging a new location would be comparatively easy because, once down 300mm it's like digging on a sandy beach.
So, I could put it in the front garden where I wouldn't have to be concerned about structural stability. However there are a couple of trees in the area which means I'll inevitably have to cut through a few roots. The other issue is that there isn't enough space to be able to comply with the 5m from building and 2.5m from boundary rule. The best I could achieve would be 4m from the building and 1m from the boundary fence (on the other side of which is a public asphalt-covered pavement, a grass verge and then a road).
My understanding of the regs is that I can dig out and renew the existing location (despite the fact that it's only 3m from the house) without involving Building Control, but a 'new' soakaway would technically require their involvement.
Is that right? If so, how do they normally deal with areas where it just isn't possible to be both 5m from any building and 2.5m from the boundary? Would you expect them to allow a compromise as I've suggested?
The subsoil here is pure sand. When installing a soakaway in my back garden years ago as part of building an extension I went down nearly 2m and there was never any sign of water. Same for the extension footings.
From the 'how big' section on soakaways on this site, there doesn't appear to be anything in the formulae that takes account of the range of difference in soil absorption rates that could be encountered. I'd expected to find that I could get away with a slightly smaller soakaway given that I'm on such dry sandy soil. Assuming I locate the pit in the front garden, rather than in the driveway, I'd planned to use the 'milk crate' system to get the maximum useful volume for the minimum sized hole. But the formula says that for my 35 sqm area of roof I still need a soakaway that's about 0.6 cubic metres in usable volume. No allowance is made for that fact that it's in sand as opposed to less absorbent soils.
Is that right, or have I missed something?
So, given the choices, what would you do?
Use the original location that's partly in the driveway - and, presumably therefore have to dig a bigger hole then fill it with chippings or rubble to give it sufficient structural integrity for a driveway location?
Relocate it into the garden area, put up with having to chop through quite a few tree roots and use the milk crate construction to reduce the size of the hole to be dug?
Involve Building Control or just get on and do it?
Finally, what's the best root-proof geotextile membrane? I've looked at the Terram site, but I'm not sure which is the best product to use. If I'm going to do this I want to make a decent job of it and ensure that roots don't cause the same problem again in a few years time.
Thanks,
Mike
so I can get both jobs done at once and earn some brownie points at the same time.
