We've commenced the final part of our house renovation and are currently doing a patio on the back garden. I've added a drawing for ease. The garden naturally slopes towards the house and has been landscaped via digger to get to where we are now. A retaining wall has been added 6m from the house and has land drainage at the rear to stop it retaining water 9 the soil turns to red clay at approx .5m down.
A line of ACO drains have been placed against the rear of the house (below DPC) in order to drain the patio, these will be draining into a soakaway that is yet to be created. There is an exsisting bottle gully that runs under the house that the ACO drains have been tapped into to effectively drain half or a little more of the patio in theory.
There is also a pre-exisiting downpipe from the extension which drained into said bottle gully but is now piped into the ACO's and then subsequently the gully.
I am aware that a soakaway or alternative system will be required due to the sheer volume of water that (once a year) will pass through the pipe work and need to go somewhere. The second diagram shows the proposed system which is to remove the poorly placed soakaway that is currently .5m from the house and is presumedly blocked or as near to blocked as it can get.
The ACO drains will be connected to a long run of underground pipe that will also join the house downpipe on its way to the front of the property. This will then drain into attenuation or soakaway crates that will be placed under the front drive. This soakaway will also serve the front house and extension downpipe which at present drains onto the driveway.
From a few quick calculations its an area of about 140m2 if I surmise that half of the patio and half of the extension roof will drain into the bottle gully at the rear of the house.
This works out at a very generous 2.5m3 soakaway that will engulf the front of the property and cost a fair whack to put in the ground.
The area on the front is approx 8.5m x 12.7m which means that to observe the 5m from a boundary or building line "Rule" would be impossible.
As I've said, we are on clay ground but as of yet I haven't dug a trial hole to do a percolation test.
I'm after some advice and another pair of eyes to look over the proposed plan and suggest an alternative drainage solution. Could I install a 1.5m3 (ish) soakaway near the front of the garden and then have an overflow which connects into the combined system that is present on the front of the house for that once a year downpour? Or is this frowned upon?
your building inspector has the call here as it is part of building regs when the roof is involved
we have had to install 4m3 soakaways before
they are there for a reason
cheers LLL
mattu wrote:we are on clay ground but as of yet I haven't dug a trial hole to do a percolation test.
You mention 'red clay' which may well be boulder clay. If so, this stuff is impermeable - my garden is built on it, so I know!
If there is a problem with permeability, you will have to consider an alternative, and the BCO should be able to help with this (it's what they are allegedly paid for!), but the first step is those permeability tests.
Thanks for the speedy replies. To be honest I hadn't thought that BCO's would need to be involved for a patio (they're a bit of a pain around here) but I suppose that would be the best course of action if I'm altering drains and so on. I shall give them a call, can I get advice over the phone or is it a "come out and see" scenario. I'd hate for them to come out and say "tear everything out and start again"
All the landscapers we had round said to do the same as we've done I.e linear drains and a soakaway at the front but I don't see how the regs can possibly be adhered to with the 5m rule from boundary's. Our neighbours all have patios so it must be possible.
4m3! Let's hope it doesn't come to that! Don't fancy digging a 2.5m3 soakaway by hand either.
Yes the clay is definitely impermiable by the looks of it, the dousing it's had over the last few weeks have proven that. I remember someone on our street saying that it goes to yellow sand if you go deep enough but I'm not sure how far that would be.
Am I heading in the right direction with my plans or can you guys see anything I've missed?
BCO involvement was assumed by me because your sketch shows an 'extension'. If that is already in place, then no need to involve BCO.
The 5m rule for soakaways is based on common sense and protecting foundations, so it's worth sticking to whenever possible. However, when the ground is highly free-draining, I wouldn't worry too much if that came down to, say, not less than 3.6m.
However, on impermeable clay, not only is a soakaway a complete waste of a bloody good hole, at such a proximity to the property, its potential for affecting the foundations is increased, so I'd be looking for any way possible to avoid one.
The planning regs allow you to connect to the existing SW system in such a situation as long as you have PP from the local authority, which brings the BCO back into the picture. They can charge (I think there's an upper limit of 150 quid or so) and they can refuse PP if they believe there is a viable alternative for source control (ie: dealing with the surface water on site), but with boulder clay extant, and such a small area available, I can't see what argument they could make to refuse PP in your case.
Hello again, the extension was done about two years ago and is a 3m projection from the house, the bulk of it is existing but it has been altered from a flat to a pitched roof as it was like a swimming pool up there. We had bco around for the small extension we did (which is why I know they're a pain) but they never mentioned drainage for the roof system. The original pipework ran into the gully on the back of the house which the Aco's now go into. So we have kept this in the same place also.
I can place the soakaway at 5m from the house but it won't be 5m from the road and I didn't want it to affect the pavement in anyway. It's just the volume of it that's the worrying aspect. As soon as some of the materials have been cleared from the front I shall dig the test pit and see what I'm dealing with. If our neighbour is right I'll find decent stuff beneath that red impervious clay that seems to be everywhere.
I did a bit of reading on it via the soakaway link on here and there are quite a few requirements for the perfect legal soakaway. I don't think it's a goer personally, and it's frustrating that there's a perfectly good pipe network directly below the front downpipe thats just begging to be tapped into an has been done so by all of our neighbours from the looks of it.
If planning permission got involved would they also challenge the patio is my worry? I haven't had weep holes in the wall but have 4" perforated drainage all along the back edge (gravel backfilled) and it's fitted with a dpc also. But would they say anything else? Were the rear house downpipes supposed to go into that gully (they were there when we moved in and have been since the 80s) or would they get me to move them?
I'll happily pay the charges proposed to do it right but I don't want them being pedantic about it. For example like how they asked me to install a radon proof dpm in the floor despite the floor next to it and the whole of the house not having it seeing as it's been there for over 60 years! :p
They can't challenge a patio, and, if it's behind the building line of the house (which ist must be, obviously) then they can't challenge a connection to existing SW system.
The regulation requires pavements to be greater than 5m² in size, be non-permeable, and to lie, at least in part, in front of the building line of the property if they are to fall within the remit of the 2008 act. That's how it applies only to driveways, which, in the vast majority of installations, must be in front of the building.
