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Posted: Mon Mar 16, 2009 10:22 am
by paul.livesey
Hi
We have recently built an extension - roughly 9.5 m2.
I managed the project myself and was advised to run the rainwater from the newbuild to a new soakaway.
I have dug a hole just over 5m from the building. It is 1m x 1m x 1.2m deep. I think I have just got through the layer of clay at the bottom - it is a bit more stoney etc.
Firstly is this fit for the purpose. Secondly what pipes should i use to run underground from the guttering downpipes to the soakaway - should they be perforated...how deep should they be etc. I have had conflicting advise from various people and the building inspector could not offer specific advise until he had seen the soil conditions etc - i don't really want to have to call him out until I have everything in position so he can sign it off there and then.
Grateful if you can offer any advise.
Posted: Mon Mar 16, 2009 10:57 am
by GB_Groundworks
read http://www.pavingexpert.com/drain08.html
you'll need to do a soil porosity test to see if a soakaway will work, plus calculate the size required from the roof area you will be draining.
Posted: Mon Mar 16, 2009 11:29 am
by paul.livesey
How do I do a soil porosity test?
Some one told me you dig a 300mm x 300mm hole in the bottom of the soakaway and fill it with water - then time how long it takes for the water to disappear.
is this correct?
the roof area is 9.5m2
Posted: Mon Mar 16, 2009 5:13 pm
by lutonlagerlout
BC will be happy as long as your 110mm upvc pipe has a 1: 40 fall from the guttering to the soakaway this equates to about 125 m of fall, the soakaway needs too have at least 225mm of topsoil on top of it on top of 1200 gauge visqueen,covering the hardcore (still told to use hardcore in luton?) its worth using a roddable back inlet gulley at the gutter end so your pipe does not become full of leaves and deitrius
LLL
Posted: Tue Mar 17, 2009 5:55 am
by seanandruby
you have the hole dug now see if it holds water, or not, run an hose to it.
Posted: Wed Mar 18, 2009 9:11 am
by Tony McC
I've been writing a guide to carrying out porosity tests, but to summarise the main points:
Hole, 300x300x300 must be at least 500mm below invert level
Fill with water, let it drain to empty. Re-fill and record how long it takes to drain to empty again.
If poss, repeat at least three times to get an average figure
Posted: Wed Mar 18, 2009 5:04 pm
by lutonlagerlout
what the gaffer has said here is 100% correct,but in 25 years i have never had 1 BCO ask us to do this
they just want 1 m3 below invert level,sometimes with crates sometimes with hardcore,sometimes with a BIG sometimes with a rest bend
they are a law unto themselves
LLL
Posted: Thu Mar 19, 2009 9:48 am
by Tony McC
There is "official" guidance on soakaway construction (BRE Digest 365) but it's not the easiest thing to follow, and so most BCOs rely on what they know: a hole filled with owld bricks.
This narticle that I'm writing is an attempt to humanise BRE365, but it's bloody hard going, and I'm not sure it's pertinent to a typical driveway/patio application. It's definitely *the* way to go for larger site-sized installations, but in my experience, the soil tests for those jobs is done by geo-technical boffins, whereas I'm looking to create something that can be used by smaller contractors and keen DIYers working on a <100m² project.
Posted: Thu Mar 19, 2009 12:03 pm
by paul.livesey
Thanks to all those who have responded
I think I know basically what I've got to do now. Will get it done this weekend and get the BCO in on monday to have a look - hopefully he'll be happy and I can get on and get it all finished
cheers
paul