Buildingtrackworld – Soak aways

I need to build one for the roof of my workshop. So far I’ve found an online calculator which reckons I need 0.5m3 volume and I know it has to be 5m from any building. Other than that, anything else I need to do?

Think there’s a distance from a road edge too but those are the basics.

So, dig a big hole, bury soak away crates of the right volume, shove some pipe into it and re-fill…

Do I need to line it with anything?

We just used a layer of large stones, no lining.

It was one of the sticking points for our PITA building control man – might be worth checking that they are happy with position and depth before you run pipe and re-fill.

Turns out my BC inspector is into mountain bikes and XC racing, so we spend more time discussing that than my workshop! He might even being buying an ex-race bike of mine….

You might want to check that the soakaway will work.

I’ve just dug one into clay soil with a high water table. It has no capacity, and doesn’t drain. With all this rain lately the water has just ended up sitting in my front garden.

Now looking into whether I can connect to the sewer instead.

I take it you have checked the suitability of the soil for porosity? You may only need 0.5m2 but you may also need to dig deeper to hit suitable strata.

Google for BRE 365 for further guidance.

Grizla, search for sand drains. May be a solution in your case if you are not allowed to connect to the sewer.

Very sandy soil here, no clay at all, so everything drains really quickly including all the nutrients from the soil, so gardening is trickier.

kevj – Member
Grizla, search for sand drains. May be a solution in your case if you are not allowed to connect to the sewer.

Cheers, will do.

Turns out my BC inspector is into mountain bikes and XC racing, so we spend more time discussing that than my workshop! He might even being buying an ex-race bike of mine….

Corrupting a public official, eh?

you need to check you can actually soak away first..

Dig a hole, measure it and fill it with water, time how quickly it soaks away and you can tailor your soakaway to suit. If you have a heavy clay then you’ll need a larger soakaway to attenuate the water, gravels, you can skimp on size a bit.

There are loads of online calculators and guidance, e.g.;
http://www.horsham.gov.uk/environment/8408.aspx

but I recommend you spend an hour doing a test first, I used to design the things and the ground conditions make a big difference, you don’t want to dig a bigger hole than you need.

Best of luck

make sure the drain to the soakaway doesn’t get clogged with vegetation that creates a blockage, breaks the pipe underground which dumps the water on your foundations, washes the soil away and causes your poorly-built extension to start falling down… 😳

If you are likely to get leafs in the gutters or drainage then make it maintainable. Otherwise reject stone filled hole (or hardcore with no fines) with a slotted pipe through it. Reject stone gives 30% void. Oh and wrap it in terram to prevent the soil over washing into it. osma crates are 1×0.5×0.4 so you a couple with some shingle bedding.

you’re in Cambridge aren’t you?

In a previous life I designed the soakaway for the new pavilion at the Cricket Ground and the attenuation pond for the road and extension at Homerton Colleg..

Check your soakaway now, Cambridge ground conditions vary seasonally….

I’m in Cambridge.

As above, the ground is saturated and the soakaway is overflowing.

I’m in Cambridge.

As above, the ground is saturated and the soakaway is overflowing.

Weird, I’ve never had water standing in my garden in the last 15 years. Was out last night and lawn was quite dry even after all the rain.

EDIT: When digging out the footings you can see it’s just sand where I am (near Railway station).

Yep – porosity test first. You need to do it a couple of times in a number of locations and then work out an average. It can be too fast as well as too slow 😉 Use this figure to determine the actual size you need.

To build it use normal waste pipe with slots cut into it using an angle grinder. Put the slots to the bottom and layer up the trenches with some sand and stone, then bed the pipes in with stone and backfill. The proper ridged drain pipe for soakaways has a habit of clogging up too fast! It is easier for roof water than dirty water (which is what I tend to deal with) but you still get bits and pieces going down the pipe so you don’t want them clogging up too fast.

Stricly speaking I’m not actually in Cambridge, I’m 5-6 miles south.
I assumed that Cambridge would have roughly the same sort of soil. You live and learn.

Can I borrow some of your sand?

I know West of Cambridge has clay, but I think the city itself is mostly sandy. My parents live in West Chesterton and have the same soil conditions.

If I put an inspection cover in, so I can check it and clear out leaves etc, what do I cement that into if there aren’t solid walls to the chamber?