Any advice on surface water drainage regs?

[Anonymous]

I have to provide surface water drainage from the roof of a new garage that I'm planning to build. First question - am I allowed to drain surface water from the roof into the main drains, or am I required to drain it into a soakaway?

If it's got to be a soakaway, can anyone give me a bit of advice about its construction, please? I'll be draining about 36 m2 of roof, and our soil is mainly Suffolk clay.

1. How far away from the structure must the soakaway be?
2. What depth and volume should it be?
3. What should it be filled with - is just 20mm gravel OK?
4. How is the water normally piped underground to the soakaway - should I use salt glazed pipes, or clay land drains?

Many thanks for any advice.

 

[Anonymous]

Never mind the law, just do what's right. If you send it to the sewer it wastes water, increases the risk of flooding and costs someone (us) to deal with it. First you need a water butt, handy for watering those hanging baskets, and then a bit of a drain leading to a nearby flowerbed just for the occasional overflow. Suffolk is on the drier side of the country. You don't want to be sending the rain to sea without letting the flowers have a go first.


Plantstuff

 

[Anonymous]

Surface water should not go into the mains drainage. However it is commonplace many builders do it and I do not believe it is ever checked.

With regard to soak aways, you want to run the pipe as far away from the building as you can in solid pipe, I would recommend at least 6 metres. Then if you have the space to take it further you could take it further away within a perforated pipe.

As for the soakaway I believe a metre cube is normal around here filled with larger uneven rubble. I would line this hole and over the top of the rubble with geotextile membrane to keep the soakaway free of silt.

As for the clay this may pose you a problem.


Soakaway guidance

 

[Anonymous]

If you want a "proper" job , follow Jon's advise.
If you want to capitalise on free natural resources and have a nice bowling green, follow Biff's.

If you are tight, just let the inspector see a downpipe pointing away from the wall.

 

[Anonymous]

I can assure you that we are already well water-butted in the garden!

As regards wasting water, I reckon that's a moot point. Which is more wasteful - sending it down the sewer to be recycled by the water company and returned to the mains supply, or pouring it into the ground?

Discuss!

 

[Anonymous]

Thanks for that info, Jon.
When you say that the soakaway should be a cubic metre, does that normally mean 1 metre x 1 metre x 1 metre, or doesn't that matter? I imagine the depth is one of the most critical considerations, isn't it?

 

[Anonymous]

... how's work going on that gorgeous house? Will it be finished in time for the big four-oh?

 

[Anonymous]

We have sadly got bogged down with groundworks at the moment so whilst I strongly suspect I will be holding my 40th out there I guess there will still be lots of things to finish as when I made yet another rash statment that failed to take into account the wait for our second re-mortgage, the wait for my borehole contractor etc...... So we still really havent got on to far with the inside although that should start taking shape during March.

I guess, dare I mention another deadline but August is our 5th wedding anniversary.....

As for your cubic metre its up to you how you work out the dimensionsn but as you rightly say deeper is better, A quick call to your local building control would enlighten you further and may be more helpful as they will know your ground and what it will behave like.

 

[Anonymous]

The details of your hole might be dependant on the local ground conditions. If the clay is impervious then going down deeper might not achieve much. It might be to spread the water out sideways through the soil, herring bone fashion, but if it's just one garage roof you don't need to go too far.

An advantae of not putting any water into the sewers is that your payment to the water company is halved. Don't stop at a water butt and soakaway - build a septic tank and reed bed!

 

[Anonymous]

I was under the impression it is now illegal to drain surface water into the foul water drainage, although it was common in the past. You either have to have a soakaway or drain into a nearby ditch. Mixing the surface and foul drainage is one of the problems with flooding.

 

[Anonymous]

Building regulations do allow rainwater drainage into a sewer but only when there is no other alternative.

Having said that I think a soakaway is the best option. If ground conditions are not ideal the environment agency prefer you to dig a longer trench rather than a deeper one.

If you want to be really technical you can do a percolation test on your soil which will indicate the size of soakaway you need.

 

[Anonymous]

Believe it or not, this is the first house I've owned that has been on main drainage. The other four were all septic tank jobs. So at least I feel that I have sort of "served my time"!
I'd much rather be on a septic tank for all kinds of reasons, but the cost of installing one and disconnecting from the main drains is simply not affordable.

 

[Anonymous]

Thanks for that further advice, Jon. And do keep us posted on progress with the house - with pictures if possible!

 

[Anonymous]

Thanks for your guidance on that, John. However, I feel that a soil percolation test is perhaps a bit "overkill" for a little garage roof. I think I'll just rely on dumb luck!