Alternatives to soakaway

[C4useway]

Hi,

Thanks in advance for any advice.

I've just had a new 6mx3m extension built and was planning to connect the gutters to the existing house's downpipe. Because the total roof of the property is over 40m2 (the original was 48m2 anyway), the water company has asked that the runoff goes through an attenuation system to slow the flow to a maximum of 1l/s. All the options I've looked at for this cost in the thousands.

Building regs, who originally suggested a standard water butt, need the water company's approval on whatever system is installed.

It's clay soil so soakaway isn't an option - although we've never had any waterlogging issues in the garden.

Are there any other options - either a cost effective attenuation system or another that doesn't connect to the sewer e.g. irragates beds?

Any ideas?

Thanks

 

[mrrusty]

runoff goes through an attenuation system to slow the flow to a maximum of 1l/s. All the options I've looked at for this cost in the thousands.

I have no idea if the water company can enforce a particular certification, but practically, discharging into a water butt and having a small outlet from that to the drain is going to achieve this. 1 l/s is quite a high flow rate.

A very quick look and a water butt with a 1cm diameter hole would give you at maximum no more than 1/3rd of that https://www.engineeringtoolbox.com/flow-liquid-water-tank-d_1753.html

 

[Dereekoo]

As above, assuming head of water in the butt at 1m and and side discharge orifice of 22mm flow would be approx 1 l/s. Next question is how big a storm event do they expect you to attenuate ie. a normal water butt could fill and overflow in 15mins as a swimming pool could take 2 days?) or is it just a token effort they expect you to take so they can convince themselves that they are policing the sewerage system. You say they have asked for it but not demanded it??

 

[C4useway]

I supposed 'demanded it' would be more accurate. Needs to attenuate for a one in thirty years storm event...!

 

[Dereekoo]

On the basis that you have done the costings of the attenuation system based on the relevant rainfall intensity figures and they are prohibitive it sounds like the lesser of the 2 evils is to send the new extension flow a soakaway which would be acceptable by BC and negate the involvement of the WC?

 

[clifford1]

What happened to the rain that used to fall on the ground now occupied by the extension?

 

[Dereekoo]

What happened to the rain that used to fall on the ground now occupied by the extension?

Why?

 

[clifford1]

Because, obviously, it must have gone somewhere. There was no soakaway, presumably the house was not surrounded by a flood of rainwater that couldn't drain anywhere - in short, the rain didn't matter. So why does it suddenly matter now, simply as a result of falling on an extension roof and then down a drainpipe?

 

[Dereekoo]

Perhaps its something to do with building regs re drainage and saying it use to just drain away naturally doesn't comply, these BC people can be a funny lot.

 

[SussexBunch]

I have a similar question. I would like to keep an existing water butt, when adding the extension, or get a bigger one for the same location. Digging for surface water pipe would damage the root of a nearby tree even more, costly and messy. I heard that building regs do not permit new water butts and also require all old ones, if at all relevant to new construction, like roof replacement, to be upgraded to underground drainage. Is this true? Would Sussex Building Control consider permitting us to get new water butts, keep water butts, or upgrade existing water butts? Extension and new roof tiling project. Thanks very much for your comments.

 

[TomSmith]

OP you've got several options for drainage systems in clay soil. Article here

It's common for water companies to want you to hold water back within the site and slowly discharge to their sewer so that the system does not become overwhelmed during storm conditions.

I notice that you mention irrigating beds in your post, have you considered rain gardens? This linked here outlines what they are and how to size them. Hope it helps.

 

[thomp1983]

Before dismissing soakaways in clay I'd dig a hole and do a percolation test, our entire estate is built on clay and all the houses have soakaways.

When we built our extension I dug out the original soakaway to replace it with crates for the increased amount of water, the old soakaway was roughly 2x5m and 1.5m deep filled with various sizes of limestone rock, it worked perfectly and probably would of easily taken the extra extension water, we just didn't know it was that big till we started digging.

There's a slightly smaller soakaway out the back which we have joined into for the rear, all rear rainfall also goes via a 1250l water butt.

So yes soakaways can work perfectly well in clay.

 

[foxhole]

Before dismissing soakaways in clay I'd dig a hole and do a percolation test, our entire estate is built on clay and all the houses have soakaways.

When we built our extension I dug out the original soakaway to replace it with crates for the increased amount of water, the old soakaway was roughly 2x5m and 1.5m deep filled with various sizes of limestone rock, it worked perfectly and probably would of easily taken the extra extension water, we just didn't know it was that big till we started digging.

There's a slightly smaller soakaway out the back which we have joined into for the rear, all rear rainfall also goes via a 1250l water butt.

So yes soakaways can work perfectly well in clay.

Agree, have clay soil and soak away, should work fine, unless your garden floods with every rainfall.