AD H - 'Roof' Rainwater drainage

I note in approved document H, section H3 - that 'Surface Water Drainage' and 'Drainage to Paved Area's' gives guidance on where rainwater can go, ie, to a drain, soak away etc etc.

However the first part of the section 'Gutters and Rain Water Pipes' gives no explanation of where rainwater can go, only explanation is where a roof may have no gutters at all.
This first section obviously refers to 'roofed' areas (although I see no reference to it) ... can rainwater goods discharge to a flat area of natural ground, or must it go to a soakaway or drain.

The rainwater should in theory soak directly into the area of ground around the discharge., I have thought of buiding a 'detention pond' which might be quite nice, not sure.

Any thoughts appreciated.

You'll tend to find that 'surface water drainage', 'drainage to paved areas' and 'drainage from gutters and rainwater pipes', is the very same rainwater. So it goes to the same places.

frank999 said:

, I have thought of buiding a 'detention pond' which might be quite nice, not sure.

Any thoughts appreciated.

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Sounds like a good idea

a 'detention pond' - a place for errant workers to ponder (excuse the pun) the errors of their ways.

'So it goes to the same places' - agreed - via gullies, drains and onto rivers or resourvoirs (or underground soakaways), but before then ...

'can rainwater goods discharge to an area of (flatish) 'natural ground', or must it go to an underground soakaway or drain.' ?
The discharge would be 5-10 metres min from any building, and 75sq mts of flat roof being discharged.

Just wondered if the Regs had anything to say on this, H3 states:

(3)Rainwater from a system provided pursuant to sub-paragraphs (1) or (2) shall discharge to one of the following, listed in order of priority:

a) an adequate soakaway or some other adequate infiltration system; or, where that is not reasonably practicable,

The Reg don't give any guidance on a ground level adequate soakaway, only submerged soak aways.

Presume a discharge point very near to buildings could cause heave ? (property is on London Clay, by 'heave' I infer a cyclical rising and settling of the ground) - could a discharge point - or other source of water even further away still cause heave ? its 75sq mts of flat roof being discharged.

As an aside - building has suffered historical differential settlement, and a large Cyprus Redwood is 8mt away from the rear of the building.

To clarify, and simplify

New rainwater drainage goes to these places in order of preference. You can only use the next on the list if the former is not possible.

1. The ground
2. Waterways
3. The drains

Thank you for that explanation, minus words such as 'where' 'adequate' and 'where' 'not reasonably practicable'.

re: 1. The Ground

Do I understand correctly that whether the rainwater 'soaks' into the ground above or below surface level - could be decided on the specific Regulations wording ... 'where reasonably practicable'.
If say the discharge point exited above ground level and said rainwater does not percolate, and ponds excessively (or causes other adverse effects - what ever those might be), then that would not be 'reasonably practicable' - and a submerged soak away should be provided (again providing 'where reaonably practicable').

You can't create a situation where water is a hazard on the surface such as in terms of potential slips, or splashes cause damp problems to the building, or have a surface that is not designed to deal with concentrated water flow so could fail prematurely and cause other problems.

And any water that you send into the ground should not cause localised soft ground which could influence foundations.

The "reasonably practical" reference is actually very helpful as it allows several options to deal with specific site conditions and design in a pragmatic way. You just follow common sense really in getting the water away from the building.

frank999 said:

Do I understand correctly

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You can't just run your roof storm water onto the ground hoping it will find a way into the soakaway - no.

You can't just run your roof storm water onto the ground hoping it will find a way into the soakaway - no.

Thanks Noseall - Is that because it will traverse overland until it hits a low spot then pond, which is not preferable if that is in back gardens in a suburban area ? surely though some of it does soak in, or the ponding would be permanent.

Is there a convention of what gulleys are where on standard 1930 semi's, at the front I observe 2 gulleys, presume one is rainwater and one grey (the front bedrooms originally contained a sink), you would expect the same at the rear ie rainwater (roof) and grey (kitchen and bathroom), on another property in the street at the rear I can only find one gully, which is grey, with the rainwater also discharging to this.

At the site, only one drain at the rear was discovered, and that has been plumbed into the foul public sewer running across the rear garden, is that wrong ... there are no other drains/sewers at the rear apart from the one foul mentioned. Whether stormwater drains at the rear ever existed and have both been buried or removed is unknown, both properties appear to have had resurfacing/drives installed in the last few decades.

My understanding is that discharge into a public sewer should only take place where the area of roof is less that 40 sq mt and other options are unavailable, I have 60sq mt. I could dig a Soak away, but when we dug down, even at 1.5 mt we still had clay. I wouold prefer to avoid the treatment plant having to deal with all this rainwater, as that seems unfair, thats why all our c**p ends up in the Thames. Isn't better for rainwater to back to the soil, than down a drain /

The properties have large gardens, and have pondered discharging at the end of ours (15 metres away from the building), hoping the water would soak away by the time it gets near to any buildings.

Top pic:Gulleys at the front of the property:, rainwater left, presume grey to the right:

Second Pic: Gully at rear on similar property in street.

noseall said:

You can't just run your roof storm water onto the ground hoping it will find a way into the soakaway - no.

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Where would the rain have gone before the building existed?

clifford1 said:

Where would the rain have gone before the building existed?

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True. But it would have fell scattered and random and not collected then dispersed through a concentrated spout only to cause a nuisance.

If you're on London clay then soakaways won't work. If you have a convenient river then use that, failing that run it to surface water drainage system. If you aren't connected to that then run it to foul drains.

If you have the space for a few IBCs to intercept the rainwater you'll be able to annoy your neighbours by lavishly watering your garden during the next hosepipe ban. You can bury IBCs.....

'dispersed through a concentrated spout only to cause a nuisance'

Sounds like someone I know ... thanks, yes I want to avoid causing any nuisance.

If you're on London clay then soakaways won't work.
At 1.5mt here we still have clay, presume you would have to get to the strata below -

'few IBCs to intercept the rainwater'
I didn't mention that this is where the rainfall is going first, we have two IBC's at the end of the garden - this is to feed Toilets in the property, its any overflow from this that I have to deal with, calculations tell me the 2x 1000L IBCs will not be enough (by 1/3rd apparently) - but the fugures are averages and I am sure in some months there will be overflow. A drain will be laid back to the foul Sewer, which seems the only viable option here to avoid any nuisances, unless i can make the overflow somehow 'rain' over the ground, so its scattered and random, and then disperses.

Didn't spot your planned ibc use, lots of words....have you got room for more ibcs?
Don't think digging through the clay will work.
Is your garden massive? Does it get waterlogged and boggy in the winter?
If yes and no you could lay a network of irrigation pipes. You could put a couple of big sprinklers in (agricultural big, litre per second or more).
The simpler option (and cheaper unless it will trigger surface water charges from your water supplier) will be to dump the excess to the foul drains.

have you got room for more ibcs?
Yes am considering it, another one or two, would help level out the variance in ranifall vs use issue in the tanks.
Will be interesting to see how much excess their will be, I will be installing various sensors on the tanks to tell me when it is full/empty etc.

Gardens are 15x8mt (it was 21x8mt before extension), gardens backing are much bigger ...

Don't think digging through the clay will work.
Soak aways can be quite expensive (with labour costed in) - so they'd need to work to be worthwhile.

There are two huge trees within 8 mts of each other here, one a Cyprus Redwood, they must be drinking up a fair amount.

Their is approx a spades depth (300mm) of topsoil here, guess the problem is how water permeates the clay underneath.

A sprinkler is an interesting bit of lateral thinking.

I will look into whether a surface water charge has already been levied by Thames Water on the previous owner, in case we need to bale out (excuse another punn) and dump it down the sewer.