Soakaway to BRE digest 365?

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Hi,
I need a soakaway for a extension that has a roof area of just under 34m2 and it needs to be done to BRE 365 standards.

I was wondering if anyone know who or where I could get the calculation for soakaway size done cheaply (and relatively quickly)?

I have looked at the testing method and I can do that without a problem but the maths calculation is where I could use some help.

Thanks.
 
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You’re probably over thinking it really, nine times out of ten your BCO will be happy with a 1m³ hole unless its in clay in which case it won’t work anyway. Speak with your BCO, he will have no doubt overseen a few within your vicinity.
 
Thanks for the quick reply, it looks like I'm the 1 in 10. The BCO has already been out and said that anything over 25m2 needs the calcs.

I have downloaded a spreadsheet from http://www.uksuds.com/tools.htm, tried it as a practice but after inputting the various details and saving it, it doesn't come up with a results page.
By the way the soil is approx. 300mm top soil over softish sand stone going into harder and harder sand stone down to 1m
 
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Thanks again, but on the planning portal the approved doc H talks about small soakaways serving 25m2 or less and then says for larger soakaways ie 34m2 refer to paragraph 3.30 which says should be designed to BS EN 752-4 or BRE digest 356 which is what the BCO wants it to :(
 
I find it hard to accept that a Local Authority Inspector would not accept an LABC guidance note. He probably doesn't even know it exists! Have you actually asked if he'll accept this method of calculating the volume? I think I would be speaking with the Head of BC if he continues being obstinate.
 
I'll try it with him but when I mentioned the soakaway on his first visit I asked how he wanted it done and he said he wanted it calculated to BRE 365.
I also need to keep him on side as I have a few other areas coming up that I will need some goodwill shall we say.:confused:

Just in case I do need to do the peculation tests and calculations done I still need to find out where from.

Thanks.
 
Well this is Digest 365 but you need a maths degree to work it out! http://www.google.co.uk/url?sa=t&rc...uqrVPeWKH1C2m2g&bvm=bv.71667212,d.ZGU&cad=rja
I suspect he will also ask for a test which involves filling a 1m³ hole with water from a bowser (hire cost) and then getting an engineer (labour cost) to stand around for an hour or so measuring by how much it drains away. Any structural engineer will be able to do the calc.

But for such a piddly soakaway completely over the top.
 
Lol tell me about it, sites of less than 100m2 only need a test hole of 300mmx 300mm but I still need to do maths. Most online examples seem to use a tool called Tedds?
 
Don't know it myself but then I’ve never had to produce calcs for a domestic installation, even whole New Builds! On commercial jobs my SE’s done the maths etc as part of his appointment.
 
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Just in case I do need to do the peculation tests and calculations done I still need to find out where from.
Answer two questions and will give you all the information that you require including working out the maths.
Is the 43m2 one side of the roof only?
Have you got one or two downpipes to this section of roof?
Regards oldun
 
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Just in case I do need to do the peculation tests and calculations done I still need to find out where from.
Answer two questions and will give you all the information that you require including working out the maths.
Is the 43m2 one side of the roof only?
Have you got one or two downpipes to this section of roof?
Regards oldun

Hi Mr Oldun, the 34m2 is the total new roof area on a single story orangery extension at the rear of our house and it will have just one downpipe.

Just a little bit more info, the main roof of the house at the back has 2 downpipes, one at each endish which already go into 2 soakaways. The front has 2 too.
 
Okay fellow, big old lump for orangery.
Forget about BRE 365.
Forget about Technical Note 10 that Fred the Tread posted. That formula is out of date and that technical note was brought out when they built Stonehenge.
Work to the formula iin AD H section 3.28 Page 46
Fit two down pipes to orangery and two soak ways to serve 21.5m2 each of total roof area..
We list a link that was updated in February 2014 which gives a more simplified guide to understand.

Rainwater Soakaway Design Guidance - Eden District Council

We also list below a copy of the last soak away design that we prepared for local BC.

Soakaway Design at XYZ

Total area to be drained. 99.33 m2, therefore form four number soakaways to drain 24.83m2 per soakaway.


A design rainfall of 10mm over 5 minutes has been assumed to give the worst case all as Building Regulation Approved Document H.


Percolation Test.
Average time to seep away from 75% to 25% = 45 minutes.
45 minutes by 60 seconds =2700 seconds divided by 150 = 18.
Therefor Vp =18


Filtration Rate. f=10-3
2Vp
f=10-3
2x18

f=0.01
36

Therefore f= 0.0003


Outflow Volume. O=as50xfxD

therefore O=2x0.0003x5 = 0.003


Area to be drained. 24.83m2 x 10mm rainfall = .2483m3 storage capacity less outflow 0.003 = 0.2453m3 total clear storage volume


Soakaway size. 1.100x1.100x1.100 depth below invert = 1.331m3 with 20% void = 0.2662m3


Therefore the above size soakaway is sufficient.

Anything that you do not understand, then come back, although you should be able to work it out yourself. Once you have worked it out you may wish to consider rain crates instead of hard core.
Regards oldun
 
Why do you reference Rainwater Soakaway Design Guidance - Eden District Council when that is only suitable for areas up to 25m2?
 
Why do you reference Rainwater Soakaway Design Guidance - Eden District Council when that is only suitable for areas up to 25m2?

Because if you had bothered to read our last post, you would have seen the following

Work to the formula iin AD H section 3.28 Page 46
Fit two down pipes to orangery and two soak ways to serve 21.5m2 each of total roof area..
We list a link that was updated in February 2014 which gives a more simplified guide to understand.:eek:

It is like a lot of things Fred, a hard way, working to BRE 365 with a shed full of money or the easy way of two digging two soakaways a tad over metre square each serving 25m2 roof area
Regards oldun
 

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