Scenario: Double garage built 20yrs ago at the bottom of a garden, with proper planning permission. But instead of digging a soakaway as on the plans, just sent the rainwater from the roof into a butt. Which when it overflows trickles away on the surface to roughly where the soakaway should have been.
Time has come to put this right, and dig the "missing" soakaway. But without access to the full original plans, how big (circumference, depth, capacity) should it be?
Part H tells you how to do a percolation test, from that you can calculate the volume, I don't know what duration of storm you should assume. Are you thinking of using crates?
Example install of crates
Have you checked with your council's Planning Department to see if they have a copy of the plans? I was able to view some old plans (on microfiche IIRC) at the council. For some reason they wouldn't let me print them, but did allow me to photograph them on the fiche reader screen.
Many moons ago, before soakaways were a thing, I got my gutters etc, replaced by plastic ones. I also had another downpipe fitted near my front door as being in a terrace I found I was getting too much water from the neighbours which tumbled onto my head when going out of the front door. The downpip was left to soak away into the lawn. Now at some time a bush was planted at the place just to the right of the end of the drainpipe. It has now almost grown up to the upstairs window and needs to be pruned, its I think been flowering non stop for years. When should one prune it and would it be of any use making a makeshift soak away by extending the downpipe to another location and hoping the bush will still be OK as the whole of the front of the house gets a little pool when it rains hard now of course. I think its camellia or clematis, there is also a rose there as well. Brian
It is even just possible that the plans have been placed on the council's planning website and might be viewable from there. Our council certainly does that, but I don't know how far back they stretch (for example, there are only scans of the approvals for 1978, 79 and 80 changes, but the full plans for 2010 changes at my house).
In message <ubi2ok$383av$ snipped-for-privacy@dont-email.me, at 09:52:36 on Wed, 16 Aug
2023, Jeff Layman snipped-for-privacy@>> Scenario: Double garage built 20yrs ago at the bottom of a garden, withYes, that's how I have plans in my possession. But it's just an outline of the garage, and a dotted line saying "soakway is over there".
They sent me a pdf.
In message snipped-for-privacy@mid.individual.net>, at 09:15:56 on Wed, 16 Aug 2023, Andy Burns snipped-for-privacy@andyburns.uk remarked:
Percolation test seems a bit of a faff. Especially as the overflow from the butt soaks in almost immediately.
Was expecting to have someone dig a hole [the one in that video is about what I expected] and fill it with rubble. If it fills up too much in a storm, the worst that can happen is it overflows onto the surface of the next few square metres of the garden slightly downhill from my proposed soakaway site.
In general a building inspector would probably tell you what would be acceptable if it was a new build. There is a formula that looks at roof area and soil type. And the BI will know what the soil type is.
In message snipped-for-privacy@perry.uk, Roland Perry snipped-for-privacy@perry.co.uk> writes
The video showed a very *expensive* soak. Perhaps the owners were seen to be wealthy. No mention of any original soak so perhaps the builder relied on the sand subsoil. My Aunts house, in Cambridgeshire, had a section of wall subsiding. The cause turned out to be a damaged drain pipe serving a second floor bathroom. The builder had miss read the plans and put a 90deg. bend in salt glaze pipe which my grandfather had damaged by vigorous rodding!
It isn't particularly critical, especially since it will gradually fill up with soil, sand, silt and stuff. The one that wasn't dug 20 yrs ago would be much smaller now.
You could do a simple calculation of how much water you might expect in
24hrs in exceptional circumstance, you know, mm of rain x length x breadth of roof.TW
Building regs appendix H3 has some maps showing rainfall intensities to design for, in litres per second per m2:
Theo
Indeed - I was getting 50l/hr measured off a small lean-to in some of the heavier recent rain.
And uphill next door's gutter was blocked, directing all the rain from the side of a large detached house and 20m extension into my 1.5m high 10m long stone wall, causing it to shift and lean a few more inches and wedge the side gate closed. Well, that's my uneducated guess, but there must have been tons of water over the recent rainy spell backing up.
In message <QyBL$ snipped-for-privacy@marfordfarm.demon.co.uk>, at 13:03:07 on Wed, 16 Aug 2023, Tim Lamb snipped-for-privacy@marfordfarm.demon.co.uk> remarked:
Somewhere I have a soil survey which was part of the searches when the property was bought. I'd expect it to be pretty porous.
Unlike one house I had in the Chilterns which had about six inches of soil on top of very solid chalk.
That -- but don't fill it with rubble.
Instead, stick crates in it, or mortar tubs, or a plastic/metal bin, oil drum, ... with large holes in it, or the bottom cut out, or ...
This makes removing the silt that eventually collects and clogs much easier. And the open volume means that the soakaway can hold a lot more water, from say a short hard rain, and then drain it away slowly.
And do make it so wide and deep that cleaning it is possible.
I have a 60 cm x 60 cm by 100 cm deep soakaway, and that is a size ratio that is "difficult": too small to get a handled tool in and work it well, and too deep to reach into easily. Ended up having to buy an auger!
Thomas Prufer
And you think that chalk isn't the most porous rock there is? Sheesh
Quelle môrone
In fact soakaways work well filled with rubble or gravel or crushed limestone or anything porous provided they have a roof on.
After twenty years, hire a digger.
But just how porous? And, more to the point, how /permeable/ is it? I've just been introduced to the wonderful world of the millidarcy. :-)
It seems that chalk has two permeabilities, the secondary of which, due to its fracture system, is 100 - 1000 times that of its primary permeability:
There's an amazing amount of stuff on the internet to waste time on!
In message <ubkh46$3mg8s$ snipped-for-privacy@dont-email.me, at 08:09:58 on Thu, 17 Aug
2023, The Natural Philos>> Somewhere I have a soil survey which was part of the searches whenBecause that chalk was tougher than concrete. Builders used to moan about being forced to excavate it to make statutory foundations, out of a softer material.
In message <ubkh83$3mg8s$ snipped-for-privacy@dont-email.me, at 08:12:03 on Thu, 17 Aug
2023, The Natural Philos>> >>I'm expecting to hire two diggers: a bloke plus a small backhoe.
Rainfall estimates: this morning's weather forecast says expect up to
6cm on Friday night, garage is 5.8m square, and some of the references given earlier say x 1.5, which gives 3 cubic metres.I suppose the water butt is 210 litre = 0.2 cubic metre. Which seems a bit undersized. And it's always full (apart from anything else the tap at the bottom is seized up). So it's all just running off at the moment.
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.