Water butts & volume of rain coming off a shed
Anna33 Posts: 310
Ok, possibly a bit subjective depending on how much rain we're getting at any one time, but that aside - I need to re-route guttering on our existing shed (approx 10' x 8', at a guess, with apex roof). The current set up is that the guttering from the left hand side is funnelled round the back of the shed through downpipes into a water butt on the right hand side. Pretty standard set up.
I need to remove that funnelling section of pipes (don't ask, long story!), so there will basically be standalone guttering on each side of the shed, unconnected to each other. The shed is about 1' - 1.5' from the house, on a concrete base laid on paving. We didn't install any of this.
I want to set up water butts to collect the water from the left hand side of the shed (and the right hand side, but that's not so tricky as better access/nearer soil for run off etc), but the only place for water butts is on paving slabs rather than soil, and is next to the house. I was going to get two linked water butts to allow for maximum rain capture/minimum run off onto paving when full, but I'm not sure on sizing.
My question (finally) - how much rain water typically comes off a one side of a shed roof of that size/design?? If I got 2x 200l water butts, that would be 400l capacity - how quickly would they take to completely fill up? Imagine a typical downpour, or a normal (!) winter's load of rain. I'm just thinking about run off when they're full. Are those sizes about right, or massively underestimating how much water we'll collect???
PS would provide photos, but that area is temporarily being used to store loads of [email protected] whilst we've had work done elsewhere in the garden.
Well your collecting surface area is about 5m2 so at an average rainfall where you are of about 750mm? (mostly at this time of year I would assume) you should collect about 3500l p.a, or about 18 x 200l butts.
So I would say 2-3 weeks to fill one, but that is a very rough guess.
You could always start with 1 x 200l and see how you go, you have the option to connect a further one later if needed.
The other question though is how fast you use it. If you have a greenhouse, you'll continue to use water in the winter, but if not, the butts will fill up after the first week of rainy weather in late autumn and then will just overflow for the rest of winter until you start watering stuff again in the spring.
My advice would be to put in as much capacity as you can fit/afford as it'll never be too much, and make provision for it to overflow for quite a lot of the time in winter - i.e. channel/slope it away from your house.
The main reason for getting it was to try and reduce the waterlogging issue in that area but I don't have any run-off facility for the excess (other than into the waterlogged area I'm trying to dry out ). The end result is that I periodically fill a few buckets from the butt and pour them down the drain Not ideal!
Once some building work has been completed later this year, I'll probably get another butt or storage receptacle (as big as they come) to put at the side of the house. I'd fill that with any excess from the shed butt.