Garage roof drainage & water harvesting

Hi all.

I've got a question about harvesting our garage roof rain water. Please excuse the long and rambling description.

Current situation is as follows...

Standard 1970s double garage (i.e. not big enough to get 2 modern cars in ;-), flat felt roof, draining to the rear of the garage.

There are 3 rainwater hoppers. Right hand one goes directly into the drain. Left hand one goes straight into a water butt (standard round green jobbie). Middle hopper drops via a 22 degree joint into a 112 degree T piece into the left hand down pipe. From memory, it's about

2.8m between the left and right hopper centre points, and about 2.8m tall (from the ground behind the garage). Looking at the back of the garage, the neighbour's fence is to the left, our garden is to the right.

ASCII art time

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This is all fine, with the exception that in heavy rain, the water butt can be filled from empty to full in about 30 minutes. This means that there's a very nasty swampy area, because all of the excess water pours out of the butt onto the ground.

What we would *like* to do is replace the standard butt with a huge

1000 litre version, because watering the garden as it is, will take ~50% of the butt. (This isn't true, what we'd *really* like to do is put a 40k litre underground storage tank in, with a floating pump, divert all of the bath & sink water in, put in a UV filtration system, and re-plumb the house to use this grey water to flush the toilets, and have an automated plant watering system, but this seems a bit pricey and over-complicated, so we're settling for a bigger water butt!)

While we're replacing the butt, we'd like to sort out all of the other plumbing.

Due to space and aesthetic reasons, the water butt *has* to stay where the current one is (i.e. away from the drain). We ultimately want to put a shed in the garden, and the garage wall is the only sensible place for it, so putting a big water tank next to the drain would limit the size/shape of shed, but putting it flat against the wall wouldn't.

I can see 2 ways of fixing the plumbing...

1) Right hand hopper drops into the drain, with a 112 degree T piece about halfway down. This goes up at 22 degrees where it goes into a 112 degree T piece (with a vertical rise) to the middle hopper, and then carries on to the left hand hopper. This means that all the rainwater will go into the drain. We would then fit one of those standard rainwater downpipe capture collars, and take it all the way back across the wall to the water tank with about 3m of the narrow flexible hose.

|_| |_| |_| | | | \ | | \ | | \ | | \ | | \| | \ | \ | \ | \ | \ | \ | \ | | |___________\| | | | |_| | Drain

The main downside (as I can see) is that the wall will look like something H R Geiger would be proud of. There's also a slight issue of making sure that the narrow flexible hose from the collar to the tank is exactly level, or it will never fill, or cause the tank to overflow.

2) Drop all 3 hoppers straight down. Left hand via a 90 bend, middle via a 90 T, into the right hand with a left facing 90, so it looks like a W with a tail on the right hand drop.

We would then put a standard collar around the left hand drop, and feed the tank as normal.

|_| |_| |_| | | | | | | | | | | | | | | | | | | |____|________| | | | | | | |_| | Drain

The downside I see with this is that there is then no drop at all on the lower horizontal pipe, which I just *know* will come back and bite me if leaves etc get stuck.

I can't see any way (other than raising the tank on a 4 foot tall pedestal), of using standard downpipe parts to put a decent drop on the pipe *and* get the left pipe to the right pipe above ground, *and* use a standard collar into the tank.

Does anyone have any ideas? Is it OK to have ~3m of horizontal downpipe without a drop? Am I just worrying?

Could I even do something like a "K"? Keep the current arrangement of the left and middle hoppers merging (so that I have maximum water capture), then going off on another 22degree drop to the right pipe and the drain, then putting a stop-end on the left hand down-pipe, and attaching a smaller bore pipe, (or using an off-the-shelf adapter, if you can get a 68mm to 12mm?) and then using a ball-c*ck valve in the tank. This way you would always have a head of water above the tank, but because of the valve, it at least wouldn't overflow.

My problem with this one is that in winter, if it froze from the top down, it could crack the downpipe/valve

Thanks.

Pete.

Reply to
Pissgums
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How about taking all (or at least some) of your rainwater into the water butt and then simply taking an overflow (full size rainwater pipe) to the drain. All water will then flow into the butt, but any excess will flow straight back out without any valves, diverters, etc.

SteveW

Reply to
Steve Walker

I've got a simple downpipe from one side of the roof, which passes by the water butt and has one of the short horizontal tubes to catch water flowing down the inside surface of the downpipe, until the water butt is full.

There are a couple of niggly issues with it.

  1. In a real downpour, the adaptor in the downpipe adds too much resistance and water spews out of the downpipe where it shouldn't, and runs all down the wall and all over the outside mains socket (although it's not got inside it yet, and it's on a 10mA RCD which should quickly notice if it does).
  2. I don't use the water in the butt very fast. It can stay there a long time.

If I was doing this again, I would consider routing all the rainwater into the butt, and have the butt overflow into the soakaway/drain. That would change the water more frequently, although it's never gone stagnent, even through long hot periods. It would also remove the effective flow restriction from the downpipe. However, it would result in much more water passing through the butt, which would become more of a settling filter, and build up sediment much more quickly. At the moment, mine has very little sediment in the bottom even after what must be 7 years since I cleaned it out (which wasn't necessary even then, but as the tap broke and it had to be emptied anyway...) The inlet does have a filter though, which wouldn't be so practical if all the water went through it. I have got a mental design for a better inlet/filter combination, but it's so far down the todo list, that it's never going to get done.

Reply to
Andrew Gabriel

That's what I do. The down pipe is diverted so that all rain goes into the butt

- through a fairly fine mesh filter - and then I have replaced the tap by a piece of largish hose, into the end of which, I have inserted a piece of plumbing with a U bend on the end. This simple hooks into the top of the remaining piece of downpipe, cut off at such a height, as to maintain the correct level in the water butt. As you say, it means the water is changed and it also does away with the fiddly tap, because you simply unhook the end of the hose and place it into the watering can. Of course the butt has to be raised, if you want to get to the last drop. If the hose/hook is not of large enough diameter, you will still get the flooding problem, but in my particular situation, it's not an issue. And lastly, I have paralleled up two butts to double capacity and would really like a third.

Reply to
Andy Cap

The important level is between the intercepter collar and the hole in butt side. Water flowing into the connecting pipe will fill that pipe until the level in it is the same as the collar, if it can't fill the pipe until the butt is full then the butt will be filled. The interconect can drop down, what it can't do is go above the level of the collar. Our collar and butt is joined by a bit of ordinary hose that drops a couple of feet and rises back up, works fine. Until the bottom of the U fills with crud, which takes at least a year or three here and is easy to clear anyway.

Why the three hoppers? Seems very odd on a single wall from a single roof. If the three hoppers can't be reduced to one I think I'd go for:

The "horizontal" sections having just a slight fall on them.

Reply to
Dave Liquorice

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