Water butt on a garage roof

Errr is grey water into surface drainage allowed?

Full water butt is a lot of weight. I would not do it.

I wouldn't!

And the waste pipes don't seem to be very far above the height of the roof. Just get some more piping and send it where you need it?

Can you get a big flat watertray to spread the load?
And check the beam sizes!!!

Errr is grey water into surface drainage allowed

Probably combined sewer, re the water butt sounds a bit risky I'd be beefing up support underneath and limiting it to a small ish volume

Every bit of drainage on that photo looks like a bodge job. Two sinks (the white pipes?) And a bath (the crooked black pipe?) should not discharge in to the surface water drainage.

However, if you are happy that your dirty bathwater is eventually going in to a river or watercourse somewhere downstream from your house then why not just have your new water butt collect this dirty water for use on your own garden?

However, if you are happy that your dirty bathwater is eventually going in to a river or watercourse somewhere downstream from your house then why not just have your new water butt collect this dirty water for use on your own garden?

It'll be combined sewerage so rather all the surface water is going into the sewerage system. We have the same setup, it's a pain to try and get anything to look tidy as connectors for waste pipes and downpipes don't seem easily available (presumably to stop people putting their waste water into surface water but not helpful when you have combined sewerage)

Disregarding the load issue, if you did it, I'd consider one of those cold water tanks designed to go in the eaves of the loft, as long as it's UV stable.
It's be lower profile, less visible, and a proper outlet to bring down to an outside tap. (And it would have a bigger footprint to spread the load)

It’ll be combined sewerage so rather all the surface water is going into the sewerage system

It may well be, but I thought that with the photo showing most likely a bathroom (3 pipes emerging from the same corner) and none of them being the soil pipe from the toilet (which is probably in a riser somewhere internal the house), then the house should be connected to the waste water system, as well as the surface water system. Therefore the pipes shown in the photo should be able to be connected to the waste water rather than the surface water.

I'm just making assumptions from a single photo so am probably wrong.
Anyway, I wouldn't load the roof. Just run a new pipe to wherever you need it.

Having surface water enter waste water systems is one of the major contributors to pollution in our watercourses, as when it rains heavily, the treatment systems are overwhelmed and it discharges to our rivers and sea. Southern Water have recently been fined for this. Linky

RE Drains and contamination it is the classic rules and common practice change over time.

Ask a planner about the correct way to make almost any modification to an old house and it starts with "Well, I wouldn't start with what you have now...."

The foundations for our single storey kitchen extension are well over a metre deeper than the foundations for the main two storey house. Almost needed to underpin the main house during the build because of the building inspectors insistence on following the proper modern regulations.

I water everything that we don't eat with our shower water.
The water pipe goes straight into a butt and I water daily.
Guilt free mid summer watering.

If you don't have space / don't want to see it, can you Bury it and have some sort of pump rather than put it on a roof.

In winter when it freezes and you get a lot of snow on a roof that's a lot of weight. Not sure your insurance company would pay out should something go wrong.

If the concern is grey water running into the butt, what's preventing you from installing a diverter in the downpipe above that level and routing from there to a water butt on the ground? Rather more pipework than you'd have with the diverter installed next to the butt, but functionally I can't see why not?

Some sort of re-enforcement under the roof where the water butt is going, something to take the weight through the slab direct to the floor?

Good to get some opinions on the weight, thanks. If I could spread the weight more evenly, with a larger footprint tank (and not necessarily a purpose made "water butt"), I'd feel better, good idea.

I suppose I should have expected unsolicited critique of my plumbing system, because STW. Yes, it's combined sewerage. Pretty common. Soil pipe is adjacent, just out of shot, but they meet in the sewer just in front of that door. Yes it's a mess, but it was like that when we bought the house, and since it works, I'm not about to go to the trouble of replacing the entire waste water and rainwater system so it looks nice. If it offends anyone's sensibilities that much, feel free to pop round and do it 😉

Oh, re. diverting from above the waste into a water butt on the ground, a) there's not really a great site for a water butt nearby, and more importantly, b) the diverter needs to be at the same level as the top of the water butt to stop it overflowing no? Or have I misunderstood?

Some sort of re-enforcement under the roof where the water butt is going, something to take the weight through the slab direct to the floor?

Would ideally be above the door, so that's tricky, and the garage is my workshop so using floorspace to support the ceiling is a no-go. But I like your thinking. If I could get a long, low, slim (modern geometry 😆) tank to sit along the top of the rear garage wall (i.e. from the left to the middle of the photo) that might work - most of the weight would be directly on the wall.

Soil pipe is adjacent, just out of shot,

In which case if you fill the butt from the bottom of rain/sink waste you're just getting dirty water not turds. Do as zippykona says.

b) the diverter needs to be at the same level as the top of the water butt to stop it overflowing no?

Ah, I see! I've not used a diverter myself, but I can see that if you want the butt to overflow back into the downpipe then that would be an issue. On mine I have a separate overflow which takes excess water down the garden and exits under the apple tree, but your topography might not allow similar.

As an aside (and adding to the criticism of the pipework 😉 ) wwould I be right in thinking that the narrow white pipe above the garage is a condensate drain from the boiler? If so, I'd prioritise lagging that before next winter. My MiL had no end of trouble with hers getting blocked with ice, and that was much less exposed, much shorter and much less horizontal!

If I could get a long, low, slim (modern geometry 😆) tank to sit along the top of the rear garage wall (i.e. from the left to the middle of the photo) that might work – most of the weight would be directly on the wall.

How about a tall, thin, cylindrical tank resting on the ground against the wall of the house. In effect, a larger diameter pipe. Fit a tap at the bottom.

While I like the idea of using grey water for watering, I'm not sure I really want to be storing a load of it, unfiltered in a big container in the sun. Sounds like a recipe for the next novel coronavirus!

Thinking about the diverter issue, I guess you can always add a separate overflow to take excess back to the drain, or wherever.

@PhilO I'll let that one slide as it sounds like a good idea, thanks 😉 It is indeed the condensate from the boiler, certainly no harm in lagging it.

@scotroutes Like a slimline water butt you mean? 😉

Like a slimline water butt you mean?

I think he meant something taller than that. From ground to as high as possible, at least as high as the top of the butt you were thinking of putting on the roof.

If I were putting a butt at shed roof level, I'd make a hanging bracket directly off the wall, not load the roof at all.

Rather than one big water butt, why not use several smaller ones joined by pipes?
Lower profile will look better. Arrange them to suit roof structure and aesthetics

I think he meant something taller than that. From ground to as high as possible, at least as high as the top of the butt you were thinking of putting on the roof.

If I were putting a butt at shed roof level, I’d make a hanging bracket directly off the wall, not load the roof at all.

Yeah, I was being a bit facetious, sorry. I think a tank slimmer and taller than a slimline 100l water butt would be quite tricky to find though.

Putting the load on top of the wall, straight down, would be ideal, but the idea of 200kg+ hanging off a few fixings makes me just as nervous as putting it on the roof.

Rather than one big water butt, why not use several smaller ones joined by pipes?
Lower profile will look better. Arrange them to suit roof structure and aesthetics

Yeah, after someone mentioned using loft storage tanks, I did wonder about using a few smaller, lower tanks, connected together to spread the load. Placed back from the edge a bit, you wouldn't even see them from outside.

I think a tank slimmer and taller than a slimline 100l water butt would be quite tricky to find though

I was thinking of a length of 300mm plastic pipe, but I've looked at the price of it - you're right, forget it!

I did wonder about using a few smaller, lower tanks, connected together to spread the load. Placed back from the edge a bit, you wouldn’t even see them from outside.

Placing them back from the edge will increase the bending moment in the roof - but (as a structural engineer) I would not put any tanks at all on the roof. It's probably got just enough steel reinforcing in the concrete to carry it's own weight and a bit of snow, or one person doing maintenance.

Southern Water have recently been fined for this

No they haven't.

Combined sewer overflows are a completely legitimate* legacy method of discharging flows that exceed the flows of a waste water treatment plant.

What they have been fined for is doing it on bloody purpose and if memory serves also some non compliance with improvements.

Your talk of surface and waste as seperate concepts is all well and good when there are seperate foul and surface sewerage systems in place which in anythign over about 40 years old is really unlikely to have anythign but a combined sewer to connect to. And that could have been put in by Balzagette 150 years ago

Anyway your chat is out also out of date. Roofs should be draining to SUDs systems to keep the water onsite and dispersed intot he ground water as would occur with the majority of rain on a greenfield site..

I’m not sure I really want to be storing a load of it, unfiltered in a big container in the sun

Australian guidance is 24hours max storage if I recall, but there is plenty options to run it to the ground through perforated pipes etc and save the rainwater for special occasions. It's much better for you garden as you'll be watering it regardless of weather unless you're a dirty minger. If you don't mind the concept you absolutely should do it. I can dig up some research if you are keen.

*I'm not saying its nice, its strictly concented and should only happen during exceedence events where its at its most dilute... this is one of the things southern water struggles to grasp.

I'm not trying to disagree with its rankness but you're calling someone out on a system that was put in place years ago and they have no control over.

Just use a tap?

Whats the payback period on your water butt?

With my shower water butt I empty it everyday. 3 showers and it overflows anyway.
It also collects rainwater. After last night's downpour I just disconnected the butt from the drain pipe.
Probably a third of our shower water is clean as it just goes down the plug waiting for the shower to get to temperature.

Just use a tap?

Whats the payback period on your water butt?

This is the kind of attitude which has got us into the mess this country is in...

Its not just a financial decision - its about using resources appropriately. Why do we need to use treated water to water the garden? What an utter waste.

But, as you were, because "I'm alright Jack"