Downpipe in cavity?

Hi all,

Is it alright if the builder is installing downpipes into cavity? Especially with zero boundary garage walls nowadays, I am guessing there isn't much of a choice? Also, if there needs to be downpipes on the front facade, then surely it will look better if they are in the cavity wall?

However, how would you find out if something is wrong with the downpipe further down the track? By the time you do find out something is wrong, the damage that it has caused is probably pretty extensive? What are the problems that could occur?

Cheers!

I do not think installing a downpipe in a cavity is a good idea at all.
As you mentioned, what happens when it clogs?
What happens when you get a large downpour and your downpipes can't cope and overflow?

I would not ever put a downpipe into a cavity.
Zero lot houses generally don't have a downpipe where the boundry is, they put it somewhere else.

Can you always avoid it though? I am not sure if you can always put it somewhere else. For example, if the length of the boundary wall is 9 meters, I don't see how they would avoid it. Do they slope the roof to one end and have 3-4 downpipes on a wall that side?

It's not the length of the wall, it's how much roof drains to it that determines the amount of downpipes required.

A zero lot wall with a large roof area draining too it should have a box gutter that runs to rainheads at either end.

With regard to running downpipes in a cavity:

Our portico is made from recycled bricks. I didn't want a downpipe for the small roof to be visible so I ran a rectangular pvc downpipe inside the pier. I wouldn't conceal metal downpipes in a wall because eventually they will rust out and then they are impossible to replace. Its discrete and works a treat.

Many commercial buildings have internal downpipes so it's not a big deal. The water doesn't escape the downpipe when its PVC and glued up, it overflows at the gutter, which can be a problem when you have an internal gutter as with zero lot walls.

Downpipe in cavity should be avoided whenever possible however if you must have it then make sure it is sewer grade UPVC so it won't corrode and can be sealed tight. Then make sure you have gutter overflows and screw cap inspection openings + access hatch in wall so in case you can get to the blockage.
Good luck

When it clogs, you clean it just as you would any other downpipe???
When there is an unmanageable downpour it behaves just like any other overflowing gutter, into the eaves or cavity.
Downpipes are sealed to gutters and have nothing to do with the results of overflow issues so I'm not sure what your point was here????

multi story buildings run plumbing (faecal matter and urine!!!) through cavities and we don't have concerns, how should this be any different

I wont sit here and be an armchair expert but I'm pretty sure where the downpipes are routed should be the least of your worries.
Worry more about the amount of drainage in total, that is where problems arise.

The downpipe is currently exposed at the front of the garage on the left as per the plans below. There are already a couple of other cavity downpipes at the front facade and side of the garage. I am looking at making the downpipe at the front of the garage a cavity downpipe.

You have a square line gutter along that garage wall and as noted on the plans they are putting in a rainhead at both ends as I suggested earlier on. You can't hide the rain head so there's no point trying to hide the down pipe.
just use round downpipes instead of rectangular and they look much better.

I didn't realize that the rainhead can't be hidden. Is there really no way to hide that whole piece?

The idea of a rain head is to operate partly as the overflow should there be a blockage in your downpipe. You could have a downpipe behind your front garage wall but I would insist on an overflow slit below the top of the box gutter coming out through the front wall to act as the overflow instead.

Stewie

There is no cavity to hide the down pipe in. It's a garage pier that is structural. It's holding the lintel and formed concrete beam for the upper floor.
Just about every double story house in WA has the identical set up.
My house is exactly the same. Get a nice rain head and use round downpipes and they look fine.

Chippy, you don't hide it in the cavity seeing as it looks like a 230mm brick wall anyway. I get that. You merely hide it behind the front wall of the garage.
We may differ in opinions but like the OP I think downpipes and rainheads look like crap. I'd hide as many of them as possible on any house by a bit of good pre-emptive design. Like vertical drainage stacks from upstairs bathrooms.

Stewie

I understand that, but I don't think the op does.
You'll notice that the portico has a pvc downpipe inside the pier and that's what the op was obviously trying to do with the garage down pipe.
That section of the garage will also have downpipes from the second story feeding on to it. Personally I'd be doing the roof differently to the way it's drawn, but that's the cheapest way to do it and rainheads are the only option with the way it designed to be constructed.

And to add to the difficulty of running the downpipes internally would be the need to core drill the second story slab.
It's just doesn't happen here in WA. It's drawn that way for a reason.
Maybe over east you have more options to run downpipes internally but with double brick and suspended slabs it's a different kettle of fish.

I guess if has already been built then to retrofit an internal downpipe as I say would be a lot harder than if it was still at the design stage. Core drilling the existing slabs etc as you say would be a pain. The few double brick homes with concrete slabs I've worked on before have had a couple of internal stacks one for sewer and the other two for downpipes and if they are designed right at the start they can be hidden. It depends how much of an issue the owner has with downpipes at the front of a house and how keen the builder or his designer are to accomodate them I guess.

Stewie

Hi stewie.
Absolutely agree with the plumbing stacks. I think the days of running plumbing down the outside of buildings is long gone. It looks so ugly.

The house has not been built yet. We are at pre-start stage. Currently the drawing shows no cavity but can't the cavity be created just like how they did it to the garage wall on the left where a cavity downpipe is there as well?

Why do you have to drill the second story slab when there isn't a slab directly above it? The builder did notify me that the variation item is done but I have yet to get the details and the price of the variation. I will post it once I get it.

I am currently finalizing my pre-start and will post what the builder proposes.

There is a slab above it. The second story slab runs right over to the zero lot garage wall as noted on the ground floor plan.
If the house is only at pre start then it is achievable but they will have to make provision for it by having a penetration through the slab and a small stack in the front corner or running the cavity wall all the way through to the front of the garage.
I would be interested in what they are going to charge you to do this.