# Forum Home Renovation Plumbing  Downpipes - should they be sealed at the joint?

## Artline

Should downpipes be completely sealed at the join or do you have to allow some air gap so an air lock doesn't form when it rains?

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## plum

That is fine, no problem.

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## Artline

That's what I thought but because some subsidence has occurred, it was one of the suggestions to go around and seal up all these joins. The builder looking after the job said they shouldn't be sealed because if they got an air-lock, they would fill up and cause a different problem. I'm not sure if any water overflows out of the join during a really heavy downpour - I don't live there so I've never been able to check.

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## cyclic

> That's what I thought but because some subsidence has occurred, it was one of the suggestions to go around and seal up all these joins. The builder looking after the job said they shouldn't be sealed because if they got an air-lock, they would fill up and cause a different problem. I'm not sure if any water overflows out of the join during a really heavy downpour - I don't live there so I've never been able to check.

  LOL< ask the Builder how you get an airlock in a stormwater drain, I would love to hear the explanation.

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## plum

> LOL< ask the Builder how you get an airlock in a stormwater drain, I would love to hear the explanation.

  Maybe we'll have to start venting stormies.

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## Artline

The following thread seems to be saying you shouldn't seal the join when above ground as the join needs to "breathe".  http://www.renovateforum.com/f194/re...sition-116101/ 
Just to clarify, what does the Building Code say eg (a) seal (b) do not seal (c) either is acceptable.

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## cyclic

> The following thread seems to be saying you shouldn't seal the join when above ground as the join needs to "breathe".  http://www.renovateforum.com/f194/re...sition-116101/ 
> Just to clarify, what does the Building Code say eg (a) seal (b) do not seal (c) either is acceptable.

  No idea what the Code states, but I can tell you there would be no point sealing the joint because the metal downpipe has a seam on the back which, unless sealed during manufacture, which they are not, would leak if there was sufficient  pressure to make the unsealed joint leak, besides, if it is raining then there is water on the ground anyway.

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## Artline

The only reason I raised this is because I want to avoid anything that contributes to subsidence, if at all possible.
Situation: brick veneer house, slab built on fill, wall cracks appeared after 15 years. Structural engineer diagnosed subsidence from flow of in ground water from the whole site terminating under the slab. Structural engineer also said that drainpipes not being properly sealed and therefore water running to ground and seeping under the slab structure was adding to the problem. Main recommendation was to seal up existing drain pipes to ensure all water from the structure is diverted away from the ground slab. 2nd recommendation was to install expansion joints every 6 m (none installed originally).
Builder refused. 
Another reputable building company that quoted but didn't get the job had no problem submitting a plumbing quote to seal all the downpipes. Unfortunately, I didn't query them at the time as I was focusing on the more worrying installation of expansion joints which did go well as it turns out but won't really solve the problem.
Next step: walk the site with a plumber and then get back to structural engineer and then builder.

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## plum

Repeat, they do not have to be sealed. Structural engineer should be looking elsewhere. If it was a site cut, possibly aggy pipes are required.

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## Artline

I tend to agree with you. 
I put the builder's refusal to the structural engineer and he demurred - was not as adament - maybe could seal half the join - said main guiding principal was to make sure no surface water was heading towards the wall and then seeping down to the foundations.

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## r3nov8or

Have you ever seen overflows from there?  
Regardless... 
The 'air gap' excuse is rubbish. Charged systems (fully sealed house-wide to enable collection in tanks) are very common and present no 'air gap' issues

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## Artline

I haven't been able to check if these types of joins (rectangular to round) overflow during downpours as I do not live on site and I'm too far away to go and check when it's raining. So that doesn't help. If they don't overflow, then there is no issue. Out of interest, I've started to look at how downpipes join to the ground level stormwater drains starting with my house which are round downpipes to round stormwater pipes. I can't tell if they are glued but in any event they would be preferable for this sort of issue as they fit very tightly into each other and even if they are not glued to an air-tight seal, it's hard to imagine any water being able to flow out of such a join as there would be so much resistance along the pipe against pipe walls for water to overcome. With these rectangular downpipes, there is often plenty of play as they just sit on the rectangular part of the adaptor - probably a bit of distortion with time as well.

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## r3nov8or

Yes, and as cyclic mentioned, the rectangle metal downpipes are not watertight along their length, due to the join at the back. Have a look at one at Bunnings, it will have a punched join and an arrow printed suggesting the direction of flow, but they won't hold water like pvc.

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## joynz

I think they would only overflow if the drains they feed into were blocked. 
Perhaps you could put a hose into the gutter to mimic rain when you are next at the property (but don't have the flow rate too high). 
Did the engineer have any other suggestions for remediation?  Sometimes experts toss around a lot of suggestions without always distinguishing between  the 'possibles' and the 'probables'.

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## Craigoss

The only time i've seen water flow out of that joint, is when the stormwater pipe is blocked. Sometimes in heavy down pours you get some water running out of the top elbow of the downpipe, but it wouldn't be enough to cause footing issues. Is the property in a mine subsidence pot hole area? Is there any surface drainage? Are you getting runoff from a neighboring property?

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## METRIX

If you seal them, and you get debris in there which blocks the downpipes, it will be difficult to get the downpipes off to clear the blockage. 
As the other guys have said, the folded pipes are not watertight, if you want watertight you could replace the metal down pipes with rectangular PVC, but I would still not glue that last fitting on for the same reason. 
If your house is having subsiding problems because they think water is getting out of the down pipe connection, I would say they need to look elsewhere, such as the amount of down pipes you have are inadequate for the given roof area. your eaves are too small and not protecting the perimeter of the house adequately. 
I would be concentrating on installing some subsoil drainage around the perimeter of the house to get rid of any excess water, has anyone given you an explanation about what exactly is causing the problem, have you had a hydrologist look at it, they will tell you exactly what is causing the problem. 
Sounds like the grand designs episode of a house in clovelly Sydney, after they knocked the old house down, and started building, there was masses of water flowing into the site, they set up pumps, dug trenches, filled with this and that, the pumps were running 24/7 and failed, they had various people look at the problem, they had special maps showing natural springs which could be causing the problem, and they would have to take drastic action to alleviate it. 
In the end they had to go through council and dig up the road to redirect the flow into the main storm water, at a cost of $50,000, problem gone, but nobody actually tested the water, if they did they would have discovered it was chlorinated water, and the problem was a broken water mains further up the street, and the water was actually running down the gutter, all the so called experts, the builder, engineer were looking for some other drastic problem. 
The whole thing was silly, as the old house on the block had been there for 80 years, if there was such a major natural spring problem under the block, the old house would have washed away within 12 months.

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## plum

Nothing to do with inadequate downpipes if they are not overflowing.

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## METRIX

> Nothing to do with inadequate downpipes if they are not overflowing.

  Either way, the builder and Engineer are not experts in this field, they can throw suggestions all day on what may be causing the problem, and still not fix the problem, which end's up costing you a fortune with no resolve. 
You need a Hydrologist to investigate and tell you where the water is coming from (if it's not obvious), and what needs to be done to fix it (this is their profession). 
Until you know where the water is coming from you won't be able to fix the problem, trust me I have seen this a few times before, builders stuffed around with half arsed attempts to divert the water with no solve, hydrologist came in, found the problem gave the solution, builder implemented the solution, problem solved.

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## Marc

If the stormwater pipe is blocked or not connected to the main stormwater, and water rises, you want the water to find a way out at ground level and not up your roof surely!
Seal stormwater pipes! What will they think of next? Silicone roof tiles together?

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## woodchip

As everyone else has said....the metal downpipe to DP adaptor does not need sealing, as long as its inside at least 10mm 'she'll be right' . The tradie gave you a price to seal this?? work is work I guess & the customer(or in this case, the structural engineer) is always right, eh!
I'd say one of the stormwater pipes has become disconnected, from memory in 'ye olde days' it wasn't a requirement to glue the PVC stormwater joints.
Put a hose down the DP adaptor & walk out onto the street or wherever to see if its working, if ALL of the water isn't coming through then get a plumber with a camera down the stormwater from the DP adaptor to find ya problem.

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## wonderplumb

There's no need to seal it   
Sent from my iPhone using Tapatalk

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