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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

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    • CommentAuthorRobL
    • CommentTimeMay 1st 2021
    *unless the drain has a water seal*
    Is the point that it's ok if there is a water trap, so propane can't propagate into the sewer?

    So I've spent some time understanding where our drains go, and hope for the wisdom of the internet:

    The pic below shows that our main sewer passes from right to left. The gully in question marked "A" in orange drains into manhole "B" from a hose pipe test, and flows down the pipe entrance marked "main sewer line".
    We have no other manholes at the back of the house. I can't smell any drain smell from "A". There is what might be a rodding point near it. Looking down "A" I can just see a clean plastic pipe bend as indicated by the orange arrow, but I can't see any water.

    So, how does A get to B?
    How can I tell if have a water trap?

    I think A and maybe the rodding point were fitted 20 years ago by a builder we hired to do quite a bit of renovation work on the house (mostly painting, plastering, removing carpets & sanding parquet floors, but also fitting a new sink near A) - but we have no idea or records of what they did. In our defence, we had a 1 month old child, new house, and I just changed job. Shortly before that I remember feeling a bit bored!
    • CommentTimeMay 1st 2021
    Posted By: RobLIs the point that it's ok if there is a water trap, so propane can't propagate into the sewer?

    Yes, I think that's the point.

    I can't smell any drain smell from "A". There is what might be a rodding point near it.

    Can you smell a drain smell anywhere else? What does the rodding point look like? Ours are just small square plastic covers over a smallish pipe. Where does the rodding pipe go? There should be a manhole above any bend or junction, but maybe there isn't? Can you put an endoscopic camera down gully A to see where it goes?

    AFAIK, water traps are pretty unusual. Normally drains are designed just to allow a clear flow of whatever is tipped into them, you don't want what are essentially 'buckets' where crap can collect!
    If it drains into a sewer, it will have a water trap, or else you will smell sewer smells and there will be beasties.

    If you suspect it doesn't have a trap, it would be easy to add one before you fit the ASHP.
    • CommentTimeMay 1st 2021
    Posted By: WillInAberdeenIf it drains into a sewer, it will have a water trap, or else you will smell sewer smells and there will be beasties.

    There are water traps in WCs and the U-bends on sinks etc and yes if they dry out you experience sewer smells. But there aren't water traps in the drains themselves, usually, AFAIK. There are none on our current property and there were none on our previous property.
    WCs don't drain through drain gullies. Google up a picture of a drain gully, if you are unsure - it has a grid on top for water to drain into it, catching leaves etc, and a water trap underground.

    If your house is not very old, your surface gullies should not drain into a foul sewer, there should be separate rainwater and foul drain systems, and the gully smell problem doesn't arrise.

    However RobL thinks that his gully does go into a combined sewer (as do many incl mine), so it needs some kind of trap to keep the smells and wildlife where they belong, and also any stray propane. Not a big job to add one.

    Gullies can be P type traps which need separate rodding eyes, or bottle type which don't.
    • CommentAuthorRobL
    • CommentTimeMay 2nd 2021
    We have separate storm drains and foul drains - the front and rear house gutters, and garage gutter, all drain into a storm drain manhole at the front of the house which is not on my drawing above. I've checked all of them with a hose pipe, and they all seem thankfully correct. All the foul drains are at the back of the house, and all go to the main sewer line - although there are only 2 houses above us in the run, so I guess it's not that main.

    I took a pic of the possible rodding point. I also tried to undo it, with the help of a neighbour who'd been here longer - he didn't know what it was either. Unfortunately, all we succeeded in doing was snapping off the head of one of the screws, and I thought best to leave it in place than knacker it further.
    Gully A from my pic earlier has a washing machine and sink going to it, and definitely connects to the main sewer line, and yet there is no smell from it.

    I guess I need to find a camera that can be pushed in it somehow, to take a look.

    To answer an earlier question - yes, I'm thinking of diy ashp. Well, dithering between that and a small gshp, ideally in that location as that's currently where our gas boiler exhaust is so it keeps the install simple. I like the use of a propane refrigerant due to low CO2e gas, and higher temp capable for DHW.
    • CommentTimeMay 2nd 2021
    Sorry, yes, I forgot* the case of rainwater drain gullies. They do have traps of course.

    What I'm trying to say is that all the traps I'm aware of are at the edge of the network and are privately owned on private land. There aren't water traps in the public drain system as far as I know. Except perhaps incidentally where there is a step level change in the drain, but even those are normally dry I think.

    * We don't have any here; our rainwater drains into a ditch. We didn't have any at our previous house either; the rainwater downpipes went straight down into the ground and joined the drains there.
    rodding point covers tend to be oval not circular, as they should be mounted on a bit of pipe that goes down and sideways at 45deg.

    I would be tempted to drill the screws off and have a look inside, maybe it is a bottle trap.

    If you have access to some drain rods or some equivalent flexible pipe, stick them down the gully (if possible) and the rodding point (or whatever it is) and measure how far they go, to locate the junction with the sewer. Edit: and tip some water down the gully and the rodding point to see if they are connected
    • CommentAuthorRobL
    • CommentTimeJul 11th 2021
    So I've dug down a bit, and uncovered the drain pipe connected to our foul gully (A) in the pic a few comments back. This carries washing m/c waste water only, and definitely empties into a foul sewer. There no complexity to it, it's just a bend and a straight pipe. I don't know how it connects to the sewer itself, there's no manhole where it joins on. There's no smell from it, but maybe our 2m clean bit makes it mostly ok. That other round possible rodding point is probably connected to our rainwater 110mm pipes where they turn a bend.

    As I understand it, to have any sort of propane based heatpump near it, I should replace this open gully with a bottle trap. That would still allow rodding if needed, but prevent propane from getting into the sewer system if there was a leak.
    I'll get one of these, and make it fit: https://www.floplast.co.uk/product/bottle-gully-traps-1.
    While I'm at it I'll move it away from the wall by 100mm, fit a bit of XPS insulation in there for when I EWI the outhouse at the back of the garage.
    • CommentAuthorjms452
    • CommentTimeJul 11th 2021
    Posted By: RobLWhile I'm at it I'll move it away from the wall by 100mm, fit a bit of XPS insulation in there for when I EWI the outhouse at the back of the garage.

    Beautiful illustration of the importance of a master-plan in renovation!
    • CommentAuthordickster
    • CommentTimeJul 13th 2021

    We got the "local" silver standard Mitsubishi man to call in.

    It's a possibility, but looks like a new water tank and convert underfloor heating to air source could do the job in a better way, with a lot of "better" money.

    Apart from the cost, a slight problem in that the silver man has not come back to us with any real figures after 2 weeks.

    Must be a busy man. Maybe I'll try "platinum".
    • CommentAuthortony
    • CommentTimeJul 14th 2021
    No need to replace gulley it has a trap, drip into it
    • CommentAuthorRobL
    • CommentTimeJul 14th 2021
    I poured a glass of water in while watching, and I could see and hear it just drain straight away. Here's a pic of down the pipe down the gully, you can just see a bend at the bottom with no water in it. There's a small chance there's a trap buried underground elsewehere without access or rodding ability, but there definitely isn't one under the concrete gully in the pic above, I'm sure that is just a bend. Within 2m of the gully is the "main" sewer line. I could dig it all up I guess(gah).

    I remember the builders who did the work 21 years ago - they were shopfitters, one of them a plasterer, one a plumber, one electrician, between them just got on with removing carpets, repainting, etc. I doubt they knew the correct way to do sewer connections (that it should have had a trap), and it's never caused an issue to be fair.
    • CommentAuthorRobL
    • CommentTimeJul 18th 2021
    32C in the shade here now, just the weather for physical labour:shocked:
    I angle-ground off the old precast concrete gully, in one piece ready for re-use I’m proud to say. There’s just a bend underground on the original stuff, and it is whiffy now I’m working next to it. The pic shows all the orig stuff, and the replacement bits I got to fit instead. I think I’ll tackle the next bit when it’s cooler, no prizes for getting heatstroke!
    • CommentAuthortony
    • CommentTimeJul 18th 2021
    That was wrong in the first place!
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