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Plumbing Part 2; Waste Pipes

Technically speaking, this should probably be part 1 - we started this some time before we did the mains plumbing, but it was somewhat more complex to plan out, so took much longer than anticipated. The waste pipes initially ran above the floor level in the bathroom and were simply boxed in.. But as we're having a freestanding bath and a new shower, they needed to run underneath the floor. Unfortunately, it's not just as simple as moving the pipes under the floor, as by doing so they would lose their downward gradient meaning they would not be able to drain. To fix this, we would have to move the pipes point of entry into the soil stack too. In addition to this, due to a downstairs extension, all the waste pipes run through the attic space of this extension, which meant access was not easy! So there was quite a bit to think about and a few problems to solve.

This was where the pipes initially left the room on their journey to the soil stack. Quite a bit higher than the floorboards..

On the other side of this wall, is the attic space above our kitchen. We had to pop out a hole in the ceiling to investigate this further...

Turns out we share the attic space with our neighbour, which answered my on-going question of "why can we only ever hear the neighbours in the kitchen?" - Not that I'm complaining about this - it just puzzled me somewhat! Apparently they also have no insulation above their ceiling either, hence the noise-travel. Anyway, pointless bit of info for you there... But here you can see the pipes on their journey to the soil stack.

After some investigations, it turns out that the pipes separately entered the large toilet waste pipe  further down in the attic space before leaving as one pipe through the end wall into the downward soil stack. I did some research and it seems this is OK to do (although apparently not recommended) but it does come with several conditions. Although it did seem dubious to me. As the toilet waste had a much steeper gradient than the existing bath and basin pipes, we realised we may be able to do the same again, but connect our new pipes further down. Or otherwise, our only other option was to connect the new pipes onto the downward soil stack on the outside of the end wall.

Firstly, we had to remove the existing pipes and create new holes under the floor for the new pipes. Unfortunately we couldn't do this was the ease of a diamond-core drill bit, as our drill isn't quite pro enough. SDS drills are required for these; particularly one with a safety clutch that will stop the drill from spinning and breaking your wrist if it hits a snag or something it cannot drill through. We didn't want to risk breaking an arm or even worse, particularly when working on a ladder. Instead we used a normal masonry drill-bit and drilled a bazillion small holes around a single brick to remove it.

We laid the new waste pipes in the bathroom and made sure we had a good downward gradient up to the hole where the pipes leave the bathroom into the attic space. We chose to use solvent weld pipe and fittings where possible, as these are the most reliable and durable. We added a new 40mm waste  pipe for the shower which we also connected the 32mm basin waste to, with the use of a non-return valve between the two to stop backward flow of water. We then used a separate 40mm waste pipe for the bath. Laying the pipes out was fairly easy, getting the gradient perfect was slightly more tedious. I think it's meant to be around a 2cm fall for every metre or something, although don't quote me on that! We then used some solvent cement, which kind-of melts the pipes together.

We then decided to see whether we could re-connect the new pipes to the toilet waste further down the pipe. Most of this work looked something like this...

Needles to say, I didn't see too much of this part of the job. But apparently we were OK to go ahead and re-connect the new pipes onto the toilet waste a little further down.

Our theory on re-connecting the pipes to the toilet waste was basically a matter of "it worked before, so why not?" - It would be highly unlikely of back flow so far down the pipe, and the traps should seal against smell. But in all honestly our real excuse was that this was much easier than drilling through to the outside, partly because we don't have the correct drill (and didn't want to remove more whole bricks!) but it also required less pipe, somewhat less mess, and we didn't have to take down as much of our kitchen ceiling! (Always a bonus!) Besides we figured we can always connect the pipes directly onto the soil stack at a later date, preferably when finances allow us a better drill. But so far, it all seems OK, everything drains well and I think I can tick this off as another job done! Hurray!


(rounded to the nearest pound)

New tools purchased:

Materials used:
Pipes x5 £21
Pipe fittings (tee's, angles, caps) £12
Flexible pipe fittings £10
Non-return valve £11
Solvent Cement £5
Bath and basin traps £6

Total: £65

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