- Joined
- 6 Jan 2019
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A few questions about laying underground foul drainage pipes underneath a concrete slab of the building. These are the orange coloured plastic push fit types that will carry toilet waste.
1. There is a rule with push fit that says that the male spigot should always be on the upstream side of each joint, i.e. pointing downstream. However, several fittings are only available with sockets on both ends so clearly this can't always be followed. Not to mention the pipes themselves aren't socketed on either end. Am I meant to ignore this rule when not convenient?
2. I have seen some places say that you should pull each joint out by 10 mm or so to leave space for expansion, others advise always ramming the joints home as far as they will go. Which is correct?
3. Where the pipe bends upwards for a ground floor WC, do I need to make sure that the 90 degree bend is completely underneath the slab, so that the penetration through the slab is a clean vertical shaft? Or is it OK if the upper part of the bend is encased in concrete?
4. I am thinking of laying a small concrete pad beneath these bends (like a rest bend for a soil stack), and maybe underneath some of the other fittings, to prevent the pipes settling and to ensure that the gradients are maintained. The pipes would still be surrounded mainly by gravel. Any reasons why the pads would be a bad idea?
5. The building regulations have a requirement for oversized holes where there is an underground wall penetration, to accommodate movement. It says that the pipe should have 50 mm clearance all around which means that I would need a 200 mm core for the 100 mm pipe. In an existing building which shouldn't have much movement, is this really necessary (I mean from a technical standpoint rather than box ticking)? I was thinking about using a 150 mm core drill I already own but this is mainly for ease of installation and I wouldn't be trying to ensure that the pipe was dead centre in the hole. Also the BR talk about "compressable sealant to prevent ingress of gas" for the void between the pipe and the cored wall, can someone explain what that is about (sewer gas in case the pipe cracks)?
1. There is a rule with push fit that says that the male spigot should always be on the upstream side of each joint, i.e. pointing downstream. However, several fittings are only available with sockets on both ends so clearly this can't always be followed. Not to mention the pipes themselves aren't socketed on either end. Am I meant to ignore this rule when not convenient?
2. I have seen some places say that you should pull each joint out by 10 mm or so to leave space for expansion, others advise always ramming the joints home as far as they will go. Which is correct?
3. Where the pipe bends upwards for a ground floor WC, do I need to make sure that the 90 degree bend is completely underneath the slab, so that the penetration through the slab is a clean vertical shaft? Or is it OK if the upper part of the bend is encased in concrete?
4. I am thinking of laying a small concrete pad beneath these bends (like a rest bend for a soil stack), and maybe underneath some of the other fittings, to prevent the pipes settling and to ensure that the gradients are maintained. The pipes would still be surrounded mainly by gravel. Any reasons why the pads would be a bad idea?
5. The building regulations have a requirement for oversized holes where there is an underground wall penetration, to accommodate movement. It says that the pipe should have 50 mm clearance all around which means that I would need a 200 mm core for the 100 mm pipe. In an existing building which shouldn't have much movement, is this really necessary (I mean from a technical standpoint rather than box ticking)? I was thinking about using a 150 mm core drill I already own but this is mainly for ease of installation and I wouldn't be trying to ensure that the pipe was dead centre in the hole. Also the BR talk about "compressable sealant to prevent ingress of gas" for the void between the pipe and the cored wall, can someone explain what that is about (sewer gas in case the pipe cracks)?
