MortarThePoint

Polypile UG425AST has an invert at 85 - 157 - 50 = -122mm relative to the bottom of the concrete surround, but the outlet can't rotate relative to the concrete. An alternative is to use UG425 in conjunction with UG427RAST which is an extension with concrete surround. That combination has a minimum invert at 32 - 157 - 50 = -175mm relative to the bottom of the concrete surround. Note that is the same as without using the concrete surround addition since in its lowest position it would sit on the rim of the bottle gully (UG425). The maximum invert would be about -(285-85) - (125 - 20) - 50 = -355mm. When used on a patio, UG425AST would likely need to have its concrete surround's bottom level with or lower than the underside of the patio paving to allow enough clearance between paving and outlet pipe (157 - (132/2) - 85 = 6mm to the OD of a ring seal and 157 - (110/2) - 85 = 17mm to the OD of a 110mm OD pipe). Interestingly, the combination of UG425 + UG427RAST is cheaper than UG425AST and certainly cheaper than that with a subsequent bend to get the correct outlet angle (though that bend could save a coupler). UG425.pdf UG425AST.pdf UG427RAST.pdf

Looking to use the Polypipe bottle gully with concrete antisplash surround (UG425AST). It's not cheap (~£50) but finishes things quite neatly. I had intended to use the concrete hopper (UG414AST) which has a square grate, but that has a 110mm vertical outlet that I would have sent into a rest bend but for levels. I just need to decide how far to position it from the wall. Pulled away from the wall slightly would make access easier but leave a gap between the wall which would need dressing. If water blasted out of the downpipe it could in theory overshoot the concrete surround if it is too far back, but that feels pretty unlikely. Positioned with concrete surround touching the wall, shoe dipping below the top of the concrete: Positioned with concrete surround 25mm from the wall, bottom of shoe level with top of concrete: Positioned with concrete surround 63mm from the wall so that shoe is just over the grate, bottom of shoe level with top of concrete:

If I needed to, I suppose I could use a section of 82mm (OD) drainage pipe where the invert is really shallow, but I'd rather not. 75mm (ID) pipe at 1:100 has a capacity of about 2.7L/s which would be enough for one downpipe (standard 63mm ID / 68mm OD downpipe has a capacity of 1.11 L/s according to Part H Table 2 page 40). It would buy me an extra 28mm of headroom, so shallowest top of pipe would 78mm rather than the 50mm with 110mm pipe. I guess it depends a bit on the make up of the patio whether that additional depth is needed. If it is, replacing the first 3m would be enough since it would drop 30mm (@ 1:100) in that distance.

Bottle Gullies have an output reasonably near the surface, though a P-trap is probably the best for that. Of the bottle gullies, UG425 from polypipe has the shortest distance between top of grate and output invert at 175mm (Osma 4D900 207mm, Floplast D515 262mm). The spigot output of Polypipe UG425 looks to be at least 60mm long which is greater then the insertion depth of most ring seal couplers 175mm + (27000/100) = 445mm so should be workable with 1:100 over 27m and an end invert of 425mm (would stick up 20mm).

That's a good thought as then it can't drift down in some spots and cause issues. I had wondered about sharing a trench for part of this section, but that feels like it's asking for problems and would stop me from adding any intermediate concrete supports since this pipe will be the higher of the two.

Yes, that's a good though as that sort of gully would have its output near the surface. I'll have to work carefully to hold the 1:100 gradient though.

The downpipe at 27m is servicing 50m2 of roof whilst the one at 32m is servicing 26m2 which hasn't been constructed yet. I'm wondering about combining that second roof area with the one serviced by the furthest right downpipe which is only handling 12m2 of roof area. The one at 27m can't be scrapped though so that's the main challenge. 27m @ 1:100 leaves a depth of 425 - (27,000/100) - 110 = 45mm which could just about work as it's a patio there.

Due to a lack of solids, rainwater gradient is less critical than for foul drainage. The minimum gradient is 1:100. The lower the gradient the harder it is to control in the laying process, so I think my ideal would be 1:80. That said, I need to connect to a pipe that is 425mm below surface with a branch of pipework with a length of about 32m, so that's likely to need the 1:100 fall to be possible, since even that will leave the top of a 110mm pipe at the surface. I may have to rethink the far end of that branch since the other points are at a maximum distance of 20m so a 1:80 gradient leaves the top of a 110mm pipe at a depth of 425 - (20,000/80) - 110 = 65mm which may just work and a gradient of 1:100 would make it 115mm which would be fine. Based on Diagram 3 on page 45 and Diagram 2 on page 43 of Part H, the following gradients of 100mm pipe can cater for up to the following areas of roof and/or paving: Even 375m2 is a large area and way beyond my needs. You need to divide by 1.5 if it's roof area, so that become 250m2 which is still lots of area. NB: Peak rainfall rate of 0.016 L/s on 1m is equivalent to 1mm or rain fall depth per minute (60mm per hour) Pipe run distances to gully/hopper entry point to 110mm underground rainwater drainage pipework:

How much higher do you think the oak step will be than the top of the woodpecker flooring? Planked flooring normally has it's long axis perpendicular to a door like this so has some strength to cantilever over a 60mm wide gap particularly with a timber over the top. If the woodpecker flooring is thick enough to be used over joists without a sub floor then it's should be fine, you just have to make sure any planks don't flip up if trodden on, but unlikely anyone would tread that close to the door. That would remove any structural requirements from what you put in the cavity

Is that a regs requirement or just sensible design? Is this in case the foul pipe leaks and cross communicates with the rainwater pipe? Unfortunately, the foul will be the higher. I can stagger pipe joints so the foul would have to pass horizontally over a metre to then enter the rainwater pipe. Such a cross communication would become too unlikely to be a genuine concern then.

I can't see, but is the door frame on top of a timber cill? I think @Mr Punter is asking what your final floor finish will be. Tile, Timber, Carpet,...

I've separate rainwater and foul systems as I have a sewage treatment plant and the rainwater is going to a ditch. Most of the area where I have both foul and rainwater drainage pipes is going to get covered by a patio, so I can happily have two separate trenches a suitable distance apart. In another area, I have a run of around 5m where both are going parallel and there is no patio. Since the pipes are shallow, I want to cover them with a concrete slab path. The slabs are supposed to bear 200mm each side of the trench. A 900mm wide slab could straddle a 500mm trench and that could have two 110mm pipe runs in. One pipe will be sloping one way and the other in the opposite direction. The slabs should be strong enough as I have tried jumping on one supported just at the ends and it was fine Does that sound sensible? Is there anything to worry the BCO in this (e.g. Building Regs)?

Actually, the socket OD of the couplers is just too big for 8" layflat tubing so would need to be 10" or larger: https://www.amazon.co.uk/Triplast-LF5001001-10-Inch-Layflat-Tubing/dp/B07BRNYC32/

I can find geotextile sleeves designed to stop silt and sand entering land drain pipes, but not one designed to sleeve over pipe couplings to stop root penetration. Three approaches I am considering are: Do nothing Wrap and cable tie each coupling with a 1m length of non-woven geotextile like this: https://www.amazon.co.uk/dp/B0DQ88WHD4/?th=1 Use a 1m length 8" temporary downpipe or layflat tubing an duct tape at each coupling (normal 150mm not large enough) I found this but not UK: https://www.mainlinematerials.com/products/underground-pipe-root-barrier

That's the plan, but you never know