Drain job done right? Your comments on local regs. appreciated

[Colin Murphy]

Hi guys, work was recently done to replace drainage pipe that runs under the house, from back to front of house, and to install a gully so that water no longer collects at the base of an external stairwell.

I would appreciate comments from anyone regards the work satisfying local regulations for the NW10 area.

The builders have laid uPVC drain pipe under the house. I am told that the pipe should be cast iron because it is running under the foundations of the house. True or false? The previous pipe was cast iron, because they have kindly left the old pipe in the garden. Should they have replaced like for like?

The gully in the external stairwell at the rear of the house, which was installed as a new component to this replacement drain, is not trapped, by looking down the gully I can see water flowing from higher up the drain run on it's way out to the main drain at the front of the house. At the gully point the drain is carrying combined rainwater and kitchen waste water, but this drain pipe continues under the house for 5M to the manhole at the front of the house which does receive foul drainage. Should a bottle gully have been used instead of the hopper gully?

[Roger Mills]

Plastic pipe is fine - and far less likely to crack due to slight ground movements than cast iron would be.

It certainly should have traps though, if it's a foul (or combined foul/surface) drain. If it were a dedicated surface drain, it wouldn't need them. Does your toilet waste go into the same manhole - or have you got separate foul and surface drains, but are putting your kitchen waste into the wrong one?

[Owain]

When I had a below-floor cast iron pipe replaced (a car drove into the front of the building and sheared off two soil outlets and a downpoipe) it was replaced with plastic as according to the plumber cast iron is now illegal inside/under houses.

Should be trapped IMHO, but not a bottle gulley.

Owain

[Colin Murphy]

I know it is a requirement for jobs in the City of London, but if you know of it being used elsewhere then that's good enough for me.

I suppose it is how 'foul drain' is defined. At the point where the gully joins the pipe it is just carrying combined kitchen water and rainwater from the roof gutters, 5M on it enters the manhole that also receives foul drainage. To my mind, this replacement pipe is connected to a foul drain manhole, therefore is also a foul drain, therefore the gully should be trapped; that's how I will now explain it to the owners of the property who are paying for the work - unfortunately I only live here and so will have to suffer the builders digging up the yard again.

[Colin Murphy]

I am surprised by this. It's embarrassing to say, because I don't already know the answer to my regs. query, but I actually sell cast iron drainage and we sell enough of it for this very application.

Why not a bottle gully?

[Owain]

Blocks easily, I thought.

Owain

[Andrew Gabriel]

The foundations are not allowed to rest on the pipe. My neighbour who has just run several soil pipes under his foundations had to cut the foundations out above the pipe and fit a lintel above to transfer the weight to either side (although the corbelling of the bricks probably makes the lintel rather OTT, as it's only carrying the weight of about 3 bricks).

[The Natural Philosopher]

Not exactly true. The foundatins WILL run under the pipe - what you can't do is build brickwork onto it, so each pipe needs a little 'bridge'.. ,