Foul drain infill near to foundation / under floor

[skinny d]

Hi, I'm renovating an old welsh cottage and its my first job. At the back of the cottage there is a small extension with a bathroom and kitchen in it. I have to reform the foul drains as they are in poor condition under the floor of the extension and leak causing dampness.

My idea is to take the toilet/sink etc water out through the back wall of the extension, join them at an access chamber and then re-lay a new pipe under the kitchen and old cottage floor. At the same time I could lay a second pipe under the floor to take rainwater from a perforated land drain and the guttering.

The complicating factor is that there is minimal room at the back of the extension, the foundations of which are only 30cm thick on bedrock and there is an old retaining wall about 40cm back from the outer wall.

Do I have to set all of the foul pipe work in concrete outside or could I lay it in some free draining material? If I can lay it in gravel I can embed a perforated drain in it and take away surface water too.

As the pipes run under the concrete floor what do I have to embed them in and how far below the slab. What sort of pipes can I use, I have had "ribbed" recommended to me but have only seen the 110mm foul piping around.

Cheers in advance, Dave

[Tony McC]

Is there no alternative but to bring the pipework under the floor? Is there no possibility of pipes being run around the property, on the outside? Running pipes internally is fraught with problems and is only ever done as a last resort.

Basically, pipes running under a floor can be laid in granular material, but where they pass through or under a load-bearing wall, they must be encased in concrete. You could use plasticware or clayware - UltraRib is but one 'brand' of plasticware and is perfectly suitable, but so are any of the other kite-marked systems.

Without seeing a layout, it's impossible for me to comment on the rest of your proposals.

[skinny d]

Hi there, cheers for the info, regarding having to run the pipe under the house, I'm afraid there is no choice as it is a long terrace with no way round.

The problem is fairly complex as the pipe has to pass through three walls to get to the front of the house. The back wall is on a relatively shall concrete foundation (35cm) on bedrock, it then has to pass through a middle wall which is part of the older house and formed from random rocks (v large), then again out through the front wall formed from the same random rocks. Unfortunately there is a 45cm drop in floor level across the middle wall which complicates things.

I shall draw up a bit of a plan and take some pictures as they tell lots more.

I see that Ultrarib only comes in 150mm dia, can it be got in 110mm?

Cheers, Dave

[Tony McC]

I'm not sure if the 100/110mm version is branded as UltraRib, but there are dozens of perfectly fine pipes of that size readily available from most decent Builders' Merchants.

[ABILITY]

Just a thought, but have you considered a macerator unit allowing for a 11/4 " outlet pipe to take waste through the house.
Could this be run along the interal wall, hidden in floor or behind skirting box etc.
Noise of unit maybe a problem, depends on situation.

[skinny d]

It is an option but because the house is one of a terrace and the terrace runs across the slope of a hill it forms a pretty nice dam. The house itself is only a few feet above bedrock (as we found out when digging down for the new floor) so any water that doesnt get drained has to pass through the thin soil layer, increasing damp problems. Hence we are very keen to run a second pipe purely for drainage but keeping the option to drain through the soil pipe if flood conditions occur.