Laying Underground Drains

[CHarr]

I'm extending my average-sized semi at the rear and side, and need to almost completely renew the foul drainage. My existing glazed vitrified clay drain starts part-way across the back of my house, where there is a 1m deep brick built chamber, and then runs under the boundary fence onto my neighbour's property.

I'm building up to 200mm from the boundary and across the whole of the back of the house, and the drains will need to serve my kitchen waste, which will be at the very front of the new extension at the side of the house. The drains will therefore have to go in an L shape around two sides of the house.

I will cut the existing pipe near the boundary (it will be exposed when I dig the footings, anyway), and use a clay to PVC adaptor, and then run 110mm plastic pipe with push-fit joins from there. The pipe across the back of the house will be under the finished floor, so I'll extend the run 1m or so beyond the far wall and site a chamber there.

Questions: The bathroom and downstairs toilet wastes will both enter the main straight section, and the only requirement for the section running at the side of the house will be for kitchen waste (sink, washing machine & dishwasher). Should I discharge those into an external gully at the front of the extension, and if so, would it be better to run a straight line of 110mm pipe as a branch directly to the gully location (under the floor), or instead, use the chamber to change direction and go around the extension externally, requiring another change of direction at the front. The ground is more easily accessible, but the run is longer and has an additional 90 degree bend.

The outlet from a bottle gully isn't very deep. Can I run a straight pipe from there (ie shallow), downhill to the junction with the other section, or should I turn the outlet from the gully sharply or even straight down, to a deeper pipe running at something like 1:40 to the next junction?

 

[noseall]

Whilst some people might view your use of DIY-not as enthusiastic amateur building, most of the pro's on here will see these long posts and sigh.

You are basically asking for a 1000 page step by step instruction manual on how to build a domestic house extension.

Your posts are long winded and tiresome. We do expect that people who dare to take on large ambitious building projects have at least a modicum of building nous, otherwise stick to putting up shelves.

 

[CHarr]

You are basically asking for a 1000 page step by step instruction manual on how to build a domestic house extension.

1000 pages to answer a couple of simple questions? And you have the nerve to call ME long-winded. Bugger off. You don't have to read anything that I write, and you certainly don't have to respond. Try the 'ignore' button.

 

[JackL]

Questions: The bathroom and downstairs toilet wastes will both enter the main straight section, and the only requirement for the section running at the side of the house will be for kitchen waste (sink, washing machine & dishwasher). Should I discharge those into an external gully at the front of the extension, and if so, would it be better to run a straight line of 110mm pipe as a branch directly to the gully location (under the floor), or instead, use the chamber to change direction and go around the extension externally, requiring another change of direction at the front. The ground is more easily accessible, but the run is longer and has an additional 90 degree bend.

The general rule is to have the simplest layout possible with the fewest bends. Just make sure you have rodding access to all points of the system.

The outlet from a bottle gully isn't very deep. Can I run a straight pipe from there (ie shallow), downhill to the junction with the other section, or should I turn the outlet from the gully sharply or even straight down, to a deeper pipe running at something like 1:40 to the next junction?

Consider the total depth of the floor. If it's solid, you will have a build up of a hardcore sub-base, sand, insulation and concrete/screed. Your drainage system must run beneath the floor, and I would plan for a trench at a minimum of 600mm below the underside of the floor, to allow for the formation of a suitable pipe bed and sidefill, then backfill.

Drainlaying is well within the capability of most DIYers, but allow plenty of time and remember that the building inspector will need to be satisfied before you cover anything over.

 

[CHarr]

How can I arrange a drain test to satisfy the Building Inspector when the only access chamber is in a section of pipe that doesn't lead anywhere (just to allow rodding through a stretch of pipe from the SVP junction and onwards under the boundary fence to cross my neighbours garden. He doesn't have a chamber either: the first is next door to him.

I can't block off the underground pipes anywhere, and the only working branch is terminated with a SVP open to the air. What can I test?

 

[Pallatrax]

OP - you're best of making a good sketch IMO and use, say red for one option, and blue for another. I for one am finding it hard to picture what you mean exactly at the end of a long week...

Tom

 

[CHarr]

OP - you're best of making a good sketch IMO and use, say red for one option, and blue for another. I for one am finding it hard to picture what you mean exactly at the end of a long week...

Tom

Thanks, but I've sorted out the layout now, and just wondering about testing. The underground pipe is a straight line across the back of the property, with an access chamber at the start end. All waste enters that pipe from a branch two metres along from the chamber, and the branch leads to the main stack with an open SVP. What can I test?

 

[Pallatrax]

When BC looked at mine they just wanted to check it can all be rodded, and that it had a fall. There isn't much to test.

Tom

 

[maltaron]

You state that the pipe will be exposed when you dig the footings. Are you aware that as the pipe serves more than just your property, and is within 3m of your build, you will require to notify your local water authority and pay an heavy fee for a Build Over Agreement and possibly divert the sewer away from the building.

 

[CHarr]

You state that the pipe will be exposed when you dig the footings. Are you aware that as the pipe serves more than just your property, and is within 3m of your build, you will require to notify your local water authority and pay an heavy fee for a Build Over Agreement and possibly divert the sewer away from the building.

It's not a public sewer: it isn't even shared. No other property is served by it.

 

[Hugh Jaleak]

If BCO hasnt asked for a test I wouldnt worry too much until he does. Provided he can see drains have been laid to a sensible fall, connections are made properly, and rodding access is available to all sections I doubt he'll have too many issues. Very difficult to get a leak on plastic pipe/fittings if laid properly, and you're not trying to pull the wool over his eyes then they may not even get a second glance.

 

[CHarr]

I'll be ready to put in the drains this weekend as long as it stops raining and my trenches don't just fill with water!

The main underground drain runs across the back of the house, and I need to bring in the bathroom waste from the main stack, a downstairs toilet, the kitchen and a rainwater gully. Three of the four branches will be quite close together. Is there any practical or regulatory problem with connecting 87.5 degree drain junctions (swept tees) one after another in a line?

 

[Hugh Jaleak]

The golden rule with drainage (and especially foul drains) is that every part of the system must be accessible for rodding in the event of blockage. Using junctions I suspect will not allow adequate access to the branches concerned.

I would be looking at bringing the the stack and ground floor WC connections at the very least via a chamber, ideally a pair of chambers with 2 inlets per side would allow for all connections to be made and satisfy access requirements. Depending on depth of inverts, shallow access chamber(s) may suffice.

I suspect use of multiple junctions, especially on branches to a WC would not impress your Building Inspector.....

 

[CHarr]

The golden rule with drainage (and especially foul drains) is that every part of the system must be accessible for rodding in the event of blockage.

The branch from the SVP (Bathroom/Toilet) has rodding access at the base of the SVP, and it's a short, straight run from there to the main drain, which is roddable along its entire length.

The branch from the kitchen runs parallel to it, but is also roddable from a bottle gully and is also completely straight.

The only branch that is awkward is that from the downstairs toilet, but THAT is directly over the main drain, and the fall is straight down into it, so it would be very hard to block it.

 

[Nige F]

[The only branch that is awkward is that from the downstairs toilet, but THAT is directly over the main drain, and the fall is straight down into it, so it would be very hard to block it.

have you ever dropped a turd onto a smooth surface - it sticks and so will the paper that follows it - directly vertical into a horizontal drain is not good