Underground drain query

I am having an extension to sort out some layout issues caused by the
previous 2 extensions done before I bought the house. This involves
moving some bathrooms and the downstairs toilet and therefore am
considering my options for rerouting the underground drains.
Looking at the building regs plans from the latest extension (dated
1988), the main drain run is from the back left, under the house to a
man hole in the hallway in the middle of the right extension. Then
from this man hole through the garage and out to the street ( this run
is from back to front of the house).
Looking under the various manholes along the route, the drains do
appear to run this way however, the manhole in the hallway doesn't
exist (would have been very odd if it had!!) but there is one about 1m
further along the pipe from where it should be to the main sewer in
the street. The only conclusion I can make is that the builders who
built the extension burried a 90 degree turn in the pipe under the
concrete floor so that the manhole is in the garage rather than on the
Based on this, I have a couple of questions.....
1. is this normal / allowable under regs?
I need to add a couple of soil stacks to the drains for a couple of
relocated bathrooms.
2. Can I have these either inside or outside the house
3. Do they have to be open to the air - my exisiting ones are but
obviously if I could have it inside, I wouldn't want this.
4. Can I plumb the toilet waste directly into the underground soil
without any form of "stack"? The exisiting toilets appear to be like
this but I thought you couldn't do that...
All help gratefully appreciated.
thanks in advance
Reply to
It is perfectly acceptable to have a manhole inside a building provided it is the sort that has a double grease seal. They're usually designed so they lay flat with the floor and have an inset tray on the lid to be filled with floor covering.
Depending on the other drains on the system you may be able to use air admittance / durgo valves at the top.
I think it's okay subject to length of pipe and other things on the same pipe.
Reply to
No, but there are issues to do with suction/siphoning - they well need to be equipped with air admittance valves.
I would strongly suggest you identify where teh pipes do run, and attempt to rationalize them to current building regulations.
Ask the BCO if you are not sure. If at all possible all rins should be straight between easily accessible manholes, andd at te corret fall. Any right angle bends below the surface MUST be accessible via a manhole, and above ground be accessible with a removable cover and rodding point.
Reply to
The Natural Philosopher
On Sat, 10 Nov 2007 09:59:48 -0800, a particular chimpanzee, snipped-for-privacy@yahoo.co.uk randomly hit the keyboard and produced:
The question you should be asking is, was it ever inspected by Building Control?
It is allowable to have a 'slow' bend on a drain run, provided it can be reasonably rodded. A cover in the garage might have been the preferable option to one inside the house.
Drainage on plans for domestic work is a bit like the notation, "here be dragons" on ancient maps. It's for symbolic reasons rather than conveying any actual meaning. You can bet that an architect or plan drawer never lifted the inspection covers and just drew some dotted lines on his plans to get it passed by Building Control, preferring to leave it to the builders and the Building Inspector to sort out between themselves.
At first floor level (or more than 1.3m from the invert of the drain) they need a vent. This can be open to the air, or an air admittance valve (aka, Durgo valve). If less than 1.3m, it could be a stub stack or direct to the drain providing it's less than 6m from a vented drain.
Reply to
Hugo Nebula
Thanks very much Hugo. Give the short proximity to the manhole in the garage, I guess rodding should be easy so sounds like that is what happened.
What do you mean by the "Invert to a drain"?
Finally, there is currently a manhole on what will be a straight run in the new design (currently there is a connection). Can I cover this over with the extension concrete floor?
thanks again for your help
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