Ground floor wc

[Pottles]

Hello

Hopefully someone can help me.

I am wanting to install a ground floor WC in a property and have browsed the Internet to find out more but have struggled to find an answer to the following:-
1. The maximum horizontal length from the wc to external access camber or inspection chamber is 6m. Is this word of mouth or supported by Building Regulations or other standards?
2. At what gradient do you lay the pipe beneath the ground floor slab. Are there maximum and minimum gradients?

Thanks to anyone who can help

[lutonlagerlout]

1:80-1:100 no max length
LLL

[stephen gibson]

I have a link for more info at http://www.wilsham.co.uk/building-regulations-part-h
The regulations are free to download.

Item 2 - check out section 2.34 table 6

All should be a minimum of 1:40 unless the peak flow is over 1 l/s and then never flatter than 1:80 under a building.

[Pottles]

Hello Stephen

Thanks for your reply.

Does this mean that most connections running below the house need to be 1in 40 gradient as they won't be serving enough appliances to achieve a flow of one litre per second.

If you are connecting to a mini access chamber external to the house which are 600mm deep a 1 in 40 gradient will be too steep.(by the time you have gone through the floor slab and installed a rest bend?


While on the subject is there a problem with running connections from near the rear of the house to save having private drainage at the rear of the property?

Thanks a lot for you help

[lutonlagerlout]

pottles
your first port of call is your existing IC or manhole in old terms
the invert of that is critical
lets say it 900mm deep (could be a lot more or a lot less)
now lets say from your outfall to this invert level is 15 metres

from this you can deduce you have a fall of 1:60
your local building control can advise but its a fairly simple job
LLL

[Pottles]

Hello LLL

Thanks for your response.

I was thinking more in terms of a new build property and fixing the depth of new manholes/inspection chambers around the building footprint.
Depending on the length of connection under the slab the manhole depth required must increase. If you had a connection from say a wash hand basin with flows below 1l/s then does this need to be laid at a gradient of 1in 40?

Thanks

[lutonlagerlout]

you need rest bends for foul water i.e. loos
but if its a new build surely the NHBC has guidelines for all this?
or the architect/BCO
IME the most important thing is that it works on gravity
i.e. gone
LLL

[stephen gibson]

LLL - You appear confused as to roles..

Drainage design is done to BS EN752 by a civil engineering consultant, who then submits the plans, levels, etc all to building control. Building Control then check and approve the designs. Then it is tendered to builders to get on with. The builder then agrees the installed work with building control as he goes.

Architects are not qualified to do engineering / drainage design and don't have any professional indemnity insurance to cover such work.
Likewise Building Controls role is to check - not to design.

Engineers like me pay £1000+ per year for professional indemnity insurance to cover our design responsibility running into millions. Our design liability is up to 12 years (similar solicitors etc), where as a builder is usually "off the hook" in 1 year.

Many people do think "I shall miss out the engineers / designers and go straight to the builder to save money". In the long term it usually costs a lot more.

It sounds like this is much more that a single DIY ground floor connection. With a whole new house you really need to employ a civil engineer.

[lutonlagerlout]

not confused by roles but confused by the OP

if someone is retro fitting drainage (which I initially thought was the case) then its a case of best practise and advice

i would expect all new build to have high quality drawings and calculations for every aspect of the job

tomorrow and thursday I will be retro fitting a drain that has to be suspended in a crawl space ,this will be an interesting challenge

BTW what is the excess now?
I know an architect who went bust over his indemnity insurance
the excess was £20k :O

back to the OP the Main sewer is the starting point for all drain design on a new build

cheers LLL