Installing new 25mm MDPE mains pipe

[bensemp]

I'm replacing lead and shared mains while my kitchen floor is dug up. Got on to Severn Trent and they've sent me a document with some rather unclear regs. There's some good info elsewhere on this site, I've also found this guide that gives slightly more info than ST http://www.unitedutilities.com/Documents/1344_How_20to_20lay_20new_20pipe.pdf but still not sure on a few points:
100mm ducting - does this mean 4inch PVC soil pipe?
Sealing the ends of the ducting - can I use foam filler for this? If no, then what?
Insulating the 25mm MDPE - How thick should this be?
My builder who's doing the kitchen floor thinks the regs are ridiculous and says he'd only use 4inch pipe coming under the external wall, then nothing but the insulation in the void under the living room floor and 76mm downpipe through the solid kitchen floor. I'm inclined to agree, but the ST document says if you don't use their aproved plumbers they'll come and inspect all your work - Is this right, can anyone give general tips, or if you've done this yourself did they inspect every inch of pipe or just the bit where it meets the mains?
Thanks,

 

[paulandfrodo]

bensemp,

100mm ducting - does this mean 4inch PVC soil pipe? YES (My Inspector said he would be happy with 3")
Sealing the ends of the ducting - can I use foam filler for this? YES
Insulating the 25mm MDPE - How thick should this be? GO FOR 25mm

My builder who's doing the kitchen floor thinks the regs are ridiculous and says he'd only use 4inch pipe coming under the external wall, then nothing but the insulation in the void under the living room floor and 76mm downpipe through the solid kitchen floor. SEEMS FINE

I'm inclined to agree, but the ST document says if you don't use their aproved plumbers they'll come and inspect all your work - Is this right, can anyone give general tips, or if you've done this yourself did they inspect every inch of pipe or just the bit where it meets the mains? THEY HAVE TO INSPECT THE TRENCHES AND INSULATION BEFORE CONNECTING THE REPLACEMENT SUPPLY. (They call it a Trench Inspection).

To be honest, I'm surprised they don't enforce flexible plastic ducting all the way through the house whilst they replace the supply. Thus allowing them to pull the pipe at some later point in life.

 

[doitall]

If you maintain the 750mm from the trench to inside the building you don't need to insulate the duct.

4" duct will take 25mm wall insulation, whereas 3" would be pretty tight at best.

If your builder is a penny pincher, and may have had a run in with the water inspector in the past, he will remember and want to see the whole job. It wont be a first where they ask for fittings to be unscrewed to check whether they have used Boss white or other banned substances.

These guys are very helpful unless you try to con them, then they are like traffic wardens,

 

[denso13]

These guys are very helpful unless you try to con them, then they are like traffic wardens,

Couldn't agree more. Just like building control etc. I find it better to ask them the question first, gives their ego a boost, and usually goes much smoother than it otherwise might.

 

[MANDATE]

It does not mean you have to use 4in soil pipe!
I purchased 1 metre of 4in straight ducting and a bend so pipe could enter into property at 75 cm below floor level and go vertical to floor level.
Insulation was stipulated as 'armaflex' but there are others available.
I also opted to lay 2in ducting in the trench, but sand is normally stipulated.
I thought it would be easier if pipe ever needed replacing.
No insulation needed in trench

 

[MANDATE]

Ref the Unitied Utilities drawings.
Diagrams 1 and 2 deal with almost identical situations, the difference being the distance of the vertical pipe from the outside wall.
Dia 2 drawing states 750mm minimum, but the heading states 'less than 750 mm' ( this should read more than 750mm to make sense)
Dia 1 drawing states 'less than 750mm' but the heading states 'greater than 750mm'. (this should read less than 750mm to make sense).

 

[bensemp]

Thanks all for your replies. My builder just thinks nobody will bother to inspect the work, or if they do it will be a cursory glance rather than demanding to see every inch of pipe. He bases that on his experience of building control, but I don't know if water company are more thorough or if they'll give me more grief because I'm a DIYer. Anyway I can leave trenches open, but kitchen floor is being laid this week and the Severn Trent process takes 10 days min before anyone comes out, so whatever I do in there will have to be right first time!
Paulandfrodo - what is this flexible plastic ducting? Sounds easier to lay than heavy and expensive soil pipe! Can you post a link to anywhere that sells or has pics of it?
Cheers