Rest Bend Location

[Jamie998]

Now,  this may seem like a stupid question but until someone tells me why its a stupid question, my ignorance will continue - I am hoping my fellow self builders can educate me a little!

 

Right, is there a minimum depth that the rest bend must sit at below the slab? Or can it sit in the slab and/or insulation in an insulated raft foundation for example.  The reason I ask, is if you need to claw as much height as possible to get the falls correct then having it as high as possible would be beneficial.  

 

I've had a scoot through the Approved Document and although there are minimum depths mentioned for the foul run under drives/footpaths etc. this can be mitigated by covering with concrete etc. where necessary,  so can I stick the rest bend as high as possible in my foundation to claw some precious height back?

 

Ignore the inaccuracies of foundation detailing - the drawing is just to 'show' what I'm getting at.

 

Ta

 

 

[willbish]

Isoquick say that pipe and ducts passing through the system should do so vertically.

 

Page 9

Isoquick Introductory leaflet and technical notes.pdf

[scottishjohn]

maybe i,m being thick 

but surely the postion of the rest bend is dictated by the level at which the drain enters the foundation  and if required you need to extend the top of the  rest bend to height you need

not fix it so it connects directly to the bog-

rest bends  or  87.5 degree slow  bends are always preferred  as a drain rod can go round them much easier --no short 90bends under ground if possible

If you are short of height I suggest that your pipe run outside house is too shallow  and maybe you should be checking and adjusting  them first 

 

Edited January 25, 2019 by scottishjohn

[epsilonGreedy]

The Building Construction Handbook 11th Edition page 953.

Quote

For a single stack discharge system is says "minimum vertical distance from lowest connection to drain invert is 450mm".

 

By my calcs a modern insulated B&B floor will exceed this, [Edit] though I note the OP is discussing an insulated raft. The diagram in the book shows the rest bend connecting to the vertical stack just below the floor concrete.

 

If say from FFL you have 80mm screed + 150mm insulation + 100mm block  + long rest bend radius of 280mm = 610mm

Edited January 25, 2019 by epsilonGreedy

[Mr Punter]

What you have shown is fine. As @scottishjohn says use a long radius bend.  You will need access at the top for rodding. Better if it is a bit more under finished ground level so it does not get damaged.

[scottishjohn]

you need a manhole outside the house where all your foul water pipes connect  in a chamber 

so this where you should calculate from to inside house at floor level to get the drop correct  before it goes to main sewer connection 

 and that connection needs a  minimum of 450mm drop into the actual sewer /septic tank

you BC man will want to check all this before you cover them up  and probably require you to do a smoke or pressure test 

Is this connected to mains or is it septic tank 

as all these heights and drops should have been worked out before fitting septic tank

Edited January 25, 2019 by scottishjohn

[epsilonGreedy]

19 minutes ago, scottishjohn said:

maybe i,m being thick 

but surely the postion of the rest bend is dictated by the level at which the drain enters the foundation  and if required you need to extend the top of the  rest bend to height you need

not fix it so it connects directly to the bog...

 

 

Or you can look at it another way and say the drain entered the foundation at a calculated depth sufficiently deep to accommodate to drainage pipe work up to FFL. For those of us dealing with marginal site gradients these numbers will have been scrutinized late at night many times, in more hilly regions of the UK the issue might be shedding excess gradient ?

[scottishjohn]

4 minutes ago, epsilonGreedy said:

 

Or you can look at it another way and say the drain entered the foundation at a calculated depth sufficiently deep to accommodate to drainage pipe work up to FFL. For those of us dealing with marginal site gradients these numbers will have been scrutinized late at night many times, in more hilly regions of the UK the issue might be shedding excess gradient ?

I am expecting to have to have multiple drop chambers with my build as septic tank is going to be 20ft below house I think  due to slopped nature of site and hard ground issues

may get away with tank being closer to house and then just driange field will be down hill a long way 

Edited January 25, 2019 by scottishjohn

[epsilonGreedy]

7 minutes ago, scottishjohn said:

you need a manhole outside the house where all your foul water pipes connect  in a chamber 

so this where you should calculate from to inside house at floor level to get the drop correct  before it goes to main sewer connection 

 and that connection needs a  minimum of 450mm drop into the actual sewer /septic tank

 

 

Are you sure about that? If true the book I was quoting has confused sewer for drain. 

[ProDave]

I understood you need a chamber whenever there is a branch or change of direction to a pipe run.

[Mr Punter]

17 minutes ago, epsilonGreedy said:

in more hilly regions of the UK the issue might be shedding excess gradient

 

There is no longer a maximum gradient quoted for below ground drainage, just the minimum, which can be stretched to 1:80 for a 110mm pipe, but 1:40 preferred.  If the gradient changes significantly along the run you will need an access / inspection point.

[scottishjohn]

12 minutes ago, Mr Punter said:

 

There is no longer a maximum gradient quoted for below ground drainage, just the minimum, which can be stretched to 1:80 for a 110mm pipe, but 1:40 preferred.  If the gradient changes significantly along the run you will need an access / inspection point.

yes

because if pipe drys out  and then a small flush leaves something sticky half way down 

and then it drys to side of pipe  it is the beginnings of a blockage ,

so  vertical drops with rodding points is better for that situation .

which is why  I think larger pipes have less drop so the bottom of pipe is always wet 

[scottishjohn]

28 minutes ago, ProDave said:

I understood you need a chamber whenever there is a branch or change of direction to a pipe run.

yes like outside house where all drains join together before going on to sewer .

easiest way anyway to get all the under foundation drains together and cleanable  if you get blockage in years to come

Edited January 25, 2019 by scottishjohn

[PeterW]

8 minutes ago, scottishjohn said:

so  vertical drops with rodding points is better for that situation .

 

Most BCOs will now not accept back drops as they are notorious for blocking and prefer to use steeper gradients. The chances of pipes drying and sticking with uPVC is vastly less than with clay. Think the guidance changed a few years ago on all of this, and know we have discussed it before.

[scottishjohn]

8 minutes ago, PeterW said:

 

Most BCOs will now not accept back drops as they are notorious for blocking and prefer to use steeper gradients. The chances of pipes drying and sticking with uPVC is vastly less than with clay. Think the guidance changed a few years ago on all of this, and know we have discussed it before.

thank you for the up date in modern thinking

[Jeremy Harris]

IIRC, Part H was amended about 10 years ago or so to remove the old maximum gradient recommendation, although there is still a lot of erroneous information around on the web, describing how to create a backdrop etc as if this was still a building regs requirement whenever there is a steep gradient. 

[Gone West]

We have an Isoquick insulated slab and all the rest bends and soil pipes run through the sub-base under the insulation. Our insulation is 300mm and with the sub-base meant the soil pipes entered the sewage treatment plant quite low down and we needed an invert on the tank.

 

[Jamie998]

I think I should change the question slightly.  If you have an established manhole to connect to and its invert is such that you are struggling to get the necessary height required to meet the minimum falls then is it possible to move the rest bend up as far as possible to gain the height you need?

 

It seems the only thing that says you can't so far is the Isoquick manual and @PeterStarcks real world experience with his foundation.

[Jeremy Harris]

Our passive slab also needed the rest bend to be in the sub-base, just like @PeterStarck, with vertical pipes coming up through the insulation.  There's no easy way to fit a rest bend into the insulation layer I'd have thought, plus ideally you want to pressure test the pipe run (which BC will sometimes ask to witness) before you have it fitted into the slab.

[Jamie998]

3 minutes ago, JSHarris said:

Our passive slab also needed the rest bend to be in the sub-base, just like @PeterStarck, with vertical pipes coming up through the insulation.  There's no easy way to fit a rest bend into the insulation layer I'd have thought, plus ideally you want to pressure test the pipe run (which BC will sometimes ask to witness) before you have it fitted into the slab.

 

Ok, so I will assume that from the experiences of both @JSHarris and @PeterStarck that the 'standard' method is to have the rest bend within the compacted sub base so that the pipe running up through the insulation & slab is vertical.

 

As mentioned, there will also be no issues then getting BC to check it before it all gets covered over.

 

Thank you all for focusing my mind on how to approach this.  I have more 'questions/thoughts' swirling in my head but I will move them to a separate thread.

[epsilonGreedy]

7 hours ago, JSHarris said:

 although there is still a lot of erroneous information around on the web, describing how to create a backdrop etc as if this was still a building regs requirement whenever there is a steep gradient. 

 

 

This includes public sector building control Orgs and drainage manufacturers. I find it odd that the construction industry had to infer the new regulation through the absence of a prior criteria. Can you imagine the world of physics discovering that Einstein was wrong and conveying this by covertly scrubbing E=MC2 in a text book reprint.