Hi

I need to reposition the soil stack for a new upstairs layout. The new
stack will need to run for ~6m under the kitchen floor before
connecting to the existing drain pipe.

I've measured 17cm between the underside of the floor joists and the
concrete slab. Subtracting 10cm for the pipe, I have approx. 7cm spare,
i.e. not enough for a 15cm fall (1:40 on a 6m run by my maths). The
joists are perpendicular to the pipe.

As an alternative to excavating a run in the slab, would removing 4"
sections from the first ~6 joists and supporting their newly-formed
ends on bricks cemented into the slab satisfy the building regs ?

Thanks
GD.

I've measured 17cm between the underside of the floor joists and the
concrete slab. Subtracting 10cm for the pipe, I have approx. 7cm spare,
.e. not enough for a 15cm fall (1:40 on a 6m run by my maths). The
joists are perpendicular to the pipe.

My maths is not that good i know it should be 2 1/2 degrees.....hence
the tees are 92 1/2 ofests
pete

In an earlier contribution to this discussion,
gasman pete wrote:

I've measured 17cm between the underside of the floor joists and the
concrete slab. Subtracting 10cm for the pipe, I have approx. 7cm
spare, .e. not enough for a 15cm fall (1:40 on a 6m run by my
maths). The joists are perpendicular to the pipe.

My maths is not that good i know it should be 2 1/2 degrees.....hence
the tees are 92 1/2 ofests
pete

2 1/2 degrees is about 1 in 25 - so a 6 metre length at that gradient would
require a fall of 24 cms - so allowing 11cms for the pipe, an overall
clearance of 35 cms would be needed.

Not sure whether that's necessary - probably not.

--
Cheers,
Roger
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In an earlier contribution to this discussion,
wrote:

Hi

I need to reposition the soil stack for a new upstairs layout. The new
stack will need to run for ~6m under the kitchen floor before
connecting to the existing drain pipe.

I've measured 17cm between the underside of the floor joists and the
concrete slab. Subtracting 10cm for the pipe, I have approx. 7cm
spare, i.e. not enough for a 15cm fall (1:40 on a 6m run by my
maths). The joists are perpendicular to the pipe.

As an alternative to excavating a run in the slab, would removing 4"
sections from the first ~6 joists and supporting their newly-formed
ends on bricks cemented into the slab satisfy the building regs ?

Thanks
GD.

You'll still need something to support the floorboards which run over the
pipe - so you can't remove *all* the joist at that place or, if you do,
you'll need a metal bridge or something.

How deep are the joists. Sticking with your 1:40 slope (but see also the
other reply suggesting you need 1:25) you need a clearance of 15 + 11 = 26
cms, and you've only got 17, so you need another 9. If the joists are only
100mm high, you ain't got a lot to play with! If they're more, you should be
able to notch the bottoms to take the pipe - starting with 9cms on the first
joist, and progressively less on the others. If you support the joists
immediately either side of the notches, I don't see a problem with building
regs.
--
Cheers,
Roger
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Joists are 10cm

The pipe will run diagonally(ish) across the floor, so removal of
joists (or notching) would be staggered. I'll use strategically
positioned T&G chipboard to avoid floorboard coverage issues.

copy of the regs i've just dug out says that 1:80 is OK for 100mm pipe
with flow rate up to 6.3 ltr/s. Anyone care to comment ? Only have two
WC's would be attached, a revised calculation of 7.5cm for the fall +
11cm for pipe = 18.5, reducing the problem cosndirerably - I reckon
only the first ~3 joists would need to be touched.

All this will be in a full plans submission, but this upfront research
is invaluable as ever !

cheers
GD.

wrote:
Hi

I need to reposition the soil stack for a new upstairs layout. The new
stack will need to run for ~6m under the kitchen floor before
connecting to the existing drain pipe.

I've measured 17cm between the underside of the floor joists and the
concrete slab. Subtracting 10cm for the pipe, I have approx. 7cm
spare, i.e. not enough for a 15cm fall (1:40 on a 6m run by my
maths). The joists are perpendicular to the pipe.

As an alternative to excavating a run in the slab, would removing 4"
sections from the first ~6 joists and supporting their newly-formed
ends on bricks cemented into the slab satisfy the building regs ?

Thanks
GD.

where has the 1:40 come from, IIRC the fall per metre needs to be between 18
and 90mm, so over 6m would give 18 *6 = 108mm, however again IIRC the BCO
may let you go down to 9mm per metre (if you have 2 toilets?? on pipe),
giving a fall of 54mm over the 6m

Jon

Roger Mills wrote:
In an earlier contribution to this discussion,
wrote:

Hi

I need to reposition the soil stack for a new upstairs layout. The new
stack will need to run for ~6m under the kitchen floor before
connecting to the existing drain pipe.

I've measured 17cm between the underside of the floor joists and the
concrete slab. Subtracting 10cm for the pipe, I have approx. 7cm
spare, i.e. not enough for a 15cm fall (1:40 on a 6m run by my
maths). The joists are perpendicular to the pipe.

As an alternative to excavating a run in the slab, would removing 4"
sections from the first ~6 joists and supporting their newly-formed
ends on bricks cemented into the slab satisfy the building regs ?

Thanks
GD.

You'll still need something to support the floorboards which run over the
pipe - so you can't remove *all* the joist at that place or, if you do,
you'll need a metal bridge or something.

How deep are the joists. Sticking with your 1:40 slope (but see also the
other reply suggesting you need 1:25) you need a clearance of 15 + 11 = 26
cms, and you've only got 17, so you need another 9. If the joists are only
100mm high, you ain't got a lot to play with! If they're more, you should be
able to notch the bottoms to take the pipe - starting with 9cms on the first
joist, and progressively less on the others. If you support the joists
immediately either side of the notches, I don't see a problem with building
regs.


I think 1:60 is allowable for a soil pipe...but you need a rodding eye
where the vertical meets it.

I can see no reasons why, if you have a decent slab underneath, you
cannot cut the joists and support them, provided there is a damp proof
later between the bricks and the wood.

DO provide at least one means of rodding the underfloor section though.
You OUGHT to have a manhole cover at the downstream end of the
section...i.e. your underfloor section should be dead straight and exit
to the outside into a pot with a cover. I recommend you don't try to get
away without this.

Hi

the 6m run will join the existing vertical 'outlet' pipe. The outlet is
embedded in the slab at the front of the house and leads directly to
the septic tank. This existing stack joins vertically onto the outlet.

Is there a minimum angle that the 6m run needs to connect to the outlet
? As it stands, it would be the angle of the fall discussed above,
i.e., very shallow !

I'd put a rodding eye at both ends of of the 6m run.

cheers.

this is really useful....thanks Charlie.

In an earlier contribution to this discussion,
wrote:

Hi

the 6m run will join the existing vertical 'outlet' pipe. The outlet
is embedded in the slab at the front of the house and leads directly
to the septic tank. This existing stack joins vertically onto the
outlet.

You might still have a problem!

It seems to me that, in order to get a fall, the bottom of the 'horizontal'
pipe needs to sit on the slab at the point where it joins into the stack.
This might be difficult - if not impossible - to achieve.

If the stack joins into a socket whose top is flush with the surface of the
slab, you'll have to fit a tee into the socket - and the branch of the tee
will be a fair bit higher than the slab.
--
Cheers,
Roger
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monitored.. Messages sent to it may not be read for several weeks.
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