I've always been puzzled as to where the soil stacks vented in our 2001
build detached house as all stacks are internal, but no external pipe
protruding from the roof or vent tiles on the roof. I have just been in the
loft and stumbled upon an open 100mm elbow which I believe is the vent for
the soil stack from one side of the house, servicing the downstairs loo and
1st floor bathroom. There is another stack on the other side of the house
for the utility and en-suite, so I reckon this is the same.
I noticed also that the loft space wasn't that cold considering the outside
temp of the last couple of weeks, but it has pretty good levels of loft
insulation. And also, there has been an unknown smell in the loft at times.
Not necessarily a bad smell, but an unexpected one nonetheless. Perhaps
familiar with stagnant water or suchlike.
Is it a good idea just to have an open ended vent on the soil stacks (being
just 90deg elbows) into the loft?
Will the open vent contribute to heating the loft space and is it really a
good idea for it to be heating the loft right now (am I losing heat from the
Will it cause any problems if I remove the elbows and replace with air
I consider it is a bad idea as in introduces smells and hot wet air into
the loft pace. In my case we took the vent trough 90 deg and ran it
through an outside wall.
That was less than ideal either, as steam condensed down its length and
led to dripping from the end. That was solved by a wood block halfway
along to make it a sort of shallow inverted U - so most of the
condensate runs back down to the drains
In hindsight an inverted U exiting through a soffit would have been better.
Air admittance valves are not a complete answer, as they can still lead
to drain pressure build up.
I can't claim it is against Building Regs, but if it isn't it should be.
What you might be able to do is to add an AAV (air admittance valve) to
the end. Bit rusty on the details, but if your neighbours have an open
to air soil stack vent, then you will be able to.
That deals with all the negative pressures in your system (ie plug of
water going own a vertical pipe after a loo flush) without allowing
anything to come out - but the sewer system also needs to vent
overpressure on occasion hence the need for some people to have open to
You might want t check out the Approve Document for drainage (I forget
which letter - try google for "Approve Document" "Drains") - that has
lots of useful diagrams.
Whilst in bed last night, I realised why we are getting so much snow melting
on one side of our roof. It's dripping so bad off the fascias as the gutters
are iced up, that it's splashing off the paving onto the brickwork and
I have no doubt this is because there is literally an inch gap between our
wall mounted boiler and the boxed in soil stack in our utility. With the
boiler working so hard with us being home all day this week, it's obviously
heating up the soil pipe quite nicely and venting this heat into our loft
space, melting the snow/ice on the roof.
I am liking the idea of using an air admittance valve at least on this soil
stack (and leave the other, much cooler one as it is now). But, I'm
wondering about heat build up in the soil pipe next to the boiler if I
effectively cap it off using an AAV. I don't want the heat entering the
loft, but I also don't want the soil pipe to get too warm internally.
Is my concern a valid one or is it nothing to worry about?
The soil pipe will cope with 70C *at least* (being PVC).
The outside of the boiler casing should not be getting that warm - so I
don't think you've anything to worry about. Besides the pipe next to the
boiler is already hotter thn the top could ever get, even if fitted with
an AAV and the pipe hasn't compained I take it?
Well in my error, I asumed the second soil stack would be the same as the
first. Wrong. The second pipe was more difficult to get to, but I had a look
this morning. When I finally found where the stack was and moved the loft
insulation aisde, all that was there was a rectangular hole with warm air
coming from it. No elbow, no PVC pipe, nothing but a hole.
The problem is due to poor design by Persimmon, lazy workmen on piecework
and sloppy building control officers (there are several houses exactly the
same design as ours, so would all have the same problem). When looking from
above, our house is L shaped, with a hip/valley roof. The stack comes into
the loft exactly where several wooden support beams meet for the roof
construction. So if there was a pipe there, I would never get an AAV in
there as there's no room for it. Couldn't get any trunking or piping in
So basically, I'm buggered.
I did take my IR thermometer up there and took a reading of the felt which
was about 1.5degC, and the top of the open stack above the boiler which was
about 20degC. So this is deffo the source of the loft heating and the reason
so much snow is melting on the roof on that side of the house.
The only thing I can think of is to cover the hole with some fibreglass
insulation which would hopefully keep the heat in, but could make the
fibreglass damp and cause other problems, so I have left it open for now.
Is there anything at all I can do about this?
Are you sure there isn't an AAV somewhere down that hole?
If there isn't, you would expect a distinct "sewer smell" to be present
over that hole - I had some open 4" pipes on mine during the intial
building work and they could lightly stink out a small room.
Can you see down the hole, maybe with a mirror?
If there is an AAV, then stuff a bit of loft insulation in the top of
the hole to prevent convection to the loft (will breath enogh for the
AAV to work).
If not, then your best solution is to estimate where the pipe ends in
the boxing and careful cut out a section of boxing which shouldn't be
too distruptive and should repair quite easily, and add an AAV.
That is one solution.
1. A AAV on each stack.
2. a flexible pipe on each running to a grill in the soffit.
It may have been scheduled to have a flexible pipe on the end and vented via
a roof tile, but never happened and through the BCO.
The end of a sewer line needs an open vent. Then only every 5th house needs
a vent. The rest can have an AAV or HepVo trap on the baths, sinks and
having it vented through the soffit isn't a good idea - the sewer stench
will come straight into the room when a window's open in summer - this is
why the stack goes a few feet past the roofline.
To the OP, persimmon homes were (or still are) in the NHBC.
The warranty is a 10 year one, if I were you I would contact them and take
it from there - it's obvious that these stacks should have been taken
through the roof tiles and a proper flashing kit installed.
A builder would do this for you now, but why should you pay for what should
have been done as standard?
We're only covered by NHBC if it doesn't comply to the regs *and* there's an
imminent danger to the occupants health and safety. I don't think our health
and safety is at risk.
To quote from their claims guidelines, section 4 of the doc:
"If there is a present or imminent danger to the physical
health and safety of the occupants of your Home
because it does not comply with the Building
Regulations that applied to its construction, conversion
or renovation in relation to the following specified
Building Regulations, we will pay you the Cost of the
Stick a Durgo Valve on the end - had one in my attic now for around 10 years
with no problems.
It only operates when a 'vaccum' is present in the soil stack.
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