Soil stacks venting into the loft

[Tom Pickles]

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 house?)?

Will it cause any problems if I remove the elbows and replace with air admittance valves?

Cheers

[The Natural Philosopher]

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.

[Tim Watts]

No.

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 air vents.

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.

[Cash]

Stick a Durgo Valve on the end - had one in my attic now for around 10 years with no problems.

only operates when a 'vaccum' is present in the soil stack.

Cash

[Tim Watts]

And (for the OP) do NOT buy from B&Q or a builder's merchant - notorious for overpricing these. Screwfix have them at around 20 quid IIRC - I have the Floplast AAV from Screwfix.

[Cash]

Tim,

I bought one from my local independant plumber merchants, and it cost nowhere near that figure (even allowing for inflation) - but that firm will out peform such places as B&Q and Plumb Center etc on price, level of stock, knowledge of products and customer service.

Cash

[Tim Watts]

Good call - last time I saw a B&Q price, they were 40 quid - as were the BMs.

[Tom Pickles]

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 freezing.

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?

Thanks.

[Doctor Drivel]

It is now and was in 2001

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 basins

[Doctor Drivel]

Put an AAV on each.

The heat will go the other way if there is air movement. Put insulation around the soil stack that is over the boiler as well.

Yes.

[Tim Watts]

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?

[Tim Watts]

That does sound vaguely familiar....

[Tom Pickles]

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 there either.

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?

Thanks.

[Tim Watts]

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.

[The Medway Handyman]

Not 100% reliable long term. Local ind est has an area of 2 story units with toilets on ground floor. Cistern behined panel, 4' high soild pipe with AAV. Found 3 in the last year not working, stuck & allowing smells into the toilet.

Dave

[Phil L]

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?

[Phil L]

forgot the link:

[Tim Watts]

I carefully fitted my AAV under a loose-lay shelf which makes unplugging trivial :)

[Tim Watts]

There are specific clearances stated on a digram in Part H section 1.31

To the OP, persimmon homes were (or still are) in the NHBC.

[Cash]

As an 'open vent', nor would it comply with the building regs with regards to height above roof or distance from any opening windows - just to clarify your statement.

Cash