No open soil pipe vents.

[COG]

My house is one year old with three toilets running into separate stacks ,one short stack at 1.5m and two stacks terminating in the loft ALL fitted with air admittance valves. Its been a while since i did basic plumbing but at present i have no outlet to expel any build up of gas, have the building regs changed or am i wrong. Anyone got a copy of the current regs that apply,thanks.

 

[chrishutt]

Download Building Regs. Document H1 from two-jag's site.

You should have one vent pipe (minimum 75mm bore) rising through roof to open air. Not too difficult on tiled roof if you've a head for heights (or a low roof).

 

[Bahco]

One yr old house will have been passed by building regs who will have ensured an outlet for sewer gases. Speak to Building Control about your concerns who will check records for you.

 

[TexMex]

I have no outlet to expel any build up of gas.

You seem to have missunderstood the purpous of the Vent on your soil stack. It's not to let gasses out, it is to allow air in. Any gasses in the drains should NOT be allowed onto your property. (Hence the use of the U Bends in the first place)

When you flush the toilet, the plunging flow of water will cause a partial vacuum behind it. If there is nowhere for this air to get in, it will suck it in through your toilet, sink waste, or wherever it can. Thus causing an empty U bend.

When you have a normal open vent pipe, a natural side effect, is to allow noctious gasses out of the sewer. This is not their purpous, just an unpleasant side effect. It is due to this unpleasant side effect that an open vent has to be placed outside and at least 1.5m higher than any opening within 10m of the vent.

The inovation of the Air Admittance Valve got around this issue. It allows the air in (to prevent your U bends being sucked dry), but doesn't allow the noctious gasses back out. This also allowed the vent to be terminated inside the building (such as in the loft).

The setup you describe sounds perfectly sound. The ideal place for any noctious gases in the sewer is in the sewer. Best leave them there.

 

[chrishutt]

Have to disagree with above. Sewers need ventilating, and this occurs through all the vent pipes. It might not matter if one or two houses get rid of their vent pipes, but what if everyone did it? That is why there is a requirement for vent pipes. Perhaps in this case, it was judged that there were enough vent pipes in the development overall for your house not to require one. On the other hand perhaps the builder just cut corners...it has been known.

 

[slippyr4]

anyone know if Air Admittance Valves can be fitted outside?

 

[Bahco]

No.
Their purpose is only to protect against loss of trap seal and do not ventilate the sewer.

 

[chrishutt]

In which case, why do building regulations require a vent pipe at all, since trap seal loss can be prevented by AAVs?

 

[Bahco]

In which case, why do building regulations require a vent pipe at all, since trap seal loss can be prevented by AAVs?

Er, to let gases out.

 

[chrishutt]

Their purpose is only to protect against loss of trap seal and do not ventilate the sewer.

to let gases out.

So what is the purpose of the vent pipe? To ventilate (let gases out) or not?

 

[Bahco]

Hi Chris

As I understand it, an AAV allows air into your drainage pipes to assist correct drainage preventing loss of trap seal. They are continually in the closed position until a negative pressure is created which opens the valve allowing air in. They do not allow any sewer gases out as opposed to the normal vent pipe which does.
I was using the word ventilate to describe allowing air in and gases out.

Hope this restores your faith in me.

 

[TexMex]

In which case, why do building regulations require a vent pipe at all, since trap seal loss can be prevented by AAVs?

Err...Actually they don't. Nowadays you can use an AAV.

As I say, allowing gasses out was never the intended function of the vent. Just an unpleasant side effect. Any gasses that develop in the sewer can just follow the same course as the rest of the sewage.

Any drains that are filled full bore will cause the same partial vacuum as I described above. Thus drawing the gasses along with them. Any that are not full bore, will have clearance above the water line to allow the any positive pressure to disipate.

 

[Bahco]

Nowadays you can use an AAV.

Tell that to my building inspector as he insisted 2 yrs ago that I installed a open vented soil pipe when I had a new toilet upstairs.

Always best to go with BCOs advice.

 

[chrishutt]

May I quote a section from the Building Regulations Approved Document H1, which you can access here - bold text is my emphasis:-

Ventilated discharge stacks may be terminated inside buildings when fitted with air admittance valves complying with prEN 12380. Where these valves are used they should not adversely affect the amount of ventilation necessary for the below ground system which is normally provided by open stacks of the sanitary pipework.......Where there is no open ventilation on a drainage system or through connected drains, alternative arrangements to relieve positive pressures should be considered.

This clearly confirms that ventilation is required for below ground drainage, as I have been saying. I await apologies....

 

[slippyr4]

place i used to live (property would now be 6 years old) didn't have an open topped soil stack. I never really looked at where the soil stack terminated, i now presume it had an aav on it somewhere.

but anyway, when it rained hard and the drains got a bit full up, the downstairs bog used to bubble air. i presume this is positive pressure in the sewer (from the increased volume of water fully filling some underground pipes) and was pushing residual air up my toilet. so this is probably why chris says that an AAV is not enough on it's own.