Shortening soil pipe

I understand that I might be able to make improvements to the our soil stack by bringing the top of it into the boxing-in in the bathroom and using an air admittance valve from Screwfix (95531).
The present stack is internal and exits the building through the roof above the bathroom. Where it passes through the roof tiles has been the source of a couple of serious leaks in the past that have damaged the bathroom ceiling so I would like to get rid of this weak point.
So, do these valves work? If they do, how low can I bring the top of the stack? Could it be, say, level with the top of the close-coupled cistern?
Removing the boxing-in in the upper part of the bathroom and reducing it to around 800mm in height would also have benefits as wall space is in short supply.
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Frank
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Hi

Before you spend a lot of time on this - double-check with your local council's Building Control people. We did a fair bit of work on drains & things around this bungalow - and Building Control wouldn't give us a certificate until we re-instated the 'through-the-roof' vent that the previous occupier had removed and replaced with an air-admittance valve...
Good luck Adrian - Suffolk UK
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On 28/08/2006 13:28 Adrian wrote:

Thanks for the warning.
Daughter's house in Leeds/Wakefield has the arrangement I describe so it'll be worth checking for her benefit as well.
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F wrote:

You can get proper waterproof shrouds etc for this sort of pipe through roof arrangement.
I would say what you really want is a competent roofer.
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On 28/08/2006 14:45 The Natural Philosopher wrote:

We came to the same conclusion...
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F wrote:

I wouldn't call that an improvement.

So, sort it out properly.

They work all right BUT thet cannot be used in isolation. Sure they prevent vacuum in the stack sucking other traps dry, but they do nothing to stop positive pressure build up - you need a stack vent somewhere in the locality to do that.

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On 28/08/2006 14:43 The Natural Philosopher wrote:

Not sure why this shouldn't be an improvement: it will remove a weakness in the watertightness of the roof and create more wall space in the bathroom...
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F wrote:

Those are not improvements to the soil pipe though.
You can *improve* any room by knocking it through to the garden,.. just a bit chilly in winter, what? :-)
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