Bigus Dicus wrote:

I have a similar situation to JMC - I only have a downstairs toilet
and I want to add an upstairs one.

Unlike JMC, I think my pipe slope should be OK, but I don't appear to
have a "soil stack" visible anywhere outside my house. My mate tells
me I must instead have an "air admittance valve" hidden somewhere near
my current downstairs toilet (either inside the house or outside under
some wooden decking I have). I've never seen it but it definitely
isn't upstairs (I have no loft).

If that is true, will there be a problem with the new upstairs toilet?
Will I have to move this "air admittance valve" to be higher than the
new highest toilet, i.e. the upstairs one?



Yes, probably.

In essence you need to have a pressure relief system that will carry the
pongs away high up SOMEWHERE in the sewer. This may or may not be shared
between houses, and it may or may not be visible. In my case I have
carried a long exhaust pipe down the length of the roof to exit under
the eaves.

Each toilet then needs some way to ensure that as it flushes, the
suction of the falling turd and water mix does not suck dry any basin
traps etc. That is the purpose of the air admittance valve.

So you need an open exhaust somewhere downstream of every bog to prevent
pressure build up, and an inlet somewhat upstream of it, to stop partial
vacuums.

Air admittance valves do the latter, but not the former.



Does the answer to this depend on whether I have a proper bog or a
pumper?

THank You.