Hi-

in my toilet downstairs, I have a soil pipe in the corner of the room
rising to about 6' high where it is capped with an air admittance
valve. I've just had dado rail fitted in the toilet, and am wondering
whether I can reduce the height of the AAV to (just) below the dado
rail and then have it boxed in (with a brass grill for ventilation).

Further details:

The toilet also has a sink, and the exit drain is joined by a 2nd sink
and washing machine outpipe in the next room before leaving the house
where it goes straight into the ground. (I have a 2nd soil pipe which
is vented from my upstairs bathroom running down the side of the house
about 10' away).

From the research I've done, the AAV "must finish above the highest
flood level of the space the valve is in...I.E. If the valve is in the
same room as a wash hand basin, it must be higher than the overflow of
that basin. This is so the pressure equalisation can occur without
breaking the water in the traps."

I'm not quite sure what the overflow means - both sinks (the one in
the toilet and the one in the next room) have S bends in their drain -
is that the level of the overflow? or does it mean the overflow hole
in the back of the sinks?

The height I'd like to replace the AAV would be only 3 inches or so
above the S bend water level.

Thanks for any advice

Jim wrote:
Hi-

in my toilet downstairs, I have a soil pipe in the corner of the room
rising to about 6' high where it is capped with an air admittance
valve. I've just had dado rail fitted in the toilet, and am wondering
whether I can reduce the height of the AAV to (just) below the dado
rail and then have it boxed in (with a brass grill for ventilation).

Further details:

The toilet also has a sink, and the exit drain is joined by a 2nd sink
and washing machine outpipe in the next room before leaving the house
where it goes straight into the ground. (I have a 2nd soil pipe which
is vented from my upstairs bathroom running down the side of the house
about 10' away).

From the research I've done, the AAV "must finish above the highest
flood level of the space the valve is in...I.E. If the valve is in the
same room as a wash hand basin, it must be higher than the overflow of
that basin. This is so the pressure equalisation can occur without
breaking the water in the traps."

I'm not quite sure what the overflow means - both sinks (the one in
the toilet and the one in the next room) have S bends in their drain -
is that the level of the overflow? or does it mean the overflow hole
in the back of the sinks?

The height I'd like to replace the AAV would be only 3 inches or so
above the S bend water level.

Thanks for any advice

I believe it means the hole at the back of the basin.

Not sure of interpretation when a basin without an overflow is fitted.
Maybe the rim of the basin itself?

--
Rod

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onset.
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Rod wrote:

I'm not quite sure what the overflow means - both sinks (the one in
the toilet and the one in the next room) have S bends in their drain -
is that the level of the overflow? or does it mean the overflow hole
in the back of the sinks?

The height I'd like to replace the AAV would be only 3 inches or so
above the S bend water level.

Thanks for any advice

I believe it means the hole at the back of the basin.

Not sure of interpretation when a basin without an overflow is fitted.
Maybe the rim of the basin itself?

I think that's right too - certainly when I fitted one myself in similar
circumstances I followed those rules, and the building control officer
didn't pass comment!

David