I am in the process of renovating my Victorian house. It has a
downstairs bathroom, and at present the toilet connects to the main
drain via a pipe in the floor. The bathroom sink and bath connect to
the drain through a drain gully in the yard. The kitchen sink connects
to the drain through another drain gully in the yard. I think these
gulleys are known as bottle gulleys, as they have additional water
At present the drain is not ventilated at the back as there is no soil
stack / ventilation pipe, nor an air admittance valve. Looking down my
street, it looks like the houses originally ventilated through a vent
at the front of the house, just above ground level in the (small)
front garden. When these gardens were resurfaced, presumably this vent
was removed. I recently had a CCTV survey conducted on the drains, and
the company suggested that as the drain feeds into a siphon trap at
the front of the house, and the front downpipe from the gutters feeds
in above this trap, that this provides ventiliation in place of the
I want to replace the drain gullys in the yard and resurface the yard
(I'm already lowered the ground level in the yard to solve a rising
damp problem). However I don't want to complete this work, only to
find later on that the drain ventilation is not sufficient. Looking at
my neighbours house, they have had this work done, and when the
builders did this, they installed a ventilation stack connected to the
drains in the yard.
I asked the builder (he's specializes in landscaping for gardens) I
intend to use to replace the gulleys / resurface the yard if I need to
do the same, and after consulting a friend, he suggested I would be
better with an air admittance valve.
However I think the valve will look rather ugly in my bathroom,
particularly as after reading the building regs I'm not sure if it
needs to be higher than the waste on the sink. I guess it can be boxed
in, but this isn't ideal either ...
So my questions are:
1. Do I need to ventilate the drain, or is the current arrangement
with the downpipe sufficient?
2. If I do need to ventilate the drain, should I ventilate it using a
stack like my neighbours?
3. Alternatively am I better using an air admittance valve?
4. If I am better using an air admittance valve, am I correct in
thinking it needs to be 10 cm higher than the sink waste? Or, because
the sink and bath connect to the drain via drain gulleys which have
their own water traps is this unnecessary and can I put the valve at
the same height as the connector between the toilet and the soil pipe
going into the floor?
Any advice here is greatly appreciated, thanks a lot