Simple AAV and Extractor Vent Questions

[Tin Soldier]

Hi there,

 

simple question, hoping for a straight answer as theres loads of conflicting information out there.

 

Whilst extending my house, which includes two ensuites, a utility room and a kitchen. 

 

Do I need to install svp out through the roof with a cowl on top as per the old house, or could I pop AAV's on all the SVPs and not poke a heap of holes in the roof

Whilst extending I am also converting a downstairs office into a family bathroom. Do I need to bring the SVP up through the ceiling, through the walls, joist hangers and out through the second storey roof as per the architects detail, or could I pop an AAV within the ground floor bathroom, but higher than any of the u bends in said bathroom?

 

Simple question for extractor fans for ensuites, the existing ones have pipes that pop up through the roof a good 30cm with a cowl on top, are there good low profile alternatives to this that still allow for effective extraction?

 

cheers

 

Scott

 

[Nickfromwales]

As long as you are on a series run of houses that all have SVP's then you can petition your BCO on the 1 in 10, or 1 in 5 as some state it, clause where your neighbours either side are providing the network sewers with vents to atmosphere. 

SVP's don't form a function for the dwelling, they are required to vent the gasses that build up in the sewers . AAV's should suffice, but your BCO may be a picky tw4t and dig their heels in. One per property max though so no need for multiples. 

 

Vents can go out the walls horizontally so that's up to you. The cowls are to stop driving rain getting into the ductwork so best to check what's available before committing to either option. Why not go for trickle vents and PIV ? 

 

[Jeremy Harris]

As a general rule, you only need a single adequate SVP per foul drain run, often for more than one house, and can fit AAVs above the highest level of all the drains fitted to all the other soil pipes.

 

Worth reiterating that there are two functions for a foul drain vent, both of which are separate and don't need to be met by the same solution.  The first is that there must be an open vent that allows the foul drain pressure to equalise with the local air pressure, and to allow the escape of any gas build up in the foul drain (not a very realistic possibility for a house, but can happen in larger sewers).  The second function is to prevent a vacuum developing behind the slug of water that is rapidly discharged down the soil pipe when a toilet flushes.  If this was allowed to happen then is could suck the water out of the basin/bath traps that may be connected on the vacuum side of the soil pipe, allowing foul odours into the house.

 

For the sake of cheapness, a combined soil vent pipe is most commonly fitted.  This can both allow the pressure to equalise and prevent a vacuum build up when a toilet flushes.  Form the perspective of a builder this is cheap and easy.  From the perspective of an energy efficient house it's a lousy idea, as the SVP acts as a chimney, allowing cold outside air to flow up/down it, so causes a thermal bridge.  It's preferable to avoid an internal SVP and use AAVs and an external vent for the foul drain if possible.

Edited March 24, 2018 by JSHarris
cross posted with Nick

[joe90]

Yup, my soil vent to the sewer ( treatment plant) is on the side of my garage ( highest point) and in the house I have a 50mm AAV just below bedroom ceiling level to prevent vacuum ( as Jeremy describes above) . This means I have no thermal bridge ( pipes out to a stack)  and the house has no external pipework stuck to the walls ( one of my pet hates).

[Tin Soldier]

There’s no one around me I’m detached rural setting, septic tank of my own

 

old bit of house has multiple svp to atmosphere so it’s just the new bit and one down stairs room in the old bit I’m focussed on

 

if I’m reading correctly above I can use aav ?

[Nickfromwales]

2 hours ago, Tin Soldier said:

There’s no one around me I’m detached rural setting, septic tank of my own

 

old bit of house has multiple svp to atmosphere so it’s just the new bit and one down stairs room in the old bit I’m focussed on

 

if I’m reading correctly above I can use aav ?

You can just put a vent in the garden. If it's your own system then no problem at all. They can go ground level, well just above so you get an invert or a cowl on it.