siphon issue

[Richieduliban87]

I’m having an issue with air flowing back through the plumbing system and siphoning dry the shower trap causing a smell in the bathroom.

I’ve teed the main 4 inch pipe up into the loft. Would putting a vent cowl or air admittance valve at the end of this pipe in the loft solve the issue.

The shower tee is before this.

 

[Harry Bloomfield]

I’ve teed the main 4 inch pipe up into the loft. Would putting a vent cowl or air admittance valve at the end of this pipe in the loft solve the issue.

Is it blanked off in the loft, so no air can get in? if so, then yes an AAV will solve that.

 

[Richieduliban87]

It is blanked off. I was planning to actually put a toilet up there but it sounds like it will be useful to solve this issue. So even though its called AAV, would it let air out also?

 

[Harry Bloomfield]

Idea of the AAV is that when there is a slight vacuum in the pipe, it allows air in which will prevent water being drawn out of your traps. Other than when there is a vacuum it will remain sealed, so smells will not escape into the loft.