air admittance valves

[fishnchips]

Hi, Just wondering if I can put a 50mm air admittance valve to vent an ensuite? My heart and mind is saying I need to use a 100mm one. It'd be great to use the smaller due to boxing size for the 4"".

also while I'm on the subject, the poorly designed barn conversion has 4 bathrooms, I'm told by another plumber where domestic plumbing is his domain that I'll get away with one vent to atmosphere with the rest using durgo's. The problem is that there is no loft for the soil pipe to get air from and they're just going to box everything in, I believe the boxing should have air vents in??

thanks in advance!!

 

[kris]

Have a read,

http://www.planningportal.gov.uk/uploads/br/BR_PDF_ADH_2002.pdf