MortarThePoint Posted June 22 Share Posted June 22 I have a soil stack in a bathroom which is taking waste from a bath, shower, two toilets (one coming through the wall) and a basin. I know that AAVs are supposed to be mounted >=200mm higher than the highest entry to the stack which I can do where I want to put it in a boxout next to the toilet. However, does it need to be 200mm above the highest entry point to the waste system that feeds the stack? That is the basin which is higher than where I want to fit the AAV. In terms of the system filling up, it would overflow into the shower and bath before hitting the level of the AAV so does that mean it's OK to have the AAV where I am proposing? Link to comment Share on other sites More sharing options...
Marvin Posted June 22 Share Posted June 22 https://www.plumbingforless.co.uk/files/ww/merlin/POLYPIPE Air Admittance Valves and Anti-Syphon Units - Technical Guide.pdf 1 Link to comment Share on other sites More sharing options...
MortarThePoint Posted June 22 Author Share Posted June 22 Thanks @Marvin That is guidance for Polyvalve which may not be a A1 rated which apparently does allow installation below the spill-over level. See below from Floplast. Annoyingly, their picture doesn't actually show it lower than the basin, but the Minimum 200mm and text makes it reasonably clear. Even if it is an OK approach, I would still have to convince the BCO though. "11.5 FloPlast AVE100, AV110, AF110 and AX110 valves must be fitted in a vertical position 200 mm above the highest branch connection (see Figure 3). As FloPlast valves are A1 designated to BS EN 12380-1: 2002 it is possible to locate them below the lowest reservoir being vented." "1.8 FloPlast AAV’s are designated A1 in accordance with BS EN 12380: 2002 and can be fitted below the flood level of connected appliances, in air temperatures between -20°C and 60°C." https://www.floplast.co.uk/uploads/related-documents/BUsohExhe3Mqhq6jYrAqs9kLySHpgjrtGe5hGvjo.pdf Link to comment Share on other sites More sharing options...
MortarThePoint Posted June 23 Author Share Posted June 23 (edited) It's occurred to me that the shower wouldn't be an overflow point as its trap will probably have a non-return valve. I think I'd want the AAV to be higher than the bath's plug hole [1] and probably higher than the toilet pan's rim [2]. [1] The basin joins the same branch as the bath that then joins the stack below the toilets branch. I think that means the basin can't overflow the AAV without already starting to fill the bath. [2] A blockage between where the basin branch joins the stack and the toilets branch joining the stack would overflow the toilet pan before reaching the level of the AAV. Edited June 23 by MortarThePoint Link to comment Share on other sites More sharing options...
Kelvin Posted June 23 Share Posted June 23 You said you can fit the AAV so that it’s >=200mm therefore why not just do that removing any future concerns. I had the same situation although my AAV is inside the coomb. To meet the right height I brought the wall out another 100mm which then gave me the height I needed. I could have done what you’re proposing but decided just to follow the guidelines. Link to comment Share on other sites More sharing options...
MortarThePoint Posted June 23 Author Share Posted June 23 1 hour ago, Kelvin said: You said you can fit the AAV so that it’s >=200mm I can >=200mm above where they join the stack but not so easily>=200mm above the basin overflow which is a fair bit higher Link to comment Share on other sites More sharing options...
Nick Laslett Posted June 23 Share Posted June 23 (edited) @MortarThePoint I used the Wavin Osma AAV 4S306, which is A2 rated. However the 4S304 appears to be able to be installed below spillover level. https://www.wolseley.co.uk/wcsstore/ExtendedSitesCatalogAssetStore/images/products/AssetPush/DTP_AssetPushHighRes/std.lang.all/ti/on/Wavin_Osma_Soil-Waste_Installation.pdf Quote When used to vent a stub stack, 110mm Air Admittance Valve 4S304 can be located 200mm above the highest branch. The Air Admittance Valve 4S306 must be installed above spillover level of highest appliance. *Edit Just had a looked at the BBA cert for the Wavin Osma AAV 4S304, this gives very clear guidance on installation location. Added another pic. https://wavin-digital-indianajones-prod.storage.googleapis.com/assets/category/1520297e-f72b-4c71-9b89-dc027056ec87/d3c79907-6216-49e4-b861-3f792432bcdc/2b939e03-ca09-4297-8f3b-828b5b200e22 The British Plastics Foundation have a good guide on AAV https://www.bpfpipesgroup.com/media/71872/Air-admittance-valves-for-domestic-properties-v2-Jan-2024.pdf Edited June 23 by Nick Laslett 1 Link to comment Share on other sites More sharing options...
MortarThePoint Posted June 23 Author Share Posted June 23 (edited) It's worth noting that the 32mm, 56mm and 82mm Durgo brand AAVs are A1 but the 110mm one isn't: https://www.hunterplastics.co.uk/media/1791/bba-durgo-certificate-06-4325.pdf Edited June 23 by MortarThePoint Link to comment Share on other sites More sharing options...
Marvin Posted June 24 Share Posted June 24 Also check if the AAV is alright for 2 toilets?? (not sure it makes any difference) Personally I ran a reduced pipe up through the stud wall and put the AAV in the loft.... Link to comment Share on other sites More sharing options...
MortarThePoint Posted June 24 Author Share Posted June 24 4 minutes ago, Marvin said: Also check if the AAV is alright for 2 toilets?? (not sure it makes any difference) Personally I ran a reduced pipe up through the stud wall and put the AAV in the loft.... Odds of both toilets being flushed at the same time should be reasonably low, even if I'm cooking Sending it up inside a stud wall is a nice approach, but this is near only blockwork walls. Link to comment Share on other sites More sharing options...
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