Air brick numbers - help!

[sean1933]

I'm just trying to work out spacing for air bricks as we have a complicated shape lots of level tresholds - my plan overall was cross ventilation left to right.

Having dealt with the rear extension where we have level thresholds pretty much all the way along (dealt with via a sunken drained void  hidden under the paving in line with NHBC guidance doc 

http://www.nhbc.co.uk/Builders/ProductsandServices/TechZone/NHBCStandards/TechnicalGuidanceDocuments/61/filedownload,65368,en.pdf ) I am now struggling to deal with the ventilation for the main house (ignoring front protrusion), although I am not sure if my understanding of the calculations as per BS5250 -  It says you need the greater of 500mm2 of ventilated area per m2 of floor or 1500mm2 per m run of ventilated wall. My assumption is that this requirement is each from each side (ie air in, and out) , rather than total vents.

 

My calcs being 139.5m2 floor space x 500m2 = 69,750mm2 / 6170 mm2 (each timlock vent) = 11.3 ie 12 vents each side. This clearly wouldnt look right on a wall thats 8.8m long as spacing would be c.3 bricks apart (not to mention the structural issues). Is this right? Assuming so, any solutions? Can I just get away with vents around the entire main building or do I need to consider double stacked vents (which I imagine wont look subtle and will take up most of the insulation space in the 200mm cavity so thermal bridge issues). Help!

 

 

[PeterW]

No the calculation is for all perimeter walls for the void so you 12 vents overall.