# Forum Home Renovation Sub Flooring  Sub floor vents, how many, where when how

## mudbrick

So i hope this is the place to ask about this.
We have a brick veneer home on raised peirs. Sloping block and split level home just to make it difficult. The space under house varies from 7 foot to about 400mm.
We had a lot of water flow under the house during recent heavy rain. I then dug a 100mm ag line into the soil on high side of house to assist diverting the water.
Anyway so there were no vents at all in the lower side of house and mould was coming through the floor. How many vents should i add, what size, and what level ie if the brick wall is 10 bricks high from ground level to timber bearers,  what is the best level to add the vents ? Are the 4 brick sized vents from hardware shop OK ?

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## ausdesign

6000mm2/met of wall evenly spaced at or close to bearer level

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## barney118

I am sure it's 7500mm 2 per meter. So calculate your side of house in m2 then divide by 7500 to get number of vents required per m2.
The buy vents to give this flow, if you have vents at 5000mm2 then you will need more.  
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## ausdesign

It's actually determined by the climate humidity zone - Zone 1 requirement is 2000m2/met, zone 2 requirement is 4000mm2/met & zone 3 requirement is 6000mm2/met
Zone 1 is typically central aus. Zone 3 basically coastal & Zone 2 in between.
This is all assuming that the ground is not sealed with an impervious membrane in which case the requirements are halved.

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## barney118

Peter, 
I just looked up my TAFE notes (carpentry) and I recall a test we had earlier this yr and it was in relation to dwarf walls and termite management for new building work AS3600.1-2000 and it is 7300mm2.
 So there must be another standard you are referring too?

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## ausdesign

Sorry Barney got side tracked - the reference was BCA2011 part 3.4.1 Sub-floor ventilation

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## barney118

Peter, 
I have my files packed in boxes at the moment, so is this clause as you mention before? or is it different for the termite management?

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## mudbrick

Wow OK, 7000mm2 is only about the area of half a brick so it doesn't sound like too big a task to solve the problem.
The builder left gaps roughly that size on one side of the house and not the other ! guess which side has the damp problem  :Annoyed:

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