# Venting A Sub-Floor



## bluechimp

I have purchased a house built into a hill, so from the front it looks two storey and from the rear it looks like just the one. Hopefully that helps explain my predicament.

My garage and the room behind the garage are two steps down to the floor, the rest of downstairs is at a two step level above. So I want to raise the level of the room behind the garage, up to the same level as the rest of the house. However if I create a sub floor using C24 joist timbers on hangers, I would need to vent the subfloor. The problem is, the room behind the garage is at the back of the house and so the best way to describe it is ‘underground’. 

Do I have any option do we think at getting venting under the sub floor?


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## dholdi

How are the existing floors in the rooms vented or are they solid ?


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## bluechimp

With air bricks mate, but those floors have access to external walls


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## Caledoniandream

Can you vent it into the garage?


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## dholdi

bluechimp said:


> With air bricks mate, but those floors have access to external walls


Sorry, I meant the existing floor which will be under the floor you are proposing to raise ?


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## Darlofan

You're just wanting to raise the floor in the room behind the garage? What's on the wall in between the two? Could you not put airbricks in that wall between, not ideal as not external but better than nothing.


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## bluechimp

Caledoniandream said:


> Can you vent it into the garage?


That could be an option, then vent the garage?


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## bluechimp

dholdi said:


> Sorry, I meant the existing floor which will be under the floor you are proposing to raise ?


Oh sorry, yeah it's concrete.


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## bluechimp

Darlofan said:


> You're just wanting to raise the floor in the room behind the garage? What's on the wall in between the two? Could you not put airbricks in that wall between, not ideal as not external but better than nothing.


Just breeze-blocks, looks like this could be an option.

The other thing i'm keen to explore is the rest of the house has a subfloor so it may be worth venting into that? Via air-bricks in the joining walls.


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## Darlofan

bluechimp said:


> Just breeze-blocks, looks like this could be an option.
> 
> The other thing i'm keen to explore is the rest of the house has a subfloor so it may be worth venting into that? Via air-bricks in the joining walls.


I'd go with the option of venting all available walls then.


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## dholdi

bluechimp said:


> Oh sorry, yeah it's concrete.


In that case the only viable option you have is to vent the new floor through the walls into the adjoining sub floors.

You could use air bricks below floor level or just core drill a number of holes and fit some vent pipes.

I would try and space them as far apart as possible to encourage cross ventilation.

You can get cavity riser vents but they are normally only for a difference of a few courses, but with some improvisation can be made to do more, bit tricky to retrofit though.


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## bluechimp

Thanks all for the advice. I only twigged that the rest of the house must have a subfloor so I’m going to pull a few floor boards up and see what is cracking.

Thanks again.


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