Venting block and beam and wood floor together?

[rssteve]

I'm in the process of adding a room to the rear of the house. Currently the house floor which is suspended wood has a concrete screed about 400mm lower and is very dry down there.
My new floor is block and beam and there will about 150mm void with a dmp laid on the earth with some sand.
My plans show for me to form some new holes in the rear wall to link the 2, then fitting 3 new vents in the rear wall.
Could any moisture from the block and beam side rise and effect the suspended wooden side? I can't vent to the sides.

 

[freddiemercurystwin]

Not really but what do you mean sand? It should be a concrete slab and no dpm required. And why have you gone for B/B instead of timber?

 

[John D v2.0]

You're basically looking for a through draught with no dead spots. You can vent all round but two opposite sides would be fine. If you draw a diagram showing existing and proposed with locations of all vents in sub floor walls we can advise.
We had 2 extensions (porch and conservatory) when we mved in, and both had air bricks but they were just for show, so you have to check they're actually venting too.

 

[^woody^]

Vent on opposite walls or duct to achieve the same.

You dont need a DPM under a suspended floor

 

[rssteve]

The extension is piled and i want under floor heating on the tiled floor so there is a screed going ontop of the block and beam. The block and beam installation guide says to use weed killer on the subsoil and place a dmp with sand to hold it down before laying the beams.

 

[rssteve]

I will have air flow front to back but I was worried any moisture which comes out he ground on the block and beam part may effect the joists on the suspended wooden part. Although the current house is suspended and vented front to back, there is a concrete Base about 400mm below the joists so it is very dry down there.

 

[^woody^]

I was worried any moisture which comes out he ground on the block and beam part may effect the joists on the suspended wooden part.

You're not worried about moisture condensing on the DPM and forming a pool of water then?

 

[tomfe]

You don't need a concrete oversite or a dpm with bnb.
The whole point in having it suspended is so moister is carried away with the air movement.
Just cut some holes in the original external wall to let the air through, BC might ask you to do a vent every 2m or even 1.5m if the depth is large.