Should the air move?

[DIYWell]

I was having a cuppa in a friend's new kitchen extension and he was muttering that it felt a little cold to hi. Sure enough, I could feel a draught by my ear. While his back was turned I had a quick look see.

Facing bricks, cavity, blocks, battens, then plasterboard on top, suspended timber floor. The draught coming round the socket. I know new builds are sealed to reduce heat loss. Does this not apply to extensions? Is it the done thing to let the air flow round the edges of the flooring up the back of the plasterboard?

 

[jeds]

In a word, no. The internal should be well sealed from external air and certainly sub-floor air should not be able to funnel up behind the plasterboard. (assuming a suspended timber floor and dot and dab plasterboard)

Shouldn't be too diffilcut to resolve. If it were me I would squirt expanding foam behind the skirting to seal the gap between floor/wall/skirting. This will mean small holes in the plasterboard just above the skirting which could be made good easily enough.

 

[DIYWell]

Well it's a suspended timber floor and, given the thickness and hollow sound, the plasterboard is on battens.

One wall he could do well enough, but the other has kitchen units on it. That'll be more tricky.

Before I mention it to him, Any advice about how far apart to make the holes and how big a 'squirt' is?

 

[Deluks]

A 'new' extension? Floor not insulated? tut-tut

 

[jeds]

Foam expands about 150ish so holes would need to be something similar.

That's a good point about insulation. I would check to make sure it is present. If it isn't you're into a different level of problem.

 

[DIYWell]

Right, casually brought up the topic with my m8 and he sketched out what was going on below the floor.

Between the joists there's mineral wool held in place with netting below it. As far as he knew, the inch or so gap between the first joist and the wall wasn't filled with anything, and neither were the similar gaps bwtween the noggins and the wall around the corner. So, looks like cold air under the floor can move up through the gap, round the edge of the floor panels and into the void between the block work and the plasterboard on it's strapping.

No idea about what happens at the top of the wall, since it's a warm ceiling but he's fairly sure no effort was made to fill any gaps.