Air blowing between upstairs floor - should I insulate ?

[volks]

I've got a dormer bungalow with a second floor with a flat roof on the dormer and some insulated pitched roof in the loft.

The floor beneath the upstairs rooms is uninsulated - just joists and boarding. The air howls through the floor between the upstairs and downstairs, when I'm in the loft and peer between the joists.

I feel this just blows away any heat that rises from the downstairs to upstairs. I was going to stuff insulation beneath the joists but read it could cause a room to drop below the dew point and cause condensation?

Should I insulate the floor between the downstairs and upstairs or leave it to blow air through? Should I insulate just at the eaves to stop air blowing in, but leave the floor gap between open to let heat into the upstairs?

What are the risks and problems I may encounter?

Final notes - the upstairs and downstairs are heated.

 

[Why Not Indeed]

If both sides of the gap that the air is howling through are heated then insulating/blocking up there probably doesn't matter so much [in my house, downstairs is always way colder than upstairs in the heating season, so I would block this gap up in my situation].
I think a more important question is why air is howling through there. There must be gaps somewhere else that is causing this air flow, presumably driven by wind?

I was going to stuff insulation beneath the joists but read it could cause a room to drop below the dew point and cause condensation?

That could only apply where you insulating the interface between the warm side/cold side of a building, which I don't think you are from what you've described.

 

[volks]

If both sides of the gap that the air is howling through are heated then insulating/blocking up there probably doesn't matter so much [in my house, downstairs is always way colder than upstairs in the heating season, so I would block this gap up in my situation].
I think a more important question is why air is howling through there. There must be gaps somewhere else that is causing this air flow, presumably driven by wind?

That could only apply where you insulating the interface between the warm side/cold side of a building, which I don't think you are from what you've described.

Thanks for the reply! Good to know I was wrong about the condensation issue.

I think the wind blows through either via the soffits /fascias and it gets easier access to the floor space than the eaves (given the dormer conversion) it also could be coming in from the ventilated cavity wall gap that opens up to the roof space.

Wonder if the air from the cavity blows up into the roof then gets taken under the upstairs floor joists.

I'll check it out. My current plan might be to insulate just before the joists go under the upstairs floor so the air flow is at least blowing inside the eaves and not under the entire floor.

 

[JohnD]

should I insulate ?

No you should draughtproof.

Mineral wool loft insulation is ideal for this, because it is non flammable and can be stuffed between the joists to block the gap with no precision cutting necessary.

Start round the edges of the room because it mostly blows up in the gap under the skirting.

If either of the rooms is unheated you can pack the entire floor.

You can use a denser grade if you want to muffle noise.

If there are other holes for plumbing of something, block them too. Downlighter holes are very pernicious and it is best to place a smoke hood over them.