Mineral wool insulation - loft conversion

[0Floz0]

Hi

Appreciate it gets asked a lot but can’t find a thread on where I’m looking to insulate.

I’m adding an en suite to a loft conversion. The conversion itself isn’t used a lot. Only for when guests stay over. However, it’s a dormer and the ceiling isn’t insulated. So I want to stop heat being lost from the rest of the house. I know this will make that room more affected by temp changes but I can heat it for a short time rather than the whole house losing heat through it.

Looking to insulate the floor with mineral wool. There was some already in there but a bit sparing in how it’s been laid.

I’ve added a lot more (pic below) but just thought about whether I need an air gap between the floor. I don’t think there is a vapour control layer. So just looking for advice before I screw down the ply on top.

Thanks

 

[jeds]

Is it a room below?

 

[0Floz0]

Is it a room below?

Yeah. Small part of it is over a bathroom. Most of it over a hallway. It’s had rockwool in there for a fair bit already with no issue but the void wasn’t completely filled.

 

[jeds]

There's no heat loss between heated rooms. The insulation in floor voids is there for acoustic purposes.

 

[0Floz0]

There's no heat loss between heated rooms. The insulation in floor voids is there for acoustic purposes.

The loft room has a small radiator and no insulation in the roof. So will lose heat. I’m trying to stop the rest of the house losing heat to that room quickly for it then to escape easily. So if I insulate the floor well that should help?

The room is only used by guests and very rarely. So would rather that room was colder and I can heat when needed then losing loads of heat through it. Appreciate I may not be making myself clear.

The issue is, is condensation going to be an issue? I’m thinking not as rooms should still be warm either side?

 

[Ivor Windybottom]

If the room above is usually the cold one then the room below should have a vapour barrier behind the ceiling plasterboard, so stop moisture from the room condensing as it finds its way through to the colder environment behind. But it's an old house so it won't, most don't and it will be fine.

I wouldn't worry about it. Presumably you'll have a waterproof floor covering anyway, hopefully not fluffy nylon carpet like in the good old days? If so then that should be sufficient.

 

[0Floz0]

If the room above is usually the cold one then the room below should have a vapour barrier behind the ceiling plasterboard, so stop moisture from the room condensing as it finds its way through to the colder environment behind. But it's an old house so it won't, most don't and it will be fine.

I wouldn't worry about it. Presumably you'll have a waterproof floor covering anyway, hopefully not fluffy nylon carpet like in the good old days? If so then that should be sufficient.

Haha. Yeah I’m going ply over the joists. Then cement board then tile. So should be ok.

Appreciate the input. Thank you

 

[jeds]

The issue is, is condensation going to be an issue? I’m thinking not as rooms should still be warm either side?

No vapour control needed. The rooms may not be the same temperature all the time but they will be environmentally stable in terms of vapour pressure and condensation risk.