Mineral wool between rafters and hardboarded over !

[isley76]

Hi,

I've just bought a house built in the 1950s and the previous owner had "upgraded" the loft insulation by lining the inside of the roof between the rafters with mineral wool and then holding it in place with hardboard screwed to the rafters and purlins.

The surveyor report recommended this be removed as it could be a condensation risk.

The mineral wool / hardboarding goes right to the apex but is not sealed behind the purlins so air can get behind the hardboard and maybe circulate a bit around the mineral wool.

To be honest, the previous owner was a hopeless bodger and I think I'll take the surveyors advice and tear it all out. I might re-use the mineral wool to improve the insulation under the boarded loft floor which currently has some kind of soft gravel type insulation I've not seen before.

The loft has a fixed staircase coming up from one of the bedrooms so will be quite hard to seal so I'm wondering how best to keep the heat in but the moisture levels down.

I'm a total novice at this so any advice greatly appreciated.

Cheers,

Isley

 

[Deluks]

Presuming there is no breathable felt: You can leave the insulation in place provided there is a min airgap between it and felt of 50mm.

But you will have to put up a barrier against the min wool, can be polythene stapled to the joists and overboarded, or use foil backed plasterboard.

You could build an insulated stud wall with an entrance door around the top of the stairs. A mini landing so to speak.

 

[scrapbook]

Im my loft I have some mineral wool between the rafters held in with a couple of batons.

Is this a no no then???

 

[isley76]

Hi scrapbook,

It could have just been the surveyor covering his a*se but the full survey report recommended removal of the mineral wool as there is no air gap between it and the black stuff behind the tiles.

The black stuff behind the tiles is thin black plastic strips (2-3mm) in a tightly woven grid pattern, not sure if this is what is know as "felt" and whether this is the breathable type or not. Mine is ripped in a couple of places and I can see the back of the tiles so maybe the ventilation is already good enough?

 

[scrapbook]

Hi scrapbook,

It could have just been the surveyor covering his a*se but the full survey report recommended removal of the mineral wool as there is no air gap between it and the black stuff behind the tiles.

The black stuff behind the tiles is thin black plastic strips (2-3mm) in a tightly woven grid pattern, not sure if this is what is know as "felt" and whether this is the breathable type or not. Mine is ripped in a couple of places and I can see the back of the tiles so maybe the ventilation is already good enough?

Interesting. I only put it up in about a third of the loft in the storage area because the books were going mouldy because of condensation. Since it has been up we havent had a problem with the mouldy books.