Insulating a ceiling

[jpowell79]

Recently had a full home re-wire and now the living room and passageway have exposed joists where the ceiling was ripped down to cable the new electrics.

before we plasterboard the ceilings I thought it might be a good opportunity to stick some insulation up to hopefully lower the heating bills and keep the living room a bit warmer in the winter months.

In my mind I’m thinking just get some rolls of rock wool mineral wool, then running lengths of string perpendicular to the joists by screwing in screws 10mm from the bottom of the joist inside each joist and then wrapping the string around the screws so that the mineral wool doesn’t fall down.

Is this the right way to do it or is there a better way?

Also is mineral wool the best option for this? Any issues with damp/condensation/airflow?

I’ve seen PIR insulation boards but these cost 4-5 times the cost of standard plasterboard and I can’t really see how they’d be any better than mineral wool?

open to comments and suggestions before I get started

 

[Deleted member 174758]

Mineral wool is a good insulator and has the advantage of giving better noise attenuation (sound proofing) than PIR boards as well. Mineral wool batting rather than roll is preferable for use in ceiling voids as it can be sawn to size (with an old hand saw or an insulation saw/knife) and will hold itself in place if correctly sized without the need for string, etc due to its' greater rigidity

 

[jpowell79]

Mineral wool is a good insulator and has the advantage of giving better noise attenuation (sound proofing) than PIR boards as well. Mineral wool batting rather than roll is preferable for use in ceiling voids as it can be sawn to size (with an old hand saw or an insulation saw/knife) and will hold itself in place if correctly sized without the need for string, etc due to its' greater rigidity

 

[jpowell79]

Cheers pal, I was looking at the Rockwool RWA45 as it looks like it’s also good for a bit of sound insulation as well which can’t be a bad thing…. They seem to only come in 600mm wide… my joists seem to be around 380(ish) mm wide…. Can I compact them in or do I need to shave 220mm off of every slab? Seems like a lot of wastage if it’s the latter…. I guess I could take the off-cuts and squeeze the two together to try and get a made up 440wide slab fit between them?

 

[jpowell79]

Actually ignore me I’m being stupid, I can cut them into 3’s for each slab as they’re 1200 mm long, so I’ll just have 400x 600 slabs, and presumbly should be able to squeeze the 400 wide into the 380 width without too much issue

 

[foxhole]

You can stick rockwool between the joists it will stay there long enough to board over, no string required.