DIY - loft insulation

[lizziecupcakes]

Hi all! I have a boarded loft in my 1907 house.
It was probably boarded a few years ago (maybe a decade ago). But it has minimal insulation.

We (me and my partner) want to add loft insulation ourselves.

I think we will use Mineral Wool Insulation - is rockwool better than fibre glass? Do I need to remove the bits of insulation that's already there before I add my own rolls?

Also, has anyone done this before in a boarded loft? I've never done this before and find it a bit daunting. Luckily we have a light up in the loft which will help.

My other question is: I've getting the ceiling replastered in the bedrooms below. They are currently plaster to laths. Sorry if it's a silly question, but when the plasterer removes the plaster from the ceilings, will the insulation rolls be seen and come between the laths? I'm a bit worried they'll ruin the insulation rolls with wet plaster (although they are using plaster boards) from the bedroom below and make them less effective.

Photo to follow of what I have. Thank you!

 

[lizziecupcakes]

That yellow spongy stuff is insulation, I think

Also another question, when I add the insulation rolls I’ll be wearing mask and protective coverings. But, we want to use the loft for storage so after i’ve added the insulation, do I still need to wear mask and coverings every time i go up there??

I ask because I think there will still be Gaps between the boards

 

[Cubist]

The guidance regarding masks and protective clothing is only concerned when you're cutting and moving the insulation around. Once its down, and in your case, boarded over again the its no longer a requirement. The object is to avoid any of the fibres coming into contact with the skin as it can result in significant itching and of course the mask helps to stop the inhalation of both stray airborne fibres and any dusts that accumulate in the insulation material.

If the ceilings below are being brought down the old insulation will almost certainly come with them as it's probably just sitting between the joists and on the upper surface of the ceilings. Your plasterer is unlikely to be kind enough to bother trying to keep it in place while the plasterboards are installed - he/she would have a conniption fit. If the boards in the loft are loose they can be easily moved temporarily to allow the new insulation to go in. If they are fixed however you would be wise to lift them - which should be easy judging by the photo - and re-install them after laying the insulation.

 

[lizziecupcakes]

Thanks so much @Cubist .
In my case then, do you recommend the plasterer do their job and plaster the new ceiling first, then get the insulation in?
I'm a bit nervous about hammering the boards back in place in the loft and the vibrations causing cracks in the new plaster below.

 

[fernicarry]

If you want to top up the insulation to the recommended depth (what is it now, 270mm?), then you'll need to lift the boards anyway and refix them on stilts (LoftLegs or similar). Take them up before work starts and screw them back down afterwards to minimise vibration. I'd actually go further and get rid of the nasty yellow stuff first and give the back of the ceilings a vacuum over to reduce the amount of muck that ends up in your living space.

 

[Cubist]

Thanks so much @Cubist .
In my case then, do you recommend the plasterer do their job and plaster the new ceiling first, then get the insulation in?
I'm a bit nervous about hammering the boards back in place in the loft and the vibrations causing cracks in the new plaster below.

Yes. Other than the old insulation coming down with the old plasterwork theres no issue and if you're very concerned about doing damage to the new ceiling you could easily use screws to fix the boards in back place rather than use nails. You will in any event have to remove any old nails or screws from the boards when you lift them out.

 

[paulc]

I recently took down an old lath & plaster ceiling. Packed the space between the joists with fibreglass insulation, making sure it went right up to the walls. Then fixed plasterboard up with lots of screws.
Some of the old insulation came down when the laths were removed, but is was ancient 25mm thick stuff of no value. On top of that was a couple more layers, so I now have over 300mm - Probably a mix of mineral wool and fibreglass. There is little difference between the two in terms of performance, permeability, or lifespan. Just use what ever you are most comfortable with.