Question about rock wool insulation

Hi. My sister is insulating her 3 bed semi attic. It's around 500 square feet. She has purchased 200 MM earthwool, cost 190. Tradesman doing some other work for her has agreed to install it. Should it be run between the joists but not covering the vents at the edge of the attic? She has no spotlights to worry about. What about the attic door ? Is there a way of insulating this also to ensure less heat loss. Sorry I know very little about this. She doesn't want to go the grant route as its more expensive. She has a mould problem on the ceiling of her ensuite so she thought adding extra attic insulation might help with the addition of an extractor fan. Is this true ?

Apologies. I should have added there is existing insulation in place ( not sure what). House was built in 1999. She is not removing the existing insulation. It is earth wool not rock wool that she bought. Not sure there is much difference between them but am open to correction.

Earthwool is just a Knauf brand.

Yes, where possible it should be run between the joists. Ideally the thickness of that roll would match the depth of the joints, and another layer would be rolled out over this to minimise gaps.

You can buy insulated attic doors that include rubber seals around the edges to minimise drafts.

The extractor fan will probably do most of the heavy lifting for the mould going forward.
But to really to get rid of it so it doesn't reappear is to cut it out, treat the area and replace with treated plasterboard.

Where do you get treated plasterboard and what is it? I've never seen or heard of it in my life.

You can get fungicidal paint, I presume that was what was meant.

She used a mould spray on it. HG brand. Removed a lot of it. Hopefully won't come back now that a fan is in place. Will it improve her BER even though it is not being done by an seai registered installer ?

Susie2017 said:

Will it improve her BER even though it is not being done by an seai registered installer ?

Click to expand...

Upgraded insulation will improve BER regardless of who does it, so long as a decent job is done of course.

If you have a cold water storage tank in there, see this thread for some advice on how to deal with that. Lots of other threads on the topic too.

I did my attic a few months ago. Fibreglass already between joists, added 200mm rockwool at 90 degrees on top of that. Try to get electrical wires above the final insulation level. You can get an attic ladder "hood" to cover the hole there. Don't block the soffit vents, you can get plastic inserts to keep the insulation from blocking them. I added a lid to the water tank and lagged over & around it, not under it so it still gets heat from below - this is all to prevent freezing now your attic will be cooler.