Loft Insulation

stripling

https://forums.moneysavingexpert.com/discussion/comment/82143467#Comment_82143467

That's really outdated. 300-400 is the recommended minimum level now plus properly sealed and insulated hatches and good roof ventilation. I already had 270 and after a government survey was told to get it increased - it made a noticeable difference.

Thermal cameras are really useful for all this - lots of councils lend them out or you can hire one. They fit on your phone and are definitely worth the (minimal) effort. You'd be shocked at how/where heat is lost.

Just an FYI but Celotex and Kingspan are flammable and noxious - read the Grenfell report. It's a sorry state of affairs that they haven't been banned.

Rockwool thermal slabs are safer if you must use boards. But loft insulation on rolls is relatively cheap and easy to install.

ComicGeek

https://forums.moneysavingexpert.com/discussion/comment/82144360#Comment_82144360

If you have money to burn, by all means install 300-400mm - but for those people who are looking to make decisions based on real economic facts (rather than sales tactics from insulation companies) then there is very limited benefit in going above 200-250mm.

270mm is still the minimum level for new builds. Developers put more in the loft (400-450mm) for new builds as it allows them to save money in a different part of the house - cheaper to throw in another £120 of loft quilt than to make the cavity 50mm wider or buy better quality windows.

That doesn't automatically make it a good financial decision for existing home owners. Payback for that extra 100mm is about 10 years - I would choose to spend that money elsewhere first if working to a tight budget.