Our loft has visible slates with some tin foil bubble wrap stapled to the rafters.
I’d like to improve it with 75 mm of that rigid insulation board from Celotex. They have at least three different products that will do the job. What is the difference between them and which will best do the job?

Go to ‘applications’ on their website and select the roof type / application that matches yours the best, then select thickness and size required. There wont be much difference between the thermal properties of different types ( for a given thickness)

I have another…..will any of these energy company backed installers lift the boards in my loft, replace the insulation with same thickness but better performance, then refit the boards?

Similar question….will any of the above type of installers do a proper endoscopic survey of my wall cavities prior to insulating? Want to check for corroded wall ties and excessive cavity rubble before going ahead…..

zippy – that probably isn’t your ‘loft insulation’ per se. If the eaves haven’t been sealed then the insulation part will be what’s between the attic space and the ceiling of the 1st floor. The tin foil bubble wrap is not great and you’ve probably not got a sealed in attic.

plums – probably not. Those that will lift the boards will likely charge you for the pleasure and any insulation that would be better performance for the same thickness would cost an awful lot more money. You’d be better off raising the floor a couple of inches and having the thicker insulation put in (I’ve just done half of my attic like that myself).

Our loft is so full of crap that the actual roof bit is the only way to add extra insulation. There is a small amount of fibre between the ceiling and loft boards.
Will go for the ga 4000 and stick it between the bits of wood. Obviously leaving an air gap.
I will have to cut it into strips that are anywhere between 29 and 33 cm. If I decide to fix it to the very outside of the beams is it just a case of whacking a long screw and washer through the insulation?

Is there much of an advantage of doing the rafters with a bit of kingspan (bearing in mind you you need to leave an air gap) than say stilts on the joists and the reccomended 250-270mm? That’s presuming the loft is ventilated?
No expert but isn’t it the fact that the loft air is dry and less likely to form condensation and creating a small volume air gap (between kingspan and slates) with a big temp difference between that and outside plus less ventilation mean more condensation?

I’m asking as I have a loft that’s half dormer roofes over windows with zero insulation and another half insulated and boarded and wondering what the best approach is but I’ll not hijack your thread with that.

Wood fibre based insulation batts or boards will be cheaper than celotex and offer a bit of assurance re condensation i.e. they take in excess moisture when required and release again later on.

Cb can you give more info on the products you mention?

zippy – take a look at Pavatex and Steico as brands.

zippy – is your loft sealed in ie is it vented at the eaves? If it is, putting insulation up in the rafters will do little at best and nothing at worst. If you have any insulation on the attic floor / ceiling of the upstairs, then that is where you need to insulate, or properly seal in the attic then insulate.