Insulating loft which you later plan to convert

11 Sep 2021
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United Kingdom
I have a c. 9x8m loft in a 1860 ish Victorian house which I'd like to insulate now*. As you can see from the below, it's barely insulated, but is currently "cold roof" construction.

1) It's possible I may ultimately end up doing a loft conversion (in maybe 5+ years). It'd be preferable to insulate it a way that's compatible with that. Otherwise it means throwing out quite a loft of loose fill insulation* and wasting a lot on labour. Or at least using materials that can be repurposed.
I'm guessing that mean PIR boards rather than loose fill, and perhaps mineral (rock) wool. If so, what depth/spec PIR? 100mm? How best to fit it? Perhaps just resting on the rafters for now, and taped across?

2) If going with traditional cold loft loose fill, normally I understand this would be done by
- Removing what's there (given it's poor condition)
- Adding covers over the lights (e.g. Loft Lids, which I gather don't really need gluing down)
- Inserting 100mm of glass mineral wool (e.g. Knauff 44) between the rafters (which I assume are 100mm - they might even be less)
- Adding a further 200mm of the laid at 90 degrees on top of the rafters (for a total of 300mm, in line with the 270mm min requirement for new builds under building regs).

Of course, you then can't see where the rafters are, which means you can no longer safely move in the loft, which might be needed for access (and possibly storage). What's the best solution? 175 or 300mm Loft Legs, plus chipboard? Presumably just over parts where you anticipate access/storage might be required.

Any tips greatly appreciated - thanks in advance!
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