How do I board my loft?

[mattiusarsius]

I've bought a new build property & I am looking to floor out the loft for storage only - boxes of clothes, etc.
The loft is insulated with one roll of insulation between joists, and another laid over the top at 90 degrees to the first. The joists are 70mm high by 35 mm wide at 600mm centres.
What I'm not sure of is if I have to lay down more joists at right angles to the existing and lay the top insulation layer between them, then floor over that ? The new joists would have to be 200 x 47mm c16 construction timber to achieve the required 270mm insulation thickness but would that be too heavy? Is it true this can be reduced to 100mm when boarding and is that with compressing it the insulation? Is that too heavy? It's about 10 sqm in total. Sounds like a lot of work... ?

 

[PrenticeBoyofDerry]

It depends how well supported your existing loft joist are!

 

[mointainwalker]

If you squash your 200 mm of fibre-wool down to 100 mm you will lose approx 50 % of its insulating properties. It relies on trapped air which you will have forced out.

 

[PrenticeBoyofDerry]

If you squash your 200 mm of fibre-wool down to 100 mm you will lose approx 50 % of its insulating properties. It relies on trapped air which you will have forced out.

Very good point.
Which means it would be complete nonsense to compact fibre/mineral/rook wool insulation.