Marine ply over ceiling joists in loft, under Kingspan?

[fogster74]

I've been thinking about boarding our Victorian loft. We've got about 270mm insulation (rockwool roll type)in there currently, which sits 170mm above the top of the ceiling joists (100mm).

I've looked into lots of options;

I've discounted 'loft legs' (price, fiddly, headroom) and running timbers to raise height (weight, headroom again)

The best solution I've seen so far has been something like jabuzzard has done here - which is very neat:
//www.diynot.com/forums/floors-stairs-lofts/increasing-joist-height.337430/#2543469

However, I did see a posting from Kingspan that suggests you shouldn't put Kingspan directly onto the joists as it will eventually crush, and should really put board down onto the joists, then Kingspan, then board on top, but that seems expensive and again I'm concerned about the weight.

As a compromise, I thought about either running wide strips of chipboard along the top of each joist (perhaps 200mm wide) so the Kingspan is in contact with a wider surface area or, alternatively, could I cover the joists (and wool in between) with marine ply, then Kingspan on top and finally tongue and groove as the floor surface. We'll only be using it for storage - it's not a working space or anything.

What are your thoughts on this type of approach?

 

[Chri5]

Last two days have been spent covering part of my loft for storage.

I left the existing insulation between the rafters, overlaid with 50mm celotex and then put the tg chipboard directly on top as a floating floor.

The intention for this space isn't for anything over weighty. It will be used to store suitcases, wrong season clothes, a collection of stuffed toys, duvets and the like.

I accept there will be some point pressure on the celotex where it sits on the rafters, but a doubt there will be any issue with the odd mm of crush / compression to the overall floor. The top floor chipboard will even this out over the whole floor area, so I'm not concerned by the suggestion from king span that what I (and many others) have done.