Loft Insulation Boards

[freestylecorsa]

Apologies if this has already been asked before, did a search but couldn't see my query.

Currently looking to sort the insulation in our loft, we currently have 100mm fibre down and I will be topping it up to 270mm.

We have some loft boards already so will be looking to install some insulated boards underneath but I'm not sure what I should be getting, should the height of the insulated boards match the additional fibre (so around 150mm depth) or should it match the R rating of the additional fibre?

Alternatively is it better to have a raised deck using something like LoftZone so that I can just fibre the whole loft space and reduce the risk of condensation building up on the underside of the insulated board?

 

[vinn]

Your question is difficult for me to understand.

Are you using the old ceiling joists as floor joists for some new kind of loft arrangements?
Has your loft been converted and passed by BCO?
Fibre glass when compressed loses much of its insulation capacity.
How well insulated loft boards work as flooring I dont know.
Insulating a loft needs many variables to be taken care of.