what rigid insulating board to buy for attic under flooring?

[drunat]

Hi. We are going to be putting flooring in our attic for storage purposes. Not all of it - just about 10-15 m2 of flooring. The rest we will top up with more fiberglass insulation to bring it up to 30cm.
There is currently about 10cm fiberglass insulation in our attic between the rafters. As our attic is a bit awkward we don't want to raise the floor too much as it will diminish its functionality.
For the area where we want to lay flooring, our plan is to remove existing insulation, put in rigid insulating board instead between rafters - ranters are 5inch so the carpenter said we should buy 4.5-5 inch board and then lay 18mm WBP board as flooring.
My questions are:
- What insulating boards to buy? - I checked Kingspan, Quinn and Xtratherm sites and am getting more and more confused between different types of insulation.
- Will 100mm board insulation plus 10mm WBP board be enough to achieve 0.16 U value? Or are there even thicker boards? (can't go over 5 inches = 12cm)
- is there anything fundamentally wrong with our plan? i.e. any issues with condensation, bridging (essentially rafters will not be insulated with only 18mm WBP on top etc?...
Any advice appreciated. I know there are some very knowledgable people on this site

 

[drunat]

Did not get any replies on my post and I think I know why - did I confuse everyone by mixing up "rafters" and "joists"? I meant to ask about insulating attic at a ceiling level i.e. between joists, not between rafters. Anyhow..., we got it done! Kept 10cm fiberglass, then put in 10cm kingspan high density board across the joists (so fiberglass did not squash) and laid flooring on top of the high density board. In the area that was not floored we just added another 20cm fiberglass. We went outside the grant process as it was MUCH cheaper! I could not believe some of the prices we were quoted from registered SEAI installers Literally the cheapest was more than double what we spent on materials plus labour, going outside the grant process.

 

[monagt]

did u use a local contractor?