Insulating the attic

Hi,
I'm insulating my attic, I have taken up the chipboard which was flooring the attic and was going to put in 100mm think combi roll ( yellow fibreglass stuff) and then put the floor back on.
However I see on the packing for the combi roll they recommend putting space board on top of the fibreglass and then put back the chipboard on top of that to have the attic floored.

Is the space board necessary, how much better would the insulation be if I put this in?

I look forward to any replies.

Current building regs is for 300mm of Fibreglass. You should consider a Polyisocyuranate foam insulation of which 100mm is the same as 300mm mineral insulation. An example of this is xtratherm raferloc or K7 which can also be used in ceiling.

Thank you very much for that recommendation...much appreciated. I will investigate it.