Raising attic floor for insulation

fissureseal

, I'm a v amateur diyer living in a standard 90s bungalow - looking to raise attic floor to allow for 300mm insulation . Currently have around 100mm under existing chipboard. My plan is to place 2x9 timber batten at right angles to existing joints and raise the existing chipboard . Because of the way the chip board has been placed , I will need to place at least 8-10 4m lengths of the 2x9 timber .

Just wondering , is there any issue with increasing the weight of the extra timber on the existing joists ? The existing joist are in excellent condition

Should I remove old insulation, fill the space between joists to 200mm and place another layer of 100mm going the other direction? Or should I just leave the old insulation and run 200mm layer at right angles to joists ?

Thanks

Biker1

Instead of using 9 x 2's you could buy risers that sit on existing joists and go with 4 x 2's. Much easier for rolling out the insulation. I would suggest 250mm over what is already there.