Loft boarding after thick insulation

[pr1970ster]

Hey all
We recently moved into a 1930s house that has had full insulation about 10 years ago, it's 30cm thick and then loads of small polystyrene balls filled in between the joists. I'd like to increase the storage as only about 10ft is boarded.
What's the best way to go about this. I've seen raised loft board system that go above the insulation, height isn't an issue but I'm wondering if I can just squash down the insulation and board over the top onto the joists?
Thanks

 

[foxhole]

Boarding over as is will reduce the effect of insulation. You can either raise the floor level to accommodate the current insulation or replace with rigid insulation which has similar thermal value at a greatly reduced thickness .

 

[Peter James]

loft lifters to support flooring above insulation?

 

[stealthwolf]

I think insulation works by trapping air. If you squash insulation and compress it, it becomes less effective. I imagine it's the same for polystyrene balls.

Look at loft legs or loftzone system or even just additional timber crossing the original joists to raise the floor up. I've got the loftzone system and it allows for 270mm of insulation plus a small gap above that for airflow.