Am I destroying the insulation qualities of the roof insulat

[drdr]

Many of the questions in this forum are similar to my own, but none addresses it specifically.
I want to increase the amount of insulation in the roof. Currently there is about 50mm of fibre glass. I want to improve this by laying additional 170mm fibre glass, on top, between the joists. Like many people I use the loft for storage and want to board over the whole lot. They are 100mm joists. When I lay the board, it squashes the fibre glass, but it all goes down ok. The point is, am I destroying the insulation value of the fibre glass by squashing it up? Is the insulation achieved by trapped air or by the fibre glass itself?. I have seen many people talking about raising the joists and I don't want to get into that.
Thanks for any responses.

 

[disinfo]

The point is, am I destroying the insulation value of the fibre glass by squashing it up?

Yes

The alternative is to buy better quality insulation with a better value, or raise the joists

 

[JohnD]

you might consider 100mm fibreglass between the timbers, rigid plastic foam on top of the timbers, and boarding on top of that. It is more expensive, though.

the foam is a better insulator than the fibreglass.

 

[Therms]

I know someone who laid down loads of insulation and then boarded the loft. He not only reduced the effectiveness of the insulation, but it pushed down on his ceilings and made all the joints crack.