Squashing loft insulation - what would you do??

[kon123]

Search function has answered most of my queries but just wanted to run a quick question for loft insulation experts out there!

Looking to top up insulation (existing is 100mm to joists - will be topping up with 170mm) & board out part of loft. For the boarded area, I did not want to go much bigger than 100 x 50 for the cross beams (due to cost & weight) so my question is:

Would you:

A) Still use the 170mm insulation in the area to be boarded and squash down with loft boards to the 100mm level; or

B) Use 100mm insulation top up in the boarded area.

I know squashing the insulation reduces its efficiency but just want to check that it would be no worse than using 100mm. (I can get the 170mm stuff for free!)

Thanks in advance.

 

[JohnD]

squashing it to 100mm makes it less effective. Because you are squashing the air spaces it is actually less effective than 100mm insulation that is not squashed

as you are pressing it down onto the ceiling it is liable to make your ceiling crack or bulge

Sometimes you can pull insulation apart and tear a layer off to make it less thick