# Compressing fibreglass insulation



## Lex Foutish (27 Dec 2008)

I've heard that compressing fibreglass insulation reduces its insulating properties. Is this true? If so, any idea why?


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## eamonn123456 (27 Dec 2008)

Yes definitely.

Because its the trapped air that acts as insulation as well, so if you compress it you have effectively a much thinner layer of insulation.


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## theengineer (27 Dec 2008)

I agree, you should not compress


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## Lex Foutish (28 Dec 2008)

Thanks eamonn and engineer - for the explanation and the advice.


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## eamonn123456 (28 Dec 2008)

I had my attic insulated recently with 300mm blown rockwool ie well above the joists, and one of the guys doing it told me if I wanted to put boards down to just throw them on top, the rockwool would compress nicely 

I told him that I didn't think that was a great idea!

Just shows that even the 'experts' can be quite ignorant of the product they are selling.

House lovely and warm now with the nice thick insulation layer, and I won't be compressing it!


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## Lex Foutish (28 Dec 2008)

eamonn123456 said:


> I had my attic insulated recently with 300mm blown rockwool ie well above the joists, and one of the guys doing it told me if I wanted to put boards down to just throw them on top, the rockwool would compress nicely
> 
> I told him that I didn't think that was a great idea!
> 
> ...


 Thanks Eamonn. Sounds toasty! I went looking at fibreglass insulation today and the best I could find was 200 mm. Do you know if a thicker one is available and if any of the big DIY stores or builders suppliers sell it?


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## sas (29 Dec 2008)

Lex Foutish said:


> Thanks Eamonn. Sounds toasty! I went looking at fibreglass insulation today and the best I could find was 200 mm. Do you know if a thicker one is available and if any of the big DIY stores or builders suppliers sell it?


 
I don't know if it comes in rolls thicker than 200mm but you're better off laying it in 2 layers anyway. 1 layer running with the rafters, 1 layer across the rafters.


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## Lex Foutish (30 Dec 2008)

sas said:


> I don't know if it comes in rolls thicker than 200mm but you're better off laying it in 2 layers anyway. 1 layer running with the rafters, 1 layer across the rafters.


 Good idea sas. Thanks.


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