Is 250mm insulation same as 400mm?

[cwr]

Hey folks, 

Today's topic of 'discussion' with our builders is over how they have fitted the loft insulation. They quoted on fitting 400mm of glass wool, to give no worse than 0.12 u value. They fitted 2 layers of '200mm think' which is measuring in total about 250mm to 300mm. Initially said don't worry it'll expand, but 4 weeks later is much the same. They are insistent that the 200mm on the label means 'equivalent of 200mm, and it's a special space saving insulation', but I don't see any such claims anywhere on the packaging... Taking 200mm thick and R of 4.5 you get a thermal conductivity of  0.044, which is nothing special.

If the R value is maintained at the reduced thickness then probably all ok, but is that really the case? A quick Google suggests R values diminish as the material is compressed.

Thoughts?

[JohnMo]

The thermo conductivity will be 0.044 that does not change.  If you compress it, it's still 0.044, or could argue it may be worse as you close up air spaces in the insulation. 

 

Overall the compression reduces the R value. R value comes from the property of the thermal conductivity (0.044) and the insulation thickness (200mm).

[SuperJohnG]

Looks like superglass loft insulation?  

[ADLIan]

One or both layers have not recovered to the full 200mm thickness - a common problem with type of material. Make a formal complaint to manufacturer and get it replaced FOC. Contractor’s excuse is laughable.

[Temp]

Instead of replacing it see if they will give you more to put on top?

 

 

[cwr]

Yes it's superglass.

I tried phoning them several times today but no answer...

[cwr]

I did get through to superglass the next day. V helpful guy confirmed pretty much everything I thought in terms of in terms of something not being right. They are investigating...