Attic Insulation 200mm or 100mm

Tidyweb

I am flooring my attic and I will be installing 4" or 100mm joists.

I will then be filling the gap between the joists with insulation.

Which gives a better insulation.

100mm of regular glass rool-out insulation with the chipboard on top.

Or 200mm regular roll-out insulation, compacted down into the 100mm space with the chipboard on top.

ie which gives better insulation the air in the 100mm or 200mm compacted down to 100mm.

Any advice appreciated. Cost is minimal.

porte

The 200mm rock wall will be denser and give better insulation against heat loss.
If you are covering it with chipboard the 100mm will be sufficient.

Tidyweb

Thanks,

yea, I know its sufficient.

But I understood its the air traped in the insulation that adds to the insulation, it you compress and make it dense you loose some of the insulation value.

paddy147

Tidyweb wrote: »

Thanks,

yea, I know its sufficient.

But I understood its the air traped in the insulation that adds to the insulation, it you compress and make it dense you loose some of the insulation value.

Exactly,dont compress or squash down the insulation.

Tidyweb

But thats my whole question.

Obviously 200mm of insulation compacted down to 100mm is better than 20mm not compacted.

But which is better

200mm compacted to 100mm

or just put 100mm not compacted.

Does the question make sense?

gman2k

As said above, never compress insulation, as it's the air that is trapped in the insulation that actually keep the warmth in.
So to finally answer your question definitively,
If your space is 100mm, use 100mm insulation. You will get very little insulation value from 200mm of insulation compressed to 100mm.

ayeboy

100mm will be better imo.

aido76

Why are you only going with 100mm? Is the regulation not 300mm? Have you other insulation installed and the 100mm is a top up?

Tidyweb

Yes there is 150mm of cellulose and I will be adding 100mm of fiberglass, 18mm chipboard and whatever storage ontop of that.

aido76

Would you not go with another 150mm to bring it up to 300mm? Is topping it up with Fibreglass a good idea? Should you not use the same as whats in it already? I'm starting to sound like I ask alot of questions. I just think you should do it right the first time.