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Hello Christian, I am a regular on your show (Live and Podcast, I have a question about the insulation of my roofing lost that dates back to the 80s (glass wool less than 15 cms). I propose to compensate the existing to get the final 30 cm with a price "gun" of 14 euros M2, a second told me that we must add at least 30 cm to the existing... but it is at the rate of 18 I am a little perplexed and I would like to have your opinion a third advised me to downright everything to remove the 30 cm needed... who believe what to think? thank you for your help.

Hello Pascal and thank you for your loyalty to my show.
The third craftsman is certainly the most serious, since he offers you to leave on a healthy basis. It is never ideal to cover a rock wool of more than 30 years which could undergo the vagaries of time (humidity), to be packed, etc... The best solution is therefore to redo this insulation to nine, with the aim of 37 to 40 cm of insulation to meet current standards... You can also consider the insulation of these attics lost by blown wool as presented in our sheet on the insulation of the attic by blown wool.

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