I live in a Phenix house since 1978, I would like to remake the insulation of the attic lost. Currently I have glass wool that is 32 years old. I would like to put wool by blowing. I made 2 quotes: the first offers me to remove the old glass wool then make a cleaning and then blow the new insulation. The second estimate is to project directly on the old insulation. I would like to know what is the best solution because the cost is not the same at all.
The first solution seems to be the best, because it is always better to start on a net basis. The direct blowing of glass wool on the old insulation risks creating differences in density and therefore inequalities in the quality of the insulation. It is even possible that thermal bridges are created inducing heat losses in places. But this second solution is not impossible, however, if your budget does not allow to implement the first.
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