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Hello everyone.

I have to insulate non-convertible attics in a building. The surface to be insulated is 70m².
The joists are spaced 60cm apart and are 17cm high.
What would be the most adequate insulation material to meet
RT for old buildings or in lost attics R> 5 m2K / W.
Goods.

Since the insulating wool with a conductivity of 0,04A / m ° C for an R of 5m2 ° C / W is a loss of 1/5 = 0,2W / m2 ° C, (a factor of 5 compared to 1m d 'insulation), the required thickness is 0,04 / 0,2 = 0,2m or 20cm of insulation wool of any kind with air immobilized with little.
If the conductivity is higher, the thickness must be increased in the same ratio.
http://de.wikipedia.org/wiki/Temperatur ... %A4higkeit
For more security and to compensate for future settlement, put a good margin with 30cm.
Otherwise for a very careful and valid installation see hack, otherwise the leaks and involuntary humidity destroy the final value of the insulation:
https://www.econologie.com/forums/post192740.html#192740

It's a personal opinion, but even if it means doing insulation now I would no longer use glass wool because as said on other posts, I think that in terms of health, it is not trivial and I will look towards a more ecological / trendy insulation such as cellulose wadding. (a priori less "toxic" but not free from doubts either ... boron salt ...)

Indeed, the glass wool on this thickness (20cm) would reach the RT in force.
The constraint is that I do not want to exceed the joist height which is 17cm with my insulation.
The ideal would be to have an insulator with very low conductivity and a thickness less than or equal to the height of the joists.
What I fear in insulating between joists with glass wool, are the air losses between it and the edges of the glass wool.
For that, I thought to deposit between joists of vermiculite on a height of 7cm in order to fill the voids (CT: 0,05W) then a layer of glass wool of 10cm above (CT: 0,04W).
vermiculite: 0,07ep / 0,05w = R 1,4
glass wool: 0,1ep / 0,04w = R 2,5
Thermal regulation not reached since R = 3,9w but is that the process can work in this way and can add thermal resistances.

You can always raise your joists ...

The idea is good, but that would entail a significant surplus of work in the sense that access to the attic is very reduced in height especially at the edge of the surface with a slight slope of the roof without counting the surface.
But why not.

With such access will you be able to correctly lay your glass wool? when you are at the end of your roof and where you have almost no access.

With loose cellulose wadding, you can properly spray the insulation into these corners.

It will not be easy in terms of access but it will have to be done. For the wadding that seems to me effective, I am not equipped for projection, in addition the weight per m3 is not to be neglected.
I bet on this solution that I indicate in the previous message only I do not know if it works.

You can rent a machine to project the cotton wool, but according to the information I had it is not that obvious when you are not used to it.

It seems to me that you have to adjust the flow of insulation to the compaction you want, but it is obvious that for a first there is a helping hand to take.
In any case if you or others on this forum have an idea of ​​the vermiculite compatibility between joists and glass wool on top, I am on the lookout for information.