What creeping insulation under roof?

[mitch021]

Hello, I currently have a creeping roof insulated by me with 10 cm of mineral wool (impossible to put more on top), I would like to be able to insulate inside without removing the wooden paneling, I was thinking of putting placo plates with expanded or extruded polystyrene screwed over the paneling, my question is that above I have my mineral wool with kraft paper turns inward so theoretically well posed that this new layer should be covered on the face of the placo another vapor barrier ???? or a vapor barrier directly on the wooden paneling, thank you to those who know the answer.

[jonule]

Hello,

normally only one vapor barrier is needed, if you put 2 layers it will go wrong between the 2 (air exchange, humidity, ...).
this vapor barrier (which is therefore not a vapor "brake") must therefore be placed on the living side, as close as possible to put the maximum amount of insulation.

at home I lost 30cm inside by insulating with blown cellulose wadding (+ vapor barrier film), but I gained a lot + in economy, I have no heating on the floor and it is as good as on the ground floor; the area lost in the rooms is almost minimal, negligible.

[Forhorse]

Rather than trying to tinker with something that was originally wrong (poultice style on a wooden leg)
it is sometimes beneficial to dismantle everything to start from scratch.

[razputin]

I am also of this opinion, sometimes it is better to start from scratch than to do, redo, undo, overrate, to ultimately have a result very often below expectations. Personally last year to resell our house in Anneny and have a more than adequate DPE we saw some advice on http://www.meteoruta.com which have been validated by our craftsman. Thus the insulation of the attic was made with wood fiber and isover hemp. Slightly more expensive than more conventional materials but perfect insulation.

[dirk pitt]

mineral wool has very good permeability to water vapor.
(µ around 1)
you can therefore put on the inside of this existing mineral wool, any insulation having a higher resistance to the penetration of steam.
in terms of water vapor,
the following rule must be observed:
increasing permeability from the inside to the outside
or said backwards: resistance to water vapor (letter µ) decreasing from the inside to the outside.
you have to let it go faster to the outside which has started to enter the insulation to avoid condensation in the insulation.
the problem in your case is the vapor barrier that was present on the inside of your rock wool.
it would be necessary to know its value and to put an internal insulator (and its vapor barrier) having an even greater resistance.
on the other hand if it was a vapor barrier with great resistance to diffusion, you risk having condensation between your two types of insulation. it would practically be necessary to put a very tight vapor barrier on the interior side, taking care of the total tightness at the joints. always quite difficult to do.
then, which says very good airtightness, says mandatory VMC.

[ATE.Conseil]

Hello,

Indeed, as it was said above, sometimes it is worth tearing off and rebuilding, than trying to sign a sick leg.

Several things are to be studied:

- The vapor barrier (or vapor barrier according to the vocabulary used ... in short, a membrane with an Sd between 5 and 10) must be as close as possible to the interior wall ... it is tolerated to place it at worst, at 1/3 inside side (2/3 outside)
- The current paneling acts as a more or less effective steam brake depending on the tightness of their joints, the treatment applied to them ...
- craft paper on the LV also ... provided that the lays have been taped ... which is certainly not the case ... suddenly, each leak is a moisture highway
- Do not confuse permeability to water vapor and capillarity to liquid water ... The point of rosé being generally placed on the outside of the insulating wall, it is in the LV that condensation will take place. . and this one is not very capillary ...

In view of these elements I would tend to give you two possible paths:

1- Add insulation as it is, but above all place - on the inside - a vapor barrier membrane with a variable Sd (Intello or Vario for example)
2 - Blow up the paneling, remove the glass wool, add a rain screen (outside to prevent liquid water from entering by powder snow, rain, etc.), replace the insulation between chevron + 1 cross layer to achieve an R> 7.5m².K / W (so as not to come back to it in a few years) + Vapor brake airtight + Finishing covering

The second solution is the most effective and sustainable for the aging of the roof ... In addition, you can also take the opportunity to switch to animal or vegetable products in order to also gain phase shift and therefore summer comfort.

I strongly recommend the following two articles which deal with the importance of managing water vapor in a home:
http://www.construction-rt-2012.fr/technique/humidite.html
http://www.construction-rt-2012.fr/reglementation/reglementation-rt-2012/etancheite.html

Philippe DESON
Council ATE manager
http://www.ate-conseil.eu

[dirk pitt]

...
2 - Blow up the paneling, evacuate the glass wool, add a rain screen (outside side to avoid the entry of liquid water by powder, rain ... etc ...), add insulation between rafter + 1 cross layer to achieve an R> 7.5m².K / W (so as not to come back to it in a few years) + Vapor brake airtight + Finishing covering

what difference compared to leaving the old rock wool ??

currently there is already a steam brake on the inside of the rock wool. we do not know if it is very waterproof and in fact it would be better if it was not too tight if we take the option of adding additional insulation on the inside.
the new insulation must in fact be very tight against water vapor, much more than the existing one to avoid that the vapor is trapped between the two vapor barriers.

[Trept1934]

If you have a CMV (extraction of air in the kitchen + bathroom), it is logical that the extracted air can be replaced by fresh air ... Hence the ventilation grilles.

If your gas heating is inside the premises, it is imperative to have ventilation provided in good practice, otherwise you risk poor combustion with production of CO, SO2, etc. There are people who die from it every year ...

In addition, the dwellings are often under-ventilated, resulting in poor indoor air quality (VOCs, formaldehydes, etc., in addition to any humidity). The French air quality observatory is developing this on its site.

Conclusion: let's ventilate!

[puntrialmoor]

Attention, always be careful not to stop the natural ventilation under the slates .. so leave at least 4cm between battens and the top of the first layer of LDV

I know someone in the Dordogne who had stuffed "to death" between rafters, touching battens or battens = rotten framework in 3 or 4 years ...

a word on IMR = it is not more effective than 3 to 4 cm of LDV and yet it costs 2 to 4 times more than LDV of 20 cm ... without comments!

Consider placing a very good vapor barrier on the warm side before finishing your soffit.