Edit: ["night owl" mode ON]
Capt_Maloche wrote:This type of building is isolated to preserve the traditional exterior appearance
These are old stones that need to breathe
Exact ! In addition ... to complete:
Capt_Maloche wrote:It is therefore necessary to mount a semi-stil partition with a rigid rock wool type insulation leaving a ventilated air space. between the wall and the insulation
Great idea if there is!
Air = free insulation and very high insulation coefficient (since it is more lightweight it isolates);
And combined with an insulator can skillfully adjust all the problems related to phase shift!
(I said brilliant ...!?) However, beware of the influence of the "surrounding environment".
Good idea because anyway, if it went wrong (coef, rtt not quite achieved, condensation due to cracks, aging or that I know) we can always cautiously swing in this technical vacuum foam expanded polyurethane then, to fix the problem due to a possible unwanted air circulation or resulting from a somewhat optimistic evaluation.
Reverse side of the internal placo insulation
If the hygrometry does not remain controlled it is a danger even for the placo!
1) Ad hoc implementation is tricky even for a professional (or not);
2) In short, 3 types of possible movements (in the placo, walls, floors, ceilings etc): thermal (expansion), hygrometric and structural. Causes: temperature changes during or after the site (expansion or contraction at different speeds of materials, when environmental conditions change). same for me hygrometry. And this as the humidity contained in the surrounding environment and / or materials, leaves or enters. And finally structural caused by displacement of certain components of a building causing dimensional variations (structural bending of the foundations, buckling, ground settlements, wind pressure, seismic forces, etc.)
3) In insulation from the inside, it is therefore better to provide expansion joints (and / or any other perimeter clearance system or element, since beware of the effects that add up).
Indeed, mediocre conditions causing a change of the environment, can lead to important effects in the materials of partitions in general (and gypsum board in particular) such as formation of ridges, dissipation of stresses. And it can be manifested by continuous bulges along the joints (or other.) Then also: all kinds of cracks, bulges of the panels (very annoying) loss of adhesion of the joints and seams, and still - in a contaminated environment by micro-organisms and humidity - the risk of mold remains and is transmitted very well on plaster / drywall, especially if the site has not been treated upstream and completely decontaminated with great care. Would it not be by the simple presence / accumulation of high humidity of the materials during transport (or a bad prior storage at the suppliers without us being able to know it if we are not careful) then innocently brought to the site (I've seen this so many times!). These unfavorable conditions can, for example, delay drying (exposing the materials to high humidity conditions for longer than expected). It is all this that can promote the growth of mold from unsuspected microscopic spores!
So when we know this, we avoid advising to insulate from the inside (because it will always remain the creeping contamination by capillarity or that I know ... as soon as the least conditions are met.)
There are even tables of risk assessment: to meditate!
Old carpenter thing
One can also take advantage of the natural expansion of the materials to use them as ... "measuring tool"!
- Beforehand measure the floor space lost perpendicular to the wall (between the wall and the overall face of the placo);
- Take chopsticks of fir spruce (or pine) perpendicular to the wood fiber and about 2cm in diameter ... then pre-cut them with a fairly small upper margin of error, but sufficient to protrude in front of the partition of a chouilla (to ultimately produce a slight protuberance - which will eventually be rectified before putting the visible finishing plaster - living room side) to do this, we will take a graduated aluminum tube of 5mm of diameter, which will be put on while groping until it touches the wall, and which will serve as a template (these rustic walls being by definition irregular, you will have to repeat the measurement each time by making a line with the marker which can be erased as and to measure with a cloth soaked in alcohol ...);
- Hunt them very delicately in holes previously drilled in the internal partitions of the placo (which form the sandwich containing the glass wool) and of a diameter slightly lower than the rods (without being definitively crimped), those -through the whole from one side to the other (this and including the technical vacuum) and come to bear the opposite on the front wall to isolate (you see me coming?);
- During any changes in hygrometry (in the event of excessive RH), the wood well chosen in the direction of the grain, will expand in length (and extremely little in width over only 2cm ...). On the contrary, he may also retract, which will mean that the hoped-for result will have been achieved and even exceeded (but which will then remain in the state of as many hidden sentries ready to appear at the first opportunity ...). can possibly wait six months before doing the operation, if you want the humidity to be stabilized, but you risk forgetting ... Or do it during a very hot summer (you can safely do it immediately) ;
- it is necessary to drill the holes at different heights in the strategic places considered most sensitive according to the construction and its condition and / or close to a possible cold bridge suspected: but that does not dispense with sanitation ...
So as long as the technical void (and the wall) are relatively dry and healthy, there will be no expansion (so the tip of the end of the wooden strip will remain buried flush with the wall). In the opposite case of a critical, chronic or whatever situation, the damp wood will automatically expand and slide outwards, forming a small growth thus signaling poorly controlled or excessive humidity, capillary rise, infiltration, etc. even the effects of a broken pipe or foundation wall drainage leaving something to be desired (and any other kind of change in the "ambient environment" is where I was coming from): and this automatically (without expensive apparatus / s of measurement, of probe / s possibly potentially broken down or captive of an electronic module in the process of obsolescence) ... And this almost free of charge!
The advantage of this is that during the expansion, the dimensional effect of changes in temperature and humidity are cumulative!
If one to two mm of dilation / retraction (in all and for all) can be considered as "normal", as soon as one has an excursion which exceeds this threshold, it is necessary to start to "watch that" in use. ... Ditto if the situation has remained stable for a long time and all of a sudden expansions of a total excursion unknown until then appear ...
Note that it still does a lot of work internally and for the super-tight budget with the aim of a maximum coef, it becomes "complicated" or even impossible to achieve ...
To go or not to go?
There are times when one has to know how to choose: to say that one does not have a circle and to want the apparent stone would not (and in my humble opinion) not mean much in somebody subjected to such a Cornelian choice of Opposite constraints ... The fact is that sometimes we do not have the choice and it is then they impose themselves on us!
So after we'll see where the balance between energy efficiency VS (which is not so much the secondhand, I explain myself ...)
Thus posited as you did Maloche, it becomes much simpler and clearer to understand and explain!
So why not from the outside while preserving a certain cachet?
Nothing prevents thus from using the "mini budget" to mount the wall in question type plasterboard or other, but supporting the life outside! So no cold bridge and exposed stone aspect preserved: inside: always better than outside, since it's not outside where you spend most of your time! Cherry on the cake, with 20W LED 6000W projectors, it's like having all year round the beautiful and shimmering sunlight ... inside the home (I do not get tired! >>> )
Joker is not a game of poker!
This is the time to take out your joker! If at first you can do this realization on a low budget (and see yourself) while falling within your budget, nothing prevents in a second time, to "work on the appearance of your new facade" either by applying rustic plaster (on a trellis placed against compressed glass wool panels, and with a technical air vacuum flush with the facade please ...), or add then ... much later on top, a light veneer in imitation rustic stone (and this once returned to better fortune) and thus we will have reconciled the following eleven points with efforts and a minimum investment and a maximum effect:
- low starting budget and maximum coef effect of insulation (your idea of screen / volume of air is impressive of simplicity and efficiency when doubled with an insulating wall ...);
- room for maneuver and rectification in use and after 1 or 2 winters to see how the concept behaves;
- de facto removal of any cold bridge;
- complete passivation possible (according to available budget);
- great renovation of the walls;
- use of the inertial heat of the interior and stored in the walls (which act like thermal balloon while reducing the necessity of heating);
- great interior sensory comfort (no "bad dew point ...")
- Possibility later to put full south a bay window in DV, which will filter the sun to heat the stone wall and store the heat that will be restored in the diurnal cycle;
- rapid amortization of the works in view of the heating savings achieved;
- no more need to invest in a boiler, convector radiators or anything else or financial pit for their maintenance ... and even less necessary heat pump;
- and then, at a better fortune: add the imitation stone thermal veneer (to be taken in light material, which will further strengthen the thermal insulation).
Condensation occurs when moist air touches a cold wall. Nothing to do with the air between the wall and the insulation. On the contrary, still air is an additional and welcome insulator.
and it's valid for everyone! 
