Adding to this -- climates that have cold winters and a tradition for building well-insulated homes have detailed construction customs for how to deal with this.
Today, it's generally solved by having an airtight sheet (plastic) between the insulation and the inner wall. Sometimes placed inside the insulation. This ensures a temperature gradient that will not cause condensation inside the house.
You'll generally put a sheet that's porous but not airtight outside the insulation, to reduce heat loss due to convection and also provide an extra layer of defense against moisture damage due to wind-blown rain.
This technique necessitates good ventilation (often powered) if it's used throughout the entire house. This is to avoid saturating the inside air with humidity due to breathing and other activity, itself leading to the condensation you're trying to avoid. It can sometimes be just on e.g. floors and ceilings. Then, the rest of the structure might still be leaky enough that mostly passive ventilation will do the trick.
Older houses handle the problem by just being so leaky that condensation won't be a problem.
Because you add the same amount of moisture (showers, cooking, breathing), and it needs to get out before it's was evenly over all 4 walls, now only one. Your total indoor humidity is going to go up because there is less taking care of it.
That said, insulation is still the right answer, but it ain't cheap. OP should probably tear down that beautiful old house for something more modern.
Most people know that hot air rises. It's helpful to think of airflow in terms of energy (temperature is a measure of the average kinetic energy of air molecules).
Hotter air has more energy and thus will naturally "flow" towards cooler areas with less energy until equilibrium is reached.
In this example, the higher temperature air holds more moisture. That moisture will be carried along and dispersed towards the cooler wall, where it could condensate.
I do see your point, you believe the air near the uninsulated wall will have even more moisture because it’s now the only cold wall out of 4 walls. So all the moisture goes there instead of being split in 4.
But a wall will stop condensating water when reaching a certain degree of humidity. So I’m not entirely convinced one can simply divide the amount of humidity in the air by the amount of uninsulated walls (or sqm).
> I do see your point, you believe the air near the uninsulated wall will have even more moisture because it’s now the only cold wall out of 4 walls. So all the moisture goes there instead of being split in 4.
The air will not have more moisture, but rather all the moisture problems will be towards/on the uninsulated wall.
> But a wall will stop condensating water when reaching a certain degree of humidity. So I’m not entirely convinced one can simply divide the amount of humidity in the air by the amount of uninsulated walls (or sqm).
Condensation will never stop on a cold wall until all the moisture in the air is removed. If you boil a pot of water the air will fill with moisture, and the entire house will have a high humidity. But because one particular wall is cold because of a lack of insulation the condensation (water going from vapour to liquid phase) will be concentrated on that particular wall.
The condensation will continue to occur as long as you continue to add moisture to the air via cooking and bathing (hot showers, baths).
Say you have a room completely insulated except for 1 sqm. Will the entire moisture condensate on 1sqm? That could represent 1cm of water on the wall, that's physically impossible. There's a maximum amount of moisture that can condensate per unit of surface, it cannot be infinite. Where does the water go after condensating? Even if you consider it drips down and stays on the floor, the amount of water on the wall at any given time still has a maximum.
That's the bit I am missing here, it just does not add up, condensation is not something that simply keeps accumulating water on a wall if it's cold enough, there's a saturation at some point. The question is, how fast is this saturation reached? If it's fast, then isolating one out of 3 walls may not create additional moisture on the non-insulated wall.
Sorry, I hope I don't come over as being stubborn, I'm genuinely interested in insulating (I have to do it at some point), I just like to understand things and so far I do not understand why isolating 3 walls out of 4 would generate additional moisture on the remaining wall.
'That could represent 1cm of water on the wall, that's physically impossible. There's a maximum amount of moisture that can condensate per unit of surface, it cannot be infinite. '
'
I do not understand why isolating 3 walls out of 4 would generate additional moisture on the remaining wall.'
you gey problems with mold way before you are anywhere near 'the physical limir of condensarion'. You dont want to be near it.
The question is not whether the amount of consensation will double or quadruple. It is weather you will have mould problems. If your wal starts getting wet, you will have mould peoblems.
Today, it's generally solved by having an airtight sheet (plastic) between the insulation and the inner wall. Sometimes placed inside the insulation. This ensures a temperature gradient that will not cause condensation inside the house.
You'll generally put a sheet that's porous but not airtight outside the insulation, to reduce heat loss due to convection and also provide an extra layer of defense against moisture damage due to wind-blown rain.
This technique necessitates good ventilation (often powered) if it's used throughout the entire house. This is to avoid saturating the inside air with humidity due to breathing and other activity, itself leading to the condensation you're trying to avoid. It can sometimes be just on e.g. floors and ceilings. Then, the rest of the structure might still be leaky enough that mostly passive ventilation will do the trick.
Older houses handle the problem by just being so leaky that condensation won't be a problem.