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No offense - but insulation doesn't really work like this. If you insulate only one part, you will get massive problems with moisture through heat transfer. Wit

No offense - but insulation doesn't really work like this. If you insulate only one part, you will get massive problems with moisture through heat transfer. With insulation of old houses, so much can go wrong and then the only solution _is_ tearing down the house and building a new one.

illiac786 4y ago
This is very interesting. I was told by some energy expert I could isolate 3 out of 4 outer walls and it would work fine. Do you have some documentation on the “moisture through heat transfer” issue?
- Helmut10001 4y ago
  I do not have one at hand, but you should find this in almost any guide. It is not complicated: If you insulate 3 walls and leave one wall untouched - this wall will always be the coldest. That means the water contained in your air will condensate always at this wall (because it is the local minimum), resulting in mould and mildew on this wall over time. Now, there are all kinds of solutions and they all have caveats. As someone said here, old houses are build so that walls are semi-permeble, meaning that heat constantly wanders to the outside. That also means that the dew point is pretty far towards the outside in winter - water can get out of the house. If you insulate the inner wall, the dew point will move more towards the inside, meaning your walls will get wet and water will take longer to move outside. If you insulate the outside, water cannot get out at all - you must find another solution to get the moisture out of the house. It gets more complicated the more you dive into this topic.
  - illiac786 4y ago
    But your logic seems to indicate that only one wall will have condensation instead of 4. It’s still an improvement no?
    - dahfizz 4y ago
      You're concentrating 4 wall's worth of condensation onto just one wall. Instead of being spread out, all the moisture gets on the one wall.
      - illiac786 4y ago
        No, that is not how condensation works, otherwise you would have automatically more condensation on the wall in a larger room. The amount of condensation on the walls is not dependent on the size of the room or the fact that it condensates on the other walls. It depends on air humidity, air temperature, wall temperature and finally, very important, wall humidity. Water will not keep on accumulating on the wall, it will reach an equilibrium at some point, when the wall itself has become moist. The fact there is condensation or not on the other walls has negligible impact on total air humidity, most of all in larger rooms. And that's the only factor out of the 4 I could imagine being impacted by condensation (or not) on the other walls. Hence, I still do not understand the logic why isolating only a subset of walls instead of all of them would be a problem. As I said, I had an energy efficiency specialist at my home which said that isolating 3 walls would be 75% as efficient as isolating 4 and totally recommended. So far, I have not seen any solid logic supporting the fact that isolating only 3 walls instead of 4 would *increase* the risk of mold compared to either, 4-walls all insulated, or, zero walls insulated.
        greycol 4y ago
        The point is it won't reach an equilibrium. The outside of the house changes temperature with the day night cycle. The one uninsulated wall will be closer to the outside temperature than the other walls. As the house cools at the end of the day the uninsulated wall will be colder than the other walls and if it's below the dew point condensation will form on it. If the temperature differential is high enough in comparison to difference in insulation between the walls then enough water will leave the air to keep the dew point below the temperature of the insulated walls and so that one wall will collect the majority of moisture (at 30C a meter cubed of saturated air carries about 30mls of water so yes condensation on a surface can heavily impact humidity). Once a wall becomes moist it will still acumulate water if it's below the dew point. You likely will have seen real life examples of this when you look at single pane windows in otherwise insulated houses and seen them fog up/ have condensate form on them while the walls around them remain dry (if you haven't seen this but have been to houses with single pane glass in your area then condensation won't be an issue where you live). As to your 75% efficiency point it will in fact have a lower efficiency as heat transfer increases with temperature differential. Since the room has a higher temperature differential with the outside the less insulated wall will be faster at transfering heat. That is not to say that insulating 3 walls is a bad idea, it will almost certainly improve a rooms U value, but the worse the insulation on the remaining original wall, ceiling, and floor the less difference the 3 walls will make to the rooms U value and thus how quickly the room transfers heat.
- throw0101a 4y ago
  > Do you have some documentation on the “moisture through heat transfer” issue? Warm/er air can hold more moisture than cold/cooler air. If part of the house is warm, and you happen to cook and/or shower in it, it will have a high moisture content. But water vapour diffuses through-out an enclosure. So that water in a gaseous phase will equally spread everywhere (eventually). When it reaches the uninsulated part/s of the structure, the air is colder and so can't hold as much moisture leading to condensation. Get lots of condensation, and you have an environment that is suitable for mold growth (which can then release spores in the air and mess up indoor air quality (IQA)). Not to mention that water is a universal solvent, and so will turn your structure (stone, masonry, concrete, wood) to mush over time. The place of condensation will most likely be a surface that is a large temperature change: so in the winter your inside is warm, and your uninsulated outside walls are cold.
  - marvin 4y ago
    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.
    - illiac786 4y ago
      I still don’t get why there would be *more* moisture on the uninsulated inner wall compared to before insulating 3 out of 4 walls.
otikik 4y ago
Several floors were mentioned. Perhaps insulating one of them completely is an option then?

illiac786 4y ago

This is very interesting. I was told by some energy expert I could isolate 3 out of 4 outer walls and it would work fine. Do you have some documentation on the “moisture through heat transfer” issue?

Helmut10001 4y ago
I do not have one at hand, but you should find this in almost any guide. It is not complicated: If you insulate 3 walls and leave one wall untouched - this wall will always be the coldest. That means the water contained in your air will condensate always at this wall (because it is the local minimum), resulting in mould and mildew on this wall over time. Now, there are all kinds of solutions and they all have caveats. As someone said here, old houses are build so that walls are semi-permeble, meaning that heat constantly wanders to the outside. That also means that the dew point is pretty far towards the outside in winter - water can get out of the house. If you insulate the inner wall, the dew point will move more towards the inside, meaning your walls will get wet and water will take longer to move outside. If you insulate the outside, water cannot get out at all - you must find another solution to get the moisture out of the house. It gets more complicated the more you dive into this topic.
- illiac786 4y ago
  But your logic seems to indicate that only one wall will have condensation instead of 4. It’s still an improvement no?
  - dahfizz 4y ago
    You're concentrating 4 wall's worth of condensation onto just one wall. Instead of being spread out, all the moisture gets on the one wall.
    - illiac786 4y ago
      No, that is not how condensation works, otherwise you would have automatically more condensation on the wall in a larger room. The amount of condensation on the walls is not dependent on the size of the room or the fact that it condensates on the other walls. It depends on air humidity, air temperature, wall temperature and finally, very important, wall humidity. Water will not keep on accumulating on the wall, it will reach an equilibrium at some point, when the wall itself has become moist. The fact there is condensation or not on the other walls has negligible impact on total air humidity, most of all in larger rooms. And that's the only factor out of the 4 I could imagine being impacted by condensation (or not) on the other walls. Hence, I still do not understand the logic why isolating only a subset of walls instead of all of them would be a problem. As I said, I had an energy efficiency specialist at my home which said that isolating 3 walls would be 75% as efficient as isolating 4 and totally recommended. So far, I have not seen any solid logic supporting the fact that isolating only 3 walls instead of 4 would *increase* the risk of mold compared to either, 4-walls all insulated, or, zero walls insulated.
      - greycol 4y ago
        The point is it won't reach an equilibrium. The outside of the house changes temperature with the day night cycle. The one uninsulated wall will be closer to the outside temperature than the other walls. As the house cools at the end of the day the uninsulated wall will be colder than the other walls and if it's below the dew point condensation will form on it. If the temperature differential is high enough in comparison to difference in insulation between the walls then enough water will leave the air to keep the dew point below the temperature of the insulated walls and so that one wall will collect the majority of moisture (at 30C a meter cubed of saturated air carries about 30mls of water so yes condensation on a surface can heavily impact humidity). Once a wall becomes moist it will still acumulate water if it's below the dew point. You likely will have seen real life examples of this when you look at single pane windows in otherwise insulated houses and seen them fog up/ have condensate form on them while the walls around them remain dry (if you haven't seen this but have been to houses with single pane glass in your area then condensation won't be an issue where you live). As to your 75% efficiency point it will in fact have a lower efficiency as heat transfer increases with temperature differential. Since the room has a higher temperature differential with the outside the less insulated wall will be faster at transfering heat. That is not to say that insulating 3 walls is a bad idea, it will almost certainly improve a rooms U value, but the worse the insulation on the remaining original wall, ceiling, and floor the less difference the 3 walls will make to the rooms U value and thus how quickly the room transfers heat.
throw0101a 4y ago
> Do you have some documentation on the “moisture through heat transfer” issue? Warm/er air can hold more moisture than cold/cooler air. If part of the house is warm, and you happen to cook and/or shower in it, it will have a high moisture content. But water vapour diffuses through-out an enclosure. So that water in a gaseous phase will equally spread everywhere (eventually). When it reaches the uninsulated part/s of the structure, the air is colder and so can't hold as much moisture leading to condensation. Get lots of condensation, and you have an environment that is suitable for mold growth (which can then release spores in the air and mess up indoor air quality (IQA)). Not to mention that water is a universal solvent, and so will turn your structure (stone, masonry, concrete, wood) to mush over time. The place of condensation will most likely be a surface that is a large temperature change: so in the winter your inside is warm, and your uninsulated outside walls are cold.
- marvin 4y ago
  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.
  - illiac786 4y ago
    I still don’t get why there would be *more* moisture on the uninsulated inner wall compared to before insulating 3 out of 4 walls.

otikik 4y ago

Several floors were mentioned. Perhaps insulating one of them completely is an option then?