Hello!
Due to new construction plans, I have been researching insulation materials.
As a result, I now understand that the insulation should ideally be separated from the indoor air by a vapor barrier to prevent moisture from condensing in or on it once the dew point reaches that area.
I have also gathered the impression that, for this reason, an insulation material should ideally be hydrophobic, meaning it should not absorb moisture. Am I correct in this assessment?
Therefore, it should ideally be a closed-cell insulation material, which quickly led me to extruded polystyrene foam (XPS).
This material will be applied to the interior surface, onto the aerated concrete blocks, and it is also planned for use under the screed.
I am now considering whether I can also use XPS for the roof due to its ideal properties...
Due to new construction plans, I have been researching insulation materials.
As a result, I now understand that the insulation should ideally be separated from the indoor air by a vapor barrier to prevent moisture from condensing in or on it once the dew point reaches that area.
I have also gathered the impression that, for this reason, an insulation material should ideally be hydrophobic, meaning it should not absorb moisture. Am I correct in this assessment?
Therefore, it should ideally be a closed-cell insulation material, which quickly led me to extruded polystyrene foam (XPS).
This material will be applied to the interior surface, onto the aerated concrete blocks, and it is also planned for use under the screed.
I am now considering whether I can also use XPS for the roof due to its ideal properties...
The original poster is probably just confusing EPS (expanded polystyrene) with XPS (extruded polystyrene).
Personally, I don't see any problem insulating the roof with XPS; it just doesn't make much sense because you end up paying for properties that aren't necessary there, while lacking others that would be more desirable.
Both insulation materials offer less soundproofing and heat protection than, for example, the commonly used mineral wool or the "premium" wood fiber insulation and are also much more difficult to work with.
Their resistance to moisture, on the other hand, is of no real benefit because you still have to use a vapor barrier. It is also not true that moisture cannot condense on EPS/XPS; it simply does not damage the insulation material itself (but it can harm the surrounding structure).
Personally, I don't see any problem insulating the roof with XPS; it just doesn't make much sense because you end up paying for properties that aren't necessary there, while lacking others that would be more desirable.
Both insulation materials offer less soundproofing and heat protection than, for example, the commonly used mineral wool or the "premium" wood fiber insulation and are also much more difficult to work with.
Their resistance to moisture, on the other hand, is of no real benefit because you still have to use a vapor barrier. It is also not true that moisture cannot condense on EPS/XPS; it simply does not damage the insulation material itself (but it can harm the surrounding structure).
T
Theodorius11 Jan 2019 10:57Hello and thank you very much for your answers!
MOLD is a major concern for me and something I definitely want to avoid! That’s why I consider hydrophobic insulation to be a good choice.
The vapor barrier is installed BOTH ABOVE (towards the roof tiles) and BELOW (towards the living space) the insulation. This vapor barrier is supposed to prevent the insulation material (e.g., fiberglass) from becoming damp. This would happen if warm indoor air could reach the insulation (fiberglass) and meet the dew point there. Is that correct?
The vapor barrier is a membrane that is vapor-permeable but does not allow liquid water to pass through. Is this designed to prevent condensation directly on this membrane, or is there another reason for this?
Would you still need this vapor barrier when using hydrophobic insulation materials?
MOLD is a major concern for me and something I definitely want to avoid! That’s why I consider hydrophobic insulation to be a good choice.
The vapor barrier is installed BOTH ABOVE (towards the roof tiles) and BELOW (towards the living space) the insulation. This vapor barrier is supposed to prevent the insulation material (e.g., fiberglass) from becoming damp. This would happen if warm indoor air could reach the insulation (fiberglass) and meet the dew point there. Is that correct?
The vapor barrier is a membrane that is vapor-permeable but does not allow liquid water to pass through. Is this designed to prevent condensation directly on this membrane, or is there another reason for this?
Would you still need this vapor barrier when using hydrophobic insulation materials?
No, the vapor barrier (actually vapor retarder) belongs beneath the insulation, and it is called a vapor retarder because it slows down vapor, not water, which usually moves from top to bottom rather than from bottom to top. Whether an insulating material is moisture resistant has nothing to do with this.
T
Theodorius11 Jan 2019 12:42@hanse: The inner shell will, of course, be insulated from the outside using Styrofoam. I think it’s quite risky to put a water-attracting (hydrophilic) insulation material into the cavity. What would you use there?
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