Hello,
Unfortunately, although the search function led me to some interesting posts, my question has not yet been answered.
Here is the starting situation: a house from 1925, built with brick masonry, single-glazed windows, and no insulation.
The house is now going to be renovated. As far as I understand, it must meet a certain insulation value (required by the energy saving regulations / building regulations?). Therefore, some form of insulation is unavoidable.
The roof will be stripped and newly insulated. The real problem, however, is that the house was built right on the property boundary, and the neighbor does not allow external insulation. Therefore, three exterior walls will need to be insulated from the outside, and one from the inside.
What exactly needs to be considered in this situation? A professional company will carry out the work, but at least I would like to know what must definitely be observed and what should be avoided.
A friend suggested simply removing the old plaster and insulating from the outside with 2cm (1 inch) of polystyrene and a very thin new plaster layer. Would something like this be accepted under the energy saving regulations? How does one determine the exact values or requirements for the materials and their thickness?
Thank you!
Best regards,
micha27
Unfortunately, although the search function led me to some interesting posts, my question has not yet been answered.
Here is the starting situation: a house from 1925, built with brick masonry, single-glazed windows, and no insulation.
The house is now going to be renovated. As far as I understand, it must meet a certain insulation value (required by the energy saving regulations / building regulations?). Therefore, some form of insulation is unavoidable.
The roof will be stripped and newly insulated. The real problem, however, is that the house was built right on the property boundary, and the neighbor does not allow external insulation. Therefore, three exterior walls will need to be insulated from the outside, and one from the inside.
What exactly needs to be considered in this situation? A professional company will carry out the work, but at least I would like to know what must definitely be observed and what should be avoided.
A friend suggested simply removing the old plaster and insulating from the outside with 2cm (1 inch) of polystyrene and a very thin new plaster layer. Would something like this be accepted under the energy saving regulations? How does one determine the exact values or requirements for the materials and their thickness?
Thank you!
Best regards,
micha27
6
6Richtige26 Mar 2010 15:27Hello Micha,
It is important to avoid improper planning and installation, as interior insulation can be quite critical.
So, consult a professional planner first, then hire a specialized company.
It is important to avoid improper planning and installation, as interior insulation can be quite critical.
So, consult a professional planner first, then hire a specialized company.
Hello 6Richtige,
thank you for your reply. My intention is not to quickly and cheaply do a DIY fix. As I already mentioned, the work will be carried out by a professional company and I am in contact with an architect.
Still, and precisely for that reason, it is important for me to have at least a basic understanding beforehand of what I should be discussing with the company. Of course, many contractors prefer when clients simply say, "Go ahead and do it," with an open wallet. But that is not the approach I want to take.
I assume that forums like this one are meant and suitable for answering questions. Therefore, I don’t find the simple suggestion to hire existing professionals very helpful.
Best regards,
Micha
thank you for your reply. My intention is not to quickly and cheaply do a DIY fix. As I already mentioned, the work will be carried out by a professional company and I am in contact with an architect.
Still, and precisely for that reason, it is important for me to have at least a basic understanding beforehand of what I should be discussing with the company. Of course, many contractors prefer when clients simply say, "Go ahead and do it," with an open wallet. But that is not the approach I want to take.
I assume that forums like this one are meant and suitable for answering questions. Therefore, I don’t find the simple suggestion to hire existing professionals very helpful.
Best regards,
Micha
6
6Richtige26 Mar 2010 17:46Some reading material:
With interior insulation, certain costs can indeed be saved—for example, no scaffolding is needed. However, when calculating expenses, all the details must be considered (such as relocating electrical outlets, light switches, window sills, and radiators, as well as repairing and insulating window reveals). Exterior insulation is often applied when a new paint job or plastering is due anyway, so it is usually more cost-effective. For retrofitting insulation in basement rooms, interior insulation is almost always cheaper, as excavation work is avoided.
Insulation performance with interior insulation:
Fundamentally, there is no difference with the same insulation thickness. Practical insulation thicknesses (starting at 10cm (4 inches)) are usually not feasible indoors due to space constraints. Caution is also necessary with exterior walls containing water pipes. There have been cases where pipes froze in winter after applying interior insulation.
Thermal bridges in interior and exterior insulation:
Exterior insulation covers all weak points with an insulating layer, effectively closing thermal bridges. Interior insulation can only do this inadequately. Exterior insulation is much better suited to prevent thermal bridging.
Moisture problems with interior insulation:
Regarding moisture issues, exterior insulation is clearly superior because interior insulation can cause building physics problems. Interior insulation reduces the temperature of the masonry (it blocks heat from the wall), which can cause moisture in the indoor air to condense on the cold masonry. This condensate can lead to mold growth and structural damage. These issues often remain unnoticed for a long time because the damage occurs behind the insulation and is not visible from the room side. Therefore, this problem requires special attention. Possible solutions include:
In any case, the issue of thermal bridges must be considered in all variants. This means that insulation at the connections between interior walls and ceilings should extend about one meter (3 feet) inward from the junction. For the same reason, insulation wedges should be used in corners.
Heat storage capacity with interior insulation:
Interior insulation slightly reduces the heat storage capacity. This effect is often overestimated because most of the thermal mass (interior walls, ceilings, and furnishings) remains intact. Also, reduced storage capacity is not always a disadvantage, as rooms with little thermal mass heat up faster. This can be desirable for hobby rooms or weekend houses.
Space requirements:
Interior insulation always reduces living space—the rooms become somewhat smaller. From this perspective, exterior insulation is always superior to interior insulation.
Other considerations:
Consider additional effects when installing interior insulation. Hanging heavy loads may become more difficult, and radiators, outlets, and switches often need to be relocated.
If a wall heating system is used, many of these issues are mitigated. In an uninsulated older building, it is even recommended to install interior insulation between the wall heating and the wall to reduce energy loss (due to higher interior surface temperature at the wall).
Conclusion:
Overall, exterior insulation is by far preferable. In exceptional cases, interior insulation can be useful or even necessary, but problem-free implementation is not guaranteed.
With interior insulation, certain costs can indeed be saved—for example, no scaffolding is needed. However, when calculating expenses, all the details must be considered (such as relocating electrical outlets, light switches, window sills, and radiators, as well as repairing and insulating window reveals). Exterior insulation is often applied when a new paint job or plastering is due anyway, so it is usually more cost-effective. For retrofitting insulation in basement rooms, interior insulation is almost always cheaper, as excavation work is avoided.
Insulation performance with interior insulation:
Fundamentally, there is no difference with the same insulation thickness. Practical insulation thicknesses (starting at 10cm (4 inches)) are usually not feasible indoors due to space constraints. Caution is also necessary with exterior walls containing water pipes. There have been cases where pipes froze in winter after applying interior insulation.
Thermal bridges in interior and exterior insulation:
Exterior insulation covers all weak points with an insulating layer, effectively closing thermal bridges. Interior insulation can only do this inadequately. Exterior insulation is much better suited to prevent thermal bridging.
Moisture problems with interior insulation:
Regarding moisture issues, exterior insulation is clearly superior because interior insulation can cause building physics problems. Interior insulation reduces the temperature of the masonry (it blocks heat from the wall), which can cause moisture in the indoor air to condense on the cold masonry. This condensate can lead to mold growth and structural damage. These issues often remain unnoticed for a long time because the damage occurs behind the insulation and is not visible from the room side. Therefore, this problem requires special attention. Possible solutions include:
- Using moisture-resistant and vapor-retarding insulation materials: Some manufacturers offer XPS boards for interior insulation. However, in cases where the diffusion resistance increases outward (e.g., concrete walls), these solutions tend to create problems.
- Airtight installation (bonding) of an interior vapor barrier or vapor retarder before the insulation: This approach is very complex and particularly vulnerable because even the smallest holes or leaks allow indoor air to enter and condense moisture on the cold masonry. If the insulation material used is moisture-sensitive (e.g., mineral wool), this leads to a reduction in insulating effectiveness and, in extreme cases, failure of the insulation layer. Another drawback is that moisture is trapped behind the vapor retarder, making drying during summer more difficult. A moisture-adaptive vapor retarder can improve this situation.
- A relatively new solution is insulating with capillary-active boards (calcium silicate boards), which mitigate some risks of interior insulation. However, the insulation thickness and thus effectiveness is quite limited in this variant as well.
In any case, the issue of thermal bridges must be considered in all variants. This means that insulation at the connections between interior walls and ceilings should extend about one meter (3 feet) inward from the junction. For the same reason, insulation wedges should be used in corners.
Heat storage capacity with interior insulation:
Interior insulation slightly reduces the heat storage capacity. This effect is often overestimated because most of the thermal mass (interior walls, ceilings, and furnishings) remains intact. Also, reduced storage capacity is not always a disadvantage, as rooms with little thermal mass heat up faster. This can be desirable for hobby rooms or weekend houses.
Space requirements:
Interior insulation always reduces living space—the rooms become somewhat smaller. From this perspective, exterior insulation is always superior to interior insulation.
Other considerations:
Consider additional effects when installing interior insulation. Hanging heavy loads may become more difficult, and radiators, outlets, and switches often need to be relocated.
If a wall heating system is used, many of these issues are mitigated. In an uninsulated older building, it is even recommended to install interior insulation between the wall heating and the wall to reduce energy loss (due to higher interior surface temperature at the wall).
Conclusion:
Overall, exterior insulation is by far preferable. In exceptional cases, interior insulation can be useful or even necessary, but problem-free implementation is not guaranteed.
Hello,
thank you for the text. Due to the moisture issue, I would now tend to choose softwood fiberboards.
However, during the site visit yesterday, I noticed that the boundary point does not exactly align with my house wall but is a few centimeters (inches) aside. This means I might still have a bit of space for external insulation. So again my question: is it possible to meet the requirements using especially high-quality materials, at least on this exterior wall (which has no windows)?
Best regards,
Micha
thank you for the text. Due to the moisture issue, I would now tend to choose softwood fiberboards.
However, during the site visit yesterday, I noticed that the boundary point does not exactly align with my house wall but is a few centimeters (inches) aside. This means I might still have a bit of space for external insulation. So again my question: is it possible to meet the requirements using especially high-quality materials, at least on this exterior wall (which has no windows)?
Best regards,
Micha
Hello
The house is built with brick construction – how thick are the walls? Maybe you’re lucky and have a cavity wall (this was common in the past), then the cavity can be filled with insulation. That would actually make more sense than exterior insulation for this type of masonry.
Best regards
Maik
The house is built with brick construction – how thick are the walls? Maybe you’re lucky and have a cavity wall (this was common in the past), then the cavity can be filled with insulation. That would actually make more sense than exterior insulation for this type of masonry.
Best regards
Maik
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