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Hausbauenxx25 Apr 2019 10:13Ultimately, the building element needs to achieve a specific U-value. The construction method does not matter in the end. Whether you have 6cm (2.4 inches) of insulation below and 12cm (4.7 inches) on top, or the other way around, makes no difference from an energy efficiency perspective.
The advantages and disadvantages may lie in the costs and the impact on the planned heights.
The advantages and disadvantages may lie in the costs and the impact on the planned heights.
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Grantlhaua25 Apr 2019 11:10Hello,
we didn’t apply for KfW funding (since the conditions were unfavorable last year), but we would have easily met the KfW55 standard. We also decided against insulation under the basement slab, probably for the same reasons your builder advised against it. Here, the energy consultant, the builder, and I all agree that placing a house weighing several hundred tons on insulation foam is not a good idea. This material has been used for about 20 years now, but no one really knows how it will perform after 50 or 70 years. From an energy standpoint, insulation under the slab only makes a significant difference for houses without basements—due to thermal bridges at the slab-to-wall transitions—making it worthwhile in those cases. For houses with a basement, this effect is minimal because the basement is below the frost line. At depths of 3–5 meters (10–16 feet), the ground temperature remains fairly constant between 10–15°C (50–59°F) year-round.
Is your basement heated? Our energy consultant mentioned that you end up heating the ground rather than the other way around. Did your energy consultant also run calculations without perimeter insulation? I just found the report and our result was 29.78 kWh/m²a.
we didn’t apply for KfW funding (since the conditions were unfavorable last year), but we would have easily met the KfW55 standard. We also decided against insulation under the basement slab, probably for the same reasons your builder advised against it. Here, the energy consultant, the builder, and I all agree that placing a house weighing several hundred tons on insulation foam is not a good idea. This material has been used for about 20 years now, but no one really knows how it will perform after 50 or 70 years. From an energy standpoint, insulation under the slab only makes a significant difference for houses without basements—due to thermal bridges at the slab-to-wall transitions—making it worthwhile in those cases. For houses with a basement, this effect is minimal because the basement is below the frost line. At depths of 3–5 meters (10–16 feet), the ground temperature remains fairly constant between 10–15°C (50–59°F) year-round.
Is your basement heated? Our energy consultant mentioned that you end up heating the ground rather than the other way around. Did your energy consultant also run calculations without perimeter insulation? I just found the report and our result was 29.78 kWh/m²a.
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hampshire25 Apr 2019 11:52Insulation can be applied partly below and partly on top of the concrete slab (as in our house, although I don’t remember why). In the end, it doesn’t really matter how the required insulation value is achieved.
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