Hello,
I am in negotiations with a property developer about building a single-family house and am currently discussing the thermal insulation of the exterior walls and windows.
The developer offers:
Double glazing, overall U-value of the window units = 1.3
Walls: 15 cm (6 inches) calcium silicate blocks, 12 cm (5 inches) external thermal insulation composite system (ETICS / EIFS) with a thermal conductivity of 0.035 plus exterior plaster
The energy certificate states a final energy demand of 73.1 kWh/(m²·a) (kWh per square meter per year), with 61.6 kWh/(m²·a) allocated for heating.
I actually wanted a better-insulated house, but the developer strongly discouraged it (although I am willing to pay extra if the additional costs are within a realistic range). I asked about triple glazing instead of double glazing and an ETICS thickness of 18 cm (7 inches) instead of 12 cm (5 inches).
The developer’s arguments were as follows:
1. With a wall insulated with 16 cm (6.3 inches) ETICS, the insulation is so good that moisture on the north side of the building may not dry out properly, potentially causing algae growth on the plaster. From a façade maintenance perspective, a certain level of “thermal transmittance” is therefore advisable.
2. The indoor climate can also be problematic in an overly well-insulated house without a ventilation system because too much moisture accumulates, increasing the risk of mold and an unpleasant living environment.
3. Regarding triple glazing, he pointed out that in winter, less sunlight would enter the house, so it wouldn’t contribute much to heating the building. Also, since I would lower the shutters at night, which further reduces heat loss, the benefit would be limited.
4. He reported problems with the hinges on heavy window units (floor-to-ceiling and triple-glazed), which require constant adjustment.
5. In conclusion, he advised me to avoid better insulation, saying the extra costs would not pay off.
I am now completely confused. When I asked the energy advisor from the consumer protection agency, they reacted very negatively. Apparently, the subject of thermal insulation is somewhat ideologically charged, and it is difficult for me to verify the additional benefits of better insulation with calculations.
I will try a simple calculation:
121 m² (1300 ft²) of living space x 61.6 kWh/(m²·a) = 7453 kWh/year = approx. 737 m³ (26,000 ft³) natural gas = approx. €516 heating costs per year
If 25% of that is lost through the windows, the annual heating loss due to the windows is €130.
If triple glazing reduces those losses by 20%, the annual saving from better windows would be about €25.
With additional investment costs of around €3000, the payback period would be about 100 years. Or am I making a fundamental error in my thinking?!
I would appreciate any help!
Ralf
I am in negotiations with a property developer about building a single-family house and am currently discussing the thermal insulation of the exterior walls and windows.
The developer offers:
Double glazing, overall U-value of the window units = 1.3
Walls: 15 cm (6 inches) calcium silicate blocks, 12 cm (5 inches) external thermal insulation composite system (ETICS / EIFS) with a thermal conductivity of 0.035 plus exterior plaster
The energy certificate states a final energy demand of 73.1 kWh/(m²·a) (kWh per square meter per year), with 61.6 kWh/(m²·a) allocated for heating.
I actually wanted a better-insulated house, but the developer strongly discouraged it (although I am willing to pay extra if the additional costs are within a realistic range). I asked about triple glazing instead of double glazing and an ETICS thickness of 18 cm (7 inches) instead of 12 cm (5 inches).
The developer’s arguments were as follows:
1. With a wall insulated with 16 cm (6.3 inches) ETICS, the insulation is so good that moisture on the north side of the building may not dry out properly, potentially causing algae growth on the plaster. From a façade maintenance perspective, a certain level of “thermal transmittance” is therefore advisable.
2. The indoor climate can also be problematic in an overly well-insulated house without a ventilation system because too much moisture accumulates, increasing the risk of mold and an unpleasant living environment.
3. Regarding triple glazing, he pointed out that in winter, less sunlight would enter the house, so it wouldn’t contribute much to heating the building. Also, since I would lower the shutters at night, which further reduces heat loss, the benefit would be limited.
4. He reported problems with the hinges on heavy window units (floor-to-ceiling and triple-glazed), which require constant adjustment.
5. In conclusion, he advised me to avoid better insulation, saying the extra costs would not pay off.
I am now completely confused. When I asked the energy advisor from the consumer protection agency, they reacted very negatively. Apparently, the subject of thermal insulation is somewhat ideologically charged, and it is difficult for me to verify the additional benefits of better insulation with calculations.
I will try a simple calculation:
121 m² (1300 ft²) of living space x 61.6 kWh/(m²·a) = 7453 kWh/year = approx. 737 m³ (26,000 ft³) natural gas = approx. €516 heating costs per year
If 25% of that is lost through the windows, the annual heating loss due to the windows is €130.
If triple glazing reduces those losses by 20%, the annual saving from better windows would be about €25.
With additional investment costs of around €3000, the payback period would be about 100 years. Or am I making a fundamental error in my thinking?!
I would appreciate any help!
Ralf
achsell schrieb:
This was "determined" by the U-value calculator based on the monthly average temperatures from the German Weather Service The only thing that comes to mind here is this quote: "A reliable calculation should normally be left to a specialist." Also, it’s worth reading up on liability issues!
Such online tools can certainly be fun and entertaining, but I would not base any major investment decisions on them!
Best regards