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
Hello,
have you already signed the contract?
If not, I would quickly send the builder packing...
Don’t let yourself be discouraged from investing more money in better thermal insulation. What the builder is telling you is really complete nonsense.
This means that we have to heat in order to maintain our facade.
Of course, you have to ventilate consistently if you wrap your house tightly, but you would need to do that even with a 12cm (5 inch) external thermal insulation composite system (ETICS / EIFS). So where is the difference (I mean in terms of ventilation)? It all comes down to the airtightness of the building.
That can be neglected!
If you are building new now, it is important to insulate your house as thoroughly as possible, and then size your heating system accordingly. Energy prices will continue to rise, and the few extra centimeters of insulation will quickly pay off. The facade installer doesn’t care whether they have to attach 12cm (5 inch) or 18cm (7 inch) of insulation. The price difference is only in the material.
Best regards
have you already signed the contract?
If not, I would quickly send the builder packing...
Don’t let yourself be discouraged from investing more money in better thermal insulation. What the builder is telling you is really complete nonsense.
Even for facade maintenance, a certain "thermal transmittance" would be reasonable.
This means that we have to heat in order to maintain our facade.
2. The indoor climate in a house that is too well insulated without a ventilation system is also critical; too much moisture accumulates, risking mold growth and an unpleasant living environment.
Of course, you have to ventilate consistently if you wrap your house tightly, but you would need to do that even with a 12cm (5 inch) external thermal insulation composite system (ETICS / EIFS). So where is the difference (I mean in terms of ventilation)? It all comes down to the airtightness of the building.
3. Regarding triple glazing, he mentioned that in winter less sunlight would enter the house through a triple-glazed window, so it might not contribute as much to heating the building.
That can be neglected!
If you are building new now, it is important to insulate your house as thoroughly as possible, and then size your heating system accordingly. Energy prices will continue to rise, and the few extra centimeters of insulation will quickly pay off. The facade installer doesn’t care whether they have to attach 12cm (5 inch) or 18cm (7 inch) of insulation. The price difference is only in the material.
Best regards
Hello,
I can’t help but smile a little at how it’s possible to perform an economic feasibility calculation using just the "U-value." If it were that simple, I could quit my job.
A genuine economic feasibility study requires a bit more!
Better insulation (lower heating loads) can, for example, lead to significant savings in investment costs for building services.
Trying to "fix" a high energy demand caused by insufficient insulation by means of a "beautified" energy saving regulation calculation has caused problems for many homeowners afterward. I deal with this almost daily.
No offense to "hobby calculators or planners," but I would base a substantial investment decision on a solid foundation!
Best regards
Aila71 schrieb:
I calculated the matter purely from an economic perspective on the website "WWW.u-wert.net" and was somewhat surprised.
I can’t help but smile a little at how it’s possible to perform an economic feasibility calculation using just the "U-value." If it were that simple, I could quit my job.
A genuine economic feasibility study requires a bit more!
Better insulation (lower heating loads) can, for example, lead to significant savings in investment costs for building services.
Trying to "fix" a high energy demand caused by insufficient insulation by means of a "beautified" energy saving regulation calculation has caused problems for many homeowners afterward. I deal with this almost daily.
No offense to "hobby calculators or planners," but I would base a substantial investment decision on a solid foundation!
Best regards
Aila71 schrieb:
Hello,
2. The indoor climate can also be critical in a house that is too well insulated without a ventilation system, ....
3. Regarding triple glazing, he pointed out that a window with triple glazing lets in less sunlight during winter, which might reduce passive solar heating. In addition, I would close the shutters at night, which would further reduce heat loss.
4. He reported issues with the hinges due to the heavy window elements (floor-to-ceiling and triple glazed), ...2. In general, such airtight houses usually require a ventilation system, which of course also costs money, but it’s better to have better insulation and proper ventilation than to face higher heating costs, right?
3. That’s true about solar heat gain in winter, but the point about shutters is wrong. From an energy perspective, shutters often make things worse because heat loss from shutter boxes usually exceeds the amount saved by lowered blinds. It’s better to have triple glazing plus specialized thermal blinds.
4. Yes and no. It’s clear that triple-glazed sashes are heavier, so the window frames need to be designed accordingly. For example, if you have triple glazing and a 50–60mm (2–2.4 inch) frame, you know what will happen.
Yes, my builder says the same thing.
And everything I’ve found so far from somewhat reliable sources online says the same.
If you want better insulation, it’s more for peace of mind than for saving money.
I’m going to install an exterior wall with a U-value of 0.3. The additional cost to go down to 0.24 would be 2400 euros.
Heating cost savings according to formula calculations: 40–90 euros per year
Heating cost savings according to the builder (estimated): 50 euros per year
Heating cost savings according to a second construction company (estimated): 50–60 euros per year
Better to put that money in the bank, where it earns 100 euros per year.
PS: I think a major quality indicator of a builder is when they have a good sense of what is worthwhile and what isn’t, and b) that they communicate this to the customer instead of trying to sell every possible and impossible upgrade.
And everything I’ve found so far from somewhat reliable sources online says the same.
If you want better insulation, it’s more for peace of mind than for saving money.
I’m going to install an exterior wall with a U-value of 0.3. The additional cost to go down to 0.24 would be 2400 euros.
Heating cost savings according to formula calculations: 40–90 euros per year
Heating cost savings according to the builder (estimated): 50 euros per year
Heating cost savings according to a second construction company (estimated): 50–60 euros per year
Better to put that money in the bank, where it earns 100 euros per year.
PS: I think a major quality indicator of a builder is when they have a good sense of what is worthwhile and what isn’t, and b) that they communicate this to the customer instead of trying to sell every possible and impossible upgrade.
Baldrian schrieb:
I am going to install an exterior wall with a U-value of 0.3. What kind of construction results in such a poor U-value? Which designer would recommend that?
What about the other components (roof, foundation slab, windows), do they have similar U-values?
And are you planning to compensate for these losses with a highly efficient heating system (that of course costs nothing)?
I seriously doubt that you meet the requirements of the energy saving regulations, but your builder has probably given you a favorable estimate.
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