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
This is a T12 brick.
Some features, like the windows, are also better, but mainly for environmental reasons rather than to save money.
However, looking at it objectively, excessive insulation is not a profitable investment.
For home builders available online (where price lists are public), each KfW efficiency level costs about 10,000 euros.
With the first level (just meeting the current energy-saving regulations to KfW standard), heating costs decrease from a maximum of 750–800 euros to about 550 euros.
So, let’s say you save 250 euros per year.
If you put 10,000 euros in the bank, you’d earn 400 euros in interest. And with each next efficiency level, it gets even more unrealistic.
Some features, like the windows, are also better, but mainly for environmental reasons rather than to save money.
However, looking at it objectively, excessive insulation is not a profitable investment.
For home builders available online (where price lists are public), each KfW efficiency level costs about 10,000 euros.
With the first level (just meeting the current energy-saving regulations to KfW standard), heating costs decrease from a maximum of 750–800 euros to about 550 euros.
So, let’s say you save 250 euros per year.
If you put 10,000 euros in the bank, you’d earn 400 euros in interest. And with each next efficiency level, it gets even more unrealistic.
P
perlenmann18 Jul 2011 07:30Since this topic is on my mind at the moment, I’m bringing it up again.
I am now facing the decision between double or triple glazing. The additional cost is 850€.
What do you recommend?
I am now facing the decision between double or triple glazing. The additional cost is 850€.
What do you recommend?
Perlenmann schrieb:
....I am now facing the decision between double or triple glazing. The additional cost is 850€. What do you recommend? The price difference is minimal! The key factors are solely the guaranteed (certified) technical parameters, especially the U-value and solar heat gain coefficient (g-value).
It is not uncommon that a lower U-value also corresponds to a lower g-value, which means the overall benefit may be limited or even worse.
Without an actual energy consumption forecast, it is impossible to properly assess this.
Best regards
Aila71 schrieb:
I calculated the cost-effectiveness on the website "WWW.u-wert.net" and was quite surprised.
Wall construction 1 (standard developer):
- 2cm (1 inch) lime-cement plaster
- 15cm (6 inches) sand-lime brick
- 12cm (5 inches) external thermal insulation composite system (ETICS) with lambda 0.035
- 2cm (1 inch) lime-cement plaster
U-value of the wall: 0.26 W/m²K
Heat loss: 18 kWh per m² per heating season
Wall construction 2 (most commonly recommended):
- 2cm (1 inch) lime-cement plaster
- 15cm (6 inches) sand-lime brick
- 16cm (6 inches) ETICS 0.035
- 2cm (1 inch) lime-cement plaster
U-value of the wall: 0.20 W/m²K
Heat loss: 14 kWh per m² per heating season
With an exterior wall area of 162 m² (1744 ft²) and an annual savings of 4 kWh per m², I calculated €45 savings per heating season at the current gas price. However, the 4% additional interest on my €2,500 investment alone is €100 per year, without recovering any of the principal.
I calculated the payback period for the €2,200 investment and arrived at 44 years(!), assuming a gas price increase of 5% annually.I came across this topic on Google while researching the same issue. Currently, we have 17.5cm (7 inches) sand-lime brick with 12cm (5 inches) of 0.032 lambda insulation planned. The idea now is to increase the insulation thickness to 16 cm (6 inches).
The calculation here is similar to the quoted post, but I’m not sure if I’m falling for an oversimplified assumption or not.
About 200 m² (2150 ft²) of wall surface; the additional cost for increasing from 12cm to 16cm insulation is roughly €3–4 per m² (€0.28–0.37 per ft²) according to online building material suppliers.
According to the U-value calculator, this would improve from 0.24 to 0.18 W/m²K and reduce the heat loss per heating season from 19 to 14 kWh per m².
Now the key question: Can the saved kWh be equated to the electricity consumption of the heat pump (ground source)? Because if so, I would arrive at a very different calculation.
Additional cost for 200 m² at €3–4 per m²: €800
Savings: 5 kWh per m² × 200 m² = 1,000 kWh saved annually
At about $0.18 per kWh electricity price, that equals almost $200 savings per year, meaning it would pay off in 4 years.
So, a clear recommendation to add 4 cm (1.5 inches) more insulation—or is this just an oversimplified calculation?
achsell schrieb:
...according to the U-value calculator, this is an improvement from 0.24 to 0.18 W/m²K and, over the heating season, a reduction in heat loss from 19 to 14 kWh per m² How were these figures determined? achsell schrieb:
...now the crucial question is whether these saved kWh can be equated with the electricity consumption of the heat pump (ground source) ? No, the demand for heating energy does decrease due to the reduction in transmission heat losses. Exactly how much should be determined precisely. The "savings effect" only applies to the electricity portion of the ground source heat pump, but not to the much larger "energy extracted from the ground". At the same time, the solar gains of opaque components (AW) are reduced.
Possibly, due to the reduced heating load, a ground source heat pump of one size smaller can be chosen (investment savings, lower financing costs).
On the other hand, it can happen that, due to improved insulation, the heat pump is significantly oversized because of its capacity increments. The seasonal performance factor (SPF) may then worsen. In that case, the intended effect may be reversed or may not take effect at all.
Whether online building supply stores are generally suitable for price comparison should be examined.
Best regards.
€uro schrieb:
How were these figures determined?These were "calculated" by the U-value calculator based on the monthly average temperatures provided by the German Weather Service.
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