Dear forum community,
We are planning the construction of a new single-family house. The house should ideally meet the KfW 70 standard in order to qualify for the corresponding funding. We have decided to equip the house in a way that minimizes the heating demand from the start. So, we want a lot of insulation and limited high-tech solutions.
Now we are wondering whether we can achieve KfW 70 with the following construction method and features:
Solid construction, no basement, 1.5 floors, gable roof, 141 sqm (1,518 sq ft) according to DIN, almost square: 9.14 m x 9.83 m (30 ft x 32 ft)
Wall structure: 17.5 cm (7 inches) Poroton bricks, 14 cm (5.5 inches) insulation, cavity, 12.5 cm (5 inches) facing brick
Windows: 5-chamber frame (70 mm / 3 inches), triple glazing, exterior muntins
Roof: 240 mm (9.5 inches) mineral wool insulation with thermal conductivity class 035 (WLG 035) up to the attic ceiling and in the ceiling to the attic
Floor: 100 mm (4 inches) perimeter insulation under the foundation slab, 110 mm (4.3 inches) polystyrene with WLG 035 under the screed
Heating: gas condensing boiler with underfloor heating throughout the entire house
Ventilation: a total of three decentralized ventilators with heat recovery (Meltem)
The gables face north (small windows) and south (large windows)
Is KfW 70 achievable?
Kind regards
Benjih
We are planning the construction of a new single-family house. The house should ideally meet the KfW 70 standard in order to qualify for the corresponding funding. We have decided to equip the house in a way that minimizes the heating demand from the start. So, we want a lot of insulation and limited high-tech solutions.
Now we are wondering whether we can achieve KfW 70 with the following construction method and features:
Solid construction, no basement, 1.5 floors, gable roof, 141 sqm (1,518 sq ft) according to DIN, almost square: 9.14 m x 9.83 m (30 ft x 32 ft)
Wall structure: 17.5 cm (7 inches) Poroton bricks, 14 cm (5.5 inches) insulation, cavity, 12.5 cm (5 inches) facing brick
Windows: 5-chamber frame (70 mm / 3 inches), triple glazing, exterior muntins
Roof: 240 mm (9.5 inches) mineral wool insulation with thermal conductivity class 035 (WLG 035) up to the attic ceiling and in the ceiling to the attic
Floor: 100 mm (4 inches) perimeter insulation under the foundation slab, 110 mm (4.3 inches) polystyrene with WLG 035 under the screed
Heating: gas condensing boiler with underfloor heating throughout the entire house
Ventilation: a total of three decentralized ventilators with heat recovery (Meltem)
The gables face north (small windows) and south (large windows)
Is KfW 70 achievable?
Kind regards
Benjih
Hello,
Whether the Qp´´ value is sufficient can’t be judged generally—you would need to calculate it precisely.
Best regards.
Benjih schrieb:Good approach!
...So we want a lot of insulation, but low-tech solutions.
Benjih schrieb:It’s hard to say based on that alone. If the heat transfer coefficient (Ht value) meets the 15% rule, then probably yes; otherwise, you may be forced to add a solar thermal system (EEWG), which is usually not cost-effective for a single-family house.
...Now we are wondering if we can achieve KfW 70 with the following construction/design:
Whether the Qp´´ value is sufficient can’t be judged generally—you would need to calculate it precisely.
Benjih schrieb:Not a good idea! If you install ventilation, do it properly with a centralized controlled residential ventilation system with heat recovery.
...Ventilation: three decentralized heat recovery ventilators (Meltem) total
Benjih schrieb:What does your planner say about this?
...Is KfW 70 achievable?
Best regards.
Thank you for your reply!
Unfortunately, the centralized ventilation system is too expensive for us. Our general contractor wants nearly €9,000. With the decentralized solution, we're looking at about one-third of that. Additionally, we are concerned about germs, loss of sound insulation, etc. There is also the space requirement in the utility room.
So far, our "planner" has been "only" the very knowledgeable sales advisor. He expects that we can achieve KfW 70 standard with this house, but he also says that it needs to be calculated by the structural engineer. I think that is a reasonable approach.
However, my concern is that after signing the contract, the €5,000 solar system will be added.
Maybe someone has enough experience to be hopeful about achieving KfW 70 based on my data?!
Best regards, Ben
Unfortunately, the centralized ventilation system is too expensive for us. Our general contractor wants nearly €9,000. With the decentralized solution, we're looking at about one-third of that. Additionally, we are concerned about germs, loss of sound insulation, etc. There is also the space requirement in the utility room.
So far, our "planner" has been "only" the very knowledgeable sales advisor. He expects that we can achieve KfW 70 standard with this house, but he also says that it needs to be calculated by the structural engineer. I think that is a reasonable approach.
However, my concern is that after signing the contract, the €5,000 solar system will be added.
Maybe someone has enough experience to be hopeful about achieving KfW 70 based on my data?!
Best regards, Ben
B
Bauexperte2 Feb 2012 13:26Hello Ben,
The fear of "germs" is often artificially generated to give unsure builders a reason to avoid "supposedly" more expensive equipment; usually a common tactic used by poorer salespeople.
The issue with sound is more of a problem with decentralized systems, which makes sense because you have to accept vents in your well-insulated exterior wall. We really should add an article about this topic on our homepage soon.
Finally, a good example of professional sales advice; at least I hope so.
No one can give a reliable answer to that. If it were that easy, €uro—whose expertise your question concerns—would have responded differently.
It depends on the location of the plot, the components used in the construction, the overall heating demand of the new build, and many other factors. I am currently facing the same challenge of realizing a KfW 70 efficiency house, where a gas condensing boiler is planned as the heat generator. At this point: Thank you, €uro, for your help
From experience with other projects, I know that KfW 70 can be achieved almost everywhere—perhaps with some additional options (depending on the above-mentioned circumstances)—where an air-to-water heat pump is used. This brings me back to your original point. If ventilation is planned anyway, you can usually rely on combination units, provided only one party will live in the new house; if there is a rental portion, each apartment should have an independent system. These units do not take up much more space in the utility room than a conventional gas condensing boiler with connections, expansion tank, and storage tank. This way, you can also avoid the solar system—which is often unpopular with most building services engineers.
If I understood your post correctly, this would mean for you: You waive the decentralized ventilation at about €3,000 and the gas condensing boiler at about €3,000 to €4,000 (depending on supplier and size) and receive a credit in return. The surcharge for the combination unit should, in my opinion, be moderate and has the major advantage that it includes an air-to-water heat pump as well as controlled residential ventilation with heat recovery. You do not have to accept loss of space in the utility room; you also save the often significant costs for the gas connection.
This sentence actually worries me more. I was initially pleased with the salesman you praised. But has he also fully informed you about the expected additional construction costs? If you have factored these costs into your financing, plus painting/flooring and exterior works, as well as a sum "X" for extras, then an extra €5,000 should not seriously concern you.
Addition:
Poorly maintained air conditioning and ventilation systems pose an immediate health risk. Delayed filter changes, dirty air ducts, or contaminated humidifiers promote the growth of dangerous germs that can cause life-threatening lung diseases in humans.
A common mistake is changing ventilation system filters too late. When the filtered air passes through overloaded filters, the systems actually blow more pollutants into indoor spaces than they capture. If bacterial and fungal colonies have already formed, dangerous germs can spread throughout the entire building and settle, for example, in kitchens.
The fine fins of coolers and heaters in air conditioning units as well as the many meters of ventilation ducts must also be regularly cleaned and checked for dirt and moisture. This is often hampered by the absence of inspection openings, a classic case of poor planning.
The most serious defects occur with humidifiers because stagnant water between 25 and 45 degrees Celsius (77 and 113°F) creates an ideal breeding ground for bacteria, especially dangerous legionella. In systems with humidifiers, continuous water replacement must be ensured.
The relevant VDI Guideline 6022 on "Hygiene Requirements for Ventilation and Air Conditioning Systems and Units" requires such systems to be regularly inspected for contamination and moisture zones and, if necessary, cleaned by qualified professionals. For systems with humidifiers, this is required every two years; without humidifiers, every three years.
Kind regards
Benjih schrieb:
Unfortunately, the central ventilation system is too expensive for us. Our general contractor wants nearly €9,000 for it. With the decentralized solution, we’re at about one third of that. Additionally, we are concerned about germs, loss of sound insulation, etc. Plus, the space needed in the utility room.
The fear of "germs" is often artificially generated to give unsure builders a reason to avoid "supposedly" more expensive equipment; usually a common tactic used by poorer salespeople.
The issue with sound is more of a problem with decentralized systems, which makes sense because you have to accept vents in your well-insulated exterior wall. We really should add an article about this topic on our homepage soon.
Benjih schrieb:
Our "planner" so far has only been the very knowledgeable sales consultant. He expects that we will achieve KfW 70 with this house but also says that this must be calculated by the structural engineer. I think that is quite professional. But: My concern is that after signing the contract, the €5,000 solar system will be added.
Finally, a good example of professional sales advice; at least I hope so.
Benjih schrieb:
Maybe someone has enough experience to give hope for KfW 70 based on my data?!
No one can give a reliable answer to that. If it were that easy, €uro—whose expertise your question concerns—would have responded differently.
It depends on the location of the plot, the components used in the construction, the overall heating demand of the new build, and many other factors. I am currently facing the same challenge of realizing a KfW 70 efficiency house, where a gas condensing boiler is planned as the heat generator. At this point: Thank you, €uro, for your help
From experience with other projects, I know that KfW 70 can be achieved almost everywhere—perhaps with some additional options (depending on the above-mentioned circumstances)—where an air-to-water heat pump is used. This brings me back to your original point. If ventilation is planned anyway, you can usually rely on combination units, provided only one party will live in the new house; if there is a rental portion, each apartment should have an independent system. These units do not take up much more space in the utility room than a conventional gas condensing boiler with connections, expansion tank, and storage tank. This way, you can also avoid the solar system—which is often unpopular with most building services engineers.
If I understood your post correctly, this would mean for you: You waive the decentralized ventilation at about €3,000 and the gas condensing boiler at about €3,000 to €4,000 (depending on supplier and size) and receive a credit in return. The surcharge for the combination unit should, in my opinion, be moderate and has the major advantage that it includes an air-to-water heat pump as well as controlled residential ventilation with heat recovery. You do not have to accept loss of space in the utility room; you also save the often significant costs for the gas connection.
Benjih schrieb:
But: My concern is that after signing the contract, the €5,000 solar system will be added.
This sentence actually worries me more. I was initially pleased with the salesman you praised. But has he also fully informed you about the expected additional construction costs? If you have factored these costs into your financing, plus painting/flooring and exterior works, as well as a sum "X" for extras, then an extra €5,000 should not seriously concern you.
Addition:
Poorly maintained air conditioning and ventilation systems pose an immediate health risk. Delayed filter changes, dirty air ducts, or contaminated humidifiers promote the growth of dangerous germs that can cause life-threatening lung diseases in humans.
A common mistake is changing ventilation system filters too late. When the filtered air passes through overloaded filters, the systems actually blow more pollutants into indoor spaces than they capture. If bacterial and fungal colonies have already formed, dangerous germs can spread throughout the entire building and settle, for example, in kitchens.
The fine fins of coolers and heaters in air conditioning units as well as the many meters of ventilation ducts must also be regularly cleaned and checked for dirt and moisture. This is often hampered by the absence of inspection openings, a classic case of poor planning.
The most serious defects occur with humidifiers because stagnant water between 25 and 45 degrees Celsius (77 and 113°F) creates an ideal breeding ground for bacteria, especially dangerous legionella. In systems with humidifiers, continuous water replacement must be ensured.
The relevant VDI Guideline 6022 on "Hygiene Requirements for Ventilation and Air Conditioning Systems and Units" requires such systems to be regularly inspected for contamination and moisture zones and, if necessary, cleaned by qualified professionals. For systems with humidifiers, this is required every two years; without humidifiers, every three years.
Kind regards
Bauexperte schrieb:
If you have included these costs in your financing along with painting/flooring work and landscaping, as well as an amount "X" for extras, then an additional 5,000 EUR should not seriously concern you. Hello Bauexperte,
No, an additional 5,000 EUR does not worry me in the context of the incidental building costs calculation. However, I do know how long I have to work for 5,000 EUR and how an extra 5,000 affects the financing.
There is a reserve included in the site planning. I would prefer to push this through until the end to then focus on priority B projects (garden shed, fireplace, etc.).
I will talk again with the seller about the alternative of removing gas & ventilation and installing an air-source heat pump...
Thanks!
Ben
I’m just going to join in here.
I’m currently planning as well and considering whether KfW70 is achievable or what additional costs it might involve...
After reading into the Energy Saving Ordinance, I came across the following on Wikipedia:
Furthermore, Wikipedia states the primary energy factor fP for a district heating network that sources its energy from combined heat and power (CHP) plus biomass is 0.0!
Consequently, this results in a primary energy demand of zero!
Since I also plan to install a mechanical ventilation system with heat recovery, the transmission heat losses should be very low...
In other words, it should actually be possible to build to KfW70 standard or better without any problems — without solar panels or heat pumps, simply by insulating the house according to the latest state of the art...
Or am I missing something here? Does district heating really offer such a big advantage compared to heat pumps, gas, or oil?
I’m currently planning as well and considering whether KfW70 is achievable or what additional costs it might involve...
After reading into the Energy Saving Ordinance, I came across the following on Wikipedia:
The relationship between primary energy demand QP, final energy demand QE, primary energy factor fP, and conversion factor for final energy fU is described by the Energy Saving Ordinance as follows:
QP = Sum(QE * fP * fU)
Furthermore, Wikipedia states the primary energy factor fP for a district heating network that sources its energy from combined heat and power (CHP) plus biomass is 0.0!
Consequently, this results in a primary energy demand of zero!
Since I also plan to install a mechanical ventilation system with heat recovery, the transmission heat losses should be very low...
In other words, it should actually be possible to build to KfW70 standard or better without any problems — without solar panels or heat pumps, simply by insulating the house according to the latest state of the art...
Or am I missing something here? Does district heating really offer such a big advantage compared to heat pumps, gas, or oil?
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