ᐅ Thermal Insulation, Energy Saving Regulations, KFW 70 / 55 / 40 – Your Experiences
Created on: 17 Feb 2015 17:09
H
Häuslebau3r
Hello everyone, as we would say here,
since I have now become quite engaged with this forum and am interested in more and more topics, the question of the right and “best” insulation has come up for me recently (still purely out of interest for now, but surely also practical at some point). I deliberately put the word best in quotation marks because there will always be different preferences and use cases.
I am fully aware that a standard house usually does not require insulation below U=0.14 W/(m²K). Therefore, I tried to look up the following values regarding the energy-saving regulations and the KfW houses 70 / 55 / 40.
I came up with the following values for the thermal transmittance coefficient:
Reference building according to Energy Saving Ordinance 2014
U-value | Roof 0.20 W/(m²K), Windows 1.30 W/(m²K), Exterior wall 0.28 W/(m²K), Basement wall 0.35 W/(m²K), Floor slab 0.35 W/(m²K)
KfW Efficiency House 70
U-value | Roof 0.17 W/(m²K), Windows 0.90 W/(m²K), Exterior wall 0.23 W/(m²K), Basement wall 0.25 W/(m²K), Floor slab 0.25 W/(m²K)
KfW Efficiency House 55
U-value | Roof 0.17 W/(m²K), Windows 0.90 W/(m²K), Exterior wall 0.18 W/(m²K), Basement wall 0.25 W/(m²K), Floor slab 0.25 W/(m²K)
KfW Efficiency House 40
U-value | Roof 0.15 W/(m²K), Windows 0.80 W/(m²K), Exterior wall 0.14 W/(m²K), Basement wall 0.20 W/(m²K), Floor slab 0.20 W/(m²K)
With the above values, it becomes clear what needs to be done regarding home insulation to meet certain standards. As mentioned above, other factors also play a role, such as roof, upper and ground floor windows, possibly the ceiling in the upper floor, exterior wall including roller shutter box, exterior door, exterior wall, and floor slab. But you have to start somewhere.
What I am curious about as a layperson is the comparison between the KfW 70 standard and the KfW 55 regarding the exterior wall. For me, this point represents basically the only difference related to the values mentioned above. Of course, you are also welcome to share your information and experience regarding windows, for example.
To achieve an exterior wall U-value of about 0.18 W/(m²K), there seem to be different options, as I have read in other threads, such as:
For me personally, only the monolithic wall construction is really an option. Of course, you have to consider that you end up with, for example, a 40cm (16 inches) thick wall to achieve certain values. Often, the windows are then described as “loophole-like” because there is so much material around them. How did you decide, or how would you evaluate this from your experience?
What types of blocks or bricks have you had good or bad experiences with? For example,
Now, go ahead and type away!
since I have now become quite engaged with this forum and am interested in more and more topics, the question of the right and “best” insulation has come up for me recently (still purely out of interest for now, but surely also practical at some point). I deliberately put the word best in quotation marks because there will always be different preferences and use cases.
I am fully aware that a standard house usually does not require insulation below U=0.14 W/(m²K). Therefore, I tried to look up the following values regarding the energy-saving regulations and the KfW houses 70 / 55 / 40.
I came up with the following values for the thermal transmittance coefficient:
Reference building according to Energy Saving Ordinance 2014
U-value | Roof 0.20 W/(m²K), Windows 1.30 W/(m²K), Exterior wall 0.28 W/(m²K), Basement wall 0.35 W/(m²K), Floor slab 0.35 W/(m²K)
KfW Efficiency House 70
U-value | Roof 0.17 W/(m²K), Windows 0.90 W/(m²K), Exterior wall 0.23 W/(m²K), Basement wall 0.25 W/(m²K), Floor slab 0.25 W/(m²K)
KfW Efficiency House 55
U-value | Roof 0.17 W/(m²K), Windows 0.90 W/(m²K), Exterior wall 0.18 W/(m²K), Basement wall 0.25 W/(m²K), Floor slab 0.25 W/(m²K)
KfW Efficiency House 40
U-value | Roof 0.15 W/(m²K), Windows 0.80 W/(m²K), Exterior wall 0.14 W/(m²K), Basement wall 0.20 W/(m²K), Floor slab 0.20 W/(m²K)
With the above values, it becomes clear what needs to be done regarding home insulation to meet certain standards. As mentioned above, other factors also play a role, such as roof, upper and ground floor windows, possibly the ceiling in the upper floor, exterior wall including roller shutter box, exterior door, exterior wall, and floor slab. But you have to start somewhere.
What I am curious about as a layperson is the comparison between the KfW 70 standard and the KfW 55 regarding the exterior wall. For me, this point represents basically the only difference related to the values mentioned above. Of course, you are also welcome to share your information and experience regarding windows, for example.
To achieve an exterior wall U-value of about 0.18 W/(m²K), there seem to be different options, as I have read in other threads, such as:
- Monolithic wall construction
- Functional exterior wall
- Double-shell exterior wall
For me personally, only the monolithic wall construction is really an option. Of course, you have to consider that you end up with, for example, a 40cm (16 inches) thick wall to achieve certain values. Often, the windows are then described as “loophole-like” because there is so much material around them. How did you decide, or how would you evaluate this from your experience?
What types of blocks or bricks have you had good or bad experiences with? For example,
- Aerated concrete plan block NeoStone U-value 0.17 W/(m²K)
- Aerated concrete plan block “SK08” U-value up to 0.18 W/(m²K)
- ThermoPlan MZ8 (mineral wool) – 42.5 cm (17 inches) 0.18 W/(m²K)
- Poroton T9 – 36.5 cm (14 inches) 0.23 W/(m²K) – therefore only suitable for KfW 70
- Poroton T8 – 42.5 cm (17 inches) 0.18 W/(m²K)
- Poroton T8 – 49 cm (19 inches) 0.15 W/(m²K)
- Poroton T7 – 42.5 cm (17 inches) 0.15 W/(m²K)
- UNIPOR W09 - Approval Z-17.1.-1042 | 0.20 W/(m²K) – therefore only suitable for KfW 70
- UNIPOR WS07 CORISO | Approval Z-17.1.-1074 0.18 W/(m²K)
- Ytong aerated concrete 0.07 – 36.5 cm (14 inches) 0.18 W/(m²K)
- Ytong aerated concrete 0.08 – 42.5 cm (17 inches) 0.18 W/(m²K)
- Ytong aerated concrete 0.09 – 48 cm (19 inches) 0.18 W/(m²K)
Now, go ahead and type away!
Häuslebau3r9 Oct 2016 10:54During our conversation this week, a construction company informed us that, for a monolithic building method—which we personally plan to use—the additional investment required to meet the KFW55 funding standards is estimated at around 20,000 euros. This estimate does not even take into account the masonry or window aspects (as there would be hardly any differences there), but is solely based on the points needed regarding heating and similar factors.
@Manuel85,
reading your input now, it seems that might not be the case. We are still in the early pre-planning phase concerning the scoring system for KFW and similar programs, so I cannot really assess the two statements at this point. Currently, we are considering whether the KFW loan interest for KFW55, the additional expenses compared to the building method following the 2016 Energy Saving Regulation (previously KFW70), and the costs for the energy consultant truly balance out.
As mentioned above, a construction company told us that the additional costs are not proportional to the savings from a better building envelope and heating system.
Best regards, Andreas
@Manuel85,
reading your input now, it seems that might not be the case. We are still in the early pre-planning phase concerning the scoring system for KFW and similar programs, so I cannot really assess the two statements at this point. Currently, we are considering whether the KFW loan interest for KFW55, the additional expenses compared to the building method following the 2016 Energy Saving Regulation (previously KFW70), and the costs for the energy consultant truly balance out.
As mentioned above, a construction company told us that the additional costs are not proportional to the savings from a better building envelope and heating system.
Best regards, Andreas
@BeHaElJa
I was referring to an "indication," which is just my personal impression. Besides, there are plenty of apartment buildings constructed using solid brickwork without exterior insulation. However, these are developed by different builders/investors, and again, this is a subjective impression—you can simply tell who is building cheaply and quickly for higher returns, and who is building sustainably and with quality.
It may be possible to disprove my points by presenting the energy concepts, structural calculations, and so on, but if I were looking for a condominium, I would prefer to move into the brick building. That’s just how I feel.
@Häuselbau3r
Of course, the overall concept has to be considered.
We requested a turnkey KfW 70 house under the old Energy Saving Ordinance 2014 (building permit was applied for back in 2015, so we could have built according to the 2014 standard!).
Even at that time, it was clear to me that I wanted a central controlled residential ventilation system with heat recovery (extra cost about €10,000-12,000), which wouldn’t have been necessary for this house.
After signing the contract, we consulted an independent energy advisor (county office) who reviewed everything. They recommended considering an upgrade to KfW 55, since with the heat pump, high-quality windows, and basement insulation, we were already very close, and the loan subsidies would become more attractive.
So we asked for a cost estimate for the upgrade, which came to about €9,000 for foundation slab insulation, W08 bricks, a few minor plaster adjustments due to the brickwork, and similar items.
Following that, we had a new energy calculation done, enabling us to meet the 2016 Energy Saving Ordinance with KfW 55.
After hours of economic assessments and experimenting with various financing models (financing was not yet finalized), I decided that overall it was more economical to proceed with KfW 55 according to the 2016 Energy Saving Ordinance.
In total, including the controlled residential ventilation, you can expect an additional cost of about €20,000.
I was referring to an "indication," which is just my personal impression. Besides, there are plenty of apartment buildings constructed using solid brickwork without exterior insulation. However, these are developed by different builders/investors, and again, this is a subjective impression—you can simply tell who is building cheaply and quickly for higher returns, and who is building sustainably and with quality.
It may be possible to disprove my points by presenting the energy concepts, structural calculations, and so on, but if I were looking for a condominium, I would prefer to move into the brick building. That’s just how I feel.
@Häuselbau3r
Of course, the overall concept has to be considered.
We requested a turnkey KfW 70 house under the old Energy Saving Ordinance 2014 (building permit was applied for back in 2015, so we could have built according to the 2014 standard!).
Even at that time, it was clear to me that I wanted a central controlled residential ventilation system with heat recovery (extra cost about €10,000-12,000), which wouldn’t have been necessary for this house.
After signing the contract, we consulted an independent energy advisor (county office) who reviewed everything. They recommended considering an upgrade to KfW 55, since with the heat pump, high-quality windows, and basement insulation, we were already very close, and the loan subsidies would become more attractive.
So we asked for a cost estimate for the upgrade, which came to about €9,000 for foundation slab insulation, W08 bricks, a few minor plaster adjustments due to the brickwork, and similar items.
Following that, we had a new energy calculation done, enabling us to meet the 2016 Energy Saving Ordinance with KfW 55.
After hours of economic assessments and experimenting with various financing models (financing was not yet finalized), I decided that overall it was more economical to proceed with KfW 55 according to the 2016 Energy Saving Ordinance.
In total, including the controlled residential ventilation, you can expect an additional cost of about €20,000.
Your construction company is a joke...
I think it’s more likely that they have little experience with other building materials or, even more likely, worse suppliers for them, and that’s why they’re trying to discourage you with the price (which is somewhat understandable, as special building physics requirements for larger detached houses probably mean significantly higher extra costs at first, since the entire concept often has to be changed).
To clarify: our heating system including drilling didn’t cost 20,000€ (about $22,000) — it is even suitable for a passive house based on its primary energy factor.
@Manuel85, I agree with you on the return on investment; I just want to say that not everything is always black and white / good and bad. A brick wall with a U-value of 0.08 (W/m²K) has little to do with a solid, everlasting structure — it’s quite heavily perforated; but still, of course, a great natural building material from a technical perspective.
I think it’s more likely that they have little experience with other building materials or, even more likely, worse suppliers for them, and that’s why they’re trying to discourage you with the price (which is somewhat understandable, as special building physics requirements for larger detached houses probably mean significantly higher extra costs at first, since the entire concept often has to be changed).
To clarify: our heating system including drilling didn’t cost 20,000€ (about $22,000) — it is even suitable for a passive house based on its primary energy factor.
@Manuel85, I agree with you on the return on investment; I just want to say that not everything is always black and white / good and bad. A brick wall with a U-value of 0.08 (W/m²K) has little to do with a solid, everlasting structure — it’s quite heavily perforated; but still, of course, a great natural building material from a technical perspective.
Häuslebau3r9 Oct 2016 12:22BeHaElJa schrieb:
Your construction company is hopeless...
I rather think they have little experience with other building materials or even worse, poor sources for them, and that’s why they want to deter you with the price (which is even understandable since special building physics requirements for larger heat generators usually mean high additional costs at first, as often the whole concept fails).
To clarify: our heating system including drilling didn’t cost 20,000€ (about $21,500) – it’s even suitable for a passive house purely based on the primary energy factor.Was that in response to my post, which was addressed to Manuel, or @BeHaElJa?
The construction company has been building what is requested for more than 50 years. Whether it’s, as with acquaintances of ours, to KfW 55 standard or even higher, or just built according to the 2016 Energy Saving Ordinance standard. So the comment about the company being hopeless can be put aside.
But your example is quite fitting, as is Manuel’s example with the mechanical ventilation with heat recovery system.
I could definitely imagine building with mechanical ventilation with heat recovery – in fact, it was planned so far (also for health reasons within the family, concerning allergies such as hay fever, grasses, pollen, etc.).
However, the idea that such a system would be absolutely necessary in a house built only to the 2016 Energy Saving Ordinance standard because of ventilation behavior or airtight building envelope is nonsense (one should not be inside the house for 200 days a year, after all).
So, one always has to weigh the benefits gained against the downside, which is certainly primarily the cost factor. Normally, no one has money left over just to say that they have this or that if economically it doesn’t really make sense, right?
@Manuel85
Why did you decide on mechanical ventilation with heat recovery, or was it clear from the start that it would be installed, if I may ask so casually? Apparently, this decision was independent of whether the house was built to KfW standards or not.
Regards, Andreas
That was directed at you – oh, I see. Of course, if you didn’t include a controlled residential ventilation system in the plan, it naturally becomes more expensive; but then you do have a controlled residential ventilation system, which not only affects heating costs but also provides a significant comfort factor. Attributing it solely to the "heating" is somewhat simplistic; it would be like equating an Opel Corsa and a 5 Series BMW just because they both take you from point A to point B.
Häuslebau3r schrieb:
@Manuel85
Why did you choose a mechanical ventilation with heat recovery system, or was it clear to you from the start that you wanted it installed, if I may ask so casually? Apparently, this decision was independent of whether you built according to KfW standards or not.
Regards, AndreasMy reasons for opting for a mechanical ventilation with heat recovery system are:
- Fresh air in the bedrooms without opening windows at night (I find this a huge comfort factor! I’m really looking forward to it since I almost always stumble backwards out of the room when I go to the bathroom early in the morning and then return to the bedroom – I expect better sleep thanks to the fresh air!)
- No need for daily, multiple airing sessions (especially important when you’re away for a few days, so the air inside doesn’t become stagnant)
- No constant opening of windows (“stuffy”) or closing them again (“I’m cold”) when having guests over
- Energy savings, especially in winter, and at least minimal cooling effect in summer (possible thanks to a ground heat exchanger – though one shouldn’t expect too much effect)
- No fear of mold, especially in humid rooms
I am simply convinced by the technology and benefits of a mechanical ventilation with heat recovery system. And only with a centralized system. New construction and decentralized systems don’t work together for me: too many potential points of failure (fans), many filters (one for each room), plus a hole in every room. The centralized system is certainly more expensive, but also less noticeable and hopefully easier to maintain.
I wouldn’t even say that the mechanical ventilation with heat recovery was absolutely necessary for the KfW55 house. As we know, it’s all a mixed calculation of primary energy, energy efficiency, and building materials.
Without the ventilation system, we would have needed more expensive materials instead.
Thanks to the mechanical ventilation with heat recovery, we easily meet the minimum requirements in my opinion, and that was also the reason why we chose to go for KfW55.
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