ᐅ kfw40plus monolithic solid construction – tips and experiences?
Created on: 8 Mar 2016 17:25
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bellamuc
Hello everyone,
we are planning to build a house in the Allgäu region. Since it will not be small and includes three residential units, we would like to take advantage of the kfw40plus subsidy. Photovoltaics are already planned extensively (covering the entire roof), so that is settled. Additionally, there will be a hydronic fireplace stove.
I definitely want to build with solid construction and prefer no external insulation. Ideally, I would like a purely monolithic wall made of materials like aerated concrete or expanded clay blocks (so without insulated blocks such as Cariso).
The house will be built on a hillside, with the basement partially exposed on one side and used as living space. Therefore, I would prefer a masonry basement if it is not counterproductive to achieving the kfw40+ standard.
I have received various opinions from construction companies and architects (including passive house planners). It seems everyone tries to sell me the solution they are familiar with.
How can I calculate whether, for example, a 42.5cm (17 inches) thick Ytong wall can meet the kfw40+ standard and which additional measures I need to take (windows, roof, basement floor, other energy-related measures...)?
Maybe there are other factors I can adjust so that the masonry can be as thin as possible (perhaps even 36.5cm (14 inches) plus plaster)? Of course, all this should not cost more than what the subsidy and heating cost savings justify.
Some say that the 0.07 W/(m·K) Ytong or Poroton blocks are so fragile they break easily in your hands… I should rather use 0.08 W/(m·K) blocks and make the wall thicker… there are so many opinions.
Is there anyone here who has really built purely monolithic solid and met the kfw40+ standard?
Any tips?
Greetings from Munich.
we are planning to build a house in the Allgäu region. Since it will not be small and includes three residential units, we would like to take advantage of the kfw40plus subsidy. Photovoltaics are already planned extensively (covering the entire roof), so that is settled. Additionally, there will be a hydronic fireplace stove.
I definitely want to build with solid construction and prefer no external insulation. Ideally, I would like a purely monolithic wall made of materials like aerated concrete or expanded clay blocks (so without insulated blocks such as Cariso).
The house will be built on a hillside, with the basement partially exposed on one side and used as living space. Therefore, I would prefer a masonry basement if it is not counterproductive to achieving the kfw40+ standard.
I have received various opinions from construction companies and architects (including passive house planners). It seems everyone tries to sell me the solution they are familiar with.
How can I calculate whether, for example, a 42.5cm (17 inches) thick Ytong wall can meet the kfw40+ standard and which additional measures I need to take (windows, roof, basement floor, other energy-related measures...)?
Maybe there are other factors I can adjust so that the masonry can be as thin as possible (perhaps even 36.5cm (14 inches) plus plaster)? Of course, all this should not cost more than what the subsidy and heating cost savings justify.
Some say that the 0.07 W/(m·K) Ytong or Poroton blocks are so fragile they break easily in your hands… I should rather use 0.08 W/(m·K) blocks and make the wall thicker… there are so many opinions.
Is there anyone here who has really built purely monolithic solid and met the kfw40+ standard?
Any tips?
Greetings from Munich.
B
Bauexperte11 Mar 2016 10:47Hello,
You should simultaneously consult a system planner specializing in photovoltaic and storage technology. They need all relevant data for the planned construction project, especially information about the heating demand. Afterwards, they can give you a precise fixed-price offer—ending the need for further calculations.
In our case, the photovoltaic system is - for various reasons - not included in the scope of the construction contract. The main reason is that you need someone who knows what they are doing and can be held liable in case KfW40+ standards are not achieved, even if the building envelope is prepared accordingly. We act *only* as intermediaries because we simply lack the expertise for exact dimensioning; however, we rely on long-standing partners. Personally, I am not a fan of *jack-of-all-trades* approaches—you either don’t do anything properly or you have to work with your current status quo. Not my thing; everyone should do what they do best!
There is—regarding cost determination—the approach I described earlier. Then you at least have the figure for KfW40 on the table and still need an offer from a system planner for relocating the photovoltaic system. Afterwards or simultaneously, an energy consultant has to do the calculations again. Either way, some money will likely be spent before you know whether everything will work out as you expect.
Best regards, Bauexperte
bellamuc schrieb:That is both correct and incorrect; a contractor must provide you with an offer based on KfW40 standards; the architect should prepare a corresponding cost estimate. What wall thickness—in centimeters—has been specified in the building application?
All contractors only offer me quotes for KfW55. I would have to sign this offer and enter the calculation phase... only then would I know the additional cost for achieving KfW40+. This is unsatisfactory. Hints are made that it will only be feasible with 50cm (20 inches) walls and that it will cost more than the repayment subsidies (3x €15,000 + €18,000).
You should simultaneously consult a system planner specializing in photovoltaic and storage technology. They need all relevant data for the planned construction project, especially information about the heating demand. Afterwards, they can give you a precise fixed-price offer—ending the need for further calculations.
In our case, the photovoltaic system is - for various reasons - not included in the scope of the construction contract. The main reason is that you need someone who knows what they are doing and can be held liable in case KfW40+ standards are not achieved, even if the building envelope is prepared accordingly. We act *only* as intermediaries because we simply lack the expertise for exact dimensioning; however, we rely on long-standing partners. Personally, I am not a fan of *jack-of-all-trades* approaches—you either don’t do anything properly or you have to work with your current status quo. Not my thing; everyone should do what they do best!
bellamuc schrieb:Planning a KfW40+ from scratch is indeed quite complex; you want to relocate an existing photovoltaic system with fixed consumers. This requires considerable calculations; for me, the offered price is reasonable.
An energy consultant and passive house planner I found, who seems competent and open enough, does foresee feasibility but does not name a price for the house construction. This requires elaborate planning, for which they initially want to charge me about €4,000. Only then will I know the price, and I might then realize that it is outside the budget or that KfW55 is economically the better alternative anyway!?
There is—regarding cost determination—the approach I described earlier. Then you at least have the figure for KfW40 on the table and still need an offer from a system planner for relocating the photovoltaic system. Afterwards or simultaneously, an energy consultant has to do the calculations again. Either way, some money will likely be spent before you know whether everything will work out as you expect.
Best regards, Bauexperte
A 42.5 cm (17 inches) thick wall wouldn’t be a problem considering the house size. That would be great. Which type of block would be suitable for this? I’ve been told that if at all possible, it would only work with the 0.07 blocks, but those tend to break easily and require complex reinforcement. The reinforcement, combined with the higher cost of the 0.07 blocks, would make it too expensive to be worthwhile.
I don’t understand why you are placing so much emphasis on the photovoltaic system? I am a photovoltaic project planner. What is so problematic about it? There is more than enough energy available; it covers the entire electricity demand of the three residential units and even the two electric cars. For poor, sun-poor winter periods (more than 2 weeks), electricity might need to be drawn from the grid, but by the time the house is completed, there will be community energy storage where wind power is stored. It’s really not that complicated.
However, I don't know how the photovoltaic system is incorporated into the KfW calculation.
At the time the building application was submitted, I was unable to hire a specialist planner – there are other reasons for this, and it’s a long story I would prefer to leave out here.
The fact is that the building permit has been granted (with 36.5cm (14 inches) walls), the financing is secured, and construction is now to begin. However, I want to be able to weigh up whether and at what effort I can meet the KfW 40+ standards. Ideally, I want to avoid committing contractually or spending money upfront to obtain a quotation.
However, I don't know how the photovoltaic system is incorporated into the KfW calculation.
At the time the building application was submitted, I was unable to hire a specialist planner – there are other reasons for this, and it’s a long story I would prefer to leave out here.
The fact is that the building permit has been granted (with 36.5cm (14 inches) walls), the financing is secured, and construction is now to begin. However, I want to be able to weigh up whether and at what effort I can meet the KfW 40+ standards. Ideally, I want to avoid committing contractually or spending money upfront to obtain a quotation.
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Bauexperte11 Mar 2016 11:02Normally made with a masonry unit having a lambda value of 0.07 W/mK, resulting in a U-value of 0.16 W/m²K. It does not matter whether aerated concrete or a perforated brick with internal insulation is chosen.
Aerated concrete is easier to work with; using the insulated masonry unit is a bit more complex but manageable, as the internal insulation can separate during cutting.
Regards, Bauexperte
Aerated concrete is easier to work with; using the insulated masonry unit is a bit more complex but manageable, as the internal insulation can separate during cutting.
Regards, Bauexperte
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Bauexperte11 Mar 2016 11:14bellamuc schrieb:
I don’t understand why you are putting so much emphasis on the photovoltaic system? I am a photovoltaic project planner. What’s problematic about it? You have already answered this yourself. The photovoltaic system has to:
bellamuc schrieb:
However, I don’t know how the photovoltaic system factors into the KfW calculation. correspond to that. Only a professional who can be held liable for their statements should answer that. In your case, it’s not _just_ the photovoltaic calculation; you already have fixed electricity consumers.
bellamuc schrieb:
However, I want to be able to weigh whether and at what effort I can achieve the KfW 40+ standards. Ideally without being contractually committed in advance or having to spend money upfront for calculating a quote. For that, you don’t need much more than a quote according to KfW 40 for the three-family house, plus the costs for relocating the photovoltaic system and an energy consultant’s calculation. It’s not rocket science for either party; although the energy consultant will hardly work on a speculative basis. So their fees represent your risk.
Honestly, I don’t understand—since you have direct access to the source—where your problem lies in finding an energy consultant? No collaborations? You don’t have to reveal any confidential details to answer; it’s none of my business, nor do I want to know.
I pay close attention to every component of a house build! I want references; not just to have a house “thrown together.” And I want to be absolutely certain that homeowners can enforce legitimate warranty claims. Overestimating oneself is highly inappropriate in this context.
Regards, Bauexperte
bellamuc schrieb:
I have now received several opinions from construction companies and architects (including passive house designers). I get the impression that everyone is trying to "sell" me what they have experience with.On one hand, it’s naturally difficult because things are not comparable, but:If someone tries to sell you something they don’t understand, that is much more risky. It’s better if the people know the type of stone and are able to work with it. In the construction industry, things are rarely black and white. There are many ways to reach the goal.
The stone must meet your requirements AND be workable for the construction company.
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