Thermal insulation, Energy Saving Ordinance, KFW 70 / 55 / 40 - Your experiences

May I ask which Ytong you used? I think you then reach a U-value of the wall around 25-20, or how thick was your stone? For me, it is exactly the same, that I actually don’t want to build with ETICS and therefore the "stone" question is somewhat more important than maybe for others. Did you notice big differences when looking for the general contractor because of the stone?

Good morning, of course you may ask. Our stone is a 30 cm Ytong Thermoblock. According to the manufacturer, the U-value of the stone is 0.29 unplastered. The next best stone would have been the 36 cm one, followed by the 42.5 cm one. We are not fans of airtight, tighter, tightest and calculated the effort/benefit for ourselves. Therefore, also double glazing. The window should fit the stone and a triple glazing would not only have been disproportionately expensive, it also didn’t suit the stone we wanted. The expert who was at our place on Monday said our glazing is top, the windows are a premium product and that it is better to invest in good double glazing than in cheap triple glazing. By the way, the friendly window builder next door agrees with that! Finding a general contractor who used Ytong was not that difficult. We are from Koblenz and the model house center Mülheim-Kärlich is not far from us. Two years of planning, information, various talks there... In the end, we had the choice of: Massivhaus Mittelrhein and Town & Country. Who we are currently building with is stated in our construction diary, which is posted here.

Morning, morning, of course you may ask questions.

Our block is a 30 cm Ytong Thermoblock. According to the manufacturer, the U-value of the block is 0.29 unplastered.

The next best block would have been the 36 cm one followed by the 42.5 cm one.

We are not fans of tight, tighter, tightest and have calculated the effort/benefit for ourselves. Hence also double glazing. The window had to match the block and a triple glazing would not only have been disproportionately expensive, but it also did not fit the block we wanted.

The expert who was with us on Monday said our glazing is top, the windows a premium product, and that one should rather invest in good double glazing than in cheap triple glazing.
By the way, the friendly window builder next door sees it the same way!

Finding a general contractor who builds with Ytong was not that difficult. We are from Koblenz and the model house center Mülheim-Kärlich is not far from us. Two years of planning, information, various talks there... At the end we had the choice between: Massivhaus Mittelrhein and Town & Country.

Who we are currently building with is in our construction diary, which is posted here.

Aha ok, great THANK YOU for the info!

Regarding the search for model houses, we have planned to go to a model house park near us next weekend. But as luck would have it, we found a model house in the prefab house world in Wuppertal that really comes very close to our "dream house". We will be with relatives in Bad Neuenahr Arhweiler in the first week of May, you surely know it too, and then we will take a day to drive there. The next model house parks for us are in Nuremberg and Munich respectively Ingolstadt. But that one house is exactly in Wuppertal.

As you said, ultimately it will come down to weighing what is economical and what one can afford. Because it makes no sense if I have to take out a 50,000 euro loan just so that I can build KfW55 and put a green thumb sticker on my forehead.

I will take a look at your diary right away.

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Have you made any further progress on the topic of wall construction? We are planning a KfW55 bungalow with a geothermal heat pump and controlled residential ventilation with heat recovery. 75% of the window areas face SE/SW, 25% NE/NW. We want a monolithic wall construction, but now our structural engineer said that KfW55 would not be feasible with a 36.5 cm aerated concrete block. In his calculation, he used an exterior wall of 24 cm aerated concrete (0.09 W/mK) and 12 cm mineral wool (0.032 W/mK). This results in a U-value (ISO 6946): 0.145 W/m²K.

Calculation result value
Qp reference building 94.45 kWh/(m²a)
Qp building 48.38 kWh/(m²a)
Relative to the specified Qp reference/target value 51 % / 55 %
Requirements for primary energy demand fulfilled
Ht' reference building 0.336 W/(m²K)
Ht' building 0.234 W/(m²K)
Relative to the specified Ht' reference/target value 70 % / 70 %
Requirements for thermal insulation fulfilled

Could the structural engineer be right that it won't work with a 36.5 cm aerated concrete block?

Hello

I have to admit that I haven't dealt with the topic any further recently, since our planning will "only" start in the winter/spring of next year. Therefore, I can't provide any more information about the values of the stones right now. If you're not sure, just ask somewhere else again and get a second opinion, so to speak. Often, several factors are connected, not just the strength of the stone.

I will definitely continue to follow the topic here as soon as you have more information.

Best regards, Andi

We are currently building a KFW55 house according to the 2016 Energy Saving Ordinance in Bavaria.

I would not have accepted exterior insulation and from the beginning it was clear to me: solid brick construction.

The brick now being used is the Leipfinger Bader Unipor W08 at 36.5cm. With this brick, the requirements for KFW55 regarding the exterior wall are fully met. The brick is unfilled and accordingly not so expensive.
The windows are triple-glazed with Uglass=0.5, but this would have been standard with my builder anyway, even without KFW70/55.

The floor slab in the basement as well as the basement itself are insulated with Styrodur (10cm), which would not have been necessary for KFW70 according to the 2014 Energy Saving Ordinance under the floor slab. So here we had additional costs on top of the brick.

I usually only see Ytong in our area in residential construction and always with exterior insulation. For me, this is an indication that it is a cheaper construction method than using proper bricks. Therefore, not an alternative for me.

Overall, the upgrade from KFW70 (2014) to KFW55 (2016) was economical for me, as the additional costs are offset by the cheaper KFW loan (higher initial investment, but paid off faster) and in the long run I simply have the better exterior envelope.

The fact that a multi-family house has different structural/acoustic/other requirements that the [Krümelkeksziegel] cannot meet hadn't even occurred to you? Every system has advantages and disadvantages.. the perforated brick is not a panacea.