Single-family house KfW55 - Extra costs: rip-off or justified?

Dear forum community,

My wife and I want to fulfill our wish of building a single-family house next year. Our draft planning is already finished and we are currently in the process of obtaining offers from potential construction companies. We want to build turnkey using solid construction methods. (BW, Stuttgart/Esslingen area)

Regarding the bidding phase:
1. We received an offer without KFW additional costs (we do not know why, as we already submitted the necessary documents from the energy consultant at the first meeting).
2. An offer included additional costs of €49,000 to achieve KFW55 according to the energy consultant's report.

We are shocked by the additional costs. Therefore, we ask ourselves whether it is even worthwhile for us. Although we were lucky that our application for KFW funding was approved in mid-January (subsidy of €26,000), we still have to pay an additional €23,000 to meet the standard. As I understand it, I could still spend a lot of money on heating in the coming years for this amount.

We are aware that the costs for building materials, etc., are currently skyrocketing. Nevertheless, the offer seems too high to us. The scope of services is also very thinly described. Does every new building not have to meet a certain minimum standard according to the Building Energy Act? Is this even covered by the scope of services? Example roof: According to the scope of services, no insulation is planned in the attic. (only preparatory measures)

I have listed the additional necessary measures according to the construction company below, in addition to the information from the scope of services. What I have checked in advance: the measures listed here largely correspond to the content/component list of the energy consultant.

Nevertheless, the following questions arise for us:

[*]Change of foundation type: Not described in detail in the offer. Is this justified? Is a slab foundation actually more expensive than strip foundations?
[*]Additional costs for building materials + labor: Are these realistic prices according to your experience? When I google the components according to the energy consultant's component list, I come to a cost ratio of 1 to 3 (one third material costs, two thirds labor) --> using the example of attic insulation

What are your experiences in this area? What would you do? Gruffly accept the costs knowing that you are doing yourself a favor in the coming years with (presumably) rising energy prices? How can such costs be further challenged? Is this now simply normal or already usury?

I look forward to your feedback and a lively discussion.

Measure 1: Additional costs: €12,190

[*]Change to load-bearing slab foundation (WU concrete) instead of strip foundations
[*]12cm insulation under the slab, as well as 12cm insulation under the screed on the slab

Standard according to scope of services:

Foundations:

[*]The design of the foundations depends on the static requirements, assuming a floor pressure of at least 0.2 MN/m². The foundation must be flush with the ground and rust-free.
[*]Poorer floor pressures, in particular sticky clay (poor and especially weather-dependent workable rock formation), result in additional costs.

Slab foundation:

[*]We produce a 15cm thick slab (in-situ concrete quality). A 10cm thick gravel filter layer serves as area drainage. A separating foil is laid between the slab and gravel filter layer. A cast-in-place peripheral joint tape serves as an additional sealing measure for the wall.

Measure 2: Additional costs: €12,710

[*]Basement exterior walls with 12cm perimeter insulation, all steel basement windows as plastic windows, color: white, clear glass with double glazing

Standard according to scope of services:

[*]The basement exterior walls are executed as 24cm thick reinforced concrete walls of concrete quality C25/30. A sealing coat protects against exposure to soil moisture. A multi-layer dimpled membrane protects the sealing coat.
[*]Galvanized metal windows are installed in the basement. These have single glazing and a mouse screen. Precast concrete light shafts are a maximum of 1m high and contain a galvanized cover grate.

Measure 3: Additional costs: €12,550

[*]Masonry 36.5cm, WLG 08
[*]Roller shutter boxes / venetian blind boxes closed on the room side

Standard according to scope of services:

[*]The exterior wall is 36.5cm thick and consists of Poroton bricks. These bricks are not only fire-resistant (fire resistance class F90). Above all, they allow healthy living: with a thermal conductivity of 0.10 W/m²K, the solid walls offer good thermal insulation and excellent moisture behavior, as well as very good summer heat protection (lowest base moisture content of 5 per mille and diffusion-open masonry).
[*]Thermally insulated and foamed masonry roller shutter boxes are installed flush on the inside and outside. The roller shutter boxes are accessible from the inside and not visible from the outside.

Measure 4: Additional costs: €9,750

[*]Gable roof, 24cm full rafter insulation and 6cm roof insulation as wood fiberboard, verge with verge board and verge sheet metal

Standard according to scope of services:

[*]Your gable roof will be covered with concrete roof tiles, the gable end with verge tiles. The ridge roof tiles are clamped and therefore crack-free.
[*]The underroof consists of a glass-fiber-reinforced, diffusion-open underlay membrane against drifting snow and moisture with roof and counter battens for ridge ventilation, suitable for full rafter insulation.

Measure 5: Additional costs: €1,150

[*]Facade windows on ground & attic floors with g-value of 0.5
[*]Front door U-value 1.20

Standard according to scope of services:

[*]Plastic windows with multi-chamber system. All windows basically have triple glazing (Uw-value 0.9) and several continuous rubber seals. The windows have basic security with mushroom head locks. The sealing between the window frame and masonry is executed airtight and windproof.

Measure 6: Additional costs: €1,000

[*]Roof windows U-value 1.0; g-value 0.5

Standard according to scope of services:

[*]In the converted attic, the indicated roof windows are installed as tilt-and-turn windows in plastic with double glazing.

Too much text…
Quite "simple". If the house normally costs 350k€, the surcharge would be high, at >600k€ it's normal.

Which building structure are we talking about here? sqm, m cubed? etc.

- The building has 3 floors (basement, ground floor, attic)
- Living area 152sqm
- Volume 980m³
- Costs: roughly ~560k

With us (signed 6 months ago) the additional cost from KfW 70 to KfW 55 was a total of 12 k€. However, we do not have a basement!! - Additional cost from 36.5 to 42.5 Poroton: 9 k€ - Additional cost for triple glazing: 3 k€ - 2 full floors, 165 sqm In case it helps you a bit

The only offer where we explicitly had additional costs was from Town & Country. At the end of 2020, about €20,000 for a house on a slab.

Basically, I get the feeling that your builder builds more towards a very basic standard? Uninsulated basement, metal windows, roof without insulation, mediocre windows, roof windows only double-glazed. Many things are now included as extras that I would have actually considered standard. Then the surcharge is of course all the higher.

Basically, I have the feeling that your builder constructs according to a very basic standard?

I think so too. The Effizienzhaus 57 is nowadays standard for most builders, so that for funding according to KfW55 – meaning a demonstrably fully fulfilled standard compliance instead of a practically nearly fulfilled one – only very few materials are actually different or differently dimensioned, and in some places simply more precise work is required. Where without extra cost you actually still only effectively get Effizienzhaus 68, it is not just Schmalhans Küchenmeister, but rather even his holiday replacement Geizhals or Faulpelz. For that reason, I would probably tend to choose another provider, not only because of the (extra) price.