ᐅ New Build KfW 55 EE: Differing Opinions Between Energy Consultant and General Contractor

Hello everyone,

We are currently in the final stages of planning our KfW 55 EE single-family house (the application has already been approved).

During the planning phase, our main contractor provided the energy consultant with a list of building components, which the consultant then used to complete the KfW 55 EE calculation. However, the energy consultant considers the listed components insufficient and therefore recommends the following changes to meet the KfW 55 EE standard:

• Ground slab
• Additional insulation below the ground slab: XPS 100 mm (4 inches)
• Exterior basement walls (north, east, south)
• Insulation: XPS 160 mm (6 inches) instead of EPS 120 mm (5 inches)
• Exterior basement wall (west only) + exterior walls on the ground floor and upper floor
• Aerated concrete 008 instead of 009
• Roof
• Above-rafter insulation PU 140 mm (6 inches) instead of under-rafter insulation 50 mm (2 inches) glass wool

Attached are the two building component lists from the energy consultant and the main contractor, as well as excerpts from the energy consultant’s calculation.

The main contractor now believes that the additional insulation measures are unnecessary and only included because the energy consultant applied a blanket calculation for thermal bridges.

We now have the following questions:

• Are the building components proposed by the main contractor sufficient for a KfW 55 EE house, or are they far from the standard?
• Are the extra measures demanded by the energy consultant unnecessary?
• How much heating cost savings can roughly be expected from the additional insulation?
• Can anyone provide a rough estimate of the costs for the additional measures?

We are simply unsure who is correct in their opinion and whether it is worthwhile to pay the extra costs for a better-insulated house or if, as the main contractor suggests, the additional measures are unnecessary and it would be better to have the thermal bridges calculated individually...

Thanks in advance!

HausJam