KfW55 calculation with/without calculation of the thermal bridge allowance?

Hello everyone,

we are building a single-family house with a gable roof. The house will be brick-faced. Our energy consultant has created two options for a KfW55 house.

Option 1) Thermal bridge flat rate 0.05, exterior wall insulation 18 cm WLG 032, roof insulation 28 cm WLG 032

Option 2) Thermal bridge flat rate with calculation, exterior wall insulation 18 cm WLG 035, roof insulation 24 cm WLG 035

Is it due to the calculation of the thermal bridge flat rate that in option 2 insulation can be done with a lower thickness and a worse WLG, or is there a typo?

Thanks and best regards Fabian

Is it due to the calculation of the thermal bridge flat rate

Flat rate is flat rate "bad". If everything is calculated individually (and then also paid for expensively), the same result (on paper) can be insulated differently (less). But you then actually get a worse house.

You will then actually get a worse house.

... which of course also has to be paid for more. However, I assume that even with 18 cm WLG 035 there is still a bit of a buffer for KFW 55.

That means that our energy consultant was not mistaken (Variant 2 with less and worse insulation than Variant 1, both KfW 55) and that with Variant 1 the calculation can be skipped, but you have to pay more for the insulation? In return, you get better insulation with Variant 1.

That's right. Although the execution calculation might cost more than the flat-rate surcharge, so calculate carefully, young Padawan. :D

A third option could be to aim for only 16cm WLG 032, with [Wärmebrückenberechnung]. When it comes to money, that could be the best option. Depending on how expensive the calculation is.