ᐅ Questions about the Energy Demand Calculation for KfW 70

Hello everyone,
I have been reading here for some time and would like to ask my first question today:

We are building a two-story solid house without a basement with a developer, which is intended to meet the KfW-70 standards (Energy Saving Ordinance 2009). For this, I have received a rather detailed energy demand calculation with individual verifications.

The energy demand calculation concludes that the requirements are met based on the specific transmission heat loss and the annual primary energy demand per unit of floor area. --> Certification KfW 70 fulfilled...

However:
1) Component calculation foundation slab: U-value ≥ 0.35 W/m²K
2) Component calculation upper floor ceiling with screed: U-value ≥ 0.2 W/m²K (+0.008)

Overall, I understand that the somewhat lower thermal protection (Energy Saving Ordinance 2009) is compensated by other measures, such as solar energy or ventilation systems.

Question:
Is this procedure formally acceptable if the individual component verifications do not meet the requirements of the Energy Saving Ordinance? This question is purely formal for me, regardless of other contractual terms.

Best regards
Käfer

Hello,

Käfer schrieb:
....concluding that the requirements are met based on the specific transmission heat loss and the floor area-related annual primary energy demand. --> KfW 70 verification fulfilled.....

So the formal aspect on paper is taken care of.
Whether this is economically viable for the builder is a completely different matter!

Käfer schrieb:
...Is the procedure formally acceptable if individual component verifications do not meet the requirements of the Energy Saving Ordinance?...

Why? The overall balance (comparison to the reference building) counts! Individual deficits can definitely be compensated, provided that the components each at least comply with DIN 4108 standards.
Example:
In verifications, the flat thermal bridge allowance of 0.05 is often applied! Completely legitimate and also permissible! However, this assumes that all thermal bridges are executed according to DIN 4108 Part 2!
Who inspects and supervises the execution on behalf of the building owner? The site manager paid by the general contractor?

Best regards.

Tip: Compare the delivered external components regarding their thermal insulation standard (WLS or WLG) with the verification documents (delivery notes)!

Thank you for the quick response.

I have also been wondering about the issue of monitoring, good point.

Again, from my layperson’s perspective, a question regarding the topic "The overall balance counts, not the individual proof."
- Can I find a passage about this in the Energy Saving Ordinance? ((The Energy Saving Ordinance 2009 requires a thermal transmittance for the slab ≤ 0.35))

Next question:
Is it normal that in the energy demand calculation there is no mention of a kitchen extractor hood, for example with a wall duct, or is this included and accounted for in other coefficients or similar?

Regarding the U-value for the floor insulation, I hope you don’t have underfloor heating?

Nutshell schrieb:
Regarding the U-value for the floor insulation, I hope you don’t have underfloor heating?

The value just over 0.35 W/m²·K is the U-value for the individual component calculation of the concrete slab. The insulation used has a thermal conductivity of 0.035 W/m·K.
What U-value should a concrete slab with underfloor heating have in your opinion, considering your general statement?

This means the formal requirement on paper is met.
Whether this is economically sensible overall for the homeowner is a completely different matter! (see post by €uro)

Perhaps someone could explain to me again why the requirements of the 2009 Energy Saving Ordinance Annex 1 / Table 1 do not have to be met at least for new builds.
There, the value for the concrete slab is listed as <= 0.35 W/m²·K.

Käfer schrieb:
The value just above 0.35 W/m²*K is the U-value calculated for the individual components of the slab-on-grade. The insulation used has a thermal conductivity of 0.035 W/mK.
What U-value should a slab-on-grade with underfloor heating have, based on your general statement?

This formally satisfies the requirement on paper.
Whether this is economically viable for the homeowner is a completely different matter! (see post by €uro)

Maybe someone can explain to me why the requirements in the Energy Saving Ordinance 2009, Annex 1 / Table 1, do not have to be met at least for a new build.
It states a value of <= 0.35 W/m²*K for the slab-on-grade.

If the slab-on-grade has a thermal transmittance of 0.35 W/m²*K towards the underfloor heating, this is not really beneficial...
Since the heating system is installed in the floor, if it is poorly insulated, heat will be lost through the slab.

Normally, a few centimeters of insulation are installed beneath the underfloor heating, which should reduce the U-value to below 0.3 W/m²*K, even if the slab itself is not insulated.