Is KfW 70 worth it in 50 years?

Hello everyone,
I just registered here because there is a topic that is really bothering me. If this topic has ended up in the wrong forum, I kindly ask the mod to move it if necessary.

We will be building this year and are currently (hopefully) at the end of the planning phase. It will be built according to the Energy Saving Ordinance 2012.
We are planning a house with about 170-190 sqm of living space, which in the basement (built partly underground in a slope) will have, besides two smaller rooms + utility room, a double garage. The house will be heated with geothermal energy in the future.

We are currently working on the cost plan, which has gotten somewhat out of control (10% deviation from the target). We have already done some personal work, cut some items, and made reductions.
Our builder now suggested that we should reconsider the planned KfW 70 standard, as the additional investments would only pay off in a very long term (30/50 years).

One more background: Whether we keep or abandon the KfW70 standard, the house will definitely have geothermal heating and the (for the KfW standard) planned bricks (thickness + lambda value).

The following (cut) items are under discussion:
- the roof insulation will be done with 180 mm instead of 220 mm (same lambda value 0.35) – due to the house size, 220 mm would be necessary
- the cladding of the reinforced concrete parts will be done with about 2 cm less Styrofoam
- a different insulation of the floor slab will be used (the new insulation would have a worse lambda value)

These changes would reduce the construction costs by 8,000 euros but would cost us the KfW70 standard.

Nevertheless, I have difficulties giving up on KfW 70 for the following reasons:

[*]I cannot assess how much energy can actually be saved by keeping the measures under discussion (is the statement about up to 50 years correct)
[*]the KfW financing is about 1% cheaper than a normal loan with a 10-year fixed interest rate à that means at 50,000 euros you save about 4,500 euros in interest over 10 years
[*]abandoning the KfW70 standard could reduce a potential resale value

My questions to you now are:

[*]What do you think about it?
[*]If I decide for KfW70 after all: Are the stated 50 years (or possibly 30 years) until the measures pay off realistic?

Thank you very much for your feedback.
f-pNo

Hello,

first of all, a single-family house according to the Energy Saving Ordinance – you probably mean Energy Saving Ordinance 2009 – is not a bad house. There are countless contributions on this; I myself have written about it hundreds of times. But why should you do that?

We are planning a house with between 170-190 sqm of living space, which in the basement (built into a hillside above ground) has, besides two smaller rooms + utility room, a double garage. The house will be heated with geothermal energy in the future.

Not exactly a small house

Our developer now suggested that we should reconsider the planned KfW 70 standard because the additional investments would only pay off very long-term (30/50 years).

Are you sure you understood him correctly or was his hint rather referring to the possible savings of the geothermal heat pump? By the way – KfW 70 can be achieved in many different ways!

Nevertheless, I have difficulties with giving up KfW 70 for the following reasons.

[*]I cannot estimate how much energy can actually be saved by maintaining the measures under discussion (is the statement about up to 50 years correct)

I can only explain this by assuming that your builder’s statement refers to the geothermal heat pump; those cost significantly more than "normal" technologies. But even with that, his statement of "50" years is not correct; by the way, no one knows today how long the new technologies will last at all.

[*]the KfW financing is about 1% cheaper than a normal loan with a 10-year fixed interest rate à i.e. with 50,000 you save about 4,500 euros in interest over 10 years

It is quite possible that you will be better off with a normal loan. You should discuss this with your financing advisor because it depends on your personal situation and therefore cannot be directly transferred one-to-one.

[*]giving up the KfW70 standard could reduce a potential resale value

I see this as the biggest obstacle because the insulation craze will not decrease in the coming years; the outlook on the Energy Saving Ordinance 2014 already confirms this.

Whatever you decide – I can only advise you to design the building shell to be KfW 70 compatible and have underfloor heating installed. Then if you want to forgo the geothermal heat pump later to save costs, you can easily replace the existing heat generator with a geothermal heat pump or other, then new technologies.

Maybe instead you think about giving up the double garage in the basement. Here, extensive measures must be taken to insulate the garage and its smells/noises from the living areas. The cost savings achieved thereby should, in my opinion, exceed the savings your builder mentioned for changed insulation amounting to around TEUR 8. And if you are a bit more liquid later, you can always still have a prefabricated garage built – always assuming the hillside location allows it.

Rhenish regards

Hello construction expert,

thank you very much for your feedback.

You surely mean the Energy Saving Ordinance 2009

Oh, look at that – until now I thought the new Energy Saving Ordinance was already passed and have now seen from your note that it is called Energy Saving Ordinance 2014.
I am aware that a house according to the current Energy Saving Ordinance is good compared to earlier houses, but maybe the KfW70 is even better.

Not exactly a small house

At first it was not planned that big either. Actually 130 sqm + office in the basement. Due to the risk of groundwater pressure, the basement has now been moved above ground, which at the same time solved the issue of the slope and terrace. But with the size specification you have to consider that the upper floor has a knee wall of 75 cm (more is no longer possible due to building regulations [eave height]), so the actual living space there is smaller. Also, due to the insulation, etc., the utility room counts as living space as well.

Are you sure you understood him correctly or was his hint rather related to the possible savings of the ground source heat pump?

Ground source heat pump = ground source heat pump?
The ground source heat pump is included as heating technology in both models.
As I understand it, if the described insulation options are omitted/reduced, more heating is required. If the insulation is built to KfW70 standard, you would save yourself this additional heating effort. According to the builder's information, however, this saving (KfW70 insulation) would only recoup the additional costs (>8,000 euros) after many years (30 / 50).
Sorry – I am a layperson who has been trying to get into this whole matter for months.

Anyway you decide – I can only advise you to align the building envelope suitable for KfW 70 and to have underfloor heating installed.

The building envelope (Ytong masonry with 36.5 cm blocks) remains as planned for KfW70. Underfloor heating will also be installed – according to information and various research the most reasonable heating option with geothermal energy.

Maybe instead you consider, for example, dispensing with the double garage in the basement. And if you are liquid again later, you can still have a prefabricated garage installed – as long as the hillside location allows it.

The consideration (also garage + carport) was already discarded due to space constraints.

(I hope I managed the quotes properly)
Regards
f-pNo

Hello,

...What do you think about that?...

The problem "Energy Saving Ordinance" has already been clarified by the construction expert. The KfW definitions do not refer solely to the building envelope, nor to the system technology. For both, certain limit values must be observed (Ht´and qp´´)! Funny is the statement of the GU/GÜ. However, it is correct that when using a brine heat pump, the influence of the insulation on the consumption costs (heating) is reduced. How much and to what extent can only be clarified when the actual demand (performance, energy) is known in each case. These basics seem to be missing here, as so often. Regards

Hello,

as far as I know, air-to-water heat pumps are considerably cheaper than geothermal heat pumps. Maybe that would be an alternative ...

Hello,

Thank you very much for your feedback.

Gladly

Oh, look at that – I thought the new energy saving ordinance was already in place and, based on your note, saw that it is now called Energy Saving Ordinance 2014.

It is planned to come into force in 2014 – but what exactly is supposed to be verified therein is (so far) known only to heaven ... and whether it will actually pass all committees by then is still up in the air. Only, the child must have a name, so we all call it Energy Saving Ordinance 2014 for now. Of course, that means that until then all buildings have to be constructed according to the currently valid Energy Saving Ordinance 2009.

When stating the size, one must consider that the upper floor has a knee wall height of 75 cm (no more is possible due to building regulations [roof eave height]), making the actual living area smaller there. Additionally, due to insulation, etc., the utility room also counts as living space.

Then you are planning an (above-ground) basement, a ground floor, and an attic floor. It is only called an upper floor if it is a full story, i.e., no slants.

Ground source heat pump = geothermal heat pump?

Yep.

The geothermal heat pump is included as heating technology in both models. As I understand it, if the described insulation options are omitted or reduced, more heating is required. If the insulation is done to KfW70 standard, this additional heating effort can be avoided. According to the builder's information, however, the savings (KfW70 insulation) would only recoup the additional costs (>8,000 euros) after many years (30 / 50).

That guy is really funny

Am I correct in assuming that no calculation of the heat demand has been made? Or, in other words, that there is no TGA planning available or planned, no heating load calculation commissioned or to be commissioned? You can only decide which heat generator (HG) is ultimately to be used after a precise calculation is presented. This calculation also determines the amount and location of insulation. Only with this can it be decided whether and, if so, how much insulation can be omitted where and at the expense of which disadvantage or not.

Statements like "we leave something out here, then it will be fine" are not very helpful and always remind me of the gas/water/crap guys from long ago who roughly estimated the size of the heating boiler.

Sorry – I am a layman trying to get to grips with the whole thing for months.

No problem, we are slowly getting closer

The building envelope (Ytong masonry with 36.5 cm stones) remains as planned for KfW70. A underfloor heating will also be installed – according to information and various research the most sensible heating option with geothermal energy.

By building envelope I mean the entire building including insulation, windows, roof covering, and exterior plaster!

What exactly do you mean here: "the cladding of reinforced concrete parts is done with about 2 cm less Styrofoam"? Is the basement being constructed from reinforced concrete?

And out of purely professional curiosity: are you building with a franchisee? That would explain your statement in the other thread regarding the incompletely specified ancillary construction costs.

(I hope I managed the quotes properly)

You did

Best regards from the Rhineland