New construction project KFW 70 Accessibility available?

Hello dear community,

We are planning to build a house this year and are currently reviewing the offers. However, I have been thinking back and forth all weekend and every developer says something different, so what should one believe regarding KFW eligibility?

Maybe you can help us a bit.
We have the following offer.

House type City villa (2 full floors) with a total of 127 m² living space

Base slab
Concrete slab made of reinforced concrete C20/25 with a thickness of 20cm (19kg of steel reinforcement per m²), manufactured and designed as a thermal base slab with 6 cm insulation under the slab.

Floor structure
-about 8cm thermal insulation / compensating layer 040
-piping (spacing of the pipes according to heat demand) does this mean underfloor heating?
-about 6.5 cm cement quick screed

External wall structure
17.5 cm or optionally (additional cost of €5,900) 24 cm aerated concrete PPW4
+ a thermal insulation composite system (ETICS) with 14 cm polystyrene rigid foam insulation WLG035
+ organically bound textured plaster with 2mm grain size

Roof
24 cm thick mineral fiber insulation WLG 035 between rafters and collar beam

Windows and doors
Triple glazed in 6-chamber profile (whatever that means) I still have to ask.
With a U-value of 0.7 W/m²K.

Heating
The house is heated and supplied with warm water by an air-water heat pump from Nibe. 270 liter buffer storage.
Modulating power (Inverter technology = continuous operation) from 3.5 kW to 12 kW.
Plus 6 kW auxiliary heating for reheating of domestic water and heating circuit.

Ventilation system
Without heat recovery from the company Lunos is installed.

Roller shutters
PVC roller shutters are installed on the ground floor + upper floor,
these consist of room-side closed and thermally insulated PVC cassette roller shutter boxes with bottom inspection opening and plastered on the room side.

Chimney
With heating stove in the living room

The living-dining area as well as the bedroom are oriented towards the south.

What concerns us now above all is the question whether the external wall should be built with the 17.5 cm aerated concrete or the 24 cm one.
And whether the price is reasonable?

On inquiry with the developer, the price for 17.5 Poroton bricks instead of the 17.5 cm aerated concrete would be the same, but the KfW values would not be met.

Who can help with such questions?
Since we are still quite young (25), we would like to get a few tips and suggestions from more experienced people.
We hope you can help us a little.

Best regards
Sonja and Andreas

So first of all, you haven't mentioned a price that one could estimate. Secondly, first the question: will you want to finance with the KfW? So do you even have the approval? 6-chamber profile can be googled.. it is related to the frame construction.. however, many chambers are not a guarantee for a great window..

Hello,

..
We are planning to build a house this year,... and every developer tells a different story, ...

First, you should find out what a developer or GU/GÜ is. Most likely, it is a GU/GÜ.

..
(2 full stories)

Is not a bad solution compared to the mostly used 1.5-story construction method.

..
Floor slab... and designed as a thermally insulated floor slab with 6 cm of bottom insulation.

The bottom insulation only makes sense if it is ensured that neither groundwater nor capillary water affects the insulation layer. Otherwise, it is thermally ineffective. So it depends on your building ground.

.. Floor structure about 8 cm thermal insulation / leveling layer 040..

That would be too little for me.

.. -Pipe spacing (spacing of pipes according to heat demand) does this mean the underfloor heating?

Yes.

.. Exterior wall structure
17.5 or optionally (5,900 € extra charge) 24 cm aerated concrete PPW4...+ an ETICS with 14 cm of polystyrene rigid foam insulation WLG035 + organically bound textured plaster with 2mm grain size

Here I would choose 36.5 cm PPW2 + ETICS + mineral plaster.

.. Windows and doors
Triple-glazed in a 6-chamber profile (whatever that means) I still have to ask about that. With a U-value of 0.7 W/m²K.

Uw or Ug?

.. Heating
The house is heated and supplied with hot water by an air-water heat pump from Nibe. 270-liter buffer tank.
Modulating power (inverter technology = sliding operation) from 3.5 kW to 12 kW. ??? plus 6 kW additional heater for reheating drinking water and heating circuit.

Whether the air heat pump is optimal cannot be said without further economic analysis. However, I have serious doubts regarding the sizing!

.. Ventilation system without heat recovery from the company Lunos will be installed.

Controlled residential ventilation without heat recovery I consider energy wasteful, thus impractical.

..
We are mainly concerned about whether the exterior wall should be built with 17.5 cm aerated concrete or 24 cm.
And whether the price is reasonable?

As said, 36.5 cm!

..
Upon inquiry with the developer, the price for 17.5 Poroton brick instead of 17.5 aerated concrete would be the same but the KFW values could not be met.

Absolute nonsense. Both aerated concrete and Poroton have different lambda values!! He probably compares apples and oranges and has a large stock position of PPW4. Check price differences at building material wholesalers.

I strongly recommend you get external support, especially regarding building services engineering.

Best regards

Hello everyone,

first of all, many, many thanks for all the responses. Because I still have doubts, I have today handed the entire house construction contract over to an expert who will also accompany me during the construction. I hope he will be able to help me further.

The construction company is a GÜ, who distributes the orders to local craft businesses.

Foundation slab
On the entire property, wastewater and rainwater may only be discharged into the sewage system; nothing may seep into the ground on the property. Therefore perhaps the sub-slab insulation? Groundwater, I don’t know yet, without a soil survey.

Windows
There is nothing about whether UG or UW hmm......for the standard windows it says something about double glazing and UG 1.1; in the upgrade package there is then only triple glazing U-value glazing of 0.7 W/m²K.

Regarding the ventilation system, this is not a central ventilation system. According to the contract, an external wall exhaust unit will be installed in the rooms bathroom, utility room, guest WC and kitchen respectively. And 4 air supply vents will be installed in dining/living room, bedroom and children's room. The exhaust fans will be switchable with single or double rocker switch (in the bathroom humidity-controlled).

Here, a suggestion from a buddy made me curious: inventer ventilation technology. I wanted to get a quote this week.

About the air-water heat pump, I can’t say much, I really have no idea. It is supposed to be a pretty new device from Nibe, which can be found on the internet, this split device. It is suitable for both cooling and heating. Whether or not through this 12 kW arises, no idea. In the house construction contract it also states from 3.5 kW up to 12 kW? I hope the expert can help me a bit further with that.

Underfloor heating
I know that the loops of the underfloor heating should be laid closer together. I explicitly asked about that but was not given an exact cm specification. Only the note that the company would generally lay the pipes closer together with an air-water heat pump than with a gas boiler.

Exterior wall

Whether the price is reasonable I meant in connection with the 24 cm brick, that would mean 17.5 cm brick without extra charge and 24 cm for 5900€ more.

Regarding the chimney, the contract states that in addition to the chimney I will also get a safety pressure monitor installed.

Can I only operate an air-independent stove in the house or also an air-dependent one?

Finally, a question to people who have built with aerated concrete. How is living in a house built from this stone? I am fascinated by the insulation effect of the stone but have a little fear that I will end up sitting in the house worrying that everything might collapse. I will probably decide on the 24 cm stone, even if it costs almost 6000 € more and also means a reduction of the living space.

Best regards
Andreas & Sonja

It is a soil survey and not a building survey.. and you have to commission that yourself as well.

Windows: exactly for that reason you should ask. I assume that it is "of course" not the total value. Therefore have it confirmed in writing.

Ventilation system: sorry, either properly or not at all. (My opinion) therefore only controlled ventilation with heat recovery comes into question. Above all, you have the entire house under control and not 4 devices in different rooms..

Also get exact information about the air-water heat pump. Especially if it is supposed to cool, this must also be integrated into the overall circuit.

Exterior wall: no one will agree with you there. no matter if 17 or 24.. but again my question, why not timber frame? there you have the best insulation, the least loss of space and can still hang everything up..