Floor plan of a single-family house on a gentle north slope

Development Plan/Restrictions
Plot size: 570 m2 (27m wide, 21m deep)
Slope: Slight north slope, gradient about 1-1.5m over 20m plot depth, street on the south side
Floor area ratio: 0.4
Floor space index: ---
Number of floors: Max. 2 full floors allowed
Roof shape: No specifications
Maximum heights/limits: WH_max = 6.20m, FH_max = 10m, roof pitch = 20°-28°

Client Requirements
Basement, floors: With basement due to slight slope, 2 full floors
Number of people, age: Family with 2 up to maximum 3 children
Space requirements on ground floor, upper floor:
GF: Living area, additional room (study or guest room), pantry, WC with enough space for a shower,
UF: Bedroom, 2 children’s rooms, office, additional small room for storage/possibly washing machine or optionally for a future 2nd bathroom
Office: Family use or home office: Study room for teacher and for home office 1 day/week
Overnight guests per year: Rarely
Open or closed architecture: Open living/dining area on the ground floor, rest closed off
Conservative or modern construction: Rather conservative
Open kitchen, cooking island: Currently planned open kitchen with cooking island
Number of dining seats: 6-8 seats for maximum flexibility
Fireplace: Fireplace planned as alternative heat source for emergencies
Music/stereo wall: No
Balcony, roof terrace: No
Garage, carport: Garage with entrance canopy

House Design
Who is responsible for the design: Own initial draft
Personal price limit for house including fixtures: €500k upper limit for house + garage. Outdoor facilities to be done later by ourselves.
Preferred heating technology: Air-to-water heat pump, as no gas connection is available
Energy standard: KFW40 standard is a must, as then there is a €40 discount on the land price afterward

If you have to do without, on which details/expansions
-can you do without: Bay window
-cannot do without: Pantry on the ground floor

Attached are the floor plans, an exterior view, and an overview of the plot. Construction is planned in Bavaria / near Regensburg.

The house on the 570 sqm plot should provide space for me, my wife, and 2 (or maximum 3) children. There should also be a study room for my wife and possibly a guest room available. Due to the slight slope, it should be possible to create a room with natural light in the basement on the north side. This could be used as a study.

On the ground floor, in addition to the living/dining area, a second room is planned which can initially serve as a guest room. This allows for the possibility of living on only the ground floor in old age. Therefore, the WC on the ground floor is generously sized to accommodate a shower.

On the upper floor are the two children's rooms, another smaller study (which could potentially be used as a third children's room), the parents’ bedroom, and the bathroom. Next to the bathroom is another room intended initially as a storage room. However, it should be prepared technically so that it can later be used as a children’s bathroom if desired.

Originally, I thought a direct external access to the basement from the north could be installed, but I have since reconsidered this, as drainage and related issues would be quite complex, given that a lot of water would run in from the north in heavy rain.

The garage is sized to fit two cars and still have room in front for other items (bicycles, tires, etc.).

The bay window on the south side has less practical use; it is mainly to break up the large facade surface. On the ground floor, it is planned to install a sliding door in the bay window to reduce interior space taken up by doors.

First the basic questions:
-What stands out to you immediately as negative/positive?
-What would you do differently or better?

Then I also have a few specific questions, which maybe someone can answer:
-Garage position: As far as I know, the rule is always either party wall construction or 3 meters distance. Can anyone say whether this still applies in Bavaria and whether it applies to garages too? Currently, the house and garage have exactly 3 meters distance on the north side to the neighboring property. This is fine for the house, but we would like to move the garage a bit further back because the space behind the garage can hardly be used for anything anyway. Possibly it could then be made a little deeper to have more storage space for items.

-Bay window: Would you also cellar the bay window? If not, that part would have to be insulated from below. Probably the additional effort for a cellar is not much greater?

-Upper floor ceiling: Currently, we planned a solid ceiling above the upper floor. The upper floor would then be insulated above the ceiling, and there would also be an attic where things could possibly be stored. Do you see savings potential if no solid ceiling is built but only beams with insulation in between?

-Ventilation system: Since we must meet KFW40, gas is not available, and we don’t want pellets, currently an air-to-water heat pump is planned. Does anyone know if a ventilation system with heat recovery is then mandatory?

-Wall thickness: Is it even possible to achieve KFW40 with 42.5 cm walls made of Poroton T7?

-Terrace: The terrace should run around the corner on the south and west sides. How would you realize a roofing? All our previous plans did not appeal to us.

-Costs: What should still be considered in planning to make the whole project as cost-effective as possible?

Overnight guests per year: rare

Do you want to reserve an almost 18 m² room for "rare"?

500k€ top limit for house+garage

It will probably get really tight.

KFW40 standard is a must, since you then get a 40€ discount on the land price afterward

Especially when you consider that you want to build solid and with a basement. Those 22k€ can disappear very quickly. (I guess at least 15k just to make the basement KfW40 compliant). And then, as far as I know, you still need a photovoltaic system on the roof.

-you cannot do without: pantry on the ground floor

I'm slowly losing understanding when it comes to Bavarians. Your pantry as it is brings you exactly 0 (in words ZERO). Extend your row of cabinets, put tall cabinets where the pantry is, and you will have more space than in this room with 1.12 m raw construction width.

Furthermore, I want to critically question 4 bathrooms in one house. Why a bathroom with a shower in the basement?
And if there are already 2 full bathrooms upstairs, why another shower bathroom on the ground floor? Either or.

Omit bay window. Move guest room to the basement. Bathroom and toilet in the basement require a lifting station.

Two offices, 1 guest room, 4 bathrooms,
laundry tourism.

Kfw 40 is achievable without a photovoltaic system. With KFW 40 without own contribution, the rule of thumb of 2000 euros per sqm fits quite well + basement or floor slab + additional construction costs.
Exterior work also costs even if done by oneself. Would definitely include materials in the planning.

If you want to plan bathroom and bedroom on the ground floor for old age (do not want to start a fundamental discussion about whether it is necessary or not) pay attention to accessibility. You only move when at least one person is physically very limited.

Pantry is quite useless that way.

I don't like the upper floor. Layout of the rooms, location of the children's bathroom. Swap child 1 and sleeping.

What else should be considered during the planning to make the entire project as cost-efficient as possible?

Simply don't try to achieve KfW40 with monolithic construction
You can forget about cost efficiency in that case.

First of all, thanks for the initial feedback.

The pantry is definitely too narrow, that is already at the very top of the change list.

Of course, having a total of 4 bathrooms would be a bit extreme. It is actually intended that the small room on the upper floor would initially be used as a storage room. I would only want to prepare it enough so that it could possibly be converted into a bathroom later on. That is why it is located on the bathroom/kitchen/heating room side, as all water and wastewater connections are already there on this side. This way, the additional effort required is very minimal.

The note about the lifting station because of the basement toilet is good. But you probably can hardly do without a drain in the basement altogether, partly because of the drip water siphon? Also for wastewater from the washing machine, even if there isn’t even a utility sink. How is this solved in such cases? Simple backflow preventers? Or are there simple pump solutions if no water from toilets is involved? That’s how I have seen it done in our rental building.

The topic of the basement was mentioned several times. Since the property is not very large and we do not want to build it out completely, we would rather not do without the basement. Besides, the property slopes slightly, so on the lower side a foundation wall + backfill would have to be built anyway without a basement. So better just to have the basement and then use it properly on one side (office, guest room, ...) instead of just dark storage rooms.

Regarding KFW40, I calculated as follows:
40€ + 570 + 10,000€ repayment subsidy = 32,800€. Of course, this means a significant additional expense. But even if that completely eats up this amount, the advantage remains that I really have the higher standard. If building according to standard requirements ultimately costs me the same, I do not have the efficiency and just pay more later.

In terms of construction method, I am rather conservative, I am not a fan of timber frame construction nor do I personally like the solid + ETICS variant. But it is more of a question of belief. In our new development areas, there are mostly prefabricated houses if anything, but the rest is almost always standard Poroton brick in various forms (unfilled hollow bricks, perlite filling, or filling with fiber material).

When I look at the houses that are sometimes built here, I’m often shocked how often very complex structural constructions are used, where entire glass fronts run around corners, etc., which then have to be complicatedly supported with reinforced concrete. That must cost a fortune. That is why we would like to ensure that the layout does not cause any additional costs in this regard, except for the extension/bay window in our case.

(I estimate at least 15k just to make the basement KfW40 compliant).

What exactly is the difference for the basement between the standard Energy Saving Ordinance and KFW40? I think external insulation is mandatory either way, of course the difference is in thickness. Also more insulation under the screed. Is insulation under the basement floor slab absolutely required? Or are there other things I am not thinking of right now?
The insulation alone can’t make up 15k€, can it?