Financing check - realistic or nonsense?

Hello everyone,

we are currently planning our heart project of building a house, and regarding our financial situation and planning, I am torn between "somewhat feasible" and "absolutely impossible." When I look at the pure numbers, it seems to work, but my gut still says this is a very tight squeeze, especially after having read some comparable inquiries here. Therefore, I would be very grateful for your input. Can we manage it like this, or should we rather plan a smaller house (which is absolutely possible! I just want to get a feel for it)? I look forward to your feedback.

Who are you?	We are a family with growth potential ;) So a married couple, not yet with children. We want to build a two-family house (single-family house with about 40sqm granny flat for possible later accommodation of possibly parents in need of care) on a hillside plot. We are currently planning quite large (just under 200sqm) to see what is even possible. However, we could reduce to about 160sqm by giving up luxury (guest room, separate office for each of us). We reasonably need to build with a basement so that we are on the garden side - facing south - with the living area on the garden level. Currently, we are planning 3 floors, but 2 would also be possible.
How old are you?	36 / 28
Are there children?	No
Are children planned?	Yes, 1-2
What do you do professionally?	IT manager in permanent employment / housewife
How many hours do you work?	40 / 0
Income and asset situation:
What income do you have (gross/net)?	I earn 3600/month net plus about 6000/year bonus net. My wife earns about €10,000 per year with her dog breeding (hobby). We do not want to rely on this money as fixed income (it can also go wrong sometimes), but rather use it if necessary for special repayments. Therefore, I did not include it in the income below.
How much child benefit is there?	-
Other transfer payments like parental allowance, sick pay, etc...?	-
How much equity do you have?	About €160,000. We have €50k ourselves, €110k we get from our parents. Another €20k we could still get if things get tight somewhere.
How much equity do you want to invest in the house project?	Everything except for an "emergency fund" for larger purchases, so about €150,000
Expense situation:
Housing costs:	Total 1595
Current cold rent	1200
Current warm rent	1400
Electricity	70
Gas	75
Water, sewage, garbage fees, street cleaning	Currently included in additional costs
Telephone, internet, mobile	50
Mobility costs:
Monthly ticket for bus and train (also for the children!)	0
Car loan (or savings rate for new car)	0
Insurance	0 (company car – tax deduction is already included above)
Taxes	0
Fuel	0
Repairs	0
Other	0
Is there a second car, motorcycle, scooter? Please provide all points again!	0
Insurance costs:	145 (total)
Private health insurance (also additional health insurance, daily sickness allowance etc.)	0
Liability insurance (also for animals)	10 personal liability, 30 animal liability
Capital or term life insurance	70
Pension insurance (also Riester, Rürup, etc.)	0
Disability insurance	0
Accident insurance	15
Household insurance	20
Legal expenses insurance	0
Other insurances (e.g., travel insurance, funeral insurance)	0
Living expenses:	1580 (total)
Groceries	650
Restaurant expenses	50
Care/Drugstore	100
Pets (food, vet, medication, stable costs)	200
Medication / Health	150
Clothing	200
Furniture	100
TV/Video/Audio/CDs/DVDs	10
Donations	20
Other	100
Savings:	750 (total)
Vacation	200 (we don't really go away for longer, maybe a week of camping)
House	500
Retirement provision	0
Hobbies/Gifts	50
Other	0
Other expenses:	0
Was something forgotten? Then please add here at the latest!	I hope not :)
Income and expense totals:
Total income	4100 (without dog breeding, with bonus)
Total expenses	4070
Balance	30
of which total cold rent and dispensable savings (e.g., savings rate for house)	1700 Question to KfW-40Plus builders: We currently live in a KfW-55 house. How much of the electricity and gas costs can I still factor in here? We will build with a heat pump and photovoltaics. Do we really generate more energy than we need for electricity, heating, and hot water? I somehow can't quite believe that. If yes, I could calculate here 1850.
General about the property:
How big is the plot?	1650sqm
What are the dimensions?	Approx. 22*75m
What is the land value?	€55/m2 → €90,750
New building, old building (year of construction), house type?	New building, prefab house, currently aiming for a KfW 40 Plus with two residential units.
Garages?	0 - carport included in the costs for the outdoor facilities
How big is the house? (living area / usable area)	Approx. 200
What is the market value of the plot and house after completion?	Currently approx. €650,000
Construction or purchase costs:
Plot costs	€99,000
Development costs	0
Acquisition incidental costs (notary, court, land transfer tax, broker)	€9,000
Construction or purchase costs (incl. architect, structural engineer)	€450,000
Renovation and/or refurbishment costs
Additional construction costs (e.g., house connections, soil expert, construction power etc.)	€20,000
Outdoor facilities/terrace, paths, garden design, fences etc...	€100,000 - due to the large plot we have estimated quite high here. However, we could probably also manage with €50k if we make compromises on the garden.
Financing costs (e.g., fees or commitment interest)	0
Total costs	€678,000
Other costs:
Kitchen costs	€10,000
Furniture, lamps, decor	2000 (we live in a rented single-family house and have almost everything)
Other "non-acquisition, acquisition incidental, construction or additional construction costs" – moving!	€5000
Cost summary:
Total costs	€695,000
Deductible equity	€150,000
KfW repayment grant – 2x KfW 40 Plus	€75,000
KfW grant for construction supervision	€5,000
Financing amount	€465,000
Necessary loan information:	Note: This calculation is done with "worse" conditions (only 1 KfW loan over €100,000) - in reality, we will get the cheap loan twice for €150,000. Interhyp has not updated their calculator yet ;-)
(For multiple components, provide for all components, for multiple variants please clearly separate):	Component 1: €365,000 loan ING Component 2: €100,000 promotional loan KfW
Loan amount	€465,000
Loan type (e.g., annuity loan, bullet loan etc.)	Annuity loan
Interest rate (p.a. nominal, otherwise effective)	1.45% mixed rate
Fixed interest period	10 years (KfW) / 20 years (bank loan)
Remaining debt at the end of fixed interest period	€65,800 (KfW after 10 years, after deduction of repayment grant still €28,300) €130,000 (bank, 2041)
Fictive total term until full repayment	29 years, so paid off before I retire
Initial repayment rate	3.00%
Monthly rate	€1,700
Special repayments possible? (Amount to specify)	Yes, 5% per year → We do not want to rely on this as fixed, but can probably make about €5000/year special repayments through income from breeding
Change of repayment rate possible? (Conditions such as number, repayment range specify)	Yes, 2 free, then €100 processing fee

Hello :-)

I am not a financing expert, but the housing costs seem very low to me. How do you arrive at that amount?
There is also the possibility to have the sleeping floor in the basement. So you don't necessarily have to have a cellar if you don't need it.

This is what we are currently discussing in the talks with the prefabricated house companies. So far, it did not sound unrealistic (we have had talks so far with Bien-Zenker, Hanse, Finger and Gussek Haus). Do you think this is set too low?

200 sqm living space plus a 40 sqm granny flat plus a basement and all on a hillside plot? I don't think the estimated costs even come close... although there are some people in the forum who can probably roughly say something about the additional costs...

But you want to manage this supposed financing amount of probably around 600k minus the equity with a household income of 3.6k? Honestly, I find that almost crazy...

465k is a large loan amount for a calculable income of 3.8k.
Is the bonus fixed or dependent on the company's success?
Can/will your partner contribute to the loan at some point?

Otherwise, I think it looks very tight. And I myself am someone who has usually financed on the "tight" side.
What you haven’t considered as far as I can see: Even after construction, you cannot completely ignore savings rates. The possibilities to set something aside for: house maintenance, major purchases, retirement provision would no longer be particularly given with your current income.

I will leave uncommented the fact that the hobby dog breeding, which I assume is running tax-free, is not included. Except for the concerns that such things tend to be discovered sooner or later and can become really expensive. By then at the latest, the house would be with the next owners anyway.

200 sqm living space + basement?
Additional construction costs are far too low, it seems to me that the earthworks let alone disposal costs have been forgotten. Overall, the costs are probably set significantly too low.