Single-family house with a granny flat on a 450 sqm hillside plot

Hello everyone,

until now I have only been a silent reader here and now I would like to present our own house concept for discussion. In doing so, I hope for ruthless criticism and your ideas and suggestions.

We are a patchwork family with four children (three are always there) and we are planning to build a detached house with a granny flat in NRW. At the beginning of last year, we purchased a sloping plot in a classic new development area and in the meantime developed a house concept with an architect. In doing so, we developed a very simple building form (four walls and a roof) with an efficient floor plan. We passed the plans on to several prefab house companies with the request for a cost calculation in the hope that the budget would still allow a "growth of the house". Now we are sitting here with our offers and have to realize that our smallest possible floor plan already exceeds our budget. This is around 550,000 euros for the house including additional construction costs (excluding the plot). With the granny flat, we had hoped for double KfW funding in the KfW 40 EE class of 67,500 euros to increase the budget. But be that as it may.

Perhaps we were a bit naive with the preliminary cost calculation. In any case, we are currently reconsidering the concept and are considering doing without the basement.

And now please fire away with ruthless criticism and unvarnished truths. :)

Development plan/restrictions

Size of the plot 450sqm

Slope yes, north slope (from the street towards south-southwest) with approx. 1.5m incline within the building window (one meter within the planned footprint) rising

Floor area ratio (FAR) ? The development plan does not specify this

Floor space index (FSI) 0.4

Building window, building line, and boundary 19.5m wide (street side), in the rear area 17m wide and 14m deep

Edge development yes

Number of parking spaces 2 for main apartment and 1 for granny flat

Number of floors 2.5

Roof shape gable roof

Architectural style classical

Orientation ridge direction west-northwest - east-southeast

Maximum heights/limits max. ridge height 9.5m above the top edge of the ground floor (this may be max. 0.5m above the reference point of the street)

Other requirements setback areas 3m on the sides, 3.5m to the street


Owner requirements

Architectural style, building type simple, economical building form with gable roof

Basement, floors basement floor with granny flat, total 2.5 floors

Number of persons, age household of 5-6 persons: parents 38 and 36, four children 7, 4, 2x2, family planning has overshot a bit and is finished :) and grandmother in the basement flat

Space requirements on ground floor and upper floor approx. 140-150sqm: kitchen, living room, 1 bedroom, 3 children’s rooms, 1 guest/office/patchwork room, 2 bathrooms

utility room in the basement

Office: 1 flexible room required

Annual overnight guests 10

Open or closed architecture form follows function

Conservative or modern design hmm, what exactly is meant here?

Open kitchen, cooking island open kitchen to dining area (also happily with a cooking island), but closed off to the living room

Number of dining seats 6-8

Fireplace no

Music/stereo wall TV in living room

Balcony, roof terrace covered terrace to the garden with pass-through window from the kitchen

Garage, carport carport with green roof and additional storage room would be great

Kitchen garden, greenhouse small kitchen garden at the plot boundary


House design

Who made the design: independent architect working with a prefab house company and lots of DIY

What do you like especially? Why? efficient use of space. Despite compactness, all wishes regarding the space requirements, especially the number of rooms, are fulfilled

What do you not like? Why? especially the ground floor could be more generous, basement and storage space could be larger

Price estimate according to architect: none

Price limit including equipment: 550,000 euros plus KfW funding if anything comes

Preferred heating technology: air-to-water heat pump


If you have to do without, which details/extensions

-could you do without: reluctantly the separate parents’ area

also the granny flat is under discussion

the sliding doors on the ground floor are due to a communication error and can go

-cannot do without: number of rooms


Why has the design become what it is now?

We basically created the design ourselves. Here and there, the architect made some optimizations. Our main focus was the compatibility of all space wishes within a compact floor plan on a small plot. Beyond that, as parents of four children, we wanted our own little domain.


What is the most important/fundamental question about the floor plan summarized in 130 characters?

Does our house concept fail due to our budget expectations? What would you do differently and why?

Hello,

how high are the initial offers?
I can't estimate how much you will have to cut.

I find the parents' bathroom next to the guest WC a luxury. You could plan a shower in the guest WC and maybe even fit 2 doors in, so that it is accessible from the bedroom.
That might save around €10,000.

Then you could also cut the dressing room and instead put the utility room on the ground floor.
That way, the entire basement could be cut.
But now the question is, what about grandma?
You would have to explain more about that.
Does she have to/should/can she move in?
Does she bring equity or pay rent?

If you move into the basement apartment (own space is absolutely understandable to me) because grandma doesn't necessarily have to come along (it doesn’t look senior-friendly anyway, everything is very cramped) and the non-permanent child moves to the ground floor, you could still streamline the layout a bit, have you tried that? The full bathroom on the ground floor could then be completely omitted, the bathtub would then go into the otherwise pretty empty children's bathroom.

Thanks a lot in advance for the suggestions.


I think we are operating in the mid-price segment of the providers. Our offers were in the range of 520,000-550,000 euros excluding earthworks, outdoor facilities, house connection costs, carport, terrace, etc. Then there were a few outliers on the high side. The rough plan is that grandma will move into the granny flat and also pay rent here. This would probably cover the monthly ancillary costs. However, we designed the floor plan of the granny flat for any tenant, so there are no mutual obligations/dependencies between grandma and us in case this "grandma in the house" project should still fail.


Interesting thought. I plan to look into that sometime. Although we also keep in mind that the rental income from the granny flat will also bring a higher total volume and thus almost cover the additional costs of the flat itself.

While keeping in mind that the rental income from the granny flat also brings a higher total volume and thus the additional costs of the apartment almost pay for themselves.

If you read through the forum, this tooth of easy money through a granny flat should be quickly pulled for you ;)

If you skim through the forum, this tooth of easy money through a rental apartment should be quickly pulled for you ;)

In my simple calculation, the estimated 350 euros cold rent at an assumed interest rate of 2% and an equally high repayment generated about 100,000 euros of additional volume. This roughly corresponds to the expansion costs of the basement floor. In this respect, the monthly burden would remain approximately the same under the assumption that one plans with a basement. The calculation looks different in my opinion if you waive the basement and build on a slab. However, with my floor plan, I would need expensive basement replacement rooms, and the suggestion from Hausbautraum20 with the technical room on the ground floor could be the solution. It is questionable whether our plot allows construction with a slab. I fear that the cost advantage of the slab could be eaten up by the additional costs of the garden landscaper.