ᐅ Single-family home with a granny flat on a 450 sqm sloped lot

Hello everyone,

Until now, I have only been a silent reader here, but I would like to present our own house concept for discussion. I am hoping for candid criticism, as well as your ideas and suggestions.

We are a blended family with four children (three are usually at home) and we are planning to build a single-family house with a secondary apartment in NRW. At the beginning of last year, we bought a sloped lot in a typical new development area and have since worked with an architect to develop a house concept. We designed a very simple building form (four walls and a roof) with an efficient floor plan. We sent our plans to several prefabricated house companies, asking for cost estimates, hoping that our budget might allow for potential expansion of the house. Now, faced with their offers, we have to admit that even our smallest possible floor plan exceeds our budget. The budget is about 550,000 euros for the house including additional construction costs (excluding the land). With the secondary apartment, we had hoped to double the KfW funding in the KfW 40 EE class with 67,500 euros to increase the budget. But it is what it is.

Perhaps our preliminary cost estimate was a bit naive. In any case, we are currently reconsidering the concept and are considering doing without a basement.

And now, please, fire away with your frank criticism and unvarnished truths. 🙂

Zoning Plan / Restrictions

Plot size: 450 sqm (4,844 sq ft)

Slope: Yes, north-facing slope (from the street toward south-southwest) with about 1.5 m (5 feet) elevation within the building envelope (1 meter (3 feet) within the planned footprint) rising

Floor area ratio (FAR): ?

The zoning plan does not provide this information

Building area ratio (site coverage): 0.4

Building envelope, building line and boundary: 19.5 m (64 feet) wide (street side), at the rear 17 m (56 feet) wide and 14 m (46 feet) deep

Edge development: Yes

Number of parking spaces: 2 for the main unit and 1 for the secondary apartment

Number of floors: 2.5

Roof type: Gable roof

Architectural style: Traditional

Orientation: Ridge runs from west-northwest to east-southeast

Maximum heights / limits: Maximum ridge height 9.5 m (31 feet) above finished ground floor level (this may exceed the reference street level by max. 0.5 m (1.5 feet))

Other requirements: Side setbacks 3 m (10 feet), setback from the street 3.5 m (11.5 feet)



Client Requirements

Architectural style and building type: Simple, economical building form with a gable roof

Basement, floors: Basement with secondary apartment, total 2.5 floors

Number of people, ages: Household of 5-6 people: parents aged 38 and 36, four children aged 7, 4, 2x 2 years. Family planning went a bit beyond the target and is now complete 🙂 plus grandmother in the basement apartment

Space needs on ground / upper floors: About 140-150 sqm (1,500-1,615 sq ft): kitchen, living room, 1 bedroom, 3 children’s bedrooms, 1 guest/office/patchwork room, 2 bathrooms

Utility room in the basement

Office: 1 flexible room required

Guests per year: About 10

Open or closed layout: Form follows function

Conservative or modern style: Hm, what exactly is meant here?

Open kitchen, kitchen island: Open kitchen adjacent to dining area (a kitchen island is welcome here), but closed off toward the living room

Number of dining seats: 6-8

Fireplace: No

Music / stereo wall: TV in the living room

Balcony, roof terrace: Covered terrace facing the garden with pass-through window from the kitchen

Garage, carport: Carport with green roof and additional storage space would be ideal

Vegetable garden, greenhouse: Small kitchen garden along the property boundary


House Design

Designer: Independent architect working with a prefabricated house company and DIY elements

What do you particularly like? Efficient use of space. Despite compactness, all requirements regarding space needs, especially number of rooms, are met

What do you dislike? Especially the ground floor could be more generous, the basement or storage spaces could be larger

Price estimate (according to architect): Not available

Price limit including fittings: 550,000 euros plus KfW funding if still available

Preferred heating system: Air-to-water heat pump


If you have to sacrifice something, which details or extensions would you give up?

-can give up: Reluctantly on the separate parents’ area

The secondary apartment is also under discussion

The sliding doors on the ground floor are due to a coordination error and can be removed

-can not give up: Number of rooms


Why did the design turn out the way it is?

We basically created the design ourselves. The architect later made some optimizations. Our main focus was to accommodate all room requirements within a compact floor plan on a small plot. Furthermore, as parents of four children, we wanted our own small private space.


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

Is our house concept failing due to our budget expectations? What would you do differently and why?

Hello,

how high are the initial quotes?
I can’t estimate how much you need to cut.

I find the master bathroom next to the guest toilet a bit luxurious. You could plan a shower in the guest toilet instead, and maybe even fit two doors so it can be accessed from the bedroom.
That might save around 10,000€.

Then you could cut the walk-in closet and instead place the utility room on the ground floor.
This way, you could eliminate the whole basement.
But now the question is what about grandma?
You would need to explain that in more detail.
Does she have to, should, or can move in?
Is she bringing equity or paying rent?

If you move into the basement apartment (having your own space is completely understandable to me), since grandma doesn’t necessarily have to come along (it doesn’t look senior-friendly anyway, everything is quite cramped), and the non-permanent child moves to the ground floor, you could still streamline the floor plan a bit. Have you tried that?
The full bathroom on the ground floor could then be completely removed, and the bathtub would go into the already rather empty children’s bathroom.

Thank you very much for the suggestions.

@Hausbautraum20
I think we are within the mid-price range of the providers. Our offers were in the range of 520,000–550,000 euros without excavation work, landscaping, utility connections, carport, terrace, etc. There were a few outliers on the higher end.
The basic plan is that grandma will move into the granny flat and pay rent here. This would likely cover the monthly additional costs. However, we designed the floor plan of the granny flat for any tenant, so there are no mutual obligations or dependencies between grandma and us if this "grandma in the house" project should fail.

@Tamstar
Interesting thought. I plan to look into that when I get the chance.
We also keep in mind that the rental income from the granny flat would increase the overall volume and thus the additional costs of the unit would almost pay for themselves.

Kristijan schrieb:

That said, we also keep in mind that the rental income from the accessory apartment increases the overall budget and thus almost covers the additional costs of the apartment itself.

If you read through the forum, this get-rich-quick idea with an accessory apartment should be quickly dismissed 😉

Tamstar schrieb:

If you browse through the forum, you should be able to quickly see that the easy money from a granny flat can be pulled out 😉

In my rough calculation, the estimated 350 euros cold rent at an assumed interest rate of 2% and an equally high repayment generates about 100,000 euros of additional volume. This roughly corresponds to the finishing costs of the basement level. Under this assumption, the monthly burden would remain about the same when planning with a basement. The calculation looks different in my opinion if you skip the basement and build on a slab foundation instead. However, with my floor plan, I would then need expensive substitute basement rooms, and the suggestion from Hausbautraum20 with the utility room on the ground floor could be the solution.

It is questionable whether our plot allows building on a slab foundation. I fear that the cost advantage of the slab foundation could be eaten up by additional landscaping expenses.