ᐅ Single-family home with a basement apartment on a hillside, designed for flexible use

Hello everyone,

I have been mostly a silent reader here for several years and have gained many ideas and suggestions. I have followed many projects here since we started planning our own house build and have benefited greatly, incorporating many considerations into our planning. After purchasing a plot about 2 years ago, our own house construction is now getting closer, with the goal to start next year.

So far, we have worked with 2 different general contractors (GCs), who provided similar concepts but different designs due to the placement of the stairs. We have made some independent changes to the design we preferred.

Due to professional priorities, the project did not have top priority since the beginning of this year. This will change from April, and we will consult several more GCs. Since we have an upcoming appointment with a GC soon, I would like to hear your critical and honest opinions about our concept and design beforehand.

Thank you in advance for your help.


Zoning Plan / Restrictions
Plot size: 600 m² (22 m wide x 27 m deep) (72 ft x 89 ft)
Slope: yes, steep slope (approx. 8 m on the north side and 7 m on the south side; see attached leveling plan)
Site coverage ratio: 0.4
Floor area ratio: 1
Building envelope, building line and boundary: see zoning plan excerpt
Edge development: no, 3 m setback; garage allowed; 5 m setback required from the street side
Number of parking spaces: 2 per housing unit, one of which must be covered
Number of floors: max. 2 full stories + half / stepped floor
Roof type: no restriction
Architectural style: no restriction, except no log houses
Orientation: west
Maximum heights / limits: eaves height max., parapet top max. 4 m (13 ft) on street side; eaves height max., parapet top max. 7 m (23 ft) above ground height on garden side
Other requirements:


Owners’ Requirements
Style, roof form, building type: Bauhaus, flat roof, solid construction, single-family house with a granny flat
Basement, stories: total 2.5 stories: basement: living cellar/granny flat + utility room; ground floor: living area + office; upper floor (stepped floor): sleeping area
Number and age of people: 28 (female), 30 (male); planning for 2-3 children in about 3-4 years
Office: home office for wife
Overnight guests per year: 3–5
Open kitchen, kitchen island: open plan, preferably kitchen island (if budget allows)
Number of dining seats: 6
Balcony, roof terrace: yes, large balcony on supports connected to ground floor with garden access (depending on budget)
Garage, carport: basement carport; due to zoning plan and granny flat, 2 vehicles must fit under carport
Utility garden, greenhouse: undecided yet


House Design
Designer:
Basic design by planner from a construction company, but revised by us. Hence, the less polished own design created by me using Sweet Home 3D.

Please initially disregard the arrangement of windows, furniture, and bathroom fittings. Our main focus is on the layout and distribution of rooms across the various floors, as well as the overall concept.

About our concept:
Flexibility is one of the most important aspects of our plan. We want to use the basement initially as a granny flat and later convert it into living space for the children (hence 2 versions of the basement plan). The granny flat would be used for about 10 years before the kids move down there. When the children later leave the house and we no longer need a house of this size, it should revert back into a granny flat. Possibly later, we may also live in the granny flat ourselves and rent the upper area, but that is far in the future. The idea behind this is to alleviate the mortgage payments especially during the first 10 years, when the children are still small and one of us may not be working full-time.


What do you particularly like? Why?
The stepped floor as the parents’ area, or initially a room also for children while they are small. The layout and orientation of the kitchen/living/dining area (maybe a bit small?) facing the sun.

What do you dislike? Why?
Basement: the layout in the rear area of the granny flat (basement version 1): bathroom and bedroom are too small... Any ideas on how to gain space or redesign the granny flat so that the effort to convert to basement version 2 stays minimal.


Cost Estimate according to Architect/Planner:
440k for the house (without fittings) + 20k for balcony,
62k for garage (which was a proper garage, basemented and connected to the house on the lower ground floor)
30k for earthworks (excluding removal of excavated material)

Personal Price Limit for House including Fittings:
450k for house + fittings + ?? balcony (what more affordable options are possible for execution)
+ 30k for basement carport (self-build possible)
+ 30k earthworks (+? removal)
+ 15k landscaping

Preferred heating system: geothermal (ideally combined with photovoltaic system but probably not feasible within budget)


Why is the design as it is now? / If you had to give up, on which details or extensions
Can give up: living area size, currently approx. 195 m² (2100 sq ft). We want to reduce this somewhat to save costs. Staircase from balcony to garden.
Cannot give up: Basically, this is our dream house. If the budget isn’t enough, we will have to build significantly smaller, especially without a granny flat. The question I ask myself: How much smaller can I go with the wish for rather 3 than 2 children? Does a much smaller house justify leaving out the granny flat (granny flat = relief in the beginning when salaries are lower)? We will still need the rooms from the granny flat for the future children…


What is your most important / fundamental question about the floor plan in 130 characters?
Does our project make sense in terms of flexibility or is it nonsense and difficult to plan due to many unknowns? Did we miss fundamental things in our concept?


Thank you very much for your help