Feasibility study multi-family house: getting the maximum out of your plot
- Simon Käslin
- Aug 17
- 12 min read
Updated: 1 hour ago
A feasibility study for a multi-family house is more than a few blocks, first floor plans and pretty pictures. It shows, in several variants, what is legally possible on your plot under building law, and it develops the project deliberately towards your goals.
Two things matter at the same time: high architectural quality and sound economic viability. A beautiful project on its own is not enough, it also has to add up. The architect's task is to interpret building law as generously as possible and to get the maximum out of it, using levers such as free bay windows, a free penthouse floor, habitable basements and optimally designed sloping sites. This article sets out the levers that are specific to a multi-family house, with a table of levers, a practical example and an apartment mix.
Table of contents
Feasibility study multi-family house: why the potential is decided right at the start
Quality and economic viability: your multi-family house has to add up
Getting the maximum out of it: the levers under building law
Practical example: from 390 to 550 to 650 usable square metres
One, two or more apartments per stairwell: how circulation changes the yield
How does parking affect the potential of a multi-family house?
What can your property do?
Arrange an initial consultation now and have your development potential assessed without obligation.
1. Feasibility study multi-family house: why the potential is decided right at the start
With a multi-family house, economic success is not decided on the building site but at the desk, and right at the start. In the early planning phase you determine how much floor area is created at all, how many apartments come out of it, how they are accessed and how much of that is rentable or saleable in the end. Anyone who sets these parameters without a sound analysis gives away potential that can hardly be recovered later.
This is the job of a feasibility study multi-family house developers commission before they commit to a plot. What a feasibility and volume study achieves in general is explained in our introductory article on the feasibility and volume study. This article goes deeper and looks specifically at the levers of a multi-family house: the maximum permitted under building law, the apartment mix, area efficiency and parking. With a multi-family house, the difference between a good and a very good project rarely lies in the facade, but in decisions that look unremarkable at first glance.
2. What a feasibility study really achieves
There is a misunderstanding doing the rounds about the feasibility study: many people picture a few blocks placed on the plot, plus first floor plans and a nice image. That falls short. A good study is not a pretty rendering, it is a decision-making tool.
It achieves three things.
Firstly, it shows in several variants what is actually possible on your plot under building law, and not just the first idea that comes along.
Secondly, it does not develop these variants at random, but deliberately towards your goals as the client. Whether you are working towards maximum yield, a particular apartment mix, owner occupation with an income share or a quick sale changes the entire concept.
Thirdly, it makes the result comparable, so that in the end you have a real choice.
3. Quality and economic viability: your multi-family house has to add up
With a multi-family house there is an additional point that is less prominent with a single-family house: anyone who wants to earn money with a project needs a feasibility study that also adds up economically. An architecturally beautiful project on its own is not enough. If the figures do not work out in the end, even the best facade is of no use.
That is why we always look at both together: high quality and economic viability. Quality means good floor plans, good daylight, good orientation and marketable apartments. Economic viability means that the rentable or saleable area is in the right proportion to the building volume and the costs, that the construction costs are affordable and that the apartments can be let at market rates.
Only when everything fits does a project emerge that carries itself and holds its value in the long term. How economic viability is expressed in concrete key figures and in a yield is not repeated here, we cover it in our article on return on investment in construction projects. For the feasibility study, this is the point at which quality and economic viability meet for the first time, and they do so before large costs arise.
4. Getting the maximum out of it: the levers under building law
This is where the architect's actual task lies. The permitted floor area, which follows from the utilisation ratio, the GFZ or the BMZ, is an upper limit, not an automatic result. Two practices can arrive at markedly different results on the same plot under the same regulations. The art lies in interpreting building law as generously as possible and getting the maximum out of it without overstretching it.
There is a whole series of levers anchored in building law for this. They create additional living area that often does not count towards the utilisation ratio, and they noticeably increase the value of the building without the formal key figure rising. The most important of them are shown in the following table.
Optimally designed sloping site : the basement on the valley side becomes a fully-fledged residential storey, does not count towards the utilisation ratio and is in effect a free storey.
Habitable free basement : rooms in the basement with daylight can be used as fully-fledged living area, without being counted towards the utilisation ratio.
Free penthouse floor and attic storey : up to a certain share these areas remain uncounted, and at the top they offer high living quality.
Free bay windows and projections : additional area and more room depth, up to a certain share not counted.
Conservatory : unheated glazed extensions remain uncounted up to a certain share.
Ancillary areas (cellar, plant rooms, underground garage) : they do not count towards the utilisation ratio and, correctly placed, they create room for living area.
How the utilisation ratio, the GFZ and the BMZ are calculated and how they differ is explained in detail in our article on the utilisation ratio, GFZ and BMZ. The message that matters: only when these levers have been properly exhausted is the plot really used to the full. Which of them apply in your case depends on cantonal and municipal law and needs to be checked professionally.
5. Practical example: from 390 to 550 to 650 usable square metres
How strongly these levers work is shown by a simplified, anonymised example from our practice. Figures and circumstances have been summarised and rounded. A step-by-step calculation for a single plot is set out in our worked example of a feasibility study.
The starting point was a sloping plot of around 975 m² in the Zurich area, in a residential zone with a utilisation ratio of 40 per cent. Formally that produced a chargeable gross floor area of around 390 m² (975 m² x 0.40). At first glance a manageable basis for a multi-family house.
The decisive lever was the sloping site. Because the terrain fell away significantly, the basement on the valley side could be built out as a fully-fledged residential storey that legally did not count towards the utilisation ratio, so in effect a free storey. Together with a well-designed penthouse floor and a conservatory, the formal 390 m² could be turned into an effectively usable living area in the order of 550 to 650 m².
Plot area : 975 m²
Utilisation ratio : 40%
Formally chargeable gross floor area : around 390 m²
Effectively usable area through the levers : around 550 to 650 m²
Gain : around 160 to 260 m²
The usable volume could therefore be increased substantially without the formal key figure being exceeded. For the client this gain was very attractive, because every additional square metre of usable living area increases income and value while the land costs stay the same. Potential like this is best unlocked before construction starts, ideally even before the purchase. What to watch out for is set out in our article on buying land in Switzerland. Anyone acquiring a plot with a multi-family house in mind should know its true potential beforehand.
6. Which apartment mix delivers marketability and yield?
Once the volume has been exhausted, the next question follows: how do you divide the area into apartments? The apartment mix is probably the most underestimated lever in a multi-family house. It decides three things at once: the absolute number of units, the marketability (how quickly and at what price they are let or sold) and the financing capacity of the buyers.
As a rule, many small apartments generate a higher income per square metre, because kitchen, bathrooms and service connections are spread over less area and smaller units usually achieve a higher price per square metre. Large apartments bring more calm in operation and less turnover and appeal to a segment with more spending power, but they tie up a lot of area in few units. The right mix depends on the location: in a central, well-connected location more and smaller units work better, while in a quiet family location larger apartments can be the better answer.
Depending on the concept, 6 to 11 apartments can be realised on the same plot. The feasibility study does not simply set the highest number, but the variant that best suits the location, the demand and your goals, in other words the one that is both marketable and economically sound. An additional apartment means additional income, but only if it can be let or sold without devaluing the remaining units. How the mix finally translates into yield is shown in our article on return on investment in construction projects.
7. What does circulation cost you in rentable area?
Now it gets concrete. Area efficiency describes the ratio of rentable living area to the total gross floor area. Everything that is not living area (stairwell, lift shaft, corridors, plant and ancillary rooms) counts as non-income-generating area. Every square metre of circulation is a square metre you build and heat but cannot let or sell.
A numerical example makes the effect visible. We compare two circulation concepts for the same typical floor with 500 m² of gross floor area (indicative values):
Criterion | Variant A (generous stairwell, two apartments per landing) | Variant B (compact stairwell, three apartments per landing) | Difference (per floor) |
Circulation and ancillary areas | approx. 20% | approx. 13% | - 7% |
Non-rentable area | 100 m² | 65 m² | - 35 m² |
Rentable living area | 400 m² | 435 m² | + 35 m² |
Result per floor | basis | plus 35 m² of living area | + 35 m² |
The difference amounts to 35 m² of rentable area per floor. With four residential floors that is 140 m² of additional living area without the building becoming larger. At an assumed net rental income of CHF 300 per m² per year (indicative value), that is around CHF 42,000 of additional income per year. Capitalised, that corresponds to an increase in value in the region of one million francs, purely from more efficient circulation.
The figures are deliberately simplified and project-dependent. The order of magnitude is not. A few percentage points of area efficiency decide six-figure amounts per year. That is exactly why it is worth treating circulation not as a technical necessity to be ticked off, but as a central economic factor.
8. One, two or more apartments per stairwell: how circulation changes the yield
Behind the numerical example lies a fundamental decision: how many apartments does one stairwell serve?
One apartment per stairwell: one stairwell serves a single apartment. Very generous and flexible, but expensive, because each apartment carries its full circulation on its own. Almost always the least efficient solution.
Two apartments per stairwell: two apartments per floor share one stairwell. Proven and marketable, but not the optimum for area efficiency.
Three or more apartments per stairwell: three or more apartments share one core. The circulation is spread over more units and the share of non-rentable area falls. The challenge lies in good floor plans, daylight and orientation, so that no poorly lit internal apartments are created.
The art lies in keeping the circulation as compact as possible and as generous as necessary. A clearly organised stairwell, a centrally placed lift and short corridors add up across all floors to considerable additional area. In real optimisations, simply reorganising an overly generous stairwell has freed up fully usable main usable area.
How the circulation, the riser zones of the building services and the arrangement of the wet rooms can be optimised together is at the core of our architecture and planning service.
9. How does parking affect the potential of a multi-family house?
With a multi-family house, parking is often the hidden cost driver and at the same time an area issue. The municipal parking ratio determines how many required parking spaces you have to provide per apartment. It varies considerably depending on municipality, location and public transport access and therefore always has to be clarified with the municipality in the specific case (there is no generally applicable figure).
Parking is central to the potential of your plot for three reasons:
It limits the number of apartments. If every additional apartment triggers another required parking space, the underground garage can become the bottleneck. Sometimes the limit is not the regulation above ground but the number of vehicles that can be accommodated below ground.
It costs a lot. An underground parking space is one of the most expensive areas in the entire project and rarely produces a cost-covering income. Every unnecessary space weighs directly on the yield.
It influences the basement. The geometry, ramp layout and column grid of the underground garage determine how efficiently the basement can be used overall. An oversized or badly organised basement inflates the building volume without generating income.
A good feasibility study therefore thinks about parking from the outset: checking reduced parking ratios in locations with good public transport, matching the ramp and the column grid to the number of apartments, and reducing the basement to what is functionally necessary. Part of the potential often lies here, and purely above-ground planning overlooks it.
10. Typical mistakes with multi-family house potential
The same patterns keep coming back in practice. These mistakes cost the most potential:
Treating the regulation as a result instead of an upper limit. Anyone who reaches the permitted area has not yet reached the optimum. Only with the levers under building law is the plot really used to the full.
Looking only at beauty instead of at the figures. With a multi-family house, an architecturally appealing project that does not add up is not a good project. Quality and economic viability belong together.
Ticking off the circulation as pure technology. An overly generous stairwell costs more across all floors than you would think at first glance.
Setting the apartment mix by gut feeling. Without a look at location and demand, you end up with either too few units or units that are hard to let.
Thinking about parking too late. If the underground garage is only resolved at the end, it suddenly limits the number of apartments or drives up the costs.
Optimising too late. After the building application, the big levers are usually already fixed. The potential lies in the early phase.
Blind spots from being too close to the planning. Anyone who works on a project for a long time rarely questions basic assumptions. An independent second opinion reveals exactly that.
As an independent practice, we bring this outside view into a feasibility study multi-family house clients can act on. We are not committed to any construction method or system supplier, only to your project goal.
11. Frequently asked questions (FAQ)
What does a feasibility study show? A good study shows in several variants what is possible under building law and develops the project deliberately towards your goals. It combines architectural quality with economic viability and delivers a basis for decisions, not just a rendering.
How do I get the maximum out of my plot? By interpreting building law as generously as possible. Levers such as an optimally designed sloping site, a habitable free basement, a free penthouse floor, bay windows or a conservatory create additional living area that often does not count towards the utilisation ratio. What applies in your case depends on cantonal and municipal law and needs to be checked professionally.
Does a multi-family house project have to add up, or is a good concept enough? If you want to earn money with the project, the feasibility study also has to work out economically. A beautiful project on its own is not enough. The goal is always both together: high quality and sound economic viability.
What produces more yield: many small apartments or a few large ones? Smaller units tend to achieve a higher income per square metre, while larger ones appeal to a quieter segment with more spending power. The optimum depends on the location and follows from the interplay of location, demand and your goals.
How strongly does circulation really affect the yield? Considerably. Even a few percentage points more area efficiency mean dozens of additional square metres of living area per floor. Across an entire multi-family house that quickly adds up to a five- to six-figure annual increase in income (indicative value, project-dependent).
Is this about a replacement new build or a renovation? No. This is about optimising a planned multi-family house on a plot. We deal with the question of whether an existing building should be replaced or renovated separately in our article on renovating or demolishing in Switzerland.
What can your property do?
Arrange an initial consultation now and have your development potential assessed without obligation.
Comments