How big could your dream house be? Our FAQ on the floor area ratio

Perhaps you’d like a castle - nestling deep in the forest? Or would you prefer a five-story lakeside tower? When it comes to your dream house, the plot of land it’s on not only has to fulfil your own (dream) ideas, but numerous other conditions to boot. The neighbours next door should be nice, work should be commutable and there must be enough space for the whole family.

But due diligence means more than calling on the neighbours, double-checking the distances and drawing the construction plans. People often neglect one key parameter when buying a property - the floor area ratio. And it could put a spoke in your wheel, however lofty your homebuilding ambitions... Best described as a necessary evil, the floor area ratio is something you just have to take on board. But worry not - our FAQ will tell you all you need to know about what to focus on during the next property inspection or when planning to convert your dream home.

What is the floor area ratio?

The floor area ratio (FAR) sets out the percentage of land area usable as living space and was devised to prevent orderly localities from degenerating into urban chaos. However, the definition of living space does not cover every nook and cranny of your four walls. Unheated winter gardens and garden seating areas and space for parking bicycles or motorcycles can be deducted. Likewise, flooring, cellar compartments, laundry or drying rooms. Similarly, not everything contained within your plot area is relevant for the floor area ratio. A look at the zoning map, for example, reveals several areas that cannot be built on. Those covered in greenery, for example or - surprise surprise - bodies of water. These areas are subtracted from the plot area accordingly.

Where do I find the floor area ratio?

If you look at the applicable building and land use regulations in your municipality or city council, generally viewable at your local authority, a zoning plan is normally included. If a floor area ratio applies, this is also where you’ll find it and it is normally a coefficient between 0.3 and 0.8.

The zoning plan sets out the configuration of which kind of property can be placed and used where. Where is the agricultural zone? Where do the residents live? This document is the reason why you don’t get a pigsty next to a school and residential buildings in the heart of the industrial area.

How can I determine the floor area ratio for my newly purchased property?

Anyone who buys a plot of land is usually also keen to know how big the dream house they want to build on it can be. Here, the floor area ratio is already specified in the zoning plan and dictates how much living space you will have to play with and develop architecturally.

So the equation looks like this:

Allowable land area × FAR = Allowable gross floor area.

So let’s make short work of these sums. A beautiful plot of land - 800 square metres of which is usable - is yours. Thoughts of a dream abode, full of spacious rooms and a huge, heated winter garden are already filling your head.

If we assume that the specified floor area ratio in the zoning plan is 0.3, the calculation is as follows: 800 m² × 0.3 = 240 m². So you can use 240 square metres of the available space for living in. With an FAR of 0.2, you’d have a mere 160 m². Woe betide your winter garden...

Why is the floor area ratio so important?

Well, as the figures you just saw clearly show: When building, it is the deciding factor! It determines how much can be built where. And that, of course, impacts on the value of a property. Think about it: Who is going to fork out for some fallow land only to find they can barely build a shoebox on it?

But imagine how the city would look without floor area ratios: Someone could build a gigantic multi-story apartment block right bang in front of your single-family house and there goes your morning sun. Instead of sunbeams to wake them, they now have construction noise. Far from idyllic.

The FAR may add layers of complication when purchasing land, but it’s also a must for urban development and local planning. It is the variable that allows the authorities to control and optimally plan how a place develops.

How does the floor area ratio work when changing or extending your property?

Can’t you just put the floor area ratio out of mind for good once the house is yours? Unfortunately not. If you want to convert or extend your home in any way, the FAR remains the key number. If you’ve already used up the living space on your property, you are not allowed to start any additional extensions. Even if your neighbours have made their home into a mansion and (literally) eclipsed your own cottage in the process, the floor area ratio may preclude any ‘two can play at that game’ building competition with them.

Turning your basement into a gym? Converting the attic into a bedroom for your eldest daughter? You also have to comply with the floor area ratio when your conversions create more living space without actually enlarging the house. Avoid the risk of costly chaos and having to deconstruct by approaching your municipality or building authority at the pre-planning stage and clarifying the extent of what is legally permissible.

How can I tell if the floor area ratio for my property is already maxed out?

To find out whether you have already reached the maximum floor area ratio on your property, you’re best off grabbing a calculator and trying your hand at the rule of three! As you read above, the FAR sets out the gross floor area you can build with. In fact, the FAR is derived from a ratio between the plot area and the calculated gross floor area for building. Also as mentioned, zones like driveways, areas of greenery and bodies of water can be subtracted from the plot area. To determine the allowable gross floor area for building, add the above- and below-ground floor areas used for living, including wall and wall cross-sections.

The calculation now reads: allowable gross floor area / allowable land area = usable floor area ratio for your property.

If the calculated result is lower than the floor area ratio recorded in the zoning plan, more living space can be added. Congratulations!

Is there any way to boost the floor area ratio?

The floor area ratio is fixed as a general rule. There are a few cases, however, in which authorities may grant exemptions. This applies, for example, to buildings where the energy standard exceeds the level required by law. In other words, there may be scope for a higher floor area ratio if you combine the extension plans with an energy-efficient refurbishment.

If you don’t ask, you’ll never know, so pay your local building department a visit. You’ll need the house plan, cadastral plan and a sketch of your project. You may also find it worth your while having a word with the powers that be if you have an existing property in your homebuying radar. Since zoning plans are repeatedly revised, a change may already be pending?

What is the floor area reserve and what can be done with it?

Nothing obliges you to use the floor area ratio right to the permissible limit. If a plot of land is built on to less than the permissible extent, so-called floor area reserve applies. Think of it like this: You are allowed to construct a living space covering up to 160 m² on your land. However, you prefer to build a smaller bungalow covering 100 m² and use the remaining land to create your very own dream football pitch. If so, you’d have a floor area reserve of 60 m².

This reserve is also transferable to other properties you own. But caution - this does not give you a green light to suddenly add on an extra floor to your Ticino holiday home. Some legal requirements also apply: In most cases, the properties have to be contiguous and located in the same building zones.

What is the difference between the floor area ratio and the floor space index?

As well as the floor area ratio, the floor space index (FSI) is another important variable, which some cantons in Switzerland use instead of the FAR. Just like the FAR, it dictates the extent to which an area of land can be built on. However, the floor space index also encompasses areas that are not considered living space. In other words, attics, basements and other construction areas are also included in the mix.

What other ratios do I need to keep in mind when building or altering a house?

Plot area ratio (PAR)
The plot area ratio (PAR) is the maximum possible floor area of the building, including only the ground floor, but not additional floors. In other words, the PAR constitutes the “footprint of the building”. Above all, it’s an important parameter to consider in the context of distance to neighbouring buildings and to the property line. Without this regulation in place, your neighbour could build their house so close to your wall, they could look directly into your bathroom while brushing their teeth. Caution - cantonal differences may apply here: Depending on the canton, the plot area ratio may be the parameter that prevails for local planning, not the floor area ratio.

Building mass ratio (BMR)
The building mass ratio (or cubing ratio) counts the effective volume of the building above the ground and excludes the basement or other floors below ground from the scope. It is used to determine how large the volume can be in relation to the overall plot area. As a rule, the permissible building mass ratio is between 1 and 2.5.

Here’s the key calculation: Plot area x BMR = building volume.

Let’s assume the following: You find a plot of land covering 500 square metres and with a BMR of 1.2. Therefore, the following constraint applies to your house: its volume must not exceed 600 m³. The building mass ratio is a pointer indicating the structural use of a property, so it comes into play for any new construction, addition or conversion.