What they are for
The purpose is more concrete than the provision suggests. One aim of the rule is daylighting of habitable rooms in the zone near windows, sufficient to allow reading and writing under an overcast sky.
Further purposes sit alongside. They include ventilation, fire separation, preserving residential amenity and avoiding excessively dense development.
These purposes explain why the rule is not at the parties' disposal: it serves not only the neighbour but public interests. Not every purpose confers a right of action on the neighbour, but separation distances remain the most important instrument by which neighbours resist development that is too close.
The underlying principle
The depth of the separation area is calculated as a fraction of the governing wall height, subject to a minimum. Both quantities come from state law.
The model building code provides a depth of 0.4 H, at least 3 metres. At a governing wall height of 7.50 metres this yields 3.00 metres.
Two principles apply throughout: . They are the same in every state.
| Principle | What follows |
|---|---|
| The separation areas lie on your own plot | the plot boundary governs, not the neighbouring building |
| They apply even where the neighbour has not yet built | the actual state of adjoining land is irrelevant |
The governing height is not the visible height
Most calculation errors arise here.
H is the governing height of the external wall, and establishing it is affected by several factors: roof form and pitch, ground profile, made ground and excavation, and the treatment of individual elements. It is not the same as the height of the building.
How roof and gable surfaces count is regulated differently in each state. One common system disregards roof surfaces up to a certain pitch, counts them proportionately above it, and counts them in full above a higher pitch. The thresholds and proportions nonetheless differ.
In practice H must be derived from the statutory text of the relevant state, not from a rule of thumb.
The states diverge considerably
A comparison of several provisions shows the range. It is wider than the model building code suggests.
| Provision | Depth in the standard case |
|---|---|
| Model building code | 0.4 H, at least 3 m |
| North Rhine-Westphalia, since the 2018 version | 0.4 H, at least 3 m; 0.2 H in industrial areas |
| Bavaria, since the 2021 reform | 0.4 H as a rule; 1.0 H in certain configurations |
| Lower Saxony | 0.5 H, at least 3 m |
The range therefore runs from 0.2 H to 1.0 H, a factor of more than five, and the allocation depends on the state, the type of area and in part on the character of the surroundings. No rule of thumb therefore holds across state boundaries.
The figures have also moved. North Rhine-Westphalia reduced the depth from 0.8 H to 0.4 H. Bavaria recast its rules in 2021, changing the calculation parameters for gable and roof surfaces considerably at the same time.
A further particularity concerns Bavaria: municipalities may set differing depths between 0.4 H and 1.0 H by local statute, though only to preserve and improve residential quality and with corresponding reasons. The governing depth can therefore differ from municipality to municipality within the same state.
The article on comparing the state codes covers the system of these differences. It also carries the further divergences between states.
The narrow-side privilege survives only in part
A widespread rule allowed half the depth in front of two external walls of no more than 16 metres, with the minimum still observed. It is known as the narrow-side privilege or 16-metre rule.
The model building code has not provided for it since its 2002 version, and numerous states abolished it when they lowered their standard depths. In some states it survives, and in Bavaria it now applies only in certain configurations.
In practice this is a model case of the dating problem: a source presenting the narrow-side privilege as generally applicable is either out of date or specific to one state. The date of a source should therefore be checked first.
What is regularly assumed wrongly
Four assumptions produce designs that cannot be consented. All four sound plausible and are nonetheless wrong.
| Mistaken assumption | What actually applies |
|---|---|
| Three metres is always enough | the minimum applies only where the calculated figure falls below it; taller walls produce greater depths |
| The local plan always prevails | it may set its own separation distances but does not always; where it is silent, the building code applies |
| The factor is the same across the state | it differs by type of area and in part by the character of the surroundings |
| The neighbour's consent solves the problem | a departure must be applied for and consented, not merely agreed with the neighbour |
What this means for design
Three consequences for the early project phase. They take effect before the first massing study.
| Consequence | Why |
|---|---|
| Check separation distances before the massing is fixed | they determine the developable area and therefore the reference quantity of every benchmark |
| Use a preliminary ruling for site decisions | it provides clarity on developability before design costs arise |
| Do not transfer between states | what is permissible in one state may be impermissible in the next |
Related articles
This article reflects the position of the rules at the date of checking and serves professional orientation. It does not constitute legal advice and does not replace assessment of the individual case.