The five classes
Under the model building code the division is as follows. The states depart from it in details.
| Class | Definition |
|---|---|
| 1 | detached buildings up to 7 m high with no more than 2 units totalling no more than 400 m²; also detached agricultural or forestry buildings |
| 2 | buildings up to 7 m high with no more than 2 units totalling no more than 400 m² |
| 3 | other buildings up to 7 m high |
| 4 | buildings up to 13 m high with units of no more than 400 m² each |
| 5 | other buildings including underground buildings |
Three refinements govern correct classification. They are regularly abbreviated in overviews.
| Refinement | What follows |
|---|---|
| The difference between classes 1 and 2 is position alone | the figures are identical; class 1 requires the building to be detached |
| In class 4 the 400 square metre limit applies per unit | not to the total; in classes 1 and 2 it applies to the building as a whole |
| Classes 3 and 5 are catch-all classes | class 3 covers all other buildings up to 7 metres, class 5 all others above |
How height and floor area are measured
Most errors arise here, and both definitions depart from intuition. Both concern the figures used in classification.
| Definition | What actually governs |
|---|---|
| Height is neither ridge height nor eaves height | what governs is the finished floor level of the highest storey containing habitable rooms |
| The floor areas of units are gross floor areas | areas in basement storeys are left out of account |
The reference to gross floor area matters, because it is a different quantity from usable or living area. The system of reference quantities is covered in the article on gross and net floor area within the cost planning subject.
What detached means
The term is defined in building regulations law rather than geometrically: detached means that no physical connection exists to other buildings or to the plot boundary. No minimum distance is involved.
Two exceptions soften the rule. Attached small garages and subordinate storage buildings observing a specified boundary distance leave the detached quality unaffected. And a procedure-free ancillary building attached to a class 1 building does not change its class.
The precise figures and conditions are to be taken from the applicable state building code. The model code sets out only the system.
Special building status is determined independently
This is the most misunderstood point of the subject. It concerns the relation between building class and special building.
Classification into a building class and classification as a special building are made entirely independently of one another. A building may be both.
A detached nursery with a floor area up to 400 square metres falls into building class 1 and is at the same time a special building. The low class relaxes requirements on structure; the special building status tightens requirements on use and procedure.
Special buildings are installations of particular type or use. The model code lists them in a catalogue including high-rise buildings, assembly venues, retail premises, hotels, hospitals, schools, garages above certain sizes and others.
Buildings over 22 metres high count as high-rise and therefore as special buildings. Extensive additional requirements apply to them, particularly on fire safety.
The procedural effect
The most important consequence of special building status concerns procedure. It therefore acts on the duration and effort of the consent procedure.
Special buildings fall in principle neither under exemption from consent nor under the simplified consent procedure, but under the full consent procedure.
All requirements of building regulations law are therefore examined in the procedure, not merely a reduced catalogue. That also opens the possibility of setting relaxations or additional requirements in the individual case.
For design that means more evidence, longer procedures and greater consultation effort. The article on consent procedures covers the differences.
The classification cannot be departed from
One point requires regular attention when preparing fire safety strategies. It concerns the non-negotiability of the classification.
A building falling under the criteria into class 5 may not be treated as a class 4 building by means of compensating measures. Classification follows the criteria, not the level of protection.
Compensation is possible within the framework of formal derogations, but it does not change the class. Derogations must be applied for and justified separately.
What follows for design
Four consequences for the early project phase. All four take effect before concept design.
| Consequence | Why |
|---|---|
| Establish the building class early | it shapes fire safety, structure, escape routes and procedure at once |
| Handle the limits deliberately | staying just below 7 or 13 metres decides the class and therefore the cost |
| Assess special building status separately | it follows use rather than size |
| Consult the state code | definitions largely coincide between states but not entirely |
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.