GRZ, GFZ and the Building Envelope Simply Explained
GRZ, GFZ and the building envelope decide how big, how voluminous and exactly where you may build. This guide explains each key figure clearly and works it through with the example of a 500-square-metre plot with a GRZ of 0.3 and a GFZ of 0.6. It shows how the three figures interact and which mistakes you should avoid. That way you know before the purchase which house is feasible.
GRZ, GFZ and the building envelope (Baufenster) – three terms from the development plan (Bebauungsplan) that determine how large, how voluminous and where exactly you may build your house. Many prospective builders fall in love with a plot and only later discover that their dream house exceeds the permitted building volume. Anyone who understands the three key figures and works them out for their own parcel knows before buying what is feasible. This guide explains each figure in plain terms and calculates them using the example of a 500-square-metre plot.
Short answer: The site occupancy index (Grundflächenzahl, GRZ) states what proportion of the plot may be built on, the floor area ratio (Geschossflächenzahl, GFZ) limits the sum of all floor areas, and the building envelope (Baufenster) determines where the house may stand. On a 500-m² plot with a GRZ of 0.3, 150 m² may be built on; with a GFZ of 0.6, a total of 300 m² of floor area may be created — roughly two full storeys of 150 m² each.
What does the site occupancy index (GRZ) mean?
Short answer: The site occupancy index describes what proportion of the plot area may be covered by structures. A GRZ of 0.3 means that 30 percent of the area may be built on — so 150 square metres on a 500-square-metre plot. What is counted is the building's footprint, i.e. the area it takes up on the ground. Under certain conditions, ancillary structures such as garages, parking spaces and driveways may exceed the GRZ by up to half again, although this is usually capped.
The GRZ is the most important figure for the question of how wide and deep your house may be. A bungalow with a large footprint reaches the limit here more quickly than a two-storey house that stacks the same living area across two floors. Our guide on building on a small plot explains which house type squeezes out the most living area with a tight GRZ. How to read the plan as a whole is covered in more depth by the development plan guide further below.
What does the floor area ratio (GFZ) mean?
Short answer: The floor area ratio relates the total floor area to the plot area. On a 500-square-metre plot, a GFZ of 0.6 allows a total of 300 square metres of floor area — summed across all full storeys. With a buildable footprint of 150 square metres, that corresponds roughly to two full storeys. While the GRZ limits the extent at ground level, the GFZ caps the building volume in height. Together, the two values determine how much living area is possible overall.
Worked example: 500-m² plot with a GRZ of 0.3 and a GFZ of 0.6 (as of 2026)
| Key figure | Value | Result | Meaning |
|---|---|---|---|
| Plot area | — | 500 m² | starting figure |
| GRZ | 0,3 | 150 m² buildable | maximum footprint of the house |
| GFZ | 0,6 | 300 m² floor area | sum of all full storeys |
| Rough result | ≈ 2 storeys | 2 × 150 m² | e.g. ground floor + upper floor |
| GRZ incl. ancillary structures | up to 0,45 | up to 225 m² | garage, driveway, terrace |
Floor area is not the same as living area
Floor area is usually calculated from the external dimensions of the full storeys and also includes walls and, in part, non-habitable areas. Your pure living area is therefore smaller than the permitted floor area. What a house costs per square metre of living area can be roughly estimated. You will find suitable floor plans in the house catalogues.
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What is the building envelope and how does it constrain the plot?
Short answer: The building envelope is the area within the building lines (Baugrenzen) drawn in the development plan — the main building may only stand there. The building limit (Baugrenze) marks the outer line: the house may not cross it but does not have to touch it. A building line (Baulinie), on the other hand, is mandatory — the building's exterior wall must stand directly on it. In addition to the building envelope, the setback areas (Abstandsflächen) of the state building code (Landesbauordnung) apply. Only these three requirements together determine where the house can actually be placed.
In practice, a large plot can be severely restricted by a small, awkwardly located building envelope — whereas a small parcel with a generous envelope offers surprisingly much room to manoeuvre. Always check exactly where the envelope lies and how it fits the desired orientation of garden, terrace and entrance. How the building limit, building line and ridge direction are shown on the plan is explained in detail by the guide on reading the development plan.
How do the GRZ, GFZ and building envelope interact?
Short answer: The three figures act as a chain: the building envelope marks out the permitted location, the GRZ limits the house's footprint within this envelope, and the GFZ caps the sum of the storeys in height. Only when all three values are met is a design capable of being approved. A house can fail on the GRZ, the GFZ or the building envelope — any one of the three limits can be the limiting factor in its own right. That is why you must always consider them together.
- Read off the plot area and building envelope from the development plan.
- Multiply the GRZ by the area — determine the maximum footprint.
- Multiply the GFZ by the area — determine the maximum floor area.
- Additionally deduct the setback areas of the state building code.
- Check which of the three limits constrains the floor plan the most.
- Include ancillary structures such as a garage in the GRZ calculation.
Anyone who does this calculation early avoids expensive redesigns in the building application. The cost calculator helps with the overall cost framework of plot and house, and the provider comparison helps with selecting a suitable provider. You will find the legal basis in the text of the Federal Land Use Ordinance (Baunutzungsverordnung, BauNVO).
Which mistakes should you avoid with the GRZ and GFZ?
Short answer: The most common mistake is having only the living area in mind and overlooking floor area, ancillary structures and setback areas. The regionally differing definition of a full storey is also often underestimated: a high knee wall can suddenly turn the attic into a full storey and blow the GFZ. Anyone who does not check the values before buying the plot risks that their dream house will not be approved. An early calculation and, if in doubt, a preliminary building enquiry (Bauvoranfrage) provide certainty.
A preliminary building enquiry instead of an expensive redesign
If the GRZ, GFZ or building envelope are borderline, clarify feasibility before purchase via a preliminary building enquiry (Bauvoranfrage) at the building authority. It costs little and prevents you from acquiring a plot on which your planned house will not receive approval. Never rely on verbal assurances from sellers or estate agents.
With an understanding of the GRZ, GFZ and building envelope, the unwieldy development plan becomes a reliable tool: before buying, you recognise which house is realistic and can search specifically for suitable floor plans. For further plot assessment, our guide to choosing a plot is worthwhile. Anyone who wants to use the permitted density for a larger building will find an entry point in the overview of the multi-family house as well as practical tips in the guide building a multi-family house on a plot.
Bring the floor plan and building law into harmony
An experienced prefabricated house manufacturer calculates the GRZ and GFZ for your plot and adapts the design to the building envelope. We put you in touch with suitable providers with transparent fixed prices, free of charge and without obligation.
What does your dream house really cost?
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Compare house prices nowImportant questions briefly explained
The most common price questions around GRZ, GFZ and the Building Envelope Simply Explained – answered concisely by the Prefabricated House editorial team (as of 2026).
