# Calculating the BAF

The BAF expresses the ratio of the ecologically effective surface area to the total land area.

BAF = ecologically-effective surface areas ÷ total land area

In this calculation, the individual parts of a plot of land are weighted according to their “ecological value”.

### Types of surfaces and weighting factors per m²

• Sealed surfaces
(Weighting factor 0.0 per m²)

Surface is impermeable to air and water and has no plant growth (e.g., concrete, asphalt, slabs with a solid subbase).

• Partially sealed surfaces
(Weighting factor 0.1 per m²)

Surface is permeable to water and air; as a rule, no plant growth (e.g., clinker brick, mosaic paving, slabs with a sand or gravel subbase).

• Semi-open surfaces
(Weighting factor 0.2 per m²)

Surface is permeable to water and air, water infiltration, but no plant growth (e.g., sand, gravel, clinker brick with high water infiltration).

• Greened surfaces
(Weighting factor 0.4 per m²)

Surface is permeable to water and air, water infiltration and plant growth (e.g., gravel with grass, wooden cobbles, grass paving blocks).

• Surfaces with vegetation, unconnected to the soil below, small substrate thickness
(Weighting factor 0.5 per m²)

Surfaces with vegetation that have no connection to the ground and 20 to 40 cm of soil covering.

• Surfaces with vegetation, unconnected to the soil below, medium substrate thickness
(Weighting factor 0.6 per m²)

Surfaces with vegetation that have no connection to the ground and 41 to 80 cm of soil covering.

• Surfaces with vegetation, unconnected to the soil below, large substrate thickness
(Weighting factor 0.7 per m²)

Surfaces with vegetation that have no connection to the ground and 81 to 150 cm of soil covering.

• Surfaces with vegetation, unconnected to the soil below, very large substrate thickness
(Weighting factor 0.9 per m²)

Surfaces with vegetation that have no connection to the ground but more than 150 cm of soil covering.

• Surfaces with vegetation, connected to the soil below
(Weighting factor 1.0 per m²)

Vegetation connected to soil below, available for development of flora and fauna.

• Rainwater infiltration per m² of roof area
(Weighting factor 0.2 per m²)

Rainwater infiltration for replenishment of groundwater; infiltration over surfaces with existing vegetation.

• Water surface
(Weighting factor 0.5 per m²)

Rainwater fed water surface. Through establishment of vegetation the BAF can increase to 0.6.

• Vertical greenery with connection to the ground
(Weighting factor 0.5 per m²)

Direct connection of the vertical greenery with the soil, supply with nutrients and water directly over the roots in the soil.

• Vertical greenery without connection to the ground
(Weighting factor 0.7 per m²)

Vertical or horizontal vegetation on a wall without direct connection to the soil on the ground, permanent planters supplying the vegetation, with artificial irrigation.

• Extensive roof greening
(Weighting factor 0.5 per m²)
since December 2019*

Nature-like design of the roof surfaces with a substrate thickness under 20 cm without artificial irrigation. Through systems for water retentionthe BAF can increase to 0.6 (only for extensive roof greening).

• Semi-intensive roof greening
(Weighting factor 0.7 per m²)

Mixture of extensive and intensive roof greening with a substrate thickness of 15 to 50 cm (depending on the chosen plantings), usually in combination with artificial irrigation.

• Intensive roof greening
(Weighting factor 0.8 per m²)

Design of the roof similar to ground-based green areas with a substrate thickness more than 50 cm, usually in combination with artificial irrigation.

Note
If the planned green volume is lower than what is possible according to the substrate thickness, the BAF can be decreased by 0.1 for roof greening or surfaces with vegetation unconnected to the soil below. For surfaces with vegetation connected to the soil below the BAF can even decrease to 0.5 without appropriate green volume.