ᐅ From what knee wall height is a story considered a full floor?

Hello everyone,

I have gone through all the topics related to full stories / knee wall height / knee plate height that I could find here but unfortunately did not find an answer to my question. Maybe you can help me with it.

How high can the knee wall on the upper floor be without the floor being counted as a full story? (Assuming no dormers)

The applicable regulations are the building code NW 1962, the land use ordinance 1968, and the development plan specifies only the following:

- 1 full story
- Roof pitch 30 degrees Celsius (86 degrees Fahrenheit)
- Gable roof

There are no further limitations (such as ridge height, etc.) and the ground floor measures 12 x 12 meters (39 x 39 feet).

Thank you very much!

The knee wall height is not the determining factor, but rather the percentage of the floor area compared to the story below that has a regular ceiling height. If the area with standard ceiling height exceeds two-thirds, it is generally considered a full story.
Simply calculated, your ground floor has 144 sqm (1550 sq ft) of area, so once 96 sqm (1033 sq ft) with a normal wall height of 2.30 or 2.40 m (7 ft 7 in or 7 ft 10 in) is reached, the attic counts as a full story. The detailed calculation is, of course, more complex.

Thank you for the quick response and the valid note regarding the two-thirds rule.

What is the maximum knee wall height allowed in a situation where only one full story is permitted?

2023HausBochum schrieb:

and unfortunately I have not found an answer to my question.

This may be because it depends on the floor area of the new building, so it cannot be answered in general terms.
In your case, it is not two-thirds (as in some other countries), but three-quarters...
You can roughly determine this yourself using graph paper and a set square. A definitive answer will come from the architect you trust... It is impossible for a forum to provide this.

North Rhine-Westphalia
Building Code NRW, § 2 Definitions, Paras. 5, 6

(5) Full storeys are floors whose ceiling upper edge extends on average more than 1.60 m (5.25 ft) above ground level and have a minimum height of 2.30 m (7.55 ft). A top floor set back from the external walls of the building (a recessed top storey) is considered a full storey only if it has this height over more than two-thirds of the floor area of the storey below. A storey with sloped roof surfaces is considered a full storey if it has this height over more than three-quarters of its floor area. Storey heights are measured from the top edge of the floor slab to the top edge of the floor slab of the storey above, or in the case of storeys with roof surfaces, to the top edge of the roof covering.

2023HausBochum schrieb:

The applicable regulations are the NW Building Code 1962, the Land Use Ordinance 1968, and the development plan only specifies the following:
- 1 full storey
- Roof pitch 30 degrees
- Gable roof

Your development plan is therefore roughly half a century old – in that case, I would see good chances for exemptions if necessary, especially if more generous conditions have already been established in the surrounding area. But even as is, it’s not very restrictive:

2023HausBochum schrieb:

How high is the knee wall / dwarf wall allowed to be on the upper floor without the storey counting as a full storey? (Assuming no dormers) [...] There are no further restrictions (such as ridge height, etc.) and the ground floor measures 12 x 12 m (39 x 39 ft).

Let’s calculate backwards: 12 m (39 ft) building depth, three-quarters of that may have a height of 2.30 m (7 ft 7 in), with the floor area identical to the ground floor, so a 9 m (30 ft) deep relevant area. A 30° roof pitch results in roughly 1.5 m (5 ft) horizontal length being about 87 cm (34 in) lower in height, which is approximately 1.43 m (4 ft 8 in) knee wall height according to Eva Zwerg or similar rules of thumb. Knee wall heights between around 1.0 and 1.4 m (3 ft 3 in to 4 ft 8 in) are very practical. Dormer windows can easily be kept under 2.30 m (7 ft 7 in) in height.

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Thank you 11ant, that is very helpful!

Would adding a balcony on the upper floor create more flexibility to raise the knee wall further? Or are there other tricks that would allow increasing the height of the knee wall?