ᐅ Calculation of the maximum knee wall height

Hello 🙂

We are about to purchase a plot of land and are currently reviewing the related development plan. We had hoped for the possibility of a second full story, which does not seem to be allowed. As a compromise, an attic with a very high knee wall and a correspondingly shallow roof pitch might be possible. My information is as follows: maximum building height 9 m (30 ft), roof pitch angle between 30° and 52°. Here is the wording regarding the attic:

"According to § 16 and § 20 of the Land Use Ordinance, construction with one full story (Z I) and a floor area ratio (FAR) of up to 0.35 is permitted. Above the approved full story, expansions with at least a pitched roof and expansions set back from at least one exterior wall of the building are only permitted if they cover no more than 3/4 of the gross floor area of the story below, with a height of ≥ 2.3 m (7.5 ft)."

Could someone recommend a software tool or calculator that allows calculation of roof pitch and knee wall height? I believe our absolute minimum requirement for the knee wall height is 1.50 m (5 ft), preferably 1.80 m (6 ft); otherwise, we would not consider purchasing. A meeting with the responsible authority has not been possible due to Covid-19 so far.

Best regards

AdamA5x schrieb:

Can anyone recommend a program/calculator or similar that can be used to calculate roof pitch and knee wall height?

The program you need is a calculator. At a 30° roof pitch, you reach a height difference of 1.00 m (3.3 ft) after 1.73 m (5.7 ft) of horizontal distance, and at 52° pitch, it takes 78 cm (31 inches).

AdamA5x schrieb:

I think our absolute minimum requirement for the knee wall height is 1.50 m (5.0 ft), preferably 1.80 m (5.9 ft);

I think differently: a practical knee wall height starts at 1.0 m (3.3 ft), a reasonable height is between 1.2 and 1.4 m (3.9 and 4.6 ft), and at 1.8 m (5.9 ft) it becomes borderline (not only regarding the full-story boundary). Increasing the knee wall height effectively raises the window base height as well.

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You can also equip yourself with a set square and draw sections on graph paper.
The building authority is not a good contact for calculations; that would be the responsibility of an architect, who often knows approaches that neither a layperson nor a construction company planner is familiar with.
A 30-degree roof pitch is quite simple using a grid layout...
But 30 degrees is not flat!

Gable roof 30°
House width 10m (33 feet)
This results in a knee wall height of approximately 1.40m (4 feet 7 inches)

Sketch

Thanks to everyone for the prompt responses and especially for the illustration with the drawing! 🙂