ᐅ How is the knee wall height calculated?

Hello,

can someone explain how the knee wall height is correctly calculated?
I currently have quotes from two builders, and they calculate it differently.

Data

Knee wall height 80cm (31.5 inches)
Roof pitch 38°
Wall thickness 36cm (14 inches)

1. 80 cm (31.5 inches) knee wall height on the outside corresponds to about 100 cm (39 inches) on the inside
2. 80 cm (31.5 inches) knee wall height on the outside corresponds to about 65 cm (26 inches) on the inside

Excerpt from the development plan

The knee wall height of the attic must not exceed 80 cm (31.5 inches). The knee wall height is defined as the distance between the top edge of the attic floor and the intersection line of the outer surface of the wall with the underside of the roof covering.

I am not asking for an exact value, but which builder is wrong?!

Best regards

Chris

Inside, our finished floor level was about the same as outside... The floor construction was slightly higher than the floor purlin. I believe the knee wall height refers to the masonry height measured from the raw floor level, adjusted according to the geometry.

OK, different!

What is the top edge of the attic floor?
- With screed and tiles or without?

What is the bottom edge of the roof covering?
- Rafters outside or inside?

According to my logic, the unfinished floor level and the height of the masonry portion – most likely the inner roof skin.
However, I could be wrong.

Chrisbo schrieb:
Hello,

can someone explain how the knee wall height (kniestock) is correctly calculated?
I currently have offers from two different developers, and both calculate it differently.

Data

Knee wall height 80cm (31.5 inches)
Roof pitch 38°
Wall thickness 36cm (14 inches)

1. 80cm (31.5 inches) knee wall height measured outside corresponds to about 100cm (39 inches) inside
2. 80cm (31.5 inches) knee wall height measured outside corresponds to about 65cm (26 inches) inside

Excerpt from the development plan

The knee wall height
of the attic floor must not exceed 80cm (31.5 inches). The knee wall height is defined as the distance between the upper edge of the attic floor and the intersection line where the exterior surface of the wall meets the lower edge of the roof covering.

I’m not looking for an exact value, but which developer is wrong?

Best regards

Chris

No one necessarily has to be wrong here. It’s more likely about the usable floor area intended. The developer calculating the 65cm (26 inches) knee wall is probably maximizing the interior space and may be using a different wall construction than the one with the 80cm (31.5 inches) measurement.

Chrisbo schrieb:

Can someone explain how the knee wall height is calculated correctly?

You can find the calculation method in your regional building code; some municipalities use the intersection with the exterior roof surface as the reference, while others use the intersection with the interior roof surface.

Each state or region has its own approach.

Regards, Bauexperte