M
Mal Bauen18 Mar 2023 22:24Searching the forum and the internet has so far been unsuccessful, so I’m asking the question here:
For our house building project, the architect expects a “very low” knee wall when installing a shed dormer in the attic and has mentioned a cross-gable dormer as a potential alternative. However, we are not very keen on that option due to the appearance and shading on the ground floor.
I wanted to understand this better and took some measurements in our current rental apartment, which has a shed dormer:
I don’t know the thickness of the roof insulation in the rental unit but will assume it meets “current standards” (built in 2019). The window sill in the dormer is about 27 cm (11 inches) higher than the knee wall, measured from the inside floor level.
Can it be assumed that with a lower knee wall, the sill height would decrease proportionally by the same amount?
In other words: would a knee wall of around 90 cm (35 inches) result in a window sill height of approximately 117 cm (46 inches)?
In my opinion, the windows in the rental apartment are too high. For our own build, I am looking for the sweet spot between having a knee wall that is “high enough” and dormer windows that are “low enough.”
I would appreciate any insights or experiences, especially if someone wants to take measurements in their own home.
For our house building project, the architect expects a “very low” knee wall when installing a shed dormer in the attic and has mentioned a cross-gable dormer as a potential alternative. However, we are not very keen on that option due to the appearance and shading on the ground floor.
I wanted to understand this better and took some measurements in our current rental apartment, which has a shed dormer:
I don’t know the thickness of the roof insulation in the rental unit but will assume it meets “current standards” (built in 2019). The window sill in the dormer is about 27 cm (11 inches) higher than the knee wall, measured from the inside floor level.
Can it be assumed that with a lower knee wall, the sill height would decrease proportionally by the same amount?
In other words: would a knee wall of around 90 cm (35 inches) result in a window sill height of approximately 117 cm (46 inches)?
In my opinion, the windows in the rental apartment are too high. For our own build, I am looking for the sweet spot between having a knee wall that is “high enough” and dormer windows that are “low enough.”
I would appreciate any insights or experiences, especially if someone wants to take measurements in their own home.
Mal Bauen schrieb:
For our house construction project, the architect expects a "very low" knee wall when installing a shed dormer on the attic floor and has suggested a cross gable as a possible alternative. However, we are not very keen on this option because of the appearance and the shading on the ground floor.
I wanted to understand this better and measured in our current rental apartment with a shed dormer: The structure in your illustration is not a shed dormer, but a shed cross gable.
Mal Bauen schrieb:
Can it be assumed that with a lower knee wall, the sill height can also be reduced linearly by the same amount?
In other words: If I have a knee wall of about 90cm (35 inches), do I get a window sill height of approximately 117cm (46 inches)? With the same roof pitch and wall thickness, that would be correct.
I recommend my post "How the Knee Wall Influences the Window Design in the Attic".
https://www.instagram.com/11antgmxde/
https://www.linkedin.com/company/bauen-jetzt/
M
Mal Bauen19 Mar 2023 08:45Thanks for the quick reply!
It’s not clearly shown in my drawing, but there are still 1-2 rows of roof tiles below the dormer. On the eaves side, the gutter runs continuously. In this case, is it still considered a cross-gable dormer instead of a "true" dormer?
Visually, I imagine it something like this:
It’s not clearly shown in my drawing, but there are still 1-2 rows of roof tiles below the dormer. On the eaves side, the gutter runs continuously. In this case, is it still considered a cross-gable dormer instead of a "true" dormer?
Visually, I imagine it something like this:
H
hanghaus202319 Mar 2023 09:55I have knee wall height of 86 cm (34 inches) and the windowsill at 104 cm (41 inches). However, there is insulation only between the rafters. The base level is the finished floor. According to the development plan, we were supposed to have a 1 m (39 inches) knee wall from the raw floor slab. Since, in my opinion, your roof appears thicker, your knee wall should be somewhat lower. At 75 cm (30 inches), you would likely have the 1 m (39 inches) windowsill height. It is also possible to go one row of roof tiles lower by adding flashing.
Mal Bauen schrieb:
In my drawing it is not clearly shown, but below the dormer there are still 1-2 rows of roof tiles. On the eaves side, the gutter is therefore continuous. In this case, would you still call it a cross-gable instead of a "real" dormer? Yes, it is clearly visible both in the drawing and in the photo that what appears to be the dormer roof on the valley side is actually just a roof overhang. The difference between a cross-gable and a dormer is essentially "genetic," meaning the classification of such a roof structure depends on its construction: a dormer always sits on a knee wall, a purlin, or another element on the uphill side of the knee wall; whereas a cross-gable—whether with decorative skirt boards or without—always rises from a knee wall. I have already updated the "building terms glossary" / "construction dictionary" accordingly this morning.
https://www.instagram.com/11antgmxde/
https://www.linkedin.com/company/bauen-jetzt/
M
Mal Bauen19 Mar 2023 22:00All right, learned something new again!
If I understand you correctly, the metal flashing would then be an extension of the external window sill? That way, the window could be set lower. The view from the dormer window looking downward at an angle might not necessarily be improved, but it’s definitely an option if you want or need to gain a few centimeters (inches).
hanghaus2023 schrieb:
You can also go one row of roof tiles lower with metal flashing.
If I understand you correctly, the metal flashing would then be an extension of the external window sill? That way, the window could be set lower. The view from the dormer window looking downward at an angle might not necessarily be improved, but it’s definitely an option if you want or need to gain a few centimeters (inches).
Similar topics