"Understanding Your Home" by Building Inspector Mark Visser
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Installing a knee wall or suspended beam is a task that should be handled by a professional. Even before starting the job the contractor has to know the size and spacing of the ceiling joists and where the pressure created by the knee wall or beam can be transferred to a load bearing wall below.
If you are not 100% sure of how to do the job than don't do it because doing it the wrong way can lead to serious structural damage to the house.

Attic Knee-Wall
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Attic knee-walls can be found in 1 1/2 and 2 1/2 storey homes where they form the walls of rooms on the top floor. The ceilings in those rooms are formed by higher than normal installed collar ties. Basically, the rooms are built in the attic. They also can be found in Cape-Cod style homes. However, in this type of home rooms on the upper floors were designed to be there and the knee-walls are much taller because there was much more headroom to begin with.
The space behind the knee-wall should be properly vented. The knee-wall and the exposed ceiling behind it should be insulated as shown.

Knee-walls can be build in any attic space to straighten and/or stabilize roof deflections. That is, if the ceiling joists are strong enough to handle the extra pressure.
If the ceiling cannot handle the extra load and if there are no load-bearing walls which can be used for support, it is recommended to install the knee-wall on a floating or suspended beam.
The beam can be nailed together in the attic (crown up!) and installed on blocks high enough to clear the ceiling joist by at least 2" (50 mm). The support blocks have to be placed on bearing walls.
The space behind knee-walls is usually wasted space except for storage.

Insulation in attic space behind knee-wall

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