The following examples and illustrations will help you determine when to select an attic or a vault (or both) and what to do with Knee Walls.
Attic: Simple roof line, no knee walls
Simply “add an attic” on the input screen and indicate the approx. depth of the insulation and the type of insulation.
Attic, Knee Wall, and Vault - Option A
Add an attic for the space behind the knee wall, insulating the attic floor
Add the total width x height of the knee wall in attic recommendation
Add a vault for the ceiling of the conditioned space
Vaulted Ceiling - Option B
Add only a vault to the input screen.
For Option B, the knee wall slopes are being insulated instead of the attic floor behind the knee wall. So you would not add a knee wall to the mix since it is inside the thermal boundary.
You can fine tune the sqft of the vault slopes by using the roof pitch chart.
Attics and Knee Walls
Add only an attic to the input screen. Combine the two attic floor areas, and indicate the knee walls in the detail section.
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References:
Written and prepared for the U.S. Department of Energy by: Southface Energy Institute & Oak Ridge National Laboratory