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March 28, 2017
At Infrared Diagnostic, we are often called to houses where there’s a kneewall attic. This is often a living space built into a sloped roof area. It can be a bonus room over a garage in a new house, or a walk-up attic in an older house. It’s called a ‘kneewall’ because of the short wall that is set in from the eaves of the roof. This kneewall ties into the attic floor and the sloped roof and might have storage behind it.
The kneewall typically separates the conditioned space from the unconditioned space. Since this boundary can be leaky, it can be the source of a lot of comfort problems, meaning your bonus room can end up being too hot in the summer and too cold in the winter.
A kneewall attic leads to all sorts of challenges for air sealing and insulation. When these two energy conservation measures are missing, or are not done properly, the kneewall attic can be a large source of of air leakage, which can lead to moisture problems inside the house and ice damming on the roof.
Why is a Kneewall Attic Challenging?
When you are carrying out air sealing work, which is your first line of defense against moisture problems and ice dams, you really need to pay attention to the way the attic is constructed. The kneewall creates several different surfaces and connection points that can be tricky to air seal and insulate properly. Here are a few problems that can happen that directly affect your comfort:
The floor joists that the kneewall sits on don’t have any blocking or air sealing, allowing outside air to overheat or cool the floor of the attic (and the living space below, as well).
Fiberglass batt insulation is not often installed properly (in complete contact with the the backside of the drywall).
Batt insulation without attic-side air barrier or sheathing is likely to fall out of the kneewall cavity and does not provide adequate air sealing and thermal performance of the installed insulation.
Batt insulation does not stop air movement, so without proper air sealing at places like access doors and electrical outlets, you will end up using more energy than necessary with more energy use than you should have in both heating and cooling seasons.
Fixing these problems has to be done in the right order, or you’ll cause more problems!