Also known as attic crawl spaces, knee wall spaces typically have a small access door in a conditioned space. The extreme temperatures the space is subject to, impacts the comfort of the home, by transferring heat between the unconditioned attic space and conditioned living space.
The insulation on the flat should prevent heat from radiating down into the space below in the summer months. However, the batt fiberglass in this space is not enough to keep the space comfortable. There are hundreds of holes connecting the living and attic spaces allowing air to escape that need to be sealed. In addition, fiberglass is only effective when enclosed on all sides, currently, it's acting as an air filter for escaping air.
The other side of this knee wall is a bedroom. The room is always too hot in the summer and too cold in the winter, leaving the occupants uncomfortable and implementing band-aid solutions like fans and space heaters. The existing fiberglass insulation is not enough to prevent the heat transfer between the bedroom and attic space and is acting like a filter for air entering through the soffit vents.
Knee walls are tricky spaces to insulate. They are basically tiny attics that share a wall and ceiling with conditioned space. This means the neighboring rooms are impacted by the sweltering temperatures in the summer and freezing temperatures in the winter.
To properly insulate knee wall spaces, we either want to air seal and insulate from the rafters or behind the knee wall and the ceiling. These approaches will reduce the transfer of heat between the attic knee wall and living space, leaving homeowners with a more comfortable home and lower energy bills.