Air Seal Attic Knee Wall

In the video it shows batt insulation in the kneewall studs then a piece of polyisocyanurate foam on the attic side of the kneewall.

Air seal attic knee wall.

That has the potential to degrade the insulation as convective air loops through the insulation. Seal attic bypasses before insulating. Create an airtight and structurally sound seal in the joist space under the knee wall. When possible insulate the slant wall with dense pack cellulose insulate knee walls with dense pack cellulose or fiberglass batts covered with house wrap.

Properly sealing and insulating attic knee walls can significantly reduce air leakage and heat loss between the conditioned space and the unfinished attic. Knee walls may create open useful space from former attics but they are heat loss and homeowner comfort disasters. The air moves right up the roof deck and out the ridge vent. It is important to choose an air barrier and insulation material that will reduce the air leakage and heat loss as much as possible.

Adding a rigid foam air barrier to the cold side of the batt is a great way to take care of this issue on a knee wall between finished and unfinished attic space. Explanation offered in the video is that. The conditioned air escapes out the unsealed top of the knee wall where the top plate is attached to the roof rafter. Scope install a top and bottom plate or blocking at the top and bottom of all knee wall cavities.

Fiberglass batts work best if they re enclosed and air sealed on all 6 sides.