Insulating A Knee Wall With A Vented Roof

Keep the attic outside insulating a kneewall and the attic floor behind the kneewall is possible but tricky.

Insulating a knee wall with a vented roof.

With 2x6 rafters this will give about an r 19 roof higher if you use thicker solid foam insulation. The quest for greater energy efficiency in buildings has led to increasing interest and need for insulation improvements in hvac equipment more airtight construction new materials and assemblies. Old school roof vents which look like rectangles on the roof work pretty well too. How to insulate knee walls 1.

Lay each unfaced strip of insulation between the. Ventilating knee wall attics is challenging. If you want the attic to be outside then using foamboard on the attic side of the knee wall is a good idea. You can use foam board to make baffles near your soffit vents and then blow in enough insulation to reach the r value you want.

Sometimes though there are no soffits. Cut unfaced batt insulation to fit between the floor joists in the space behind the knee wall. Use an r value map to determine the amount of insulation you need. I installed baffles between the roof and insulation shown to allow for the air to flow from the soffit to the roof attic as shown in the second picture.

More details online 1. The first point is sealing the soffit venting. Bring the attic inside insulating between the rafters simplifies the air sealing details. In an ideal world we install soffit vents as intakes make sure the slopes can breathe with ventilation baffles and exhaust through a ridge vent.

Fill the remaining space with fiberglass or cellulose. If you choose to insulate along the horizontal and vertical walls you have four key air sealing points. The first picture is looking up at the angled roof of the knee wall. In the knee wall area the insulation is in the floor and on the back of the knee wall.

The critical issues are the location and integrity of the air barrier and whether the roof is vented or should be. The ceiling and knee wall drywall will act as your air barrier. If there is a well defined air barrier following the upper roof slope to the knee walls and down into the floor joists sealed blocking and the lower slope insulation is not blocking roof ventilation then there s no harm in leaving the lower slope insulation or repairing it as. Insulating the floor and kneewall requires more careful air sealing but is sometimes easier to insulate since you can use blown insulation.

Senior engineer manager at icynene john broniek makes the case for the unvented attic assembly and why insulating the underside of the roof makes sense. Insulating and air sealing knee walls vented version.