Insulating A Knee Wall With A Vented Roof

The specific r value for the insulation you need.

Insulating a knee wall with a vented roof.

Now that the kneewall is. 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. 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. Ventilating knee wall attics is challenging.

Sometimes though there are no soffits. The first point is sealing the soffit venting. With 2x6 rafters this will give about an r 19 roof higher if you use thicker solid foam 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.

Keep the attic outside insulating a kneewall and the attic floor behind the kneewall is possible but tricky. If you choose to insulate along the horizontal and vertical walls you have four key air sealing points. Cut unfaced batt insulation to fit between the floor joists in the space behind 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 first picture is looking up at the angled roof of the knee wall. Lay each unfaced strip of insulation between the. How to insulate knee walls 1. If you want the attic to be outside then using foamboard on the attic side of the knee wall is a good idea.

The third shows the baffle extending up into the roof attic. Insulating and air sealing knee walls vented version. 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. More details online 1.

Old school roof vents which look like rectangles on the roof work pretty well too. Use an r value map to determine the amount of insulation you need. Fill the remaining space with fiberglass or cellulose. 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.

In the knee wall area the insulation is in the floor and on the back of the knee wall. Bring the attic inside insulating between the rafters simplifies the air sealing details.