Attic Knee Wall Insulation R Value

At an r6 per inch it provides an air barrier and outstanding thermal break.

Attic knee wall insulation r value.

Now that the kneewall is located within the home s thermal enclosure it s no longer necessary to air seal electrical boxes or access doors in the kneewall. Bring the attic inside insulating between the rafters simplifies the air sealing details. Walls are entered by the type of assembly and the r value of insulation. A 2 x 4 wall cavity with blown in fiberglass insulation will provide on average an r 13 to r 15 insulation value.

According to a report by the washing state university extension energy program blown in fiberglass insulation provides an r value of between 2 2 and 2 7 per inch. Cavity insulation as indicated in approved construction documents completely fills the knee wall cavity with no compression or gaps the manufacturer s r value mark is readily available and meets the approved r value per construction documents. Most computer programs allow the user to calculate gross wall areas and subtract window and door areas. The attic tent is the ultimate attic access insulation cover ever invented attic stairs scuttle holes knee wall doors and full size doors its primary design is to stop air infiltration between the home and attic the most common medium for wasting costly residential energy during both hot and cold seasons.

Georgia recognized this problem about a decade ago and started requiring all attic kneewalls to have sheathing on the attic side and to be insulated to at least r 18. This gives a total r value of r 17 r 13 fiberglass plus r 4 for the solar guard sometimes we will change the solar guard out for r 30 fiberglass rolls which gives a total r value of r 43. The best way to provide that sheathing is to use a rigid material. This knee wall has been encapsulated with 2 part closed cell spray foam.

Don t forget to verify that the r value of the roof insulation meets minimum code. By adding an r19 to the existing r13 cavity insulation the knee wall assembly total r value is near r30 and is air tight. Insulating this space inside the knee wall improves the energy efficiency of the home and prevents heat transfer from the attic. A 1 5 wide strip of 3 4 polyiso held in place with a 1 5 wide strip of 3 4 cdx or 1x furring doubles the r value of 2x4 framing and 5 deep cavity can fit a compressed r20 which would deliver a true r18 3 slightly better than an r19 stuffed in a 5 5 deep 2x6 cavity.