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.
Attic knee wall insulation r value.
Bring the attic inside insulating between the rafters simplifies the air sealing details.
At an r6 per inch it provides an air barrier and outstanding thermal break.
Most computer programs allow the user to calculate gross wall areas and subtract window and door areas.
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.
A 2 x 4 wall cavity with blown in fiberglass insulation will provide on average an r 13 to r 15 insulation value.
By adding an r19 to the existing r13 cavity insulation the knee wall assembly total r value is near r30 and is air tight.
The best way to provide that sheathing is to use a rigid material.
All r values are insulation only tested labeled per ftc rule16 cfr 460.
Superb thermo insulating parameters r value 5 2 along with high air tightness keep heat loss to a minimum.
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.
This knee wall has been encapsulated with 2 part closed cell spray foam.
0 19 btu hft f loft ladder hatch u value 1 1 8 insulation thickness 5 2 attic ladder r value the knee wall access door dwk is intended to be built into l shaped walls.
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.
1 use an r value map to determine the amount of insulation you need.
Don t forget to verify that the r value of the roof insulation meets minimum code.
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.