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k or k-Value
thermal conductivity; the time rate of heat flow through a unit area of a homogeneous material in a direction perpendicular to isothermal planes induced by a unit temperature gradient. In English (inch-pound) units of measurement, it is the number of BTUS that pass through a 1 inch (25 mm) thickness of a 1 square foot (0.09 m2) sample of material in 1 hour with a temperature difference between the two surfaces of 1 degree F. It is expressed as Btu.inch/h.ft2.degrees F.

k-factor
thermal conductivity for a unit thickness of material. Expressed at BtuoIn/HroFt2o_F. R-value is equal to the thickness of the thermal material divided by the k-factor (R=x/k where x = thickness).

Kerf
(1) a slit or notch made by a saw or cutting torch; (2) the width of a cut made by a saw or cutting torch.

Kesternich test
simulates acid rain conditions by subjecting test specimens to a sulfur dioxide atmosphere as well as condensing moisture for the purpose of evaluating rust/corrosion characteristics.

Knee cap
a metal cover trim that fits over a panel rib after it has been cut and bent.

Knee joints
see Knuckle.

Knuckle
a metal closure, either shop-or pre-fabricated, installed over the cut seam of a continuous metal roof panel at the transition from a steep-slope roof to a vertical roof or wall.