intermediate member u201d may be used herein to refer generically to both the girts 20 and purlins 22 in the illustrated example each of the girts 20 and the purlins 22 is a member formed from sheet metal having a generally u201c z u201d shaped cross section other sectional shapes such as u201c c u201d and u201c hat u201d are known as well the girts 20 and purlins 22 would typically be attached to the posts 16 and rafters 18 using mechanical fasteners such as bolts and nuts insulation 24 is laid over the purlins 22 a frequently used type of insulation comprises a thick mat of glass fibers e g u201c fiberglass u201d in the form of a blanket roll or batt as an example in its free state the insulation 24 would typically be about 10 cm 4 in to about 20 cm 8 in thick with a corresponding thermal resistance or u201c r value u201d of about 12 to 25 typically the underside of the insulation 24 would include a paper facing and or vapor barrier material roof sheathing 26 and siding 28 is secured to the purlins 22 and the girts 20 respectively the sheathing 26 and siding 28 are pressed sheet metal shapes and are often attached using self drilling screws 30 of a known type the insulation 24 is crushed or compressed to a very small thickness for example less than about 1 3 cm u00bd in at the attachment points over the purlins 22 this crushing greatly reduces the r value of the insulation 24 not only at the points of minimum thickness but also in the.