deformed and thereby exert a force against joint 12 when inserted therein also the upper part of tongue 10b could be split to divide it into halves with each half slightly offset from the vertical this construction would also enable the spring of the material to contact the sides of joint 12 and increase the resistance to withdrawal in fig4 there is shown a second embodiment of the retaining means 10 wherein lip portion 10a has been cut along dotted line 20 see fig3 lip segment 10d is then bent 180 u00b0 from lip portion 10c the advantage to the construction as illustrated in fig4 is that alternating retaining means 10 need not be used but rather the embodiment of fig4 provides for support of insulation boards 18 on either side of tongue 10b in a preferred embodiment the retaining means 10 of the present inventon is constructed of 20 gauge steel 11 2 inches in width and 13 8 inches deep along the tongue portion lip portion 10a is constructed with a width of 1 inch insulation board materials of 1 2 inches depth may be advantageously employed wih retaining means 10 having the dimensions above described of course different dimensions may be used the dimensions being dictated by the size of the roofing panels and the insulation board material additional advantages of the retaining means of the present invention are apparent from the fact that once the insulation board material is secured in place less heat will be transferred between the top of the panel and the space disposed beneath the insulation board if insulation board were not used aluminum roofing panels can become quite hot and radiate heat into a mobile home or the like thus the insulation will prevent excessive heat buildup.