THERMAL EXPANSION/CONTRACTION RATE FORMULA:

EXPANSION/CONTRACTION = LENGTH IN INCHES  x  DELTA  T  x  .0000129

Delta T = 100° F

Illustration: An installer attaches 60' of continuous aluminum rail with no provision for expansion/contraction and the material temperature is 120° when installed. The next winter the temperature goes down to 20° (Delta T (DT) 100°). Following the formula above the aluminum could potentially move:
                            
                                720" (60') x 100° DT x .0000129 = .9288"

EXPANSION RATES - WHY IT'S IMPORTANT TO KNOW THEM
Q: Why should I be concerned with the expansion rate of aluminum?
A: Aluminum has a very high expansion rate, but the expansion rate of the roof structure is negligible. If aluminum supports are rigidly bolted into the roof structure, and expand based upon the formula above, they will expand/contract at a different rate than the roof causing stress on the sealed connections. This could result in sealed connections failing and potential roof leaks. 

Q: How does the Roof Trac™ mounting system address this issue?
A:  We do this in two ways:
        1) Our specially designed splice kit can be installed to take up or allow for thermal expansion in the support rail (see below)
        2) We recommend that no more than 30' of continuous rail be installed in any one array. 

Illustration of splice kit