b'ARCHITECTURAL SHEET METALContinued from page 7lock seam, and like trapezoidal panels, have two-piece floating clips folded into the seam. There is an abundance of portable and factory roll formers out there that make a 2 tall asymmetrical panel. This seam height is probably okay down to a 1/12 slope. There are a few manufacturers that offer a site-formed vertical rib panel that is over 2 tall, and this is what is needed to go under 1/12 slope.Anasymmetricalpanelhasseveraladvantages overasymmetricalpanel.Theyaremuchmore common than a symmetrical panel, and they cost less money because there is only one manufacturedFigure 5 shows the actual closure.component and they use less material to make. The disadvantagesofanasymmetricalpanelarethat there is a break in the seam sealant at each clip Figure 6 shows the same location, and the amount of thermal movement isdiagonal headwall with a 3 limited to the slide mechanism of the two-piece clip.vertical rib panel instead.Also,thereisareasonablechancetherecanbe damage done to the roof panel during the double-lockseamingoperation;andfinally,thesepanels are extremely difficult to remove, replace, or repair after they have been installed. AD HEREA T-shaped symmetrical panel is run in two pieces: a panel and a separate seam cover that is machine seamed on the roof. These panels cost more money because they use more material and two component partspanelandseamcoverarerequired.Since thereisnocontactbetweentheseamsealantEAVE CONDITIONandtheclip,thereisnointerruptionoftheseamWhen using a vertical rib panel on a low slope, it sealant,yieldingamorewatertightseamdesign.is best to fix the panel at the eave and allow it to Symmetricalpanelsallowmoreflexibilityduringexpand toward the ridge. This is done for several installation, have a higher wind uplift capacity andreasons;mainly,thisprovidesamorewatertight can be easily removed, replaced, or repaired aftereave condition than a panel that is hooked on the installation. eave trim like on a steep-slope architectural panel. TRAPEZOIDAL RIB VERSUS VERTICAL RIB Fold the end of the panel straight down so the water runs off of the panel and does not try to work its way back into the eave trim (Figure 7).Figure 4 shows a misapplication of a trapezoidal panel on a low slope, terminating into a diagonal headwall.Figure 7Continued on page 108 www.mrca.org Midwest Roofer'