b'ARCHITECTURAL SHEET METALontheleft,andaliberalapplicationofcaulkandare great on rectangular buildings with few if any coatingstostopthewaterfromcomingintothecurb penetrations and short eave-to-ridge lengths buildingthroughthelapjoints.Consultantsmight(under 50). They come with preformed closures at notgetthecallaboutthoseleaksbecausethetheridgeandeaveandhavea3tall,watertight maintenance man can smear some more goop toseam.slow them down (Figure 2), but for sure, someoneTrapezoidal rib panel advantages diminish as the is getting a call about this. panellengthincreases,theroofgeometrygets more complicated, and the number of penetrations increases. If the goal is to eliminate places for the roof to leak, a good place to start is to eliminate panel end laps. Trapezoidal panels are rarely site-formed, so it would be extremely difficult to cover a run of more than 60 without introducing end laps into the roof (Figure 3).Figure 2 Figure 3There are thousands and thousands of these roofs hidingbehindparapetwallswithinternalgutters andhugecondensers,ACunits,andventpipes penetrating them. The question is how to use metal on a low slope and have the greatest chance for success? Most low-slope metal roof leaks can be sourced to one of four things: exposed fasteners penetrating the building envelope; panel end laps,Also, while the shape of the seam lends itself nicely both in the field and around curbs; and alterationsto preformed closures at the ridge, it is a hindrance aftertheinitialinstallationbecause ALLoftheseif the panel has to be cut on an angle for a hip or roofsaredifficulttomodify/repairaftertheyhavevalleycondition.Inthoseconditions,itismuch been installed. moredifficulttomakeawatertightjointbetween Lets see how to address each of these for the besttheclosureandthepanelseamthanavertical chances for success. ribpanel.Finally,largecurbpenetrationscanbe PANEL CHOICE custom made to fit a trapezoidal panel seam, but When choosing a metal roof panel to be installed onthese panels rely on exposed fasteners penetrating a low slope, one need only consider mechanicallythoughtheroofatalloftheseconditions,which seamed structural standing seam panels designed toopen up opportunities for water infiltration.go over open purlins. Stay away from snap togetherIftheroofhasalongerpanelrun,complicated panels on this type of application. The seam heightgeometry, or curbs, then a site-formed vertical rib should be over 2 on roofs below 1 per foot slope.panelmaybeabetterchoice.Sincethegoalis One may choose between a trapezoidal shaped ribtoeliminateasmanypotentialleaksaspossible, and a vertical rib. Both have their advantages. the easiest way to start is to eliminate all end laps. A mechanically seamed, 3 tall trapezoidal rib panelTherearetwotypesofverticalribbedstructural has a couple of advantages over a vertical rib panel.standing-seamroofpanels:thosethatare Mainly, trapezoidal panels are the least expensiveasymmetrical and those that are symmetrical. Both structural standing seam panels available. They arehavetheiradvantages. Anasymmetricalpanelis verycommonandtheycostlesstomanufacture,one piece, installs from left to right or right to left, will most likely be seamed to a 180-degree double package, and ship than a vertical rib panel. TheyContinued on page 8www.mrca.orgMidwest Roofer 7'