How To Install Metal Roofing Panels

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I’m a big fan of roofing with metal. As a kid growing up on a western Montana cattle ranch, I always admired the shiny, corrugated aluminum roof over the woodshed. That admiration has only grown over the years, though my preference these days is for steel over aluminum and for pretty, painted, ribbed panels over those wavy, shiny things. Shingles are fine, but where steel is possible, that’s the way to go for this cowboy.

However, there are a few details that shouldn’t be ignored. Such as, before ordering the panels (unless you’re lucky enough to find what you want in stock at Home Depot), it’s necessary to come up with a color choice your rowdy redheaded wife will accept without ralphing. In our case, Pam did not give me the green light until Choice #6, an off-white tone somewhere between very light-colored sand and clay.

Next, just like when you’re going to add shingles, it’s standard practice to apply a well done layer of roofing felt between sheathing boards and steel panels.

...apply a...layer of roofing felt....

…apply a…layer of roofing felt….

First And Foremost

When all is ready for the first panel to hit the roof, look out for the wind! Even a fairly mild breeze can take a lightweight chunk of metal that’s three feet, three inches wide and 20 feet long…and turn it into a “flag ironed against the sky” if you’re the least bit careless. Once the panel is about where you want it, one super-key question pops right up: Where exactly is the roof centerline? Even if the underlying sheathing board runs downridge in a perfectly straight line (not likely), the tarpaper (roofing felt) disguised everything quite effectively when it wrapped over the rooftop.

This challenge was met by tacking a nail at each end of the ridge–not on top, where it would have penetrated the felt and ruined its water repellency, but a bit “over the edge”–and then a string was stretched tightly between them. Voila! Perfect ridge centerline! The trick was to get that first panel square to the center-string and hanging over the roof edge evenly from top to bottom at the same time. Since our house is built by hand and not exactly square in the first place, that was literally impossible…but the final compromise wasn’t bad at all.

Placing the roofing panel square to the ridgeline-finding string. Never mind the dried mud; we had rain, and it will wash off during the next downpour.

Placing the roofing panel square to the ridgeline-finding string. Never mind the dried mud; we had rain, and it will wash off during the next downpour.

Applying The Fasteners

When it comes to “stitching” panel to roof, the process couldn’t be simpler. These premanufactured panels are marvels of invention, not the least of said marvels being those ridges that provide strength and contain rainwater on its downward course…and at the edges, “nest” each panel to its neighbor. There are basically two factors to consider:

1. What to use for fasteners. The only real choice is the made-to-order screw, preferably in a complementary color, with self-sealing neoprene washers included under little metal collars. There is one option, namely the length of the screw. I decided to use only 1 1/2″ screws. That length leaves a full inch sticking down through the sheathing board where the 1″ length might more than do the job, but I wanted all the “grab” I could get whenever a screw happened to dig into a truss–not just the sheathing board–and decided it was easiest to simply go with the idea that “bigger is better”. There was one “surprise” in the 20 pound bag of screws I dug out of the hardware store’s bin–it came out looking more like a rivet. No threads!

2. How many screws to apply. I almost messed up on this one. A friend warned me in time, though–and instead of applying a “hem” of one screw every nine inches, I doubled that (for the bottom roof edges). On the other two, sloping edges (where the panel runs up the rafter slope), the spacing is slightly larger–roughly six inches on average–but those screws go directly and deeply into the rafter 2″ x 4″ lumber, which adds enough strength to balance things out. For the “interior” area, a strip of screws was applied vertically alongside each rib at the rate of one per every 17 1/4 inches. Nothing magic about that figure; I just cut a “spacing stick” intuitively, and that’s the way it worked out. Which should be good, since the maximum recommended spacing is one screw every 30 inches.

The "threadless screw" that showed up in the bag of fasteners.

The “threadless screw” that showed up in the bag of fasteners.

Screws WITH threads (and neoprene washers) showing an optimal way to recycle those old Mayonnaise jars.

Screws WITH threads (and neoprene washers) showing an optimal way to recycle those old Mayonnaise jars.

The spacer stick, resting against one screw-head, waiting for the next upslope screw to be applied.

The spacer stick, resting against one screw-head, waiting for the next upslope screw to be applied.

Application Techniques

How the screws are applied is a matter of choice. In my case, I started with nothing but a ten penny nail for bashing pilot holes through the steel, then followed with a hand-operated ratchet that came straight from my auto maintenance tool kit. There were some advantages to this–applying each screw by hand power only does give you a great feel for how the fasteners are cinching down. But, yes, it is infuriatingly slow when you’re looking at a 2,000 screw total for a single roof (about the number for our house).

So, next step, out came the power drill. Replacing the nail with power-piloting did speed things up considerably.

But not enough. Pam kept saying, “Get yourself a nut driver! You don’t need to work yourself that hard!”

Off to Home Depot once again…and whaddya know? Didn’t have to buy a nut driver after all. Turns out DeWalt makes a cool little adapter that immediately turns a power drill into a power ratchet for the outstanding sum of $2.99 (plus tax). Zipppety-zoom! With this attachment, a quarter-inch socket added, and bearing down to get the screws started, hey–no need for any more pilot holes, either!

The adapter slips right into the drill chuck.

The adapter slips right into the drill chuck.

Add a quarter-inch socket and you're ready to go.

Add a quarter-inch socket and you’re ready to go.

Two hands for beginners, but one was needed to hold the camera.

Two hands for beginners, but one was needed to hold the camera.

The Ridge Cap And Trimming The Edges

With a custom home built by professionals, perhaps everything works out neatly…or at least is made to look that way. With a hybrid earthbag-walled home thrown up single handed by guess and by gosh, the edges aren’t exactly laser-straight and/or sized to the millimeter. When it came to the rafter overhang on the downslope edges, things worked out very well. On the east and west edges, though, the overhang had to be trimmed with the Skilsaw so that (a) the steel wasn’t jutting out far enough to let the wind really push at it and (b) the “crookedness” of those edges was not so noticeable to the naked eye. This was done by simply reversing the Skilsaw blade–an old contractor’s trick to produce a metal-cutting blade without having to go buy one. Works like a charm.

That left the ridge cap. In the case of the cap, a roofing screw is applied over (and through) each high rib on the underlying panels, and that’s all there is to it (except for overlapping the ridge cap pieces, which come in 10 foot lengths, so that the end result looks from the ground like a single unit).

We get a lot of wind here, so it was with significant relief that we saw the final screw cinched down without having had any roofing horror stories to tell.

Done...

Done…

Whole house view.

Whole house view.

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