The Details behind Metal Roof Details Part Two

Manufacturers of metal/profile systems put a lot of time and money into their installation details to ensure their details are weathertight and structurally sound. What follows are considerations about installation details to remember.

#1: A bad installation doesn’t mean the roof looks bad.

Installation details exist solely to protect the roof from leaking and failing, which then prevents damage to other parts of the structure. Just remember that because the roof looks good on the outside doesn’t mean that it was installed to the manufacturer’s recommended details. That’s why it’s critical to verify this fact with the contractors.

#2: Just because the installation details don’t match the manufacturer’s details doesn’t mean they’re invalid.

While it’s typically recommended that you follow the details provided by the manufacturer of the metal, this doesn’t mean that other details won’t work as well. Just be aware of this fact and discuss any concerns with the manufacturer before the installation.

#3: Do not use details that are illegible, unorganized, or difficult to understand.

If you run into a situation as a property owner or installer where you don’t understand the details, the measurements are off, or the document is unorganized, it’s best to question if you should use them. Again, the best course of action is to talk to the manufacturer to see if you can get clarity on their details, or find other, more concise details to follow before the installation takes place.

#4: As a property owner, it’s recommended that you go over the installation details with your contractor.

Ten Bad Installation Details

Not only does going over the details give you some insight into how the roof will be installed on your property, but it also helps verify the installation details are appropriately utilized. Next up are ten bad metal roof installation details you should avoid on projects.

Bad detail #1: Putting rivets in valleys.

If installed correctly, there should be no need for rivets in the valley. When you drill a hole for a rivet, you are pretty much ensured to poke a hole in the underlayment, which can create a spot for potential leaks. On top of that, the center of the rivet has a hole in it. So, now not only do you have a hole in the underlayment, but now there’s a hole in the center of the rivet to allow water in.

Bad detail #2: Exposed fasteners that go through the flat portions of the panels.

Luckily, exposed fastener metal roofing is a category of its own and is different from the standing seam metal roof systems that we’re referring to here. If there are any panels on your roof that have an exposed fastener (this does not include flashing points), the potential of springing a leak increases significantly. It also can pin the panel if fastened through to the decking, which will stop the thermal movement of the panel and create stress points. 

Bad detail #3: Double pinning the panels at the eave and ridge.

In standing seam roofing systems, the panels generally aren’t double pinned (if installed to our recommended details). Not double pinning the roof means that the panels can expand and contract better, which reduces the likelihood of oil canning, fasteners backing out, etc. For reference, SMI’s details pins all panels at the top to allow the expansion to take place at the eave.

Bad detail #4: Putting pipe boots over the seam.

Pipe boots are not designed to make sharp right angles to properly fit over a standing seam on a metal roof, which means it won’t make the penetration completely water-tight and you are counting on caulking for water-tightness.  

Bad detail #5: Using sealant as a primary defense against water.

Sealant is added to a roof system as a secondary defense against water intrusion at flashing laps or penetration locations. In other words, you shouldn’t see sealant if you’re looking at the roof, especially big globs of it being used as a primary water defense.

Bad detail #6: Modified J (or J-channel).

A J-channel is a type of flashing material that is used in metal roofing. However, we’ve seen these materials trap water and dirt, which can accelerate corrosion of the metal in some instances. On top of that, J-channels can restrict the expansion and contraction of the roof system as well.

Bad detail #7: Using a C/Z-closure (especially in snow environments).

In this detail, the top of the panel is slid into a receiver at the ridge cap. Most of the time, the top of the panel is not fastened off, which could allow the panel to slide down the roof. Also, you are counting on sealant as the primary defense against water intrusion, which is never recommended. 

Bad detail #8: Any roof penetration that isn’t correctly flashed.

Details exist to tell you or the installer exactly how to install the flashing materials around penetration points correctly. However, there are some flashings, such as those for skylights that come with kits or other “recommended” installation directions. These are often not recommended by the manufacturer for use on a metal roof system.

Bad detail #9: Large, visible gaps of any kind.

Gaps are the recipe for leaking – it’s as simple as that. There shouldn’t be gaps at any point in your roof system, so if there are, it’s critical to correct it immediately. Gaps can also invite unwanted “guests,” such as insects, rodents and other destructive critters.

Bad detail #10: Leaving exposed edges where there isn’t a hem on the metal.

Painted metal sheet and coil are rollformed to make the panels, trim and flashing materials, which means it needs to be slit to the correct size for the project. When there’s an exposed edge from a cut to the metal, it needs to be hemmed to avoid edge creep and excessive rusting that can be detrimental to a metal roof. Plus, a hemmed edge generally is tidier and aesthetically pleasing.

Final Detail Thoughts

Your roof is the first and last defense from the elements that have taken their toll on everything around us. Why not protect the inside of your property and the roofing project in the best way possible by ensuring it’s done right the first time?

One thing to keep in mind is that nothing will ever be “perfect.” And just become something doesn’t look perfect on your roof, doesn’t mean that it’s wrong—it might be exactly what the manufacturer recommends.

Remember this fact when considering installation details: It’s much easier to make sure the right manufacturer’s installation details are used from the start than it is to go back, tear up various parts of the roof and then redo it. 

Additional Detail Concerns

• Lapping sheet metal to look compressed.

• Using drywall or other generic fasteners instead of metal roofing specific fasteners.

• Seams on a mechanically seamed system that look mangled, unengaged or improperly seamed.

• Cutting panels with saw blades not designed to cut metal.

• Drilling pop rivets into the roof without a barrier on top of the panel that can lead to swarf particles creating rust.

• Leaving dead valleys, narrow valleys and other improper water drainage spots.

• Installing the wrong panel profile for your low-slope or steep-slope roof application.

• Using too much touch up paint or the wrong color (touch up paint will fade differently than the rest of your roof).

• Running metallics or other lot-specific finishes in differing directions instead of the same direction.

About the author: Julianne Calapa is a writer at Mazzella Companies, Cleveland. For more information, go to www.mazzellacompanies.com.