A successful standing seam metal roof project goes beyond the obvious panels, substrate and frame. In order for the roof to look great and perform properly, don’t neglect the importance of selecting the proper roof clips for your given project. What may seem like a minor detail is, quite literally, what’s holding it all together. Here we’ll take a look at the key factors that go into selecting the correct clip type and see why this is so essential for the well-being of any standing seam metal roof.
When you are looking at the installation manual or if you’re ordering your materials directly—or even if you’re submitting the order to MBCI to do the engineering for you—you’re going to need to know and identify certain details. The roof clip selection criteria will be based predominantly on two main factors: 1. What is your insulation system and 2. What are the expansion and contraction requirements for your roof? You’ll also need to know your project’s roof geometry and how the panel you’ve selected is able to meet the roof clip range on a particular plane, because the distance the panel spans impacts what type of clip you would use. Additionally, the type of substrate you are attaching the clip to will dictate what type of clip you should use. Is it going over wood, metal decking, open framing?
With that information in hand, you’re ready to do your due diligence. MBCI classifies clips in two ways: high or low; fixed or floating.
The high and low clips are predominantly determined by insulation systems. For a low clip, for instance, MBCI will typically will go up to a maximum of four inches of insulation; a high clip will go up to six inches of insulation.
Here’s a bit of a caveat. What we’re referring to is how much insulation you’re trying to compress between the roof panel and the substrate—and particularly the purlins or the steel frame you’re attaching it to. The clips are designed with a “stand-off” that elevates the roof panel above the substrate to permit insulation to pass between the roof panel and the substrate at the structural attachment points. A low clip is typically a 3/8-inch stand-off; a high clip, depending on panel type, can be 1-inch, 1-3/8-inch or even possibly 2-inch.
Knowing this helps determine whether you’re choosing the right clip because, let’s say, you go with too tall of a clip or not tall enough to accommodate your insulation system, then the system’s going to be difficult to install and will not perform correctly. And watch out for roof systems that have roof clips with no stand-off that do not permit fiberglass insulation to be installed or is discouraged from being installed at the clip lines due to impact on the panel appearance.
Another factor here is if you are putting the roof over a solid substrate, such as wood or metal decking. In this case, we will typically default customers to a low clip system because they don’t need to accommodate for any sort of fiberglass insulation systems. We’re assuming the insulation is occurring elsewhere below the decking or incorporated with the decking, such as rigid board insulation. In the case of rigid board insulation over decking, a low clip is still utilized but with an added bearing plate. The clip is attached through the rigid board insulation into the decking or structure below.
The more particulars you know of your intended insulation system to determine the clip height needed, the better prepared you will be in determining the right clips. Will there be fiberglass insulation or rigid board insulation or no insulation? What is the insulation thickness? What type of insulation system? Share these details with your MBCI sales rep to help you get started selecting the right clip height.
You can also find much of this information on the MBCI website by searching the roof type and then reviewing the corresponding installation manual and details to determine what clip height to use based on your insulation and substrate.
Which brings us to the other main factor in selecting the right clip. A fixed or floating clip is dependent on the substrate and how much anticipated movement is needed for the roof size.
With fixed clip systems, there are no moving parts in the clip. The ability for that clip to expand and contract as the roof expands and contracts is dependent on the substrate. In layman’s terms, if you were to screw that clip to a purlin, as the purlin heats up and cools down, it’s going to allow for some of the movement of that roof. Generally, when a fixed clip is installed over a metal building purlin, the manufacturer advises a limit of 100-foot maximum on a single roof surface. This is an average and can be impacted also by roof color and geographic location of the roof install that control temperature swing ranges, i.e., 100-foot maximum is a guide.
It is advised that the fixed clip always be installed over open framing in order to permit the greatest ability to accommodate roof panel expansion/contraction. It is not advised to use fixed clips attached to a solid substructure because those don’t accommodate roof panel movement.
If the roof needs to be installed over a solid substrate OR if the roof plane is over a slope more than 100 feet, then the manufacturer would prescribe a floating clip system. [Note: A floating clip can also be used even if the slope is less than 100 feet.] The floating clip system permits the roof panel to move (expand/contract) independent of the substrate to which the clip is installed. The system either contains a clip with a tab seamed into the roof panel rib that is able to float/slide where it attaches to the clip, or the clip is such that when it engages the panel seam is doesn’t restrict the panel movement. The only thing controlling for floating clips is the maximum range of the clips that allows it to float. In other words, how far can the clip tab or panel slide at the clip attachment. The panel manufacturer again will have information as to this amount. You will need to make sure they’re aware of what the maximum single panel run distance is from low side to high side.
One more thing to note is that not every roof system is available with fixed clips and not all systems have high and low clips (although the majority do). That said, educating yourself and researching the panel you’re looking at will give you the information you need to make the determination as to which clip will not only work best, but potentially will work at all. Every panel has its own roof clips, so the roof clips are not interchangeable across all systems. An essential part of selecting a roof panel is verifying that its clip attachment is suitable for your project.
It might not be immediately obvious that you have the wrong clip. For instance, let’s say you ordered an Ultra-Dek® roof and you ordered an Ultra-Dek® clip. That sounds straightforward, but did you order the RIGHT Ultra-Dek® clip for your particular project? The roof may even be able to be installed regardless, but, after installation you may discover it doesn’t perform properly or as intended due to the wrong combination of clips, insulation and substrate. That’s why it is so critical to check with the manufacturer that you have the right clip before you purchase or start putting down the roof.
Part of the beauty and appeal of standing seam metal roofs is that the fasteners holding the metal panels in place are concealed. That gives the roof its clean, continuous appearance that is often desirable, but it also avoids the issue of potential roof leaks around exposed through-fasteners. Concealed fastening doesn’t mean that there aren’t any fasteners, though, it just means they are installed out of sight – underneath the panels. The industry standard approach is to use a metal clip that fits over the edge of a panel and that is secured with a screw type fastener to the structure or substrate below. Then it is covered by an adjacent panel or trim. The important thing to know is that not all panel clips are made the same – for good reasons.
What determines the type of panel clip to use? Here are the most common things to keep in mind:
Each manufacturer of metal roofing typically has a range of metal panel types, profiles, and brands that have their own traits and characteristics. As such, they need clips to match and fit with the manufactured panels. Hence, the first place to start with panel clip selection, is for the roofing manufacturer to be clear on the options and choices available that are compatible with their roofing products.
Building Size and Type
Manufactured metal buildings that include metal roofing commonly use very predictable, coordinated systems. Accordingly, a standard, one piece, “utility clip” is commonly used, primarily for snap together roof panels, on metal buildings that do not exceed certain widths causing undue expansion and contraction. One piece clips allow the roofing panels to expand and contract within the clip profile, but there are limits based on the amount of movement tolerated. Alternatively, in projects where the roofing is attached to something other than a metal building frame or where standing seams are used to secure the panels together, it is advisable to use a two-piece or “floating” clip. In these cases, a base piece is secured to the structure or substrate and the clip fits both into the base and over the roofing panel where it is seamed or folded into the vertical leg of the panel. Using this approach, the clip expands and contracts directly with the metal panel thus moving across the base and keeping the roofing attached.
Roof insulation comes in different thicknesses, appropriately so for different climate zones and different roof designs. Since energy codes require at least some of the insulation to fit between the underside of the metal roofing panel and the structure (i.e. above the metal roofing purlins), the metal panel clip needs to be the right height to reach the full height of the insulation up to the top of the roof panel. Hence, manufacturers offer different sizes and heights of panel clips designed to work with different heights of insulation. In many cases, they also recommend the use of a thermal spacer underneath the clip to separate it thermally from the steel structure below. Note that the thermal spacer thickness is dependent on the insulation thickness over the steel purlin only, not the thickness of any insulation under the purlin.
The panel clips connect the roof panels to the roof structure, so they need to be installed in a manner that allows them to do that job under normal and demanding circumstances. The driving issue in this case is not keeping the panel down, but preventing it from blowing off in a strong wind. Therefore, a structural engineer or other design professional may need to determine the proper spacing of the clips, the type and size of fasteners (i.e. screws) to use, or similar important details. Similarly, the proper installation of clips so that they seat and nest the way they are intended, means that qualified and certified installers / erectors should be used. In this way, roofing crews with the needed experience and training can help assure that the whole roofing system, including the panel clips, are installed properly.
To find out more about the most appropriate panel clips to use on a metal roof that you are involved with, contact your local MBCI representative.
Oil canning is defined as the visible waviness in the flat portion of a metal panel. Oil canning is a visual issue, not a weatherproofing or performance issue. However, building owners will complain about waviness in metal panels on roofs, walls, and perimeter edge metal. Edge metal and metal wall panels are more of a concern than low-slope metal panels because edge metal and wall panels are visible from the ground. Steep-slope metal panels and shingles are also visible, so awareness of potential oil canning is important.
What Causes Oil Canning?
Oil canning can happen when unwanted stresses are introduced at fasteners, clips, and over purlins and uneven substrates. Over-driven fasteners, clips that are slightly misaligned relative to the clip/seam interface, and too much insulation between the purlins and panels can introduce these unwanted stresses. A misaligned panel or edge metal clip, certainly after the seam or drip edge is crimped tight, will add stresses to metal panels and edge metal
Tips to Help Prevent Oil Canning
- Place clips correctly: Setting clips in the proper location for edge metal and metal panels (roof and wall) is critical. The clip needs to fit into a panel seam without forcing the vertical seam out of plane. The clip needs to be aligned correctly and sized appropriately to not compress the vertical portion of the seam. Clips that secure edge metal need to be positioned correctly so that crimping the drip edge won’t twist or bend the edge metal.
Although not highly visible, low-slope structural panels can oil-can at clip locations and where insulation is draped over purlins. Compressed insulation at purlins can “push back,” adding stress to the panel and resulting in oil canning.
- Consider the roof color: Sometimes oil canning is inevitable. The color of the metal or coating won’t really make a visual difference, but darker colors panels will heat up more in direct sunlight. This may make oil canning worse in some cases. However, striations and small ribs (which also add strength) may help prevent or hide oil canning.
- Choose a thick metal: Metal thickness matters, so specify metal that’s as thick as possible to avoid oil canning. Thicker metals are stiffer, so they may resist deformation due to unwanted stresses. This reduces the chance of oil canning in edge metal and wall panels, which are most commonly smooth-surfaced.
For more information on oil canning and its causes, see the Metal Construction Association’s white paper on the subject, which can be found at www.metalconstruction.org.
Consider these ideas on your next job.