Choosing Metal Roofing Types

All metal roofing is not the same. There are different profiles in different shapes for different reasons and to suit different performance needs. How to choose? Here’s the process that metal building engineers go through at MBCI to zero in on the most economical selection that will still meet the performance requirements of a particular metal roof project.

Snap Together Trapezoidal Panels

Offered by MBCI under the name Ultra-Dek®, the trapezoidal shape is among the best for channeling water off of the roof. However, because of this shape, it is most appropriate for typical sloped roofs with single plane roofs areas free of valleys or hips. It’s snap together installation makes it quick and easy to install economically with wind resistance capabilities adequate for many situations. It also carries basic air leakage and water penetration testing approvals.

Mechanically Seamed Trapezoidal Panels

For roofs that require a higher degree of performance than snap together systems can provide, MBCI Double-Lok® panels can be considered. The mechanically field-seamed, trapezoidal legs provide higher wind and water resistance with test results to satisfy UL-90, FM ratings, and Miami Dade County approvals. This makes them ideal for many industrial, commercial, and architectural roofs without hips and valleys that are subject to higher wind and rain demands. While the material cost for the panel is the same as for the Ultra-Dek®, there is more labor cost due to the mechanical field-seaming compared to the snap together installation. The Double-Lok® panel is also used often for retrofit installations over pre-existing metal roofs either to update the roof or to provide additional insulation. In either case, there is no need to disrupt the existing roofing or structure below allowing for a very cost-effective solution. Check with MBCI on the details of how to properly do a retrofit with these panels though to be sure things work out as intended.

Vertical Legs with Mechanical Seams

BattenLok
Regardless of which metal roofing type you choose, they all use high grade steel in standard gauge thicknesses and can be specified in many colors.

In cases where the trapezoidal legs aren’t appropriate or desired, then vertical leg, standing seam metal panels are the next logical choice. The MBCI BattenLok® HS system uses 2” tall legs that are mechanically field-seamed once along each panel joint to create a high strength, structural standing seam roof system that can be installed directly over purlins or bar joists – no additional solid substrate is required. It is also capable of transitioning from roof to fascia with the use of accessory seam covers.

Double Seamed Vertical Legs

In cases where very rigorous weather conditions may be encountered, the MBCI SuperLok® roof panels provide the highest degree of roof performance. While the manufactured SuperLok® roof panel is essentially the same as the single seamed BattenLok® panel, the profile is modified slightly to allow for standing seams to be rolled over twice, thus creating a stronger, thicker seal between adjacent panels. Once again, there is no difference in the material cost between the two, but the added field-seaming step will obviously add to the labor cost of this roof choice. Nonetheless, that can be a small price to pay for the higher performance and added peace of mind that the system offers.

While we have pointed out the differences between these four different metal roofing choices, note that there are some basic similarities too. They all use high grade steel in standard gauge thicknesses and they can all be specified in the same wide choice of colors. They are all offered in multiple panel widths, although check with the manufacturer to be sure the width you prefer is available for the specific panel selected. They all can be used for low slope applications down to ¼” per foot except for the retrofit solution which requires a 3:12 pitch. Finally, they all do have some minor variations in the profile which can help with the final desired appearance of the finished roof on the building.

To find out more about the differences in roof deck types and how to choose the best ones for on a metal roof that you are involved with, contact your local MBCI representative, and sign up for our newsletter to subscribe to our blog.

 

Five Retrofit Choices Using Metal Roofing Systems

Buildings usually need new or replacement roofing installed at some point during their service lives. New metal roofing is an ideal roofing retrofit option due to its longevity and durability, which can extend the life of the roofing and require fewer replacements over time. The aesthetic appearance of a new metal roof can also make a notable visual impact to upgrade the building itself.

When considering such a metal roof retrofit on an existing building, the first thing to realize is that there are a number of choices available. Here is a quick look at five of the most common ones that can be selected from and tailored to suit a particular building. Note that since all of them will add some structural loading to the roof, all the retrofit solutions should be reviewed by a professional structural engineer to be sure the existing building can accommodate the changes.

1. Double-Lok® Clip System

When an existing building has an existing PBR roof panel or similar, a Double-Lok® clip and panel system can be installed directly over the existing roof with minimal alterations. In this case, 2″ standoff clips are run from eave to ridge and fastened through the existing roofing panels down into the existing purlins. Then new standing seam metal roofing panels are installed along these clips so they are held 2″ above the purlins and 3/4″ above the major ribs of the existing panel roof. Because of these clearances, the cavity between the old and new roofs can either be vented or additional insulation can be added. Venting the cavity can be a good option when the existing roof slope is 3:12 or greater, as this allows for convective air flow during the summer and can help reduce the chance of ice damming in the winter. For any slopes of 1/2: 12 or greater, adding insulation can improve the overall thermal performance of the building. Generally, this system allows for considerable versatility, even if it takes more parts and labor than some other solutions.

2. Retrofit Roof Panels Over Existing

For cases where a standoff isn’t sought, new, non-structural metal roof panels with a specifically retrofit profile can be installed directly over existing roof panels on roof slopes of 1/2: 12 and greater. That means there is no need to tear out the old roof, since the new panels are through-fastened into the old ones and the purlins below, all in a pattern that avoids the original fasteners. Such retrofit panels are available in 29 and 26 gauge in full range of colors and come with a factory-applied vapor barrier on the underside. Even light-transmitting panels are available for this retrofit panel system.

Retrofit
5 most common choices for retrofit metal roofing systems

3. Notched Sub-Purlins

A variation on the metal-over-metal roofing approach is to use specifically designed z-purlins with notch-outs that are screwed down to the existing purlins. Unlike other systems that run retrofit support members from the eave to the ridge, the notched purlins run parallel to both (in line with existing purlins) with the notches spaced to clear the ribs or corrugations in the existing metal roofing. Profiles are available to match virtually any metal roof produced in the last 50 years. That means they can be installed over existing roofing and, in the process, provide enhanced structural capabilities because of the added sub-purlins.

4. Grid System

When an existing purlin spacing doesn’t meet current code requirements, then the use of crisscrossing hat sections in a grid pattern can provide the additional support needed. Such grid systems are designed to go directly over existing sloped roof systems but many require the use of specific metal roofing panels to work properly.

5. New Framed Roof System

In some cases, a full, steep-sloped roof (greater than 4:12) is sought to be installed over a low-slope roof (1/4:12 – 4:12). In this case, a full metal framing system is available that will create the desired roof slope and transfer the new roof weight to the existing roof deck above the existing roof structural members. As such, the coordination of the new system with the existing roofing, insulation and structure needs to be addressed by licensed engineers. Once designed and installed, an “attic space” will be created by the new retrofit roof system, which should include proper venting in accordance with applicable codes, allowing trapped moisture to escape. It is also recommended that such “attic space” be reviewed by other building, fire, or insurance-related officials for possible sprinkling or extension of existing fire walls to the bottom of the “new” roof system. Regardless, a minimum of 3″ vinyl-faced roll insulation between the retrofit panels and the retrofit purlins will help prevent condensation and roof noise in addition to improving energy efficiency.

To find out more about which retrofit options, or options, are best suited to a particular building that you are involved with, contact your local MBCI representative.

Proper Care and Usage of Roof Seamers

As more standing seam metal roofs are being installed than ever before, it is imperative for roofing contractors to have the proper tools when quoting jobs. Remember, a properly formed seam is important for aesthetics, weathertightness and wind uplift. With the right tools in hand for these complex installations, you can get the job done faster, better and with greater cost efficiency than your competitors.

Know Your Type

Seamer use depends on the type of metal standing seam panels on the project: double lock seam, symmetrical seam, one-piece snap-lock interlock and two-piece snap-lock interlock. You will need to identify the type of panel in order to choose the right seamer and confirm that you are using the right seamer for the job. The double lock seam, also known as a Pittsburgh seam, is double-folded, meaning the finishing seam is 180 or 360 degrees. This applies to MBCI’s Double-Lok® and SuperLok® panels. A single-lock seam is 45 or 90 degrees, such as MBCI’s BattenLok® HS and Curved BattenLok®.

Follow Manufacturer Instructions Explicitly

Adherence to the field manual instructions is critical to ensure proper installation that will not result in damage to the seamer and/or panels. It is critical to carefully read the manufacturer’s manual thoroughly before beginning the seaming operation, whether renting or buying the equipment. Not only will this give you the best possible result, but it can also save you the headache of incurring costs of replacing or repairing the seamer due to misuse.

Step-by-Step Guide to Pre-Seaming

  1. Locate field manual in the seamer box and review operational procedures.
  2. Locate power source and check against power requirements in field manual.
  3. Check seams for proper engagement.
  4. Clean dirt, debris and excess sealant from seams and panel surfaces to avoid interfering with the seaming operation.
  5. Panels should be seamed with an electric seaming tool as panels are being installed.

Seamer Equipment Checklist

Keys to Seaming Success

  1. The seamer should be supplied or recommended by the manufacturer. Don’t assume another manufacturer’s seamer will work on the panels you are installing. For example, other manufacturers may have a panel similar to MBCI’s BattenLok® HS but that doesn’t mean that an MBCI seamer would work on any of those panels. It is important to use the seamer recommended for the specific product. It must be the proper seam for the engineering. That is if you don’t seam it properly, the manufacturer won’t know if its load charts and tables are accurate.As previously stated, carefully read and follow seamer instructions for proper results. You will need a properly formed seam to ensure you achieve the desired aesthetics and weathertightness as well as mitigating risk from wind uplift. The seamers are miniature roll formers and need to be installed in a very specific way.
  2. Take care of the seamer—don’t leave it out in the rain or in other weather conditions where it could suffer damage.
  3. If not forming seams properly, stop immediately and call the manufacturer or company providing the seamer
  4. If renting, when returning the seamer make sure all equipment is returned, i.e. hand crimpers or hand seamers.

For more information on MBCI seamers, please review the manuals for specific panel types.

Using Wind Clamps to Improve Wind Uplift on Standing Seam Metal Roofs

Among the most important factors to account for when specifying a standing seam metal roof are wind control and wind uplift. It is imperative to take the necessary measures to ensure the safety and efficacy of the metal roof. The wind clamp—an extruded piece of aluminum that is placed on the panel seams at clip locations—is one accessory that can be used to improve wind uplift characteristics on metal roofs, delivering substantial time and cost savings as these devices help mitigate risk of wind uplift and improve overall wind design.

Panel Deflection
Standing Seam Panel Deflection as a Result of Wind Uplift

Why Use a Wind Clamp

A typical failure mode of a standing seam metal roof panel is the clip top pulling out of the panel seam when the panels are subjected to high winds.  With a standard install of a standing seam panel, the seams just fold into each other. With enough pressure, wind will force seams to come apart—be it a vertical failure, horizontal movement of the seam or from clip disengagement. The clip top can then pull out of the panel seam.

The wind clamp resists the panel seam being opened, allowing for higher uplift loads. The purpose of wind clamps, in fact, is to prevent Windclamprszdfailures at the seam openings due to any deflection of the panel. The wind clamps provide more strength, thereby dramatically improving wind uplift performance.

The clamp is installed over the panel seam at clip locations, in the edge and corner zones of the roof.  This allows the roof to resist the higher wind pressures in these zones, usually eliminating the need for additional purlins or joists. On large roofs, the savings can be substantial.

Another benefit is shorter installation time. Since additional purlins or joists are typically not required at the edge or corner zones of the roof, the building can be erected faster.

Choosing Wind Clamps

When choosing the type of wind clamp, it is important to consider the type of panel and the special features of the clamps. MBCI, for example, uses S-5!’s patented wind clamps, which work for two panel types—Ultra-Dek® and Double-Lok®. The S-5! wind clamps do not penetrate the steel, thereby eliminating the risks of corrosion and water leakage that can be introduced by a hole in the steel. Since the screws are hidden from the weather elements, it helps to maintain waterproofing.

Quantitative Difference with Wind Clamps

One of the biggest benefits of using wind clamps in the edge and corner zones is that usage minimizes the quantity of purlins needed, resulting in substantial cost savings. For example, let’s look at a comparison using MBCI’s Double-Lok 24” – 24 ga. panels with and without wind clamps.Chart for blog image

In this example:

  1. The use of wind clamps in the edge and corner zones eliminated 3,800 linear feet of purlins.
  2. Assuming 8” x 2-1/2” Zee 14 ga. purlins were used, there would be a cost savings of $10,400.

Conclusion

Utilizing wind clamps to protect the investment of a standing seam metal roof can increase strength, make installation faster and lower overall cost.

Choosing the Right Type of Standing Seam Roof (SSR)

When it comes to specifying standing seam roofs, one type doesn’t fit all. While a standing seam metal roof system can be one of the most durable and weather-tight roof systems available in the industry, its benefits can be negated if you fail to understand the details in application parameters of the specific system. Do your research, though, and for your next design that requires an aesthetically pleasing and structurally sound metal roofing system, you can choose with confidence the standing seam metal roof system that suits your project to a tee.

How to identify a good standing seam roof system

A good standing seam roof system is one that can satisfy both the project’s specific design criteria and adhere to building code standards. Standing seam profiles can include those that are utilitarian or architectural in nature, are of numerous widths and profiles and have varying seam joinery (e.g., snap or field seamed).

Why specify a standing seam metal roof system

When properly installed, standing seam metal roof systems are an extremely effective and long-lasting material choice. Key advantages include:

  • Weather-tight roofing system
  • Can be engineered to withstand high winds (150 mph and higher)
  • Class A Fire-resistance rating from UL
  • Class 4 Impact-resistance rating from UL
  • Long service life—up to 60 years
  • Lightweight
  • Special clips designed to accommodate thermal roof expansion and contraction and various thicknesses of fiberglass insulation

Matching the roof system to the project

In basic terms, there are four unique styles of metal standing seam panels: Double lock seam, symmetrical seam, one-piece snap-lock interlock and two-piece snap-lock interlock. These styles can be further delineated by seam shape or profile, i.e. trapezoidal rib, vertical rib, square rib and tee rib. The choice of the rib profile, as well as the rib spacing is generally an aesthetic preference of the designer. Knowing which style will best suit a given situation will help ensure a successful installation.

Popular Standing Seam Metal Panels

Double Lock Standing Seam
Shown: MBCI Double-Lok®

One-Piece Snap Lock Interlock Standing Seam
Shown: MBCI LokSeam®

Two-piece Snap Lock Interlock Standing Seam
Shown: MBCI Craftsman™

Some criteria to consider are roof slope, roof run (distance from eave to ridge), weather conditions (such as ice or snow) and architectural features, i.e. hips, valleys, dormers, parapet walls, etc.

For instance, if your project has a roof slope of 1/2:12 you will need to ensure the product being installed is approved for this low pitch. In this case, you would likely use a “double lock” or mechanically “field-seamed” panel. You also want to ensure that all details are able to provide for a weather-tight seal even if temporarily submerged during a heavy rain. Field-seamed panels are also the best choice in areas that experience heavy ice and snow.

Additionally, it is imperative to recognize complicated design details that should be carefully specified and reviewed regardless of the roof slope. Design conditions that require special attention include: roof transitions, dead valleys, dormers, eave offsets, ridge offsets and offsets in parapet walls.

It cannot be overstated that you should always consult a metal roofing manufacturer about the capabilities of the standing seam metal roof system, including what warranties are available, prior to specifying it.

Browse the standing seam product manual for more information.

Design and testing

Familiarize yourself with wind uplift testing as prescribed by Underwriters Laboratories (UL-90 – 580 Test) and ASTM E-1592.

For more information on standing seam metal roofing, visit MBCI’s CE course on the topic: http://www.bdcuniversity.com/standing-seam-metal-roofing

MBCI Welcomes Insurance Institute of Building & Home Safety to Witness In-House Testing

To ensure our products perform as expected, MBCI conducts a variety of tests at our onsite laboratory in Houston, Texas. On April 16, MBCI and our parent company, NCI Building Systems, welcomed several researchers from the Insurance Institute of Building and Home Safety (IBHS) to our Houston headquarters to witness ASTM E1592 testing on MBCI’s standing seam roof panel Double-Lok. This test is designed to evaluate the structural performance of a standing seam roof system under uplift loading experienced by roofs during wind events.IBHS, NCI and MBCI at MBCI Testing Facility

IBHS conducts research to improve loss prevention-related design practices and better understand the risks of insuring buildings and homes.  IBHS’s facilities include a full-scale wind tunnel in South Carolina which recently tested a 30’ wide, 50’ long building by our sister company, Ceco Building Systems, using the same standing seam roof system used in the E 1592 test.  IBHS’s researchers joined our testing to observe how manufacturers test their own products so they may develop design-related loss prevention strategies which can help reduce insurance costs for consumers of metal roofing.

NCI’s Senior Research and Development Engineer Mark Detwiler, who was present at the testing, said “[IBHS] indicated that the test they witnessed reinforced that the industry rigorously tests their roof systems. They also noted that the failure mode they witnessed was consistent with what they have seen in their loss investigations, meaning that the test yields realistic, predictable results.”

Learn more about Double-Lok, ASTM E1592 testing and IBHS and their research efforts.

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