Join Us at METALCON 2022! Learn More

What is the SMI 1.5” Mechanical Seam Profile? Uses, Pros, Cons & More

Mechanically seamed metal roofing profiles have been a standard in the architectural standing seam panel industry for decades; one such mechanical seam option is the Sheffield Metals 1.5” Mechanical Seam profile. Discover the best uses, engineering, specs, and more for the SMI 1.5″ MS profile.

Mechanically seamed metal roofing profiles have been a standard in the architectural standing seam panel industry for decades. 

Not only do mechanical-lock profiles perform to the high standards that many architects, contractors, manufacturers, and homeowners desire for their project(s), but they often have excellent warranties and can be used for a variety of different applications. 

One such mechanical seam option is the Sheffield Metals 1.5” Mechanical Seam profile. Our customers frequently use this profile, but there are still many considerations to keep in mind before you specify or choose this profile. 

In the last couple of decades, Sheffield Metals has focused on offering engineered and non-engineered standing seam profiles for metal roof and wall systems. Whether your project is residential or commercial, big or small, solid decking or otherwise – we have a panel profile that will work for you.

So, let’s discuss the SMI 1.5” Mechanical Seam profile, its specifications, when to use it, and when not to use it. 

Sheffield Metals 1.5” Mechanical Seam Specifications

The Sheffield Metas 1.5” Mechanical Seam profile is known by a few different names or nicknames, including:

  • SMI 1.5” Mechanical Seam
  • SMI 1.5” MS
  • The 1.5” Mechanical Lock

Keep in mind: There are other 1.5” mechanically seamed profiles that other manufacturers offer in the market. For this article, we are ONLY discussing the Sheffield Metals 1.5” Mechanical Seam profile. Please refer to a specific manufacturer’s specifications for details on their 1.5” mechanical-lock profile options.

Panel & Seam Type

The Sheffield Metals 1.5” Mechanical Lock profile is a standing seam panel type with a mechanically locked seam. This means that the panel edges have vertical legs that line up, so the male leg goes down, then the clip goes over that leg and is fastened down. Then, the female leg of the panel goes over the clip to conceal it. All of these components are then seamed together by either a single lock (90-degree bend) or a double lock (180-degree bend). Because there are two different folding options, it’s critical that you know which is required with the engineering; though, most of the time, it’s the double-lock 180-degree seam. 

For reference, mechanically-seamed profiles usually connect/seam using a robotic seaming tool, including the SMI 1.5” MS. These robotic seaming tools give the finished roof a much cleaner, more consistent look than hand seaming tools. Installers can use these hand seaming tools; however, it will take a significant amount of time and extra labor to hand seam the entire roof to 180 degrees. 

Pro tip: Hand seaming tools work well for making 90-degree bends at the clip locations. This creates a fixed point while you’re laying down the panels so you can go back and seam with a robotic seaming tool later (per the seamer manufacturer’s instructions). Also, putting this 90-degree seam in over the clip makes it easier for the robotic seaming tool to finish the 180-degree seam.

Metal Materials 

For the SMI 1.5” Mechanical Seam profile, you can use 22 to 24-gauge steel (Galvalume) or .032 to .040 aluminum to form the panels. You can also use the same metal materials in a heavier (thicker) gauge or a narrower width panel and still have valid engineering.

Panel Width

On the 1.5” Mechanical Seam profile, the finished panel width for our engineering is 16” for both steel and aluminum panels. This specific panel requires approximately 4” of metal sheet/coil to rollform the appropriate seams and edges. If you rollform your panels and/or plan to use on-site portable rollforming, you will use a 20” coil or sheets to make the panels.

For reference, if you take the square footage of the roof and multiply that number by 1.25, it will equal the total amount of coil needed to manufacture the SMI 1.5” MS profile panels (this does not factor in waste).

Seam Height

The seam high for this profile is 1.5 inches.

Slope Minimum & Requirements

You can use the 1.5” Mechanical Seam profile on a 2/12 roof pitch or above. However, there are some particular circumstances where this profile is suitable down to a roof slope of 1/12. We’ll discuss these circumstances in detail in the “When to Use the SMI 1.5” Mechanical Seam” section of this article.

Roof Deck Substrates

For the engineering on this profile, we have tested the 1.5” Mechanical Seam assembly on plywood, b-deck (metal decking), and b-deck with ISO (polyisocyanurate insulation). This profile is not recommended for use over any open framing applications. 

Weathertight Warranties

Sheffield Metals offers optional 5 to 35-year weathertight warranties on commercial structures that use select SMI engineered profiles. The SMI 1.5” Mechanical Seam panel profile qualifies for these weathertight warranties (based on the project design).

Paint & Substrate Warranties

Both aluminum and steel SMI 1.5” MS roof systems carry a 40-year transferable PVDF paint/finish warranty (available from Sherwin-Williams). Additionally, there are substrate warranties available; warranty length, inclusions, and exclusions will vary depending on the material type. 

Installation Details

The SMI 1.5” MS profile has installation details for steel and aluminum systems over plywood, b-deck, and b-deck with ISO. Metal roof installation details provide an in-depth product guide detailing the location of components/accessories and explain the basic practical installation methods for these products at various points on the roof.

As always, make sure to follow the engineering guidelines as to what deck substrate you can install over, proper clip spacing, approved accessories, and other additional requirements.  Please visit the profile product page to download any of the 1.5” Mechanical Seam installation details.

Miscellaneous Specifications & Requirements

There are a few other key elements that are specific to the SMI 1.5” Mechanical Seam profile, including:

  • Panel surface options: Smooth or embossed (optional) 
  • Panel clip requirement(s): Required per engineering. 
    • There are multiple types of clips used for various engineering conditions with the 1.5” MS profile. The specific engineering requirements for your project will determine the appropriate clip to use; please see the individual installation details for your particular assembly.
  • Compatible S-5! attachment clamp(s): S-5-E (double lock) and S-5-S (single lock)

Metal Roofing Materials Pros & Cons Guide - Embed

Engineering, Testing, & Approvals on the SMI 1.5” Mechanical Seam Profile

Uplift Testing: UL 580 & 1897 (Standard for Tests for Uplift Resistance of Roof Assemblies)

Substrate material(s): Steel and aluminum

Deck types: Plywood, b-deck, and b-deck with ISO

Result: Pass (completed Class 90 and went on into UL 1897. During UL 1897, the system maintains a positive pressure and increases negative pressure until the system fails).

Air Infiltration Testing: ASTM E1680 (Standard Test Method for Rate of Air Leakage Through Exterior Metal Roof Panel Systems)

Substrate material(s): Steel and aluminum

Deck types: Plywood, b-deck, and b-deck with ISO

Result: Pass

Water Penetration Testing: ASTM E1646 (Standard Test Method for Water Penetration of Exterior Metal Roof Panel Systems by Uniform Static Air Pressure Difference)

Substrate material(s): Steel and aluminum

Deck types: Plywood, b-deck, and b-deck with ISO

Result: Pass

Water Submersion Testing: ASTM E2140 (Standard Test Method for Water Penetration of Metal Roof Panel Systems by Static Water Pressure Head)

Substrate material(s): Steel ONLY

Deck types: Plywood ONLY

Result: Pass 

Impact Resistance Testing: UL 2218 (Impact Resistance of Prepared Roof Covering Materials)

Substrate material(s): Steel and aluminum

Deck types: Plywood, b-deck, and b-deck with ISO

Result: Class 4 (best rating / most likely to resist surface penetrations based on testing criteria)

Fire Rating: UL 790 (Standard for Standard Test Methods for Fire Tests of Roof Coverings)

Substrate material(s): Steel and aluminum

Deck types: Plywood, b-deck, and b-deck with ISO

Result: Class A (best rating / least likely to combust or catch fire)

Florida Building Code (FBC)

Substrate material(s): Steel ONLY

Deck types: Plywood, b-deck, and b-deck with ISO

Result: Approved

Texas Department of Insurance (TDI)

Substrate material(s): Steel ONLY

Deck types: Plywood, b-deck, and b-deck with ISO

Result: Approved

UL 90 Construction Numbers

SMI 1.5″ MS UL 90 Test – Construction No. 605

  • 16″ wide 24-gauge 16 oz copper over plywood

SMI 1.5″ MS UL 90 Test – Construction No. 603

  • 20″ wide .032 embossed aluminum over plywood

SMI 1.5″ MS UL 90 Test – Construction No. 554

  • 90° seam 16” wide 24-gauge over plywood

When to Use the SMI 1.5” Mechanical Seam Profile

Low or steep-slope applications – Mechanically seamed profiles are effective on both steep-slope and low-slope roof surfaces, including the SMI 1.5” Mechanical Seam profile. While we don’t always recommend going below a 2/12 roof pitch for every project, there are low-slope scenarios and specific conditions where you can properly install this profile. If you are installing this profile below a 2/12, we require continuous in-seam sealant use to keep the seam as water-tight as possible.  

Your roof system is/needs to be hydrostatic – Going along with slope factors is the term “hydrostatic,” which refers to panel systems that are a 3/12 slope or less and are designed to hold water and drain slower. Hydrostatic systems have a higher potential to become submerged as the water moves slowly off the roof surface. This is why it’s critical to protect against water intrusion, which you get with the SMI 1.5” Mechanical Seam profile (it’s tested to ASTM E2140 water submersion standards). Keep in mind, your roof system must adhere to the manufacturer’s details and recommendations, which often includes sealant in the seams and an ice and water shield synthetic underlayment.

You want a commercial weathertight warranty – One common reason that architects specify and contractors install the 1.5” Mechanical Seam profile is that it qualifies for our commercial weathertight warranties (limited and no dollar limit weathertight warranty options available). If your project is commercial, you’re likely already spending a significant amount of money on your new standing seam metal roof. That’s why we strongly recommend looking into protecting your investment with a weathertight warranty.

You want or need to install an engineered metal roofing system – One reason the SMI 1.5” Mechanical Seam is so popular is that it’s engineered, tested, and proven to perform on numerous roof deck assemblies (plywood, b-deck, and b-deck w/ISO) with different materials (steel and aluminum).

Your project is residential or commercial The SMI 1.5” MS system is often installed on both residential and commercial projects, which further adds to the versatility of this profile.

When NOT to Use the SMI 1.5” Mechanical Seam Profile

If you don’t have a robot or hand seaming tool – As we discussed, this profile requires seaming for the panels to be engaged and secured to the deck. If you don’t have access to a robotic seaming tool, if you don’t have a hand seaming tool, or are physically unable to seam the panels together, do not specify or install the 1.5” MS profile. 

(Note: If you are looking for seaming tools, we recommend renting or buying the equipment through our partners at Quality Roof Seamers.)

Over open framing – We do not recommend installing the 1.5” Mechanical Seam profile over an open-framed roofing structure (without a solid roof deck). However, there are still standing seam profile options available for use over open framing, including the Sheffield Metals 2.0” Mechanical Seam

You have a limited budget – Due to the seaming requirements for this profile, there is additional labor required, which means it will likely be more expensive. Plus, the seaming tends to take longer and can raise the price due to more time requirements.

You’re a DIY home/building owner installing your roof – There are some metal roofs (mostly metal shingles) that skilled DIYers can typically install, but the SMI 1.5” Mechanical Seam is not one of them. This profile requires a roofing professional to do the rollforming, installing, and seaming, which is often beyond the capabilities of most DIYers. And when it comes to something as critical as a roof, it’s often not worth the risk, as a roof failure could cause significant damage to a structure and property. 

Completed Project(s) Using the SMI 1.5″ MS

Final Thoughts on the SMI 1.5” Mechanical Seam Standing Seam Profile

The Sheffield Metals 1.5″ Mechanical Seam isn’t the only mechanically locked profile that we offer, but it remains a popular option for architects to specify and contractors to install on their projects.

In this article, we discussed the specifications, engineering/testing, and use cases for this profile. However, if you’re still trying to decide between the 1.5″ MS or another profile, you can better understand which one is best for you by asking yourself these questions:

  • What is the pitch of my roofing structure?
  • Is my project commercial or residential?
  • Do I want/need an engineered metal roofing system?
  • Do I want/need a weathertight warranty?
  • What is the roof deck substrate material?
  • Is this roof being installed by a professional? DIYer?
  • Will the installer have access to a seaming tool? Can they rent one?
  • How much do I want to spend?
  • Is my budget flexible? Am I able to cover added labor or material costs?
  • How long and wide do I want/need the panels to be?

Here at Sheffield Metals, we provide our customers with everything they need to successfully specify and install a standing seam metal roofing, including profile engineering, materials, instructions, details, and technical support. That’s why we offer a variety of tested and proven panel profiles, including the SMI 1.5″ Mechanical Seam, designed to meet your project requirements.

To learn more about the 1.5″ MS or any of our panel profile options, please contact one of our experienced technical representatives today.


Contact Sheffield Metals today!