Single Lock Vs. Double Lock Standing Seam

Thomas Szkutak
Jul 21, 2025
4 min read

Mechanically Seamed Metal Roofs

Mechanically seamed metal roofs consist of roof panels with a concealed fastener standing seam system. They are designed with clips that line up with one another so they can be locked together by a mechanical or hand seamer. The way the panels are fastened together makes the roofing more weather resistant and less likely to have any leaking issues.

These panels can use one of two locking systems: single lock or double lock.

Single Lock Standing Seam

A single lock refers to the seams of the panel being folded once (90 degrees). A single lock system is an easier installation that is best suited for milder climates as it is not as weather tight as double lock.

Advantages Of Single Lock Standing Seam

Faster And More Affordable Installation

The biggest advantage of a single lock system is that less labor is required so your installation goes faster. You’ll find the installation costs to be less for a single lock system as less work is required.

Easier Repairs

A less time-consuming installation is also beneficial if there are problems with your roof in the future. A single lock system makes it easier to replace a damaged panel.

Double Lock Standing Seam

A double lock system features seams that are folded twice (180 degrees). These panels are more labor-intensive with higher installation costs. However, they are also more commonly used. Double Lock Systems are more secure, weather tight, and have an overall better performance over a single lock system.

Advantages Of Double Lock Standing Seam

Compatible With Low Slopes, Is your roof almost flat?

Roofs with low slopes (less than 2:12) require extra weather resistance since they are more prone to water accumulation. As a result, the single lock system and double lock system should always be used with any roof under 2:12 pitch up to .5:12 or greater with in-seam sealant. They will provide extra weather tightness which works well with low slope roofs where it is harder for water to run off.

Standing seam panels can be made with seam heights of 1”, 1.5” or 2”. If you like the look of standing seams, we recommend a higher height as it makes the appearance of the seams more pronounced.

As you’ll see below, the higher the height, the lower your roof pitch will need to be.

2-inch double lock profile: Can be installed on a .5/12 pitch or greater with in-seam sealant.
1.5-inch double lock profile: Can be installed on a 1/12 pitch or greater with in-seam sealant.

If you’re not sure what your roof pitch is, we recommend reading our blog on how to determine roof pitch.

More Weather Tight Fit

Double lock panels provide you with better performance as they are more secure and weather tight. By being folded twice, the panels are seamed tightly together and do not have any potential entrances for water to seep through that would result in leaking.

Higher Quality Performance

The double lock system also decreases the chances of your seams coming undone. By having the two seams instead of just one, it makes the panels hold firmly in place.

Durable In Freezing Temperatures

The double lock system is the preferred standing seam roofing choice in cold climates such as snow country. This is because metal will expand and contract in the freezing temperatures. The extra secure fit of a double lock system will keep the panels from coming undone and it will also keep out any moisture from melting snow on your roof that could cause leaks.

Double Lock Standing Seam Tools

Whether you choose a single lock or double lock, both mechanically seamed connections require a tool for installation. Some contractors will use a mechanical seamer, while others choose to work with a hand seamer for panel seaming. Part of the longer installation process of mechanically seamed roofs is that every clip needs to be hand seamed on the entire roof on every panel prior to using a seaming machine.

The quality of your standing seam roof’s performance is dependent on its installation. Like with any roofing material, a poor installation will lead to problems in the future. Both tools bring quality results if the roofing professional is experienced with standing seam installations. When choosing a roofing professional to do the installation, be sure to ask about the contractor’s experience, specifically installing mechanically seamed metal panels.

Mechanically Seamed Standing Seam

There are multiple parts of a Mechanically seamed roof that contribute to its total cost including:

Accessories
Trim
Underlayment

These parts will be an additional expense. Every project is different and will require different trim pieces and quantities.