How a standing seam roof goes together
Clips hold, folds join, and the panel slides. Understanding those three is most of the system.
Clips hold, folds join
Each panel has an upstand at both edges. A concealed clip is fixed to the deck and engages the upstand of one panel; the next panel's upstand hooks over it, and the two are then folded together into a raised seam that stands above the water line.
Nothing is screwed through the panel face, so there is no penetration to seal and none to fail. That single property is why standing seam is used on low pitches and long runs where a screwed sheet would leak eventually.
- No face fixings
- Nothing penetrates the water plane. That is the whole reason to use the system.
- Clips carry the panel
- Fixed to the deck, engaged by the upstand. The panel is never fixed directly.
- The seam stands above the water
- A raised fold, so water in the pan never reaches the joint even at low pitch.
- Single or double lock
- One fold for lower exposure, two for higher. Double lock is the weatherproof one.
Closing a seam in stages
A seam is never closed at one point and then along its length. Each stage is worked the whole way down the panel before the next begins: hook the upstands, close to a single fold along the full run, then return and close the double.
Working point by point pulls the panel out of line, because closing a fold shortens the upstand slightly and that has to be taken up evenly. A panel closed unevenly ends up bowed and the next panel then will not sit.
- Whole length per stage
- Single fold all the way, then double all the way. Never finish one point completely.
- Start at the eaves
- Work up the slope so any accumulated length runs out at the ridge where it is detailed.
- Check the panel line
- Every few metres against a chalk line. A seam pulls the panel, and small errors compound.
- Hand tools before a machine
- A seaming machine follows a seam already started by hand. It cannot begin one.
The panel must be able to slide
A long metal panel expands and contracts noticeably between a cold night and a sunny afternoon. On a 10 metre run that movement is several millimetres, and if the panel is fixed at both ends it has nowhere to go, so it buckles between the seams.
Sliding clips exist for exactly this. The panel is fixed positively at one point, usually the ridge or the eaves depending on the system, and slides at every clip along its length. Substituting a fixed clip for a sliding one is a common and expensive mistake.
- Fixed at one point only
- Ridge or eaves, depending on the system. Everywhere else the panel slides.
- Sliding clips on long runs
- They have a movable tab. Fitting a fixed clip instead is what buckles a panel.
- Millimetres matter
- Several on a 10 metre run. Enough to buckle a pan visibly and permanently.
- Detail the ends for movement
- The eaves and ridge details must allow the panel to grow into them, not restrain it.
Ends, ridges and penetrations
The seam itself is straightforward compared with what happens at each end of it. At the eaves the pan is turned down and hooked over a drip; at the ridge it is turned up so water cannot run back. Both are folded, not sealed.
Penetrations are the awkward part, because the system's whole virtue is not having any. Anything through the roof needs a curb formed and flashed with folded metal, which is skilled work, and it is the detail that fails when it is done with sealant instead.
- Turn the pan, do not seal it
- Down at the eaves over a drip, up at the ridge. Folded metal, not mastic.
- Close the seam ends
- The seam is folded over or fitted with a closure at each end, or wind drives water into it.
- Curb every penetration
- A raised curb flashed with folded metal. Sealant around a pipe through a pan will fail.
- Sealant is a backup, not a joint
- Every detail here should work with the sealant removed. If it does not, it is the wrong detail.
Protecting the finish
Standing seam panels are usually coated steel, aluminium, zinc or copper, and all of them show damage permanently. A steel hammer face, a dropped tool, a stone under a panel or a footprint on an unsupported pan all leave a mark that stays for the roof's life.
So the forming tools are nylon and hardwood faced, the panels are set down on battens rather than on the ground, and the film on prefinished panels is left on until as late as possible in the work.
- Nylon and wood faces only
- A steel hammer prints every blow into a coated or soft metal panel.
- Leave the protective film on
- Peeled as late as possible, and always before it bakes on in the sun.
- Set panels on battens
- One stone under a panel dents it, and the dent is visible from the ground forever.
- Walk in the pan, on a board
- Never on a seam, and never on an unsupported pan. Both deform permanently.
Frequently asked questions
- What tools do I need for a standing seam roof?
- Hand seamers and folding tongs to close the seam, a clip setter or driver for the concealed clips, a portable bending brake or panel folder for the pan ends, snips and a nibbler for cutting, a chalk line, and a nylon mallet. A seaming machine speeds up long runs.
- How does a standing seam roof stay watertight without fixings?
- The panels are held by concealed clips fixed to the deck, and joined by folding their upstands together into a seam that stands above the level water reaches in the pan. Because nothing penetrates the surface, there is no fixing hole to seal or to fail.
- What is the difference between single and double lock seams?
- A single lock is one fold closing the two upstands together, suitable for steeper pitches and lower exposure. A double lock folds again so the seam wraps twice, which is far more weathertight and is the standard for low pitches and exposed positions.
- Do I need a seaming machine?
- Not to make a seam, but it saves a great deal of time on long runs. A machine follows a seam that has already been started by hand, so hand seamers are still needed for the start, the ends and any detail the machine cannot reach.
- What are sliding clips for?
- They let the panel expand and contract along its length while still holding it down. A long metal panel moves several millimetres between a cold night and a hot afternoon, and a panel held by fixed clips at both ends has nowhere to go, so it buckles between the seams.
- Can I walk on a standing seam roof?
- In the pan and preferably on a board, never on a seam. An unsupported pan deforms permanently under a foot, and standing on a seam distorts the fold and can open it. Where regular access is needed the roof should have walkway provision designed in.
- How are penetrations handled on a standing seam roof?
- With a raised curb formed and flashed in folded metal, so the detail sheds water by shape rather than by sealant. Anything relying on mastic around a pipe through a pan will fail, because the panel moves and the sealant does not.
- Why are the forming tools not steel faced?
- Because a steel face prints permanently into coated steel, zinc, copper and aluminium, and those marks are visible from the ground for the life of the roof. Nylon, hide and hardwood move the metal without marking the finish.
