By The Roofing Brief Team. Last reviewed: August 2026.
Metal roof expansion and contraction is a number you calculate before the first panel goes up, not a vague risk you hope the system absorbs. A 40 foot steel panel run moves about 5/16 inch across a 100°F swing in panel temperature. Aluminum moves about 5/8 inch, copper about 15/32 inch. Those figures decide your clip type and whether the slope needs an expansion joint.
The formula that governs metal roof expansion and contraction
Thermal movement follows one equation: change in length equals the coefficient of linear thermal expansion times the original length times the change in temperature, or ΔL = α × L × ΔT. Wiss, Janney, Elstner Associates states it in exactly that form. Length must be in inches if you want inches out, and ΔT is the change in panel temperature, not air temperature.
That last distinction is where most estimates go wrong. Panel surface temperature is driven by solar gain, not the thermometer on the porch. The Copper Development Association notes that exposed copper can run 70 to 80°F or more above surrounding ambient air.
The Metal Construction Association puts hard numbers on the cycling in its Standing Seam Roof Clips Best Practices Guide (2017, reviewed April 2022): panel temperatures “may range more than 200°F in a season, 150°F in a single day, and 100°F within minutes as cloud cover inhibits direct sunlight and a cool rain begins.” A 100°F swing is not the worst case. It is closer to an afternoon.
Coefficient of linear thermal expansion for roofing metals
The coefficient (α) is the per-degree stretch of one inch of material. Steel sits near 0.0000065 in./in./°F, aluminum near 0.0000128, and copper near 0.0000098. Aluminum moves roughly twice as much as steel for the same temperature change, which is the single most consequential material fact in this whole subject. The table below converts each coefficient into movement you can measure with a tape.
| Material | α (in./in./°F) | Move per 10 ft at 100°F | 40 ft run at 100°F | 40 ft run at 200°F |
|---|---|---|---|---|
| Galvanized or Galvalume steel | 0.0000065 | 0.078 in | 0.312 in (about 5/16 in) | 0.624 in (about 5/8 in) |
| Aluminum | 0.0000128 | 0.154 in | 0.614 in (about 5/8 in) | 1.229 in (about 1 1/4 in) |
| Copper | 0.0000098 | 0.118 in | 0.470 in (just under 1/2 in) | 0.941 in (about 15/16 in) |
Coefficients for steel and aluminum are as published by Metal Sales Manufacturing Corporation. The copper value of 9.8 × 10⁻⁶/°F is the figure given by the Copper Development Association and by Revere in Copper and Common Sense. Zinc and stainless also move more than steel, and rolled zinc behaves differently along the rolling direction than across it, so pull those values from the specific mill data sheet rather than a generic chart.
Why the coefficient is not actually a constant
Published coefficients are averages over a stated temperature range, and the real value drifts with temperature. Jeffrey S. Levine of Wiss, Janney, Elstner Associates documented this for copper: SMACNA’s Architectural Sheet Metal Manual lists cold-rolled copper at 0.0000094 in./in./°F, while the CDA and Revere both give 9.8 × 10⁻⁶/°F, a value the CDA qualifies as applying between 68°F and 572°F.
Levine recalculated the average across the range a real building actually sees, minus 45°F to 155°F, and got 9.2 × 10⁻⁶/°F. His conclusion is the useful part: the practical effect on design is negligible, because the handbook value of 9.8 is the conservative one. Designing to a published coefficient overestimates movement slightly at roofing temperatures, which is the direction you want the error to run.
Worked example: a 40 foot panel run across a 100°F swing
Take a 40 foot panel, fixed at the eave, free at the ridge. Convert to inches (40 × 12 = 480), then multiply by the coefficient and the temperature change. Steel gives 480 × 100 × 0.0000065 = 0.312 inch. Aluminum gives 0.614 inch. Copper gives 0.470 inch. All of that movement shows up at the ridge end, because that is the only end free to move.
Double the swing to the 200°F seasonal range the MCA describes and steel reaches 0.624 inch, copper 0.941 inch, and aluminum 1.229 inch. An aluminum run that short is already asking a clip for more than an inch of travel. That is why the choice between aluminum and steel roofing is a detailing decision as much as a cost or corrosion decision.
The 1/8 inch per 10 feet rule of thumb, checked against the math
A common shop rule, cited in Metal Construction News, budgets about 1/8 inch of thermal expansion for every 10 feet of panel length, so an 80 foot panel gets one full inch. Run that backward through the formula and you can see exactly what the rule assumes.
- Steel: 0.125 ÷ (120 × 0.0000065) implies a 160°F panel temperature swing. Reasonable for a dark steel roof in a continental climate.
- Aluminum: 0.125 ÷ (120 × 0.0000128) implies only an 81°F swing. That is less than a single hot day of cycling.
The rule of thumb is a steel rule wearing no label. Applied to aluminum it can under-predict movement by a factor of two, which is enough to bottom out a sliding clip and buckle a panel. Calculate aluminum runs; do not estimate them.
When a fixed clip is acceptable and when you need a floating clip
Fixed (one-piece) clips are generally acceptable on mechanically seamed runs under about 30 feet, where accumulated movement stays near or below a quarter inch. Beyond that, two-piece sliding clips carry the movement inside the clip instead of forcing it into the seam, the fastener, or the panel. Western States Metal Roofing draws the line at 30 feet, and many manufacturers also prescribe floating clips on any slope run over 100 feet.
| Factor | Fixed (one-piece) clip | Floating (two-piece sliding) clip |
|---|---|---|
| Construction | Single piece, fastened to substrate, engages the panel leg | Base fastened to substrate, upper hook seamed to the panel, the two slide against each other |
| Where movement goes | Into flexure of the clip and the structure | Into the slotted interface between the two clip halves |
| Typical run length | Under about 30 ft (mechanically seamed) | Over about 30 ft, or any slope run over 100 ft |
| Movement capacity | Minimal and undefined | Defined and published, but finite |
| Failure if undersized | Seam distortion, clip damage, fastener distress | Clip bottoms out, then behaves like a fixed clip |
The MCA is direct about the consequence of skipping the arithmetic. A clip analysis “will determine the adequacy of clip travel and the movement capacity versus the maximum degree of expected longitudinal expansion/contraction. Lack of attention in this area can lead to panel buckling, clip damage, fastener distress and objectionable noise to room side.” Oil canning is the mild version of that list. Structural distress is the expensive one.
A one-piece clip is not automatically a fixed clip
This is the detail that trips up specifiers reading a submittal. Per the MCA guide, when a one-piece clip is used with a snap-fit seam, the clip “engages the panel in such a way that allows the panel to move along the clip axis inhibited only by minimal friction.” The panel slides over the clip, so the connection is not fixed at all.
What makes a one-piece clip fixed is the seaming operation. When the seam is machine-folded around the clip, the MCA notes the connection is fixed and “allows for only minimal differential movement.” So the same clip part number can be a sliding connection on a snap-lock profile and a rigid one on a mechanically seamed profile. Read the seam type, not just the clip type.
Where the point of fixity goes
Every panel run needs exactly one anchored location. The MCA is explicit that panels “must be adequately fixed to the building structure at a single location” using fixed clips or a positive screw-fastened point of fixity, both to control which way the panel travels and to keep panels from migrating down the slope under snow, foot traffic, and gravity.
Where that point sits is where published guidance genuinely splits, and it tracks the type of roof:
- Structural standing seam over open framing, low slope: Building Research Systems places the line of fixity at the low eave, with panels expanding and contracting toward the ridge.
- Architectural sheet metal, steeper slopes: Stortz recommends moving fixed cleats up near the ridge on steep pitches and letting expansion run down toward the eave, on the reasoning that movement tends to follow gravity. On low pitches Stortz puts fixed cleats at the panel center with expansion cleats toward both ridge and eave.
Center fixity is worth understanding even when you do not use it, because it halves the problem. A 40 foot run fixed at its midpoint accumulates only 20 feet of movement in each direction, so the aluminum case drops from 1.23 inch at one end to about 0.61 inch at each end. Follow the specific system manufacturer’s manual, since the fastening pattern that resists drag loads is engineered around their chosen fixity location.
When a metal roof needs an expansion joint
An expansion joint is required when accumulated movement exceeds what the clips can absorb, or when the structure beneath the roof has a joint of its own. Building Research Systems states the structural rule plainly: if the structural system is long enough to require an expansion joint, the panel should include an expansion joint at that location. A roof panel cannot bridge a building that is moving underneath it.
The panel-driven trigger is arithmetic. Work through these in order:
- Measure from the point of fixity to the far end of the run, not the total panel length. If fixity is at the eave on a 60 foot slope, the design length is 60 feet. If fixity is at midspan, it is 30 feet in each direction.
- Pick a design temperature range for the panel. The MCA cites more than 200°F seasonally and 150°F in a day. The CDA’s Larry Peters uses a 175 to 200°F range for copper design calculations. Dark finishes push toward the high end.
- Calculate ΔL = α × L × ΔT using the coefficient for the actual metal, not a generic steel value.
- Compare ΔL against the published travel of the specified clip. If the movement exceeds it, you have four fixes: shorten the run, move fixity to midspan, specify a longer-travel clip, or add an expansion joint.
- Check every terminal detail for accidental pinning. Ridge cap, rake and gable trim, curbs, and end laps must all let the panel slide. PAC-CLAD’s guidance is to allow thermal movement at ridge, eave and transitions, and never rigidly fix both ends of a long panel.
Sizing the joint itself uses the same number split in half. The CDA’s worked copper example takes a 20 foot panel across 200°F, calculates 0.47 inch of total potential movement, and sets the joint gap dimension at 1/4 inch, roughly half the total, because the panel has to be able to close as well as open.
Install-day temperature decides how you preset the clip
Total movement range and required travel in one direction are different quantities. A panel installed at the midpoint of its service temperature range needs roughly half the total movement available in each direction. A panel installed on a 20°F January morning needs nearly all of it as expansion, and a panel installed on a 140°F August roof deck needs nearly all of it as contraction.
The MCA notes that some two-piece clips carry an integral centering device specifically to prevent an installation where the traveling hook element is bottomed out at the time of installation, which would eliminate travel in one direction and cause in-service jamming. On a hot or cold install day, offsetting the hook against that centering position is the point of the exercise, and the manufacturer’s manual should state the offset.
How fastener slotting relates on exposed fastener panels
Through-fastened panels do not eliminate thermal movement; they redirect it into the fastener holes. Because the screw pins the sheet at every fastener, the hole elongates around the shank over thousands of cycles. The industry term is slotting. Once the elongated hole grows larger than the sealing washer, the fastener stops sealing and the roof leaks at a point that looks tight from the ground.
That mechanism, not uplift capacity, is the reason common guidance recommends standing seam systems for panel runs of 40 feet or greater, and why Metal Sales describes direct-fastened systems as commonly limited to 60 to 80 foot runs while clipped standing seam can accommodate 150 foot runs or more. The tradeoffs between the two families are covered in our comparison of standing seam versus exposed fastener metal roofs.
Three detailing rules follow directly from the slotting mechanism:
- Screw in the flat, not the rib. A long unsupported screw shaft passing through a rib is loaded in bending by every thermal cycle and eventually snaps. Nearly all manufacturers specify the flat between ribs.
- Do not overdrive. A crushed washer has less overlap to lose before slotting defeats it, and the sealing surface fails long before the withdrawal connection does. Withdrawal capacity itself is a separate question, covered in our guide to metal roof screw pull-out strength.
- Use slotted or oversized holes where the panel meets fixed metal. End laps and trim connections are where movement concentrates, and a round hole tight on the shank there converts panel movement straight into fastener stress.
Putting the numbers into a specification
Thermal movement changes three line items on a metal roof submittal: the clip type and its published travel, the location of the point of fixity, and whether an expansion joint appears on the slope. Everything else on the roof follows from panel length and material, which is why the panel length decision and the movement calculation belong in the same conversation.
For the ordering side of that decision, including transport limits and cut-to-length practice, see our breakdown of metal roofing panel lengths. For how clips fit alongside decking, underlayment, closures, and trim, see every part of a metal roof system named. And because the coefficient gap is the whole story, the material choice covered in aluminum versus steel roofing effectively doubles or halves every number on this page.
One practical caveat on all of it: Building Research Systems reports that measured field movement tends to run roughly 20 percent below theoretical because of friction and clip binding. That is a margin, not a design allowance. Size to the calculated number and let the friction be the safety factor.
Frequently asked questions
How much does a metal roof expand and contract?
A 40 foot panel run moves about 0.31 inch in steel, 0.47 inch in copper, and 0.61 inch in aluminum across a 100°F change in panel temperature. Across the 200°F seasonal range the Metal Construction Association describes, those figures double to roughly 0.62, 0.94, and 1.23 inch. Movement scales directly with both run length and temperature swing.
What is the coefficient of thermal expansion for roofing metals?
Steel is about 0.0000065 in./in./°F and aluminum about 0.0000128, per Metal Sales. Copper is 0.0000098 per the Copper Development Association, though SMACNA lists cold-rolled copper at 0.0000094. Aluminum expands roughly twice as much as steel for the same temperature change, so a detail that works in steel may not work in aluminum at the same run length.
At what panel length do you need floating clips?
Western States Metal Roofing recommends two-piece floating clips on mechanically seamed panels longer than about 30 feet, and fixed clips below that. Many manufacturers also require a floating clip system on any roof plane with a slope run over 100 feet. The governing check is whether calculated movement exceeds the published travel of the specified clip.
Where should the fixed point be on a standing seam roof?
Every run needs exactly one fixed location, and guidance varies by roof type. Building Research Systems places the line of fixity at the low eave for structural standing seam over open framing. Stortz recommends fixed cleats near the ridge on steep architectural slopes so movement follows gravity, and at the panel center on low pitches. Follow the panel manufacturer’s manual.
Does a metal roof need an expansion joint?
An expansion joint is needed when calculated movement exceeds the clip travel available, or when the structure below carries an expansion joint of its own. Building Research Systems states that if the structural system requires an expansion joint, the panel should include one at that location. Shortening the run or moving fixity to midspan can sometimes avoid the joint entirely.
Why does a metal roof make popping or ticking noises?
Those sounds are panels sliding against clips and fasteners as temperature changes, usually loudest during rapid swings such as morning sun or a cool rain on a hot roof. The Metal Construction Association notes panel temperatures can shift 100°F within minutes under those conditions. PAC-CLAD reports the noise typically diminishes as the assembly settles into its cycling.
What is slotting on an exposed fastener metal roof?
Slotting is the elongation of a screw hole caused by the panel expanding and contracting against a fastener that pins it in place. Each thermal cycle enlarges the hole slightly. When the elongated hole grows wider than the sealing washer, the fastener stops sealing and the roof leaks, which is why long runs favor clipped standing seam systems.