Tag Archives: oil canning

Does 24 Gauge Steel Make Sense?

Does 24 Gauge Steel Make Sense?

Reader TED in INDIANAPOLIS writes:

In terms of longevity, long term resistance to weather damage and price difference, does a painted AZ50 galvalume R-panel with PBR-leg in 24 gauge (min. .0239″) make more sense than a 26 gauge panel?”

Mike the Pole Barn Guru answers:

In all reality, even 26 gauge steel is far thicker than you need.

American Iron and Steel Institute (AISI) has published accepted measurement standards for steel thickness. 29 gauge steel (post frame industry’s standard) has an average .0172 inch thickness (with a .0142” minimum). 28 gauge steel has an average.0187” thickness (minimum .0157”) and 26 gauge is .0217” (minimum .0187”).

These thicknesses are all measured prior to any primer or paint applications.

Steel coil is sold by steel mills or wholesalers to roll formers by weight. Roll formers sell finished formed roofing and siding by lineal foot. Roll formers make their greatest profits by ordering steel coil as close to minimum thickness as possible, as it produces more lineal footage per pound. When roll formers order steel coil, they place orders by minimum steel thickness (e.g. .0145 min would be 29 gauge).

To give a perspective on steel thickness differences, from 29 gauge to 26 gauge difference in thickness is .0045 of an inch. A sheet of 20# paper measures .0038 of an inch. Roughly speaking, thickness differences between these two gauges is about a sheet of notebook paper! In comparing minimum thicknesses, although a sheet of paper may not sound like much, 26 gauge steel is 31.7% thicker than 29 gauge, based upon minimum thicknesses.

Now more importantly – how much load will a steel panel carry? A post frame building’s “weak link” is not load carrying capacities of its steel roofing and siding, it will be found somewhere in its underlying framing system. Taking a look at span tables provided to us by Union Corrugating Company for their MasterRib® (MasterRib is a registered trademark of Union Corrugating Company) panel, when spanning 24 inches, 29 gauge will support a live load of 112 pounds per square foot (psf) and 26 gauge 150 psf. These differences equating basically straight line with thickness differences.

Unless a building is at a snow ski resort, roof snow loads are probably not going to approach 112 psf, but what about wind loads? This same 29 gauge MasterRib® panel will support 118 psf in wind load, roughly equal to 214 miles per hour! For a perspective, highest officially recorded wind speed measured in United States was 231 mph. It was logged on 12 April 1934, at New Hampshire’s Mount Washington Summit Observatory.

But, what about hail? Please read https://www.hansenpolebuildings.com/2020/11/steel-roofing-hail-dents/ and https://www.hansenpolebuildings.com/2020/11/how-to-minimize-possible-hail-damage/.

But, but – oil canning?

Oil canning is a visible, wavy distortion affecting cold-rolled metal products. It’s seen in metal panel’s flat areas, and can be characterized as a moderate aesthetic issue. Typically, rippling, waviness, or buckling is especially seen in a metal roof or wall’s broad areas.  Most popular 36 inch net coverage, through screwed, steel panels are manufactured with high ribs every nine inches and two low profile ribs in between. These low profile ribs almost guarantee no eye-visible oil canning will occur.

Bottom line is… do you need 26 gauge steel?  No, you probably really don’t.  29 gauge is going to do everything you need it to do.  When would you need 26 gauge steel?  If you are going to purchase an all steel building and have five feet between your purlins and seven feet between your girts.  On a wood framed building with half those spacings or less, it’s almost always just overkill.  Beware those who try to sell you something you don’t really need.

Avoiding Oil Canning of Standing Seam Steel Roofing


“I was talking to a contractor and he really thinks it is a big mistake to use a 26 gauge thickness vs a 24 gauge. He is stating “I will have less issue with oil canning and it will look a lot better for the extra cost over the life of the roof. I don’t think Fabral even makes a 24 gauge for this roof panel. Any thoughts to his statement?”

Mike the Pole Barn Guru says:

If I would not have recently sold our home near Spokane, Washington I would have re-roofed it with 24 gauge standing seam steel panels. This thickness was not determined by avoiding oil canning, it was a function of being able to get my color choice with Kynar paint.

Fabral Stand N Seam

Oil canning in metal roofing is an observed waviness or buckling across sheet metal panels not normally affecting a roof’s structural integrity. While sometimes caused by inferior metal or too-low-gauge thickness, too often, it is caused by under- or over-tightening of roof fasteners causing metal roofing to stretch, pull and dimple in various directions. An over-tightened fastener will pull cladding down locally and can create deformations. Generally speaking, thicker metal means less likelihood there will be oil-canning. Other causes include:
• Uneven substrate
• Width and spacing of seam
Don’t start a panel installation out of square. Leave room for thermal expansion at eaves to lessen oil canning. Most panels accommodate transverse thermal expansion by flexing of webs and by “take-up” at sidelaps. When panels are over-tightened, these relief features are hindered or eliminated, particularly for flat panels without corrugations.

Substrates are often a source of oil canning. Substrate must be made of a material, or set of materials, not adhering to metal underside or restricting metal’s normal thermal movements. Deck deviation, bows, ridges and camber all induce stress in finished panel installation. Substrate needs to be in a level plane. Make sure the substrate has no defections and shim panels when needed. Also, “slip sheets” between metal and underlayment can prevent oil canning. Some underlayments have a surface acting as a slip sheet.

Improper storing, handling, carrying and installing panels can contribute to oil canning. Twisting, buckling and other mishandling of panels can introduce oil canning into a previously flat panel.

Narrower width panels help to alleviate the appearance of oil canning. Darker colors accentuate oil canning, while earth-tone colors hide it best.

Avoiding Oil Canning With Standing Seam Steel for Barndominiums

Avoiding Oil Canning With Standing Seam Steel for Barndominiums and Post Frame Buildings

As post frame construction grows by leaps and bounds into post frame homes (barndominiums and shouses), more clients look to them for upgraded features. Standing seam roofing may appeal to some who appreciate the aesthetics of no visible screw fasteners.

Standing seam roof, or SSR as it is commonly abbreviated, has a profile of flat panels intersected with evenly spaced vertical legs or seams. Fastenings are concealed on these panels – hence why this profile is commonly called “concealed fastener”. SSRs can be attached to 5/8” plywood roof decks with a fastening flange.

Fasteners are driven into roof deck without piercing metal panels. (In order to maintain a building’s structural integrity, a plywood roof deck is required: https://www.hansenpolebuildings.com/2015/08/standing-seam-steel/). All fasteners are then hidden within standing seams. Thus, panels are locked together by snap-fit seam geometry. SSRs come in a multitude of shapes and sizes, single-folded, double-folded, T-Shaped, even Bulb-Shaped. Industry consensus favors standing seam, for its higher quality, ability to respond to “thermal cycling” and aesthetic design.

Sidebar – I am actually having our fourth generation family home outside of Spokane, Washington reroofed with SSR panels! Yes me, who has specified, sold and/or installed tens of millions of square feet of through screwed steel!

While material and finish warranties are generally equal, most standing seam systems are offered with better entire system warranties. Some manufacturers also offer extended assurance their roofs won’t leak (weather-tightness warranty) over some given period of time. Absence of exposed fastening lends itself to a much lower possibility of leakage as compared to exposed fastener systems where thousands of screw fasteners with EPDM washers are subject to installation error and because they penetrate weathering surfaces, and “pin” panels to roof purlins.

Exposed Fastener (EF) roofs involve driving screws through panels and directly into roof purlins, remaining visible. Keep in mind, properly installed these screws will never leak (https://www.hansenpolebuildings.com/2019/01/solving-steel-roofing-leaks/).

EF roofs are less expensive than standing seam systems. Lower cost comes from these panels being able to be manufactured with thinner gauge and wider-dimensioned panels, reducing material handling aspects of installation. This generally means less roofing material is needed overall and thinner panels typically cost less. Additionally, EF roofs don’t require use of expensive plywood decking and 30# felt (or an ice and snow shield) further reducing costs (i.e. fewer components, and cheaper to install so overall total cost of roof is less).

EF roofs do still offer substantial protection against harsh weather elements. But it is important to note industry standards for standing seam versus exposed fastener are not necessarily equal. So, for example, wind uplift testing may or may not have been performed on EF roof profiles. Also, don’t expect weather-tight warranties to be included. Holes are required to secure roof attachment to purlins – a process more prone to installation error. It’s not called an exposed fastener roof for nothing.

SSRs require more finesse during installation. Common exposed fastener roof panels DIY project-ready for weekend warriors.

I have always had an aesthetic complaint with SSR roofing – it oil cans. Oil canning is a perceived waviness in flat areas of steel panels. Generally “period” and “amplitude” (in layperson’s terms – frequency and size) of waves depends upon continuous width of flat portion of panel.

Mason from Metal Roofing University provides quick tips to avoid oil canning of SSRs:


As much as aesthetics are touted with standing seam roofs, this lack of hidden fasteners on roofs is still appealing to many for practical reasons. If cost, ease of installation, and a need to match it to surrounding buildings are aspects you are weighing in your decision, then EF might be a good choice.

 It is always advisable to perform routine maintenance on any roof (metal or other). One should still remove debris, clean gutters, remove stains, scan for scratches, and check for trouble-spots for potential corrosion. 

 Standing seam and exposed fastener are distinctly different concepts for metal roofing. Ultimately these two steel roofing options serve different purposes depending on location, weather, design, and more. Aesthetically-speaking and weather-wise, standing seam offers secure zero-panel-penetration as well as a long-lasting roofing solution. If cost is a big one for you, and you are also considering installing it yourself, exposed fastener may be a smart choice.