# Do Post Frame Barndominiums Need 26 Gauge Steel?

Through Screwed Steel Roofing for Post Frame Barndominiums – What Gauge?

If I need to have major surgery, I am probably not going to ask for expert opinions on social media. However apparently, when it comes to construction expertise, Facebook is where to go. Always plenty of armchair engineers, semi-educated builders and competing structural systems to throw out their two bits worth.

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 thickness of .0172 of an inch (with a minimum of .0142). 28 gauge steel has an average thickness of .0187 (minimum .0157) and 26 gauge is .0217 (minimum .0187).

These thicknesses are all measured prior to application of any primers or paint.

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 the 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, the 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? The 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 the United States was 231 mph. It was logged on 12 April 1934, at New Hampshire’s Mount Washington Observatory at the summit.

But, but – oil canning?

Oil canning is a visible, wavy distortion affecting cold-rolled metal products. It’s seen in flat areas of metal panels, and can be characterized as a moderate aesthetic issue. Typically, rippling, waviness, or buckling is especially seen in the broad area of a metal roof or wall.  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 5 feet between your purlins and 7 feet between your girts.  On a wood framed building with half those spacings or less, it’s almost always just overkill.  Beware of those who try to sell you something you don’t really need.

# Galvanized Steel Coil

Before Steel Coil Can Be Coated

I think far too often we take for granted the many processes companies spend lots of time and resources (not to mention money) to give us products with features we come to take for granted.  Like making sure metal such as steel does not rust and corrode after years of use.  Before steel can even be painted, it goes through a series of steps to ensure the coating (painting) process is top of the line.  And not just for today, but for many years down the road.

Unprotected steel corrodes quickly as oxidation activity consumes the metal, but this process is preventable by protecting the steel from water and oxygen, thus interrupting the oxidizing action. Surface coatings such as paint are permeable to water and oxygen and eventually permit rusting. Hot-dip galvanizing, however alloys molten zinc to steel metallurgically and forms an impenetrable barrier to water and oxygen. The zinc coating, which is much more durable than painted coatings which often chip during assembly or exposure to the elements, then acts as a sacrificial anode protecting the steel from rust and corrosion, even if the surface has been damaged. Unpainted galvanized steel parts can last 25 years or longer without maintenance.

Galvanized steel coil is defined as a carbon steel sheet coated with zinc on both sides. Continuous hot dipping, or electro-galvanizing are the two processes used to produce both galvanized sheet steel and steel coil. Generally speaking, the hot dip process consists of passing the steel through a bath of molten zinc. The electro-galvanizing process consists of the application of zinc by electrolytic disposition. The result is a layer of zinc tightly adhering to the base metal through an iron-zinc bonding layer.

Continuous hot dipping is the process used in the application of zinc to steel coils which will later be roll formed into steel roofing and siding.

A zinc coating is one of the most effective and economical methods of protecting bare steel from a corroding environment. The zinc not only serves as a barrier between the steel and the environment, it will sacrifice itself to protect the underlying steel sheet. Sacrificial, or galvanic protection occurs when two dissimilar metals are in contact and coupled with water and oxygen. Zinc corrodes preferentially to the iron in steel. This protection prevents corrosion of the steel at areas not covered with zinc. Thus, the spread of corrosion from cut edges, drill holes, etc. is minimized.

Hot-dipped Galvanized products are manufactured to ASTM A-653 specifications, and are available in a variety of coating weights such as G-90, G-60, G-40, and G-30. With galvanization, the larger the “G” value, the thicker the zinc coating is. For related reading: https://www.hansenpolebuildings.com/blog/2014/02/steel-siding-2/

Typical applications for Galvanized Steel Coil and Sheet products include exterior building products (like steel roofing and siding for pole buildings), ductwork, HVAC products, flashing, electrical boxes and other electrical products, roofing, doors, sashes, automotive parts, appliances, commercial and residential steel framing, truss plates (read more on truss plates here: https://www.hansenpolebuildings.com/blog/2011/10/metal-connector-plates-have-teeth/ ), metal building purlins, and any other products requiring a corrosion resistant material.

Once the galvanized steel is protected, it moves on to the painting process – so stay tuned for tomorrow’s blog to learn the many magical steps of steel coil coating.