Address moisture control in metal buildings

The right insulation system in metal buildings can prevent dire consequences

By William Lotz, P.E. and Joseph Haugh February 4, 2021

Metal buildings are built of metal; usually galvanized steel or galvalume – a combination of steel and aluminum. The first metal buildings date back to the beginning of the twentieth century when they were used to store Ford Model-T cars. Some of the earliest companies pioneering metal buildings were Butler Manufacturing Co., Austin Co. of Cleveland and Liberty Steel Products of Chicago.

The Metal Building Manufacturers Association (MBMA) estimates that 14 million metal building have been constructed over the past 80 years. The MBMA also estimates that 35% of low rises are built of metal.

Metal buildings have many advantages as well as disadvantages. The biggest single advantage of metal buildings is their ability to span longer and wider dimensions and thereby serve a specific commercial purpose. Most metal buildings are built in a repetitive pattern. This accounts for the popularity of metal buildings in commercial occupancies. For disadvantages, the most common single disadvantage is the variable construction quality between different manufacturers; especially when it comes to insulation systems.

Inattention to moisture control is a problem in metal buildings. Neglect will lead to corrosion, internal “raining” of rusty water in your facility, thermal inefficiency, high energy bills, structural instability, mold and “ugliness.”

How does a moisture problem start in a metal building? It starts by condensation. This occurs most frequently in northern climates during the winter season.

Condensation ensues when the warm air inside a metal building ceases to carry any further moisture. The moisture is impelled to move outside but finds no natural way out. So instead, moisture sneaks into the cold walls of the metal building — as is the case with most metal buildings lacking the proper insulation and vapor barrier — and condenses into water droplets.

Metal buildings, in the long run, are never fond of these water droplets. Water starts to eat away at the metal, causing corrosion, erosion and structural failure — not to mention mold. It’s for sure not a healthy environment.

Plants requiring moisture content

The consequences outlined above are even more accentuated when the activity inside a commercial facility produces additional moisture. This is typical in recycling, food processing, wastewater, lumber kiln-drying, grain-storage and other type facilities. In reality, any facility whose operations entail dealing with materials that originally had high water content or processing that involves significant amounts of water is a perfect candidate to moisture problems.

The truth is that any facility or building that has greater than 30% relative humidity in 4000-heating degree days climates is highly susceptible to moisture problems. This corresponds roughly to those northern climates that lie north of an imaginary line drawn between Saint-Louis and Washington D.C.

A heating degree day is a measurement designed to quantify the demand for energy needed to heat a building. It is the number of degrees that a day’s average temperature is below 65°Fahrenheit, which is the temperature below which buildings need to be heated.

Is there a solution to condensation problems? Yes, by modifying the industrial process to produce less moisture and by lowering the chances of water condensation.

However, modifying an industrial process is ever rarely doable. For instance, in a granite-cutting mill, an owner used 10,000 gallons of water a day to cool the huge saw blades used in “slicing” the granite. There was no viable alternative to this arrangement.

It’s true that ventilation can control moisture. Nonetheless, ventilation necessitates a building designed to deal with moisture, and costs more in the long run than does durable, properly installed insulation having a vapor barrier.

Other examples of industrial facilities that require high moisture content are feminine hygienic products plants, cigarette manufacturing facilities, and hospitals. Each of these milieus need at least 80% humidity to pursue production.

Another “universal” cause of moisture in metal buildings (or, for that matter, any building) is direct-fired heaters. Direct-fired heaters are ubiquitously used to heat metal building in the winter season. A one million Btu heater (either propane or natural gas), over a 24-hour period, generates a ton or more of moisture into the building. Imagine the havoc placed on a metal building by a ton or more of moisture generated every 24 hours.

Insulation in metal buildings

How can a plant lower the chances of condensation, if the production process itself mandates a high content of moisture?

As pointed earlier, water condensation stems from moisture encountering coldness. The solution, then, is to minimize coldness of walls. The only known way to do that is through insulating the walls of a metal building. Not only will insulating a metal building result in energy efficiency and a better work environment, it also allows better moisture control. Insulation commonly used in metal buildings includes rigid insulation (the most common of which is polystyrene and polyisocyanurate), foam-core sandwich panels and, less commonly, spray-on cellulose.

Rigid insulation in metal buildings has the advantage of holding its own form and being very friendly to sealing its seams with quality tapes. Foam-core sandwich panels have the advantage of being pre-manufactured in a controlled environment. Spray cellulose may have the advantage of price and environmental friendliness, but most reports confirm that it “blots and drops.”  In other words, cellulose blots because of moisture absorption, and then drops to fill the floors following the blotting. These “blue-cheese” walls have insulation at the bottom but lack it at the top.

Insulation by itself is no guarantee

However, the insulation by itself in not enough to prevent condensation faithfully. But why is that?

Insulation is hardly ever continuous to cover every single square inch of the metal building evenly. Actually, most insulation products have to be assembled “piece-by-piece.” Naturally, there are gaps between the insulation units. Water can still penetrate through these gaps and condense on the cold walls.

The solution is to seal the seams between the insulation. Seams are sealed using a quality construction sealing tape – any tape other than duct tape. This can work with rigid foams up to a certain point, as quality tapes stick nicely on the rigid insulation surfaces.

A better solution than simple sealing is to add another layer of water-proofing material. This water-proofing material constitutes a “vapor barrier.” The vapor barrier regulates the passage of moisture through the wall structure to the outside. The vapor barrier regulates the passage of moisture to a rate that allows water to diffuse through walls in an organized way so as not to cause condensation. Vapor barriers have a long, positive history of being effective to halt almost any kind of condensation in metal structures.

This type of performance can be expected, if the vapor barrier is installed properly and sealed tight along its seams. However, electricians, HVAC technicians, fire sprinkler journeymen and others have been known to tinker and interrupt the continuity of the vapor barrier. For example, that would be the case if they shove a switch or pipe through the insulation without sealing the holes. The interruption of the continuity will defeat the purpose of the vapor barrier, allowing moisture to condensate, and ruin the metal building.

Proper workmanship is paramount for the adequate performance of any insulation. If workmanship concentrates in getting insulation installed without attention to the gaps between insulation, and without attention to pipe, electrical and HVAC penetrations the the insulation will not fulfill its intended function.

Thus, plant owners should keep an eye on their vapor barrier integrity. If a hole appears here or there it should be sealed immediately using two-and-half-inch quality construction tape. Better yet, a conscientious owner will keep a couple of quality construction tape rolls in their facility.

It is worth mentioning that if a vapor barrier is designed to be exposed in metal buildings, then it must be UL-rated fire-resistant vapor barrier.

Final words

In short, the best way to guard against corrosion, internal raining, and mold in a metal building is the proper installation of insulation along with a vapor barrier. The insulation as well as the vapor barrier must be continuous and sealed throughout the whole building to carry on its function. Not only are insulation and vapor barrier the dependable method to offset any damage caused by moisture, but also proves to be the most important factor in accounting for a durable, viable metal building.

Author Bio: William Lotz, P.E. is a consulting engineer who has published more than 300 articles pertaining to all aspects of moisture control, including his most recent. He can be reached at 207-636 2625. Joseph Haugh is a project manager and builder/consultant. He is also the editor of William Lotz’s new book, “Moisture Control and Insulation Systems in Buildings, Chilled Water Pipes and Underground Pipes.”