Metal Wall Panels Archives | Page 4 of 4

Understanding Today’s Vapor Barriers

Posted on February 6, 2018 by Randy Tweedt

One of the most misunderstood aspects of a metal roofing system is the proper use of a vapor barrier. There are many sources of information about this topic – some of which are based on science, some based on anecdotal field experience, and some based on journalism. Here, we will try to break it down to the basic principles that can be used to understand the latest options for a metal building roof system today.

What is Vapor?

The observed science tells us that water can take three forms, depending on temperature and its ability to interact with other things around it. Water can be a liquid that we drink, solid ice that we can skate on, or a gaseous vapor that is part of the makeup of the air we breathe. We can’t see water vapor in the air but we can feel it – we call that humidity. High humidity means a lot of water vapor is in the air, typically coupled with higher air temperature – and both can make us feel uncomfortable and “sticky.” Low humidity means the air is dryer – more typical in lower-temperature air – but this may also be uncomfortable for our breathing, skin dryness, etc.

Why is Vapor a Concern?

As long as the gaseous water vapor stays in the air at a moderate or comfortable level, there is no real concern. However, since water vapor responds quickly to temperature, it can turn back into water as soon as it encounters a surface that is cold enough for it to make the transformation. We know this phenomenon as condensation, and anyone who has seen a cold drink collect water on the outside of a glass on a humid summer’s day has experienced it. It is the same phenomenon that shows up on the surface of windows in a building when there is a big difference between inside and outside temperatures. We know that the amount of water vapor (i.e., humidity) present and the air temperature can both be variable at any given time, but there is always a predictable point at which water vapor will condense and form water drops – this is called the dew point. When vapor in the air encounters a temperature at or below the dew point, condensation occurs.

What Does This Have to do With Metal Roofing?

Metal roofing systems and condensed moisture are not a good combination. If airborne moisture seeps into a metal roof assembly, finds a cool surface, and condenses on any surface there, it likely won’t be visible from inside or outside of the building. That trapped water can then cause rust and corrosion of metal parts, resulting in real damage. It can also collect and saturate building insulation, rendering it ineffective. If enough water condenses, it can cause visible staining or grow mold, causing concerns for people inside the building.

Vapor barriers are used in metal buildings to reduce the rate at which vapor can move through a material.

Do Building Codes Address This?

Absolutely – they require that the building be protected from the possibility of damage caused by water vapor. Since the concern is to restrict the flow of airborne moisture in relatively warm air from reaching a cooler surface to condense on, they call for something to be installed on the “warm” side to prevent that flow. For most buildings across the United States, the warm side is the interior face of the roof and walls. However, if the building is kept cold as in a refrigerated warehouse or storage building, then the warm side is likely on the exterior. The same is true in southern climates where warmer, humid air is the exterior condition and cooler interiors are common.

What is the Best Solution?

Manufacturers of insulating products have been involved in addressing the best ways to provide not only insulation to keep building temperatures warmer, but also vapor barriers to restrict the flow of airborne moisture. After literally decades of trying different types of vinyl and polyethylene facings over fiberglass insulation, most have realized that those membranes simply don’t provide enough protection to be effective. Instead, most are now offering a choice of laminated facings over the insulation that can be installed so they are exposed to the appropriate warm side of the roofing system. These fairly sophisticated laminations include:

Polypropylene-scrim-kraft consisting of layers of white or metalized polypropylene, fiberglass reinforcing, and white kraft paper on the order of 11-30 lb. weight
Polyprolene-scrim-kraft consisting of aluminum foil, fiberglass reinforcing, and 30 lb. kraft paper
Vinyl-reinforced polyester

All of these latest advancements in vapor barriers can provide comparable, high levels of protection, but their selection can depend on a variety of other building factors. Therefore, it is always best to engage an architect or engineer in the design to review the needs of the entire building to select the most appropriate, specific solution for an given project. It will also be important that all seams, connections, and penetrations of the vapor barrier are addressed in the design and construction, which are similarly best addressed by an architect or engineer to assure there are no breaches in the protection provided by the barrier.

To find out more about vapor barrier and insulation products for metal roofing systems, contact your local MBCI representative.

Air Leakage and Water Penetration Testing of Metal Roof and Wall Panels

Posted on January 9, 2018 by Jason Allen

Metal roof and wall panels have many test standards they must meet under certain environmental conditions. Test standards that are specified for metal panels in our industry are ASTM E283 (air leakage) and ASTM E331 (water penetration) for wall panels, and ASTM E1680 (air leakage) and ASTM E1646 (water penetration) for roof panels. While the corresponding tests are similar, the orientation of the panels is a little different for the wall and roof panels. Here we’ll take a brief look at these testing protocols and what they mean for the integrity of the metal panel system at hand.

For air leakage tests, the protocol has been to test at a specified pressure. It should be noted that some manufacturers have changed it from the standard as many in the market are testing at a higher pressure. And while it’s true that you are going to have air pass through, you want the air to be minimized. Air leakage is tested in terms of cubic feet per minute, with a lower number indicating a better, more efficient product. For water penetration testing, water is sprayed and is tested for the water getting through the seam or side lap of the panel system.

The purpose of air leakage and water penetration testing is to establish air and water infiltration rates on the referenced test specimen in accordance with ASTM E283 and ASTM E331.

Metal Wall Testing Standards

As indicated above, the wall test standards are: ASTM E283 (Standard Test Method for Determining Rate of Air Leakage Through Exterior Windows, Curtain Walls, and Doors Under Specified Pressure Differences Across the Specimen) and ASTM E331 (Standard Test Method for Water Penetration of Exterior Windows, Skylights, Doors, and Curtain Walls by Uniform Static Air Pressure Difference).

The procedure for ASTM E283 is as follows: 1. Seal off test unit and measure air leakage (extraneous leakage); 2. Unseal test unit, then re-measure (total system); 3. Subtract extraneous air from total air = Performance.

According to ASTM, this test method is a “standard procedure for determining the air leakage characteristics under specified air pressure differences at ambient conditions.” Furthermore, the air pressure differences across a building envelope can have significant variation with numerous factors acting to affect air pressure differences relative to the particular building environment. For instance, the test method described is for tests with constant temperature and humidity across the specimen. These factors should be considered when specifying the test pressure differences to be used.

Additionally, rates of air leakage are sometimes used for comparison purposes but these comparisons would only be valid if the tested/compared components are of essentially the size, configuration, and design.

Using a Pass/Fail criteria, “Pass” results of this test indicated that water did not penetrate through control joints in the exterior wall envelope, joints at the perimeter of openings, or intersections of terminations.

The laboratory test procedure for ASTM E331 dictates that the test is conducted for a specified duration with water applied at 5.0 gal/ft 2 hr. at a specified pressure. The test has applied pressure and water spray for a period of 15 minutes.

According to ASTM, this test method is a “standard procedure for determining the resistance to water penetration under uniform static air pressure differences.” Furthermore, in applying the results of tests by this test method, ASTM points out that “the performance of a wall or its components, or both, may be a function of proper installation and adjustment. In service, the performance will also depend on the rigidity of supporting construction and on the resistance of components to deterioration by various causes, vibration, thermal expansion and contraction, etc.,” noting that exact simulation of real-world wetting conditions can be difficult (i.e., large wind-blown water drops, increasing water drop impact pressures with increasing wind velocity, and lateral or upward moving air and water) – and that it may depend to some degree on the design.

Metal Roof Test Standards

The Roof Test Standards are ASTM E1680 (Standard Test Method for Rate of Air Leakage Through Exterior Metal Roof Panel Systems) and ASTM E1646 (Standard Test Method for Water Penetration of Exterior Metal Roof Panel Systems by Uniform Static Air Pressure Difference).

According to ASTM, test method E1680 covers the determination of the resistance of exterior metal roof panel systems to air infiltration resulting from either positive or negative air pressure differences. The test method described is for tests with constant temperature and humidity across the specimen. (This test method is a specialized adaption of Test Method E283.)

ASTM literature explains that variables such as the slope of the roof and other factors can affect air pressure differences and, therefore, affect the implications of the resulting air leakage relative to the environment within buildings. Just as with wall panels discussed earlier, these factors need to be taken into consideration when specifying the test pressure difference to be used.

ASTM describes its E1646 test method as a “standard procedure for determining the resistance to water penetration under uniform positive static air pressure differences, and simulates win driven rain imposed on sidelaps and rain that is free to drain while building a water head as it flows.” For this test method, the slope of the roof is a significant factor.

According to ASTM, this test method covers the determination of the resistance of exterior metal roof panel systems to water penetration when water is applied to the outdoor face simultaneously with a static air pressure at the outdoor face higher than the pressure at the indoor face, that is, positive pressure. (This test method is a specialized adaption of Test Method E331.)

To learn more about MBCI wall and roof panels, please visit www.mbci.com.

What to Know About Dissimilar Metals in Metal Roofing Installations

Posted on June 1, 2017 by Jason Allen

While metal roofing is often used because of its resiliency, strength and longevity, there are circumstances under which corrosion and other reactions can become real issues, to the great detriment of the system’s performance and life cycle. Some basic knowledge and awareness of common causes of galvanic corrosion (also called “electrolytic corrosion”) from the use of certain dissimilar metals, can go a long way in mitigating potential problems.

Lead and Copper with Metal Roofing

Lead from pipe penetrations can deteriorate the metal.

Lead and Copper are the biggest culprits when it comes to shortening the service life of metal roofing due to corrosion. It almost goes without saying to make sure these metals don’t come into contact with the roof, specifically roofs with Galvalume Plus products. Here we’ll take a brief look at some of the common problems that can arise.

Due to the high probability of corrosion, it is not advisable to use lead roofing products, such as lead roof jacks for pipe penetrations.

Additionally, graphite, which is the primary material in the common pencil, is extremely corrosive to aluminum and aluminum alloys. Therefore, it is not advisable to write on a metal panel with a graphite pencil. In time, the element will eat through the coating and it will rust out. Eventually, you’ll actually be able to see whatever you wrote on there (that’s not what you want!). Instead, using a Sharpie or a grease pencil will solve the problem with little to no effort.

Chemical damage caused by corrosion and other reactions.

Copper is another metal that does not react well with galvanized metal panels used in many metal roofing systems. Contact between copper parts and metal roofing can greatly increase the likelihood of corrosion. Some specifics to keep in mind:

Don’t use treated lumber, which has copper in it. Sometimes, an installer will set some type of treated lumber post and place something on top of it.

Copper in condensation can eat through metal, damaging the structure.

Over the course of a year or even a few months, the panel will face deterioration at that spot since once moisture invades it will corrode the panel due to chemical reaction. A possible solution to avoid this scenario if treated lumber or a lightning system with a cable is needed is to ensure the cable has aluminum instead of copper.

Another situation where copper can be an issue is with an AC unit on the roof. The AC unit may have copper in the coils, and when condensation drips out on to the roof with copper in the water, those drips onto the metal roof will cause corrosion. The solution in this case would be to install PVC piping all the way up the roof so the copper does not make contact.

Conclusion

An understanding of these and other potential corrosion pitfalls that exist from using dissimilar metals and knowing the basics behind galvanic reactions will provide a solid basis for the smart, proper selection of roofing installation metals. With this knowledge in hand, problems can be eliminated before they occur, which in turn can save time, money, and resources, not to mention meeting the all-important goal of extending the life of the metal roof.