Moisture In Metal Buildings Part I: Causes

Download the BlueTex Guide to Moisture in Metal Buildings here.

This is part one of a two-part series that covers condensation and moisture in metal buildings. In this article we are going to cover everything you need to know about what causes moisture or condensation inside metal buildings. In the second part, we are going to teach you how to prevent or eliminate moisture issues whether you are building a new metal building, or if you have an existing metal building and want to fix it. Finally, we will show you exactly how to make the building significantly cooler and more comfortable in the hot summer months. Imagine the difference in your building if you had a big shade tree over the building - we're talking results like that!

There is a lot of info here but we promise, if you read both articles, you should have a complete understanding of what causes condensation in metal buildings, and you will learn some real solutions how to fix it. Click HERE to read Part II.

What buildings does this include?

When we use the term “metal buildings” interchangeably, we mostly mean any non-conditioned building. This includes garages, barns, sheds, airplane hangars, agriculture facilities, and storage units. Buildings that are typically not using air conditioning inside.

In some cases the building may be classified as “semi-conditioned” and this just means that you may heat or cool the building occasionally on as as-needed basis. For example, a garage that you use on weekends to fix cars, or a metal building that is used as a photo studio. These kinds of structures are not usually buildings that you want to keep at a constant temperature when it’s hot or cold, you just want them comfortable when they're in use.

When you have a building you want to keep at a constant temperature (like an office building or a barn-dominium), these buildings are referred to as “conditioned buildings" and they need to be treated differently. 

Will BlueTex™ fix the moisture problem?

We get this question every day. The first thing to understand is that in order to control moisture, you need a process more than a specific product. Will our product fix your moisture problem? Maybe, but we need a lot more information before we can say definitively either way. Many times how you install a product is key to how it performs and what results you can get. 

What causes condensation?

Let's get technical for a minute and talk about the science behind condensation (or moisture). So, why does a building "sweat?" What happens to cause condensation? 

The most basic rule that never changes is this: moisture (also called condensation) occurs when relatively warm-moist air comes in contact with a relatively cold surface. The key word here is “relatively” because condensation can occur at pretty much any temperature if given the right circumstances. However, for most metal buildings we are usually talking about when it’s cold outside.

Below are a couple examples of condensation. Notice how they have different temperatures and the details for each. In all examples warm-moist air is present. 

Example #1: If you close the bathroom door and turn on the hot shower, eventually the glass shower door and the walls (and maybe the mirror) in the bathroom will start to get condensation (fog) on them. The air inside the shower and bathroom is obviously warm and moist, and the glass shower doors, walls, and mirror are relatively cold compared to the air temperature – even if it’s 75-80 degrees inside the bathroom.

 

Example #2: Go back to the same scenario in example #1 except use a hair dryer on the mirror for a minute or two before the shower is turned on. Now, the mirror probably won’t fog up because the glass has been warmed up and it is no longer a relatively cold surface.

 

 Example #3: If you exhale on to a cold window, it will probably fog up from your breath. Once again, you are breathing out warm-moist air, and the window is a cold surface. If you do this experiment on a warm day, you usually don't get any condensation because the window is not cold enough.

Condensation in metal buildings

Now, let's talk about what’s going on inside of your building and how condensation might occur. Remember, the first basic rule: relatively warm-moist air needs to come in contact with a relatively cold surface.

Here is a typical scenario: You have a garage, barn, shed, airplane hangar, or some other metal building, and it’s a sunny, but cool 40º - 60º day. You open up the doors and the building warms up throughout the day. Even if you DON’T open the doors, the air inside the building will still continue to heat up throughout the day. At the end of the day, you close all the doors and the sun goes down, and the outside nighttime temperature drops to around 40º or less.

What happens? Two things happen in this scenario. First, the metal cools down quickly and get pretty close to the outside temperature (in this example, 40º). Second, you still have 40-60 degree air trapped inside the building. Now remember the rule and consider what’s going to happen. If you said that the warm moist air inside the building will come in contact with the cold metal and create condensation, you are right! Under the right circumstances (between temperature and humidity) it can actually rain inside of your building, because condensation is typically most common on the roof area and the upper parts of the walls.

Sometimes under the right circumstances, condensation can occur with only a few degrees difference between the inside and the outside temperature. Under these conditions it’s almost impossible to totally eliminate condensation without adding some additional heat to the inside surface. Remember the example above where we talked about how using the hair dryer warmed up the cold surface of the mirror? 

However, adding enough heat to a plain metal building will get very expensive if you just try to heat the building without any other efforts. What you have to do is create a NEW interior surface that can easily stay above the dew point (unlike the metal). See Part II: Moisture Prevention about how to do this.

Even more confusing is that you can have two identical days (as far as temperature), but on one day you will have condensation inside your building, and on the other day you will not.  What's happening here? This is based on what is called relative humidity and this is a deep dive into a whole other topic we're not going to cover here. You can find more information about that topic by referring to a “psychrometric chart” that considers the air temperature and the relative humidity to determine the dew point of a surface. This is helpful because it can tell you the temperature of the metal at which point moisture in the air will start to form condensation (or liquid water). Here is a link to an online “dew point calculator” if you want more info on this.

What could be contributing to the moisture in a metal building?

We want to emphasize that having some moisture (condensation) is not usually a big problem. In the building science world, it’s OK for something to get wet, to dry out, and get wet again. Yes, even if this cycle happens over and over.  Problems with moisture usually occur when things stay wet, for an extended period of time and can’t dry out. This is problematic because it can lead to mold, rot, rust etc.

Here are some examples of things that can contribute to moisture problems inside your building. Under normal circumstances, we know the metal is almost always going to be the cold surface in the scenario, so the question becomes: “Where is the warm-moist air coming from?”

• Anything that involves using water inside the building. This includes washing / cleaning / drying things - especially with hot water or steam.
• Parking vehicles/equipment that have been out in the mud or snow.
• Storage of any type of plants, seed, feed, produce, hay, grains, etc. 
• Indoor GROW facilities. Water and lights create a lot of moisture in the air.
• Storage of compost, dirt, manure etc. These items tend to have a high moisture content in them.
• Animals and livestock. Heat and moisture from breathing puts lots of moisture in the air, as does their food and water supply.
• Wet slabs. Poor drainage around the building can put water into the slab since concrete can absorb the water like a giant sponge. 
• New slabs may also contribute to moisture issues. When first poured, they need some time to dry out.  A 1,000 sq. ft. new concrete slab can easily put over 200 gallons of water into the air. We recommend leaving doors and windows open for a couple weeks to “vent” the moisture from a new slab.

Any of these situations can produce a high level of moisture in the air. When you combine these with cold metal, you will get condensation every time!

Now that you know what causes moisture in metal buildings, read Part II to find out how you can stop it from forming in the first place by installing BlueTex™ Insulation products.