Surface Air Film Coefficient (F)

The amount of heat flow in BTU's per square foot per hour between an exposed surface of a material and the adjacent air. It is the measure of the conductance of heat through the air film that clings to all surfaces.

Controlling Condensation

Two things must be present for condensation to occur: warm moist air and cool surface temperatures below the dew point. The proper control of these two factors can minimize condensation.

In metal buildings, we are concerned with two different areas or locations: visible condensation which occurs on exposed surfaces below dew point temperatures, and concealed condensation which occurs when moisture has passed through the vapor retarder and into interior roof and/or wall cavities and then condenses on a surface below dew point temperature.

Installation Overview

The metal building is rapidly becoming more popular for a variety of reasons. They can be built very quickly and are extremely low in cost. They can easily adapt to any number of external architectural treatments without restricting their interior floor planning. A primary reason for this flexibility is the development of insulation specifically designed for metal buildings. The development of advanced insulation systems with more efficient thermal performance is so advanced that it has enabled metal buildings everywhere to evolve into many of the showrooms, retail outlets, schools, offices and shopping centers we see today.

Today's high-energy costs have made insulation a critical consideration during any construction planning. An insulation system that is properly selected and professionally installed will return more on its investment than any other building component.

Insulation provides many benefits:

Improved appearance, Greater comfort, Substantial reductions in fuel and electricity costs, Condensation and noise control, Reduction of the amount of investment dollars and space needed for heating and cooling equipment.

Thermal Conductivity (K-Value)

A unit used to express the amount of heat, in BTU's per hour, that passes through one square foot of homogeneous material that is exactly one inch thick and has a temperature difference of one degree Fahrenheit between its surfaces. As the K-Value decreases, so does the amount of heat permitted to pass through the material.

Condensation Control

The condensation process occurs when warmer moist air comes in contact with cold surfaces such as framing members, windows and other thermally conductive accessories, or the colder region within the insulation itself (if moisture has penetrated the vapor retarder). Warm air, having the ability to contain more moisture than cold air, loses that ability when it comes in contact with cooler surfaces or regions. When this happens, excessive moisture in the air is released in the form of condensation. If this moisture collects in the insulation, the insulating value is decreased.

In dealing with condensation, air may be considered to be a mixture of two gases-dry air and water vapor. One thousand cubic feet of air at 75°F can hold up to 1.4 pints of water. At 45°F, it can hold only 0.5 pints.

Relative Humidity is a percentage measurement of the amount of water vapor present in the air in relation to the amount it is capable of holding at that temperature. Therefore, 50% Relative Humidity would mean that the air is carrying only one-half of the total amount of moisture that it could be holding at that particular temperature. Cold outside air is usually much drier than warm inside air. Therefore, you can lower the Relative Humidity by bringing in outside air to mix with and dilute the moist inside air. At 100% Relative Humidity, the air is "saturated."

The temperature at which the air is saturated and can no longer hold additional moisture is called the dew point temperature. Whenever air temperature drops below its dew point, excess moisture will be released in the form of condensation. Condensation problems are most likely to occur in climates where temperatures frequently dip to 35°F or colder over an extended period of time.