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.

Steel Building Manufacturers

Finding a bona fide steel building manufacturer is sometimes difficult. Everywhere you look there seems to be someone selling a "factory clearance" or "cancelled order" buildings. Well 99% of it is a farce. There are too many brokers and re-sellers out there to count. What they want is your deposit. You can fight with them about the actual details later. They just want the deposit. Take advantage of all the resources available to you. Try locating the manufacturer to match your expectations. This may be slightly more time consuming, but well worth it when your new steel building is delivered exactly to your specifications.

Getting multiple bids for any kind of service is key. Ask several steel building manufacturers to quote your building and explain precisely by line item what your price includes. You can turn to the Internet to seek out steel building manufacturers, but be warned. You will encounter many wolves in sheep's clothing. Contact the Better Business Bureau, or other affiliations to ensure a company has a good track record. Form a list of qualified steel building manufacturers, do your research and you can gauge which manufacturers you prefer to deal with. Once your bids are returned to you, the selection process should be easy to complete. You can choose to follow up with the most qualified companies to purchase your metal building or to ask additional questions.

Perm Rating

The perm rating, or permeance, is a measure of the amount of water that passes through one square foot of material per hour. The lower the perm rating, the more effective the barrier. A facing material with a perm rating of 0.1 or less is considered excellent. Anything with a rating above 1.0 is not considered a vapor barrier.

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.

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.