Metal buildings make good storage additions

Metal buildings are a common part of many greenhouse operations. They are popular for head houses, storage garages and maintenance shops. Their low cost, ease of construction and low maintenance makes them a good choice when constructing new facilities.

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The typical metal building consists of a steel frame anchored to concrete piers and a concrete floor. The frame is covered with painted sheet metal roofing and siding. Doors and windows can be placed where access or light is needed. Insulation can be added to provide comfort if the building will be occupied. The warranty provided by building manufacturers is usually 20-25 years.

Pre-engineered design

Most buildings are of modular design to use materials efficiently. They are pre-engineered and certified so that obtaining a building permit is easy. The building usually comes with drawings for the foundation and floor, design loads and erection plans.

Assembling a metal building is like putting together a large erector set. Construction can be done in-house with local help, contracted out with the grower acting as the general contractor or by the manufacturer.

Metal buildings come in many more sizes than greenhouses. They are available in widths from 18 to 300 feet wide. Length is usually a multiple of 8, 10 or 12 feet.

Buildings less than 60 feet wide are clear span using rigid frame or truss construction. Wider buildings will have post lines to support the roof.

Building height to the eaves can be between 8 and 20 feet. Select a height that is at least 2 feet taller than any equipment that may be used inside.

Ease of construction

To anchor the building to the ground, place piers below the frost line. The piers have to be large enough to support the load of the frame. Rebar is incorporated in the piers to add reinforcing. The frame is attached to the piers with bolts set in the concrete. In some designs, a perimeter concrete beam may be used between the piers.

The concrete floor is poured with reinforced edges. Insulation may be placed vertically around the perimeter or under the edge of the floor.

Usually a 4-inch-thick floor is adequate for foot and light vehicle traffic. If forklifts and delivery trucks will be driven inside, the floor should be 5-6-inches thick. Wire mesh and expansion joints are necessary to prevent cracking. A light brush finish is desirable to give a good walk surface.

The frame is either steel tubing for narrow buildings or structural steel for wider buildings. Purlins attached across the frames support the roofing and siding. Bracing rods are added to provide lateral strength and to prevent racking. All parts should be galvanized after cutting.

Roofing and siding options

Steel, aluminum and copper are used for roofing and siding. The sheet metal can be anywhere from 24 to 29 gauge with 24-gauge material being the thickest. The thinner material usually has more maintenance due to greater flexing. Because of fluctuations in metal prices, it affects the building cost.

The metal is formed into sheets that are corrugated or have standing seams. The design of the sheets determines the strength, interlocking of the individual sheets and the water drainage. Skylight panels of polycarbonate or acrylic can be substituted for a metal panel to allow natural light to enter the building.

Today, most steel and aluminum panels are painted for protection and appearance. A coating of zinc is sprayed on first. The zinc coating should have a thickness of at least 0.90 ounces per square foot on both sides. This is designated by G90.

Several coatings of paint are then applied. Common paints are polyester, fluoropolmer and polyvinylidene fluoride.

The panels are attached to the frame with self-tapping screws. Usually they have a rubber gasket to seal the drill hole. Snow guards may be added to the roof over doorways to keep snow from sliding off. Endwall vents or a ridge vent are usually installed to remove moisture that collects inside.

Several companies offer metal roofing systems that collect solar energy. Both liquid systems and photovoltaic electric systems are available. If possible, locate the building with an east-west orientation to have the potential for maximum solar gain.

Easy to add accessories

Steel-frame windows with insulating glass are provided by many manufacturers. These can be sized and located to fit the use. Personal doors usually come attached to the frame. Swinging, sliding or overhead doors for vehicle access are also available. If the building is to be heated, insulated doors are desirable. These doors should be at least 2 inches wider and 2 feet taller than the largest vehicle.

For buildings that will be occupied and heated during the winter, insulation should be installed in the roof and walls. Commonly an R-11 reflective insulation blanket is laid over the purlins before the metal panels are put in place. Foam-insulated sandwich panels are also available and give a smooth surface.

For buildings in a warm climate, a radiant barrier under the metal roofing will reflect the heat out reducing cooling costs. Metal roof panels with a high solar reflectivity are also available and may benefit from a rebate on taxes.

The cost of metal buildings varies with the size, height, snow and wind loads and the type of construction. Cost also fluctuates with changes in the price of steel. Typically, a building costs $8 to $10 per square feet of floor area excluding the foundation, floor, doors and windows. Equipment that has to be rented for construction usually includes a man-lift for small buildings or a 15-ton hydraulic crane for large ones.

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- John W. Bartok Jr.

May 2008