When Does Concrete Make More Sense?
There are several factors that may make other methods of construction, most notably tilt-up construction, a better choice than steel buildings.
The most obvious factor is the building's size. For projects less than 50,000 square feet, steel is generally the least expensive alternative. For a building of this size, the fixed or "open the door" costs of a tilt-up construction project (like the rental of a large crane, for example) make it more expensive than steel, even though concrete is usually a less expensive raw material. As projects become larger than 50,000 square feet, however, the lower price of concrete starts to offset tilt-up construction's fixed costs and this method becomes cost-competitive with a metal building. The larger the building, the more advantageous tilt-up construction becomes.
The cost of the steel building kit will usually be lower than a price quoted for a concrete building, even a tiltwall building. If customizing or modifications to the kit are necessary to meet the owner's needs, these design costs must be included when comparing the prices. Also, the kit price may not include costs that are normally incorporated into a quote for a tilt-up or traditionally constructed building. Some of those costs include concrete foundation, permits, erection and assembly costs, taxes, electrical wiring, plumbing, environmental controls, ductwork, interior finishing, etc.
The location of the project will also influence whether a steel building is even an option. Builders in agricultural or lightly populated areas generally have fewer code restrictions placed on them. The closer a building is planned to a densely populated area, the more stringent the fire codes, building permitting requirements and other municipal standards become. In some cases steel buildings can not be used in certain areas for this reason. Other times, fire codes may require steel buildings to be built further apart than tilt-up structures, requiring a larger plot of land for the project. This is why, in urban areas, buildings closer to the downtown area are generally made of concrete and steel buildings become more common on the outskirts of town.
The reason steel buildings face greater code limitations is that they generally offer less fire protection than tilt-up or other concrete buildings. While steel is not combustible, it is not considered fireproof because it can distort or lose its structural strength when exposed to heat. Further, a fire on one side of a metal wall can generate destructive heat on the other side, damaging the property inside. Steel building designers use a variety of technologies, from sprays to fire-retardant panels or blankets, to mitigate the fire-resistive problem. By comparison, a typical 6.5" concrete wall has a fire resistive rating of four hours or more. Tiltwall and concrete provide superior fire protection for the property and people inside a building.
The intended use for a building will also influence whether steel or concrete is the best choice. In general steel buildings work very well for storage buildings, indoor sports facilities, work shops, and aircraft hangers, but they are less suited for higher-trafficked buildings. Comparatively speaking, steel walls are less durable than concrete walls. This holds true in the face of natural forces (bad weather, earthquakes) as well as for truck or forklift accidents. When a building is damaged by a vehicle, the damage is generally more localized and less expensive to repair for a tilt-up or concrete building than for a steel building. For owners who want to build a warehouse or other facility where trucks or forklifts will be used, this can be a very important consideration. Defense contractor facilities, prisons, or other buildings that require positive security also are much better suited to impenetrable concrete than to comparatively unsecure steel.
While steel is reasonably durable, concrete remains the material of choice for buildings that require less upkeep and maintenance over the years. Concrete is impervious to corrosion, rotting, rust or insect infestation; tiltwall buildings created in the 1940s are still standing today with little apparent wear. The fact that builders in earthquake-prone California now use tilt-up construction for 90% of their single-story commercial buildings indicates that concrete buildings are cost-competitive and extremely durable.
When factoring in potential repairs and ongoing maintenance, it's apparent that the real dollar difference between operating a steel building and a concrete building can be significant. Further, the added fire safety and durability of a concrete building will usually be reflected in lower insurance premiums. If the owner decides to sell the property, they will most likely find that a tilt-up or other concrete building depreciates less and than a steel building will.