As the self-storage industry has matured, multistory projects have increased in popularity. This is the result of many factors: decreasing availability of land, increasing land costs, the rise of climate-control space, and planning and zoning requirements, to name a few. Whatever the reasons, multistory projects have become an integral part of the industry. This article addresses important considerations for new-build, multistory self-storage.
Site Layout and Topography
One of the first things to consider is the layout of the site. As with all development, it is necessary to determine the requirements for building setbacks, green space, landscaping, impervious coverage, etc. These factors can greatly affect land use. If they are not an issue, you can build a square or rectangular multistory building with a 25-foot wide driveway around it, preferably using one-way traffic flow; but in most cases, things will not be this simple.
Another item to consider is site topography. Multistory projects can be built on the side of a hill or inset into a hill, on pieces of land where a standard facility would not be possible or the cost of changing the topography would be prohibitive. For example, you can build a project that uses the natural slope of the property, with a drive across the front and down one side. In doing so, it may be necessary to inset a portion of the building into a hill, using the back wall (which is underground) to retain the earth behind the building. In this case, the retaining wall also acts as the rear wall of the storage area.
It is possible to put a portion of a building below grade or in a basement configuration. This puts the primary point of entry on one of the upper floors. For example, on a steep slope, you can place two floors into the side of the hill below grade and actually enter the building on the third level. If the slope allows, it may also be possible to create split-level loading, whereby you enter the lower level of the building on one side, or drive up and around the end of the building and enter the upper floor on the opposite side. This can eliminate the need for elevators.
It is a foregone conclusion that with multistory buildings, you will have interior corridors. This will take away from your netrentable square footage. A good rule of thumb is you will lose 24 percent of your gross building area to hallways. The efficiency may be a little bit better on the ground level, assuming you have some drive-up units around the perimeter of the building.
This is always an important issue, even with single-story structures. It is much more so with multistory buildings because of the added weight and wind loading being imposed on them. The weight of multiple levels and horizontal pressures from wind forces are transferred to the foundation of the building. The ability of the soil to withstand these forces must be carefully considered. If the soil has expansive properties, ensure it is properly treated to minimize its ability to swell and push up on the structure. Any reaction to movement in the soil is exaggerated in a multistory building.
Depending on the soil type and its condition, preparing the site can involve excavation of rock, removal and replacement of bad soils, chemical stabilization of soils, installation of piling systems, installation of retaining walls, sub-grade special drainage systems, and a host of other considerations. Although these items can be expensive, the ability to develop a project in an otherwise unproductive area can offset the costs costs.
Multistory building is a specialty. For this reason, not all metal-building suppliers are properly qualified to erect these structures. Multistory, like traditional self-storage, is most commonly constructed in steel frame. Most builders limit the construction of light-gauge framing systems to four stories. Levels above four are generally constructed of heavy, class-A structural steel, consisting of columns and I beams.
Builders who regularly construct multistory structures usually install the framework in one of two design formats, with post and purlin on a 5-by-10-foot grid or a load-bearing wall every 10 feet on center. There are one or two other framing systems that are used less frequently. Each has its pros and cons. It is important to discuss the different systems with your building provider.
Designing structures to resist natural forces such as earthquakes and high winds can present engineering challenges. These possibilities, and the design requirements they dictate, can greatly affect the number and placement of steel members, weight of the structure, thickness and consequent cost of concrete flooring systems, and the overall cost of the building. Consult with a qualified architect, engineer or building supplier to determine if your proposed site is in an area of seismic activity or a high-wind zone, such as coastal areas.
The exterior of the building can be treated as a curtain wall. In other words, it is mainly a decorative facade. It can be installed with numerous products, such as metal exterior panels, stucco systems, tilt-wall concrete panels, glass systems, glass block, brick, CMU block, EIFS synthetic stucco, rock, and many other products and finishes. You can also mix and match different finish systems to create a complex and architecturally appealing exterior.
Of key importance in multistory building is elevator placement. A common trend is to put elevators in the middle of the building, which forces tenants to bring their goods to an elevator lobby, and then travel down a corridor to their units once on the appropriate level. I prefer to place elevators along the perimeter of the building. This allows tenants to drive up to the loading area and immediately place their goods on a cart. The distance traveled to the unit is the same, but it seems more convenient when the elevator is right where they drive up.
Elevators can be expensive and require a fire-rated enclosure. Many other factors will need to be considered as well, such as emergency-exit stairwells, additional life-safety systems, sprinkler systems, fire-separation walls, placement of mechanical systems, etc. This adds to the cost of the project; however, the facility location generally offsets the additional development cost by allowing higher rents.
The Office and Apartment
One final consideration is the location of the office and managers’ apartment. Most projects have a separate office and residence. In a multistory site, depending on the available land, you may be able to put these inside the building envelope. Usually, the office is inside the building on the ground level in front of the drive.
Generally speaking, the office area is big enough to require larger spans between supporting members and the use of structural steel. It will also need air-conditioning ducts and other mechanical lines installed under the structural beams. This means the first level will be taller than the typical metal-grid framing system used for storage units. A typical floor-to-floor height on the office level is just a little over 10 feet.
As installation of an apartment will create a similar situation, some might be tempted to put it on the ground floor by the office. I prefer to put it on the top floor, which simplifies some of the structural issues and provides a living space with a very nice view, sometimes even a balcony. Separating the managers’ living and work space also prevents some of the spillover from work to home life and vice versa, which can help maintain the facility’s carefully crafted business image.
This article touches on a few of the complex issues involved in building a multistory site. The results can be rewarding; but it is important to work with a properly qualified and experienced architect, design team and building contractor who understand the requirements of this building type.
Charles Plunkett is the president and founder of Artistic Builders Inc. and Capco Steel Inc. Both companies, based in San Antonio, Texas, specialize in the design and construction of self-storage facilities, having been in business for more than 19 years and constructing in excess of 20 million square feet of self-storage in 42 states. Artistic Builders handles general construction, while Capco deals in design, supply and erection. Project types range from small, single-story facilities to large, complex, multistory sites. For more information, visit www.artisticbuilders.com or www.capcosteel.com.