In the early years of the self-storage industry, most facilities consisted of easy-to-build, single-story, garage-style structures. Put down a flat slab, build concrete block walls, add simple wood-truss roofs and voilà! You’re in business. Today, everything has changed.
A scarcity of available land now forces many owners and developers to build multi-story. This requires new construction systems and upgraded code requirements, particularly those mandated by new standards of energy efficiency. Minimally insulated buildings using prescriptive methods (i.e., R13 insulation in the walls) are obsolete. An architect or engineer must now provide a certified energy analysis to acquire a building permit.
Developing a profitable self-storage facility takes more than a good location and unit mix. The type of construction you choose can make or break a project. Following is an analysis of conditions on the ground and within the industry that can impact decision-making and affect the bottom line—from an architect’s point of view. Let’s look at the materials and requirements for constructing single- and multi-story buildings.
One- to Three-Story Structures
These projects are popular and cost-effective. I typically design this genre on a “mat slab” of 5 to 8 inches, depending on the number of floors. The first-floor walls are generally constructed of load-bearing, “split-faced,” colored concrete masonry unit (CMU) because the ground floor needs to be secure from intrusion. I routinely use a lightweight, bearing wall, cold-rolled, C-channel structural system. The bearing walls are set 10 feet on center and spanned by a metal floor deck and 4 inches of lightweight concrete. This system achieves the 125 pounds per square foot required to meet codes for self-storage loads.
Upper-floor exterior walls can be a mix of corrugated metal, insulated metal panels or an exterior insulated finish system (EIFS), which lends itself to the inexpensive creation of decorative façades. For this system, I generally specify 2 or 3 inches of extruded polystyrene foam covered with a thin, latex-modified, concrete scratch coat and colored latex finish. For a simple shed roof, I use a standing-seam metal roof system.
I try to use a shed roof because it’s easy to construct and maintain; however, one of its drawbacks is the need to drain it to one of the façades. I’ve encountered many instances in which an owner wants a decorative façade that isn’t compatible. Tall parapets around the top of the building are a prime example. The inherent drainage problems can be overcome to some degree by using a hidden gutter, but these are leak-prone and tricky to construct.
One solution to a parapet façade that encloses the roof is a rubber or polyvinyl chloride (PVC) adhered roof with internal drains. For this type of construction, I specify polyisocyanurate sheet insulation on top of a roof deck and then adhere the rubber or PVC roof to it. These roofs are twice as costly as metal roofs and don’t last as long; but if a client demands a façade that needs a rubber roof and is willing to pay the price, I’ll accede.
What benefits accrue by limiting construction to three stories or three stories and basement? Cost-savings, efficiency and flexibility. If you want a building that’ll allow you to change the unit mix—which you can’t easily do with a lightweight bearing-wall system—investigate widespan concrete plank as an alternative. I’ve built three- and four-story self-storage facilities with CMU bearing walls 30 feet on center and concrete plank floors that clear-span the distance between them.
Buildings with fewer than four stories don’t require fireproofing, which is a plus. They also allow access to the roof by a simple hatch, and can be built on lightweight mat concrete slabs. Once the shell is built, the partitions, corridor walls, and roll-up and swing doors can be purchased from many manufacturers. Typically, these suppliers will deliver and install the components as a total package. The cost per square foot (exclusive of land and land improvements) to build a heated and cooled three-story structure using this type of system is typically in the range of $50 to $55. (Keep in mind, all new buildings must comply with Americans With Disabilities Act (ADA) regulations, including all doors, door handles, restrooms, counters and access ramps.)
Four-Story and Taller Projects
Structures exceeding three stories are subject to a new level of building codes. First, they must meet fireproofing standards. Steel columns and joists must be sprayed with cementitious fireproofing and surrounded by 8-foot, 6-inch metal covers to prevent from being damaged during use. Patented steel structural systems that only require one hour of fireproofing are available for buildings up to five stories; however taller structures require a more sophisticated construction system and two- to three-hour fireproofing.
In a typical self-storage building, the columns will be 10 feet on center in all directions. Floor-to-floor height will be 10 feet to 10 feet, 8 inches depending on beam height, which is often 8 feet with a composite steel deck and a concrete floor 4.5 to 5.5 inches thick.
In an all-steel-frame building, the walls are typically non-load-bearing, although I’ve designed an eight-story building that used a combination of CMU bearing outer walls with the remainder of the structure being steel columns and composite concrete deck. It’s imperative that the structural engineer have expertise in the design requirements of self-storage because these projects differ structurally from other building types.
Façades on tall buildings can be made of any type of non-load-bearing wall such as steel stud and EIFS, insulated panel, or masonry such as brick or cast concrete tile. Roofs follow the same parameters as low-rise buildings. They can be standing-seam, composite deck, insulation, adhered PVC or rubber roof, or a simple metal deck. Because of the height, internal roof drains are commonplace. Above four stories, a building requires a stairway to the roof, not a roof hatch.
The architect and the mechanical, electrical and plumbing engineers must satisfy the requirements of the International Energy Conservation Code and submit a COMcheck (federal energy analysis) certificate to the permitting department. Again, all buildings must comply with the ADA.
A caveat: Tall buildings are designated “high-rise” if the total footage of the occupied floors (not including the roof) is higher than 75 feet. Building beyond these limits should be avoided if possible, as high-rise structures require more expensive elevators, emergency generators and additional fire-alarm equipment. I recently designed an eight-story self-storage building in Washington, D.C. To avoid the classification, I was forced to limit the floor-to-floor height to 10 feet. I ended up under the cutoff by half an inch! Well, you know the old saying, “A miss is as good as a mile.”
As with all self-storage projects, once the shell is built, there are several manufacturers that will deliver and install the building components as a total package. You can expect to spend approximately $90 to $100 per square foot to construct a four-story or higher structure with these systems (exclusive of land cost and site improvements).
In some locales, all-concrete construction may be cheaper than steel. In any concrete building, fireproofing isn’t necessary, but the structure requires larger columns that reduce rentable space. All stairways and elevator shafts will still have to be enclosed in two-hour fire-rated construction. I’ve only designed one all-concrete storage structure, and that was 20 years ago, so I don’t have any data on current costs.
Here are some additional recommendations for building multi-story self-storage structures:
Heating systems. Check for adequate gas or electric capacity nearby. I used to design all electric buildings, but now gas is my preference if I can get it to the site inexpensively.
If possible, HVAC units should hang from the ceiling deck. If located on the floor, they reduce your rental space. If I have a floor-to-floor height of 10 feet, 8 inches, I extend my corridors to 8 feet, 6 inches and place channels at 8 feet on center to the ceiling. I then take all the internal unit partitions to within 8 feet of the deck above. I run ducts only down corridors, and push air throughout the floor above all the units.
Lighting. I place 4-foot-long, single-tube fluorescent or LED lights down the center of the corridors at 10 feet on center. I hang them at 8 feet above the finished floor. Some clients like to put lay-in tile ceilings or metal-soffit ceilings (from the corridor and partition manufacturers) in the corridors, but lately many of them have just hung lights in the corridors. Any unit with a capacity of less than 150 square feet doesn’t require a light!
The office. Lately, offices have been getting smaller, with 90 square feet seeming to be the optimum choice. The area should include a handicap-accessible restroom, breakroom, display area, one to two desks with chairs, and a couple of lounge chairs with a coffee table. Expect to have two large-screen monitors, one to display units for sales purposes and a second for security. Don’t forget the office must also meet ADA code requirements for customers and employees.
Self-storage projects are a specialty item. Given increased competition, a changing regulatory climate, new systems of construction, rising costs, and the ever-present challenges of location, adaptation or remediation of buildable sites, it’s more important than ever to hire experienced design professionals with expertise in the field. I’ve seen projects flounder because the architect, unfamiliar with self-storage, underestimated the difficulty of turning out workable, cost-effective plans. As an owner/developer, you can’t afford to pay dues for someone else’s learning curve. It can be a steep one! Take it from someone who’s been there—experience is the best teacher.
H. Edward Goldberg is a registered architect and president of HEGRA Architects Inc. in Baltimore. He’s designed self-storage projects in Connecticut, Delaware, Maryland, New Jersey, the Virginias, and Washington, D.C. For more information, call 443.690.0403; e-mail [email protected]; visit www.hegra.org.