By Wayne Woolsey
The most basic components of a self-storage building can be the most difficult to master. When it comes to selecting and installing your roof system, there are a multitude of factors that will affect construction. The most notable of these are roof type, pitch, penetrations, insulation and drainage. This article provides an overview for the novice developer. While the roof installation may seem simple, critical details can mean the difference between a profitable business and a bed of insurance claims.
The first decision to be made is the type of roof panel to use. You can choose from screw-down panels or standing-seam roofing. Screw-down systems are somewhat cheaper but will not serve for the long term. Instead choose a standing-seam system with a 24-gauge panels to accommodate 5-foot spans. The panel finish should be Galvalume or a painted, not Galvanized.
In a self-storage application, you can choose a single- or double-pitch roof. Double-pitch roofing is preferred on a project that is 80 feet or wider, as shipping 80-foot roof sheets is not cost-effective in most cases. In this preferred installation, roof sheets are taken to the apex of the building and the ends of the panels folded to create a positive stop end. The joint is then covered with a ridge cap.
Due to lot sizes and building locations in relation to property lines, you may not be able to pitch the roof in both directions. In this case, you can pitch the roof sheets in one direction, using a roof step to eliminate expansion issues. Adding a roof step that accommodates gutters and downspouts will allow you to control and isolate water drainage from the roof. This design will help in the long-term maintenance of your standing-seam system.
A single-pitch roof involves caulking and screwing roof sheets together, which is just a leak waiting to happen. A standing-seam roof works on a floating-clip system. During expansion and contraction, which is likely to happen in extreme changes in temperature, the sheets rub together, creating elongated holes in their surfaces. The unfortunate thing about stitched roof sheets is once they start leaking, they are very difficult to repair. When you cannot use a single roof sheet due to excessive building width, stick to a double-pitch roof with a ridge cap or add a roof step.
The goal of a standing-seam roof is to get all water that lands on its semi-flat surface to move as quickly as possible, without obstruction, to the gutters and downspouts. This is why it is particularly important to consider the placement and number of any roof penetrations.
The biggest penetration to the roof is the elevator shaft, which typically takes up an area of about 200 square feet. Unfortunately, it acts as a dam for water. After the roof type, the location of this huge water stop is the next design question that must be answered. The most logical choice is at the highest point on the roof line. This will allow the least amount of water to travel behind the shaft.
Air-conditioning units, vent pipes, roof hatches and smoke vents are other common roof penetrations. These should be kept to a minimum to avoid standing pools of water or opportunities for leaks. There are many mistakes that occur during installation of these fixtures, but the most common is failure to divert water from the roof pans. This can be easily accomplished by capping off the pans involved or installing diverter sheets. If you can prevent water from standing in the pans, you won’t have to rely on caulking and rivets to maintain a watertight seal.
Another common mistake is choosing a poor location for a penetration. Most of the time, there are options, but they are often overlooked. Sometimes, penetrations are positioned to accommodate trades working below the roof, creating convenience for those installing plumbing, ductwork or electrical wiring. Ideally, penetrations should be kept as close as possible to the high side of the roof. In the case of multiple installations, they should be run in a line parallel with the roof sheets to ensure the least obstruction to water flow.
Insulation is critical, as metal roofs will always accrue some amount of condensation, which can damage tenants’ goods. Insulation is designed to resist heat transfer and is rated by R-value, or heat resistance. The greater the R-value, the more effective the insulation is at slowing heat flow. Roof insulation comes as either a vapor barrier or part of a complete climate-control system.
If you use a vapor barrier only, the minimum insulation required for the roof is R6, with a thickness of 1 inch to 2 inches. If your facility is climate-controlled, your insulation value will range from R13 to R19, from 3.5 inches to 6.25 inches. The important thing to remember about insulating your roof system is there are proper roofs for different climates. Consult your supplier if you are uncertain which product is best for your area.
You have installed and insulated your roof and sealed your penetrations. Now you need to consider the system by which water will drain from the roof: your gutters and downspouts. These are among the last items to be installed and common areas for problems. It is not unusual for architects to include insufficient gutters and downspouts in their designs to create the look they want for a facility. Yet they overlook the practical necessity of shedding water from the roof. While it is appropriate to keep aesthetics in mind, the No. 1 priority of the roof design should be to accommodate water runoff.
Water flow is critical. Therefore, roofs subject to large volumes of water or those with longer roof sheets need gutters and downspouts designed to carry the right amount of water per square foot of roof. As a general rule, you need one 4-by-4-inch downspout for every 1,200 square feet of roof area. The roof must also have the correct pitch for the gutters and downspouts to do their job. The minimum roof pitch for a standing-seam roof is 0.25:12. For longer distances, you may want to increase your roof pitch to 0.5:12 to get the water flowing off the roof.
Gutters must be installed with a minimum 1- to 3-inch gap between the inside face of the gutter and the outside face of the building. This is to protect the building in the event water overflows the gutters. It is also imperative to “drip form” the roof sheets. This is done by bending the last inch of the roof pans down toward the gutters. Failing to do this is another common mistake made by inexperienced installers. If the roof sheets are not drip-formed, it gives water the opportunity to flow back underneath the roof panel and into the facility.
Gutters for snow and ice need to be handled differently than those designed for normal rainfall. They will typically have added supports to accommodate the weight and a low-profile front to allow snow to exit the roof without removing the gutter with it. In areas subject to excessive amounts of snow and ice, it may be a good idea to add heat strips to the gutter to avoid ice-damming.
One final word of wisdom here: When you build a self-storage facility, the first three words that come to mind are “location, location, location.” I agree: location of the sun to location of the roof to location of the gutters. When possible, position the roof so the sun always shines on the gutters. This will help melt snow and ice and assist in drainage.
Following the above guidelines will help you avoid common mistakes in the design and installation of your roof system: inadequate roof type or pitch; insufficiently protected screw points; improper overlaps at flashings; excessive, misplaced or poorly installed roof penetrations; and lack of water drainage. Always follow the roof manufacturer’s guidelines or work with a qualified, trained professional to ensure the best possible installation.
Wayne Woolsey is sales manager for Kiwi II Construction Inc., which offers in-house installation, design and engineering services nationwide. The company specializes in light-gauge building systems, conversions, climate control and roofing systems for the selfstorage industry. For more information, call 877.465.4942; visit www.kiwiconstruction.com.