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Self-Storage Roof Design: New Factors That Drive Decision-Making

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Self-storage roof design used to be pretty basic, but modern structures and changing municipal requirements have upped the ante. Read about the factors that are driving decision-making and how they impact the look of your project.

As the self-storage industry has grown into a leading real estate sector, so has facility design evolved. We’ve moved on from single-story barn- or shed-style buildings to multi-story structures with complex features. Often, facilities are designed to blend with surrounding architecture. Where they were previously “skinned” with metal, they now feature brick, EIFS (exterior insulation and finish systems), insulated metal panels and a variety of other finishes.

It isn’t surprising that these more sophisticated buildings require different roofing systems. Not long ago, the only question a developer really had to consider was whether to go with a screw-down roof to save money or a standing-seam model to greatly increase lifespan. Today, there are a multitude of factors that drive decision-making around roof systems.

Zoning Impact

Local zoning requirements play a significant role in roof design. In many places, codes are stringent and specify how a building is expected to fit aesthetically with surrounding properties. Compliance often requires building a four-sided parapet wall above the roof line and around the perimeter of the building.

This poses a problem for metal roofs because the design isn’t a good match for an internal drainage system. It’s difficult to build and can become a nightmare if roof maintenance is neglected. In snow-prone regions, it can be an even bigger concern because the internal gutter is exposed to drift, which is a buildup of windblown snow. That can cause structural concerns below the roof, as it exposes the building to potential water intrusion as the snow melts.

Single-ply roof systems with more flexible drainage methods have gained traction with self-storage developers, particularly when a parapet is required. One solution is to strategically place drains evenly throughout the roof. This is achieved by using tapered insulation to create a slightly sloped surface, which funnels water to the drains. There’s a base layer of insulation to create the required R-value (the measure of how well building insulation prevents heat flow) and another layer of tapered insulation to create the slope.

Another, more common solution preferred by roofing contractors is to drain the roof using wall scuppers. A scupper is a simple architectural device that allows water to escape from a roof, guiding it away from the building. Essentially, you channel the water through small holes in the building’s perimeter walls, into a collector box, and then to the ground or an underground drainage system. An added benefit is this approach uses much less tapered insulation, which is more economical.

Energy-Code Influence

The biggest factor driving self-storage roof design is the ever-changing energy code. The 2012 code dictated that we move from R-19 roof insulation to R-30. The most common method for meeting that additional requirement is to install a “bag and sag” system using two layers of fiberglass batt insulation perpendicular to each other. The combined layers achieve the R-30 condition.

Revisions to the 2015 energy code added a requirement that commercial roofs use “continuous” or “liner” insulation systems. However, the compression of traditional fiberglass batt insulation resulting from the standard 5-by-10-foot grid systems used in most buildings makes meeting this condition a challenge.

To meet this code, architects often specify a single-ply roof system with two layers of rigid board insulation. The system is then installed over a metal-roof deck. This changes the structural design from metal roof over framing to a heavier gauge roof deck, ridged-board insulation and a single-ply membrane. On average, this solution is more expensive by $3 per square foot of roof area; but the cost can be higher or lower depending on roof size, region, complexity and the required R-value on the project.

The 2018 energy code is even more severe and complex, requiring that all low-slope roofs in certain climate zones have a specific SRI (solar reflective index) rating. SRI measures a roof’s ability to reject solar heat. Per the code, any commercial roof with a pitch of less than 2/12 (two inches of vertical drop for every 12 inches of horizontal distance), or 9.46 degrees of slope, must have an SRI rating if it’s within Climate Zones 1, 2 or 3 on the International Energy Conservation Code Climate Zone Map. This is most of the South and Southwest, and a good portion of California.

One way to meet the code is to install a pre-painted metal roof. Unfortunately, it’s more expensive than a standard metal roof with a traditional Galvalume finish. However, the good news is a white, single-ply thermoplastic polyolefin roof meets the SRI ratings with no additional cost.

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Rooftop Solar Panels

While the latest energy codes have become more stringent, many self-storage owners are going beyond the code to install rooftop solar panels, which provide an opportunity to be a good community citizen while reducing operating expenses and increasing profit. Photovoltaic solar energy has simple scalability and doesn’t produce pollution or greenhouse emissions.

Technological advancements and manufacturing improvements have made this alternate power source more reliable and affordable. Many states have also incorporated favorable policies and incentive programs that further reduce the cost of a solar project. Given that an array’s lifespan can be more than 25 years, the product is proving to be a valuable component for existing self-storage facilities and new builds.  The latest generation of panels and racking systems can be non-intrusively attached to metal or single-ply roofs, and installation on flat roofs with ballasted racking will allow you to maintain any existing roof warranty.

For an existing self-storage facility, there are a couple of important things to keep in mind. First, consider the useful life of the roof. A solar installation would be a bit shortsighted if the anticipated roof life doesn’t match or exceed the 25-year life expectancy of the panels. Removing and reinstalling solar to replace a worn-out roof requires a significant labor and cost. You must also consider whether your roof can bear the extra weight. Solar panels weigh two to five pounds per square foot. It’s rare that a roof can’t handle it, but you must be sure.

On a new build, the facility design should accommodate the additional load of the array and account for the installation of the necessary conduit from the electrical room to the roof. In some cases, the roof type can be leveraged to increase the production of the photovoltaic system. If you need assistance with a potential project, a solar development or management firm can help you analyze, build, install and maintain it.

Professional Guidance

The rising size and complexity of self-storage buildings coupled with stricter energy codes and opportunities to add solar efficiency have changed the way we think about self-storage roof design. There are numerous factors to consider. A trusted roofing expert should be able to guide you in making important decisions. Bringing a partner into the process during the pre-planning stage will ensure the most cost-effective, efficient roof for your current and future needs.

Andy Sullivan is president of ReRoof USA, a commercial roofing contractor that offers a full spectrum of metal and single-ply options for the replacement, recover or retrofit of all roof types. He’s worked in the commercial roofing and metal-construction industry for more than 20 years, experienced in fabrication, manufacturing, installation, estimating and management of projects of all sizes and types, including self-storage. To reach him, call 770.490.4189; email [email protected].

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