Roof as a Platform
Because Today’s Roofs Are Required to Do More than Ever, Careful Planning Will Lead to a Successful Project
By Thomas W. Hutchinson, AIA, CSI, FRCI, RRC
For decades, “keep it off the roof” has been the mantra of knowledgeable roof system designers. Keeping the roof free of mechanical equipment; superfluous items, such as IT cables, satellite dishes, antennas, conduit and gas pipe; and unnecessary foot traffic always has been a first means of extending the roof’s potential service life. This forethought and hypothesis in the design phase has actually proved to be correct as roof system service life increased. (See Photo 1.)
In recent years, a great many outside influences have been affecting roof system design: the U.S. Green Building Council’s LEED program; the U.S. Environmental Protection Agency’s ENERGY STAR Program; energy codes; and an overall acceptance of the environmental movement, including regulation and code changes to reflect current trends. In addition, the recent federal government endorsement of renewable-energy sources has inadvertently increased pressure on the roof’s ability to perform.
In less than one decade, the concern of “keep it off the roof” has evolved to “how can the roof surface be used most effectively for other non-roof related activities?”. Roofs are now being asked to be the base support for functions that need to be designed and integrated into the roof system, such as solar arrays, wind turbines, vegetated roofs, etc. These outside influencers create a maze of requirements for the designer, placing a great deal of liability on his or her shoulders. Until revisions are adopted, the roof system designer is obligated to work within this framework.
Planning and Design
As with all successful construction projects, the necessary first step is planning and understanding the required needs of the ancillary equipment to be placed on the roof. Knowing the construction process and how the building and roof will be constructed is a benefit, as well. The designer must think about constructability and design within those parameters.
Most roof consultants would be involved in these decisions in roofing removal and replacement projects while new construction purview tends to belong to the architect, engineer and registered licensed professionals. Although the process involved for each is similar, decisions and implications for new construction situations will be assumed in this paper because they are broader in scope.
Decisions and implications for new construction situations will be assumed in this paper because they are broader in scope.
As soon as it is known the roof will be asked to perform functions above and beyond those normally associated with roofs, the designer should immediately start a matrix of those functions, their design, construction and maintenance requirements. (See Figure 1.) For each item, the effect on the roof and needed design considerations can then be determined. This preplanning will help organize the designer and the design and coordination issues they will face.
Roof Deck: The type of equipment, its need for securement, dead load and potential live-load weight will need to be determined and coordinated with the equipment-related design engineer/structural engineer. The roof deck and structure will need to be designed to accommodate the systems’ weights and potential support. Characteristics, such as potential resultant snow loads, drifting and reduced snowmelt because of shading, will need to be accommodated.
Wind: Rooftop equipment that extends above the roof surface often results in sail-like manifestations that will need to be accommodated by the structural engineer and roof system designer. Potential wind uplift to the roof surface by vortexes created by the rooftop equipment needs to be considered.
Service Supports: Optimally, it is recommended that rooftop equipment be elevated above the roof surface on a raised-platform curb to isolate it from the water plane of the roof. The platform should be structurally sound and fulfill the requirements of the roof deck and wind concerns noted above. If a platform curb is not possible, an appropriate support base is required. It should integrate into the structure and be appropriately flashed into the roof system. It should also provide proper clearance to the roof membrane for the purpose of maintenance or repairs. Redundancies are important; the base of the support should be waterproofed at the roof-deck level, perhaps into a vapor retarder. Vibration and harmonic movement will work on the rooftop flashing and a secondary barrier will provide added protection.
Vapor Barrier/Air Barrier/Temporary Roof: The use of a vapor retarder/temporary roof as a design element (as opposed to being required by building environments) is highly recommended when the roof surface will be a platform. Much of the construction of the ancillary rooftop equipment has roof-surface-damage potential. Therefore, if a large portion of the rooftop equipment can be installed over the vapor retarder/temporary roof and the finished roof installed afterward, the inherent quality of the roof can be improved. The vapor retarder/temporary roof also provides temporary interior protection from moisture intrusion and allows for the installation of interior HVAC and piping in dry conditions.
Insulation and Protection: Higher thermal values and greater insulation thicknesses are becoming the norm. As a valued component of the roof system, insulation now is being called upon to support a roof acting as a service corridor and should be protected from potential damage by a cover board of substantial density and point-load resistance. Most roof system manufacturers produce walkways that protect the roof membrane but do not have the thickness to prevent damage to the roof insulation.
Foot Traffic: The roof system that performs as a platform will need to be designed for heavy foot traffic and access to it and rooftop equipment. (See Photos 4 and 10.) The key for roof system designers is to understand construction sequencing. Often, the roof surface is designed to resist physical abuse after the roof is installed. With platform roofs, the need is immediate to prevent damage by other trades installing energy equipment. The roof surface will be impacted not only by foot traffic but by material packaging, tools, and work set-up and construction. As recommended previously, the most quality-oriented design parameter would be to install a vapor retarder/temporary roof and then have the new roof installed free and clear of this other work. If this is not possible, the use of the most robust and puncture-resistant membrane is recommended: 80 and 90 mil for single plies. Additionally, in known areas of construction and anticipated maintenance foot traffic, a second sacrificial protective layer of membrane should be installed. (See Photo 9.)
The designer must coordinate in the specifications and indicate who will provide the protection. For example, a roofing contractor should protect the roof during major masonry demolition, rather than asking the masonry contractor to do so. On new construction, it is recommended that the installing roofing contractor be required to provide this protection and the scope of protection be defined in the specification and on the drawings.
Material and Equipment Storage: Roofs that perform as platforms typically will involve the placement of packaging, equipment and assembly construction, which can damage the roof membrane, insulation and flashings. (See Photo 11.) The designer should specify exact protection measures for material storage, debris storage, work areas and assembly. This author has found that generic requirements, such as “roofing contractor shall protect new roof installation until accepted by the owner,” are insufficient.
If ropes for fall protection are required they should not by any means be allowed to wrap roof curbs, vents, etc. Base flashing corners should be doubled if it is anticipated that ropes and extension cords will abrade them.
Specify Rooftop Maintenance: Following the completion of the roof and installation of the rooftop equipment, undoubtedly the equipment will require maintenance. This maintenance and the first couple years of climatic cycling can affect the roof systems; seams may pop, flashings pull, punctures and cuts may reveal themselves, debris may accumulate at roof-drainage systems. On a roof with activity occurring on it after the initial construction, proactive and specified roof maintenance for the first two years is recommended. This can be specified and included in the project documents. By requiring the roofing contractor to return, minor items can be attended to before they manifest into larger concerns not covered under any warranty.
Codes: Roof system assemblies are tested sans rooftop equipment. Consequently, the addition of such equipment on the roof surface may impact code compliance. The design professional must:
- Verify and coordinate with the electrical engineer that all required rooftop electrical components are code compliant.
- Verify compliance with all applicable codes.
- Consult with the roof-membrane manufacturer to verify potential rooftop products will not adversely impact the fire classification of the roof system.
- Verify the rooftop equipment will not produce wind vortexes that will result in roof system wind damage.
Commissioning: The roof system designer, when performing punch-list inspections, should look at the entire roof platform as a holistic concern and indicate all items that affect the roof system’s performance. Items that need to be completed by electricians, plumbers and mechanical trades, when coordinated with the roof punch list, tend to indicate the importance of one to the other.
Roof Construction
Even the most attentive roof system designer who endeavors to provide a fine set of all-encompassing details cannot anticipate all construction sequencing and field modifications and nuances. As a result, the roof system acting as a platform will benefit greatly from on-site observation by qualified roof consultants and architects who have been involved in the project. These individuals must not only confirm installation in accordance with the contract documents, but also make field decisions and provide design and details for alterations as they arise. Field sketches for conditions that have changed need to be expeditiously produced to the appropriate parties.
The roof system acting as a platform will benefit greatly from on-site observation by qualified roof consultants and architects who have been involved in the project.
This individual will also need to take a leadership role in preconstruction and coordination meetings, raising questions regarding sequencing, protection, and all other concerns that have potential to damage or affect the roof system.
The receipt, review and coordination of shop drawings related to the specific rooftop equipment are imperative. For example, solar-array-rack-support shop drawings should be provided to the architect, who in turn should forward them to the roofing contractor to verify detailing. Conversely, any questions and concerns raised by the roofing contractor should be shared with the solar-array-installing contractor, and the process of revising and resubmitting shop drawings should begin again.
Staying at the Top of Your Game
Roof systems today are required to perform many more functions than their predecessors; they must be designed in a way that reflects these new needs. Failure of building owners, builders, architects, roof consultants, manufacturers and contractors to maintain the fundamental purpose of the roof while achieving a greater good will result in long-term concerns and litigious activity.
Taking a holistic approach to the roof system design, its construction and management will result in watertight performance while supporting many other rooftop activities. The days of the “out of sight, out of mind” approach to roof systems is over. Today, the roof is a valuable contributor to a building’s environmental, aesthetic and energy performance.
Thomas W. Hutchinson is principal of Hutchinson Design Group, Barrington, Ill.
To view a PowerPoint presentation based on this article, click here.
REFERENCES
Biasell, Natasha. "Innovative Roofing Inspires Solar Energy Collaboration." RCI Interface July 2009: 22-24.
Dregger, Philip D. "Retrofit Rooftop Solar Voltaics--How to Save Money on Energy ... and avoid spending it on repairs." October 2008. (PowerPoint Presentation).
Gumm, Michael. "Integrating Photovoltaics onto Building Envelope Surfaces." RCI Interface December 2008: 11-23.
Hutchinson, Thomas W. "Designing Replacement Roof Systems to Achieve Long Term Service Life: A Sustainable Solution." 11th International Conference on Durability of Building Materials and Components (DBMC). Istanbul, 2008.
Kane, Ed. Division Manager, Technology, Firestone Building Products Interviewed by Thomas W. Hutchinson. October 2009. (Interview)
Malepezzi, Joe. Code Enforcement, Carlisle Syntec Interviewed by Thomas W. Hutchinson. October 2009. (Interview)
Sopko, Allen. Warranty Service, Firestone Building Products Interviewed by Thomas W. Hutchinson. October 2009. (Interview)
St. John, Ashley "Thomas Co. installs a roof system on the Atlantic City Convention Center." Professional Roofing August 2009.
Photo 1: Roof designers in the past strived to keep all equipment and foot traffic off the roof. This 22-year-old ballasted EPDM roof is in excellent condition in part because of the lack of rooftop activity.
Photo 2: Lakeshore Athletic Club rooftop tennis court: In addition to watertightness, the author designed this roof to serve a function.
Photo 3: This 24-year-old fully adhered EPDM roof is in excellent condition. As part of the roofing removal and replacement design 24 years ago, the author removed all abandoned rooftop equipment and placed mechanical equipment below in an effort to “keep equipment off the roof.”
Photo 4: The inclusion of rooftop equipment, such as solar arrays, is becoming more common. The designer of this roof did a fine job of raising the panels off the roof and spacing the support to allow for access. It is unknown if additional protection in the areas of foot traffic has been installed.
Photo 5: The installation of wind turbines on roof areas will become commonplace in the near future. Designing the roof system to accommodate turbines and their maintenance is an important consideration for sustainable roof systems.
Photo 6: The roof of today has become a valuable piece of real estate and often features a solar array, cellular antennae and large HVAC equipment.
Photo 7: Roofs performing as platforms for ancillary activities need to be designed to accommodate construction and usage after installation.
Photo 8a: Roofs have become prime candidates for the installation of cellular towers. Therefore, roofs must be designed to accommodate the installation of the tower and associated piping, cables, etc., as well as maintenance.
Photo 8b: Roofs have become prime candidates for the installation of cellular towers. Therefore, roofs must be designed to accommodate the installation of the tower and associated piping, cables, etc., as well as maintenance.
Photo 9: A sacrificial protective layer of 90-mil EPDM membrane was installed in and around all the mechanical equipment on this roof area as added protection in addition to 2-inch rubber walkways.
Photo 10: This solar panel installation allows little room for maintenance of the roof surface below--a requirement of the roof warranty.
Photo 11: Roofs acting as platforms should be designed to withstand the impact of not only construction crews unfamiliar with roofs, but also for the equipment packaging, debris and assembly areas.
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