Modification or Addition of Rooftop Equipment

by Terry Simmons, RRC

For some property owners, roofs can be very complex, especially on commercial and industrial facilities. These facilities often experience many rooftop equipment changes during new processes and facility improvements. A prudent property owner or facility manager should consider the following important points when making modifications or additions to rooftop equipment.

Manufacturer Notification: To avoid roofing problems associated with new penetrations or equipment, notify the manufacturer prior to installation. This will allow the manufacturer to recommend how to incorporate the new penetration or equipment, and how to protect the membrane warranty, if one exists.

Utilizing a Professional Roofing Contractor: The addition of penetrations or equipment to the roofing system should be undertaken by a professional roofing contractor qualified to perform such work. If the original roofing contractor is not available, contact the roofing membrane manufacturer for the name of a qualified contractor. It's important to select a contractor with experience in installing and repairing the roofing system that's in place, along with having the knowledge of the most appropriate methods for installing watertight details.

Compatible Materials to Repair the Roof System: All too often, inappropriate materials are used to repair the roof membrane when modifications are made. Problems most often occur when incompatible materials are used.

For instance, the photo below shows a prefabricated EPDM single-ply membrane pipe flashing adhered to a pipe stand that was added to an asphalt built-up roof. The EPDM is not compatible with the asphalt membrane and will fail prematurely. In addition, when incompatible materials are used together, it can be difficult, if not impossible to establish and maintain a watertight seal.

Selection of appropriate materials is determined by the type of roof membrane to be modified. It's important that the type of membrane in place be correctly identified, so compatible materials can be utilized. When the type of membrane, or compatibility of materials is in question, a roofing professional should be consulted.

Appropriate Mounting Techniques: Since a variety of equipment is mounted on roofs, rooftop equipment usually requires a myriad of service lines. These range from electrical to natural gas, as well as related duct work. In order for equipment to be successfully incorporated into the roof system, support and flashing of the equipment and service lines is critical. General guidelines regarding the appropriate techniques for mounting and flashing rooftop equipment are presented below. Due to the variety of equipment in use today, consult a roofing professional for specific recommendations.

• When considering placing equipment on the roof, also consider not placing it on the roof. Rooftop equipment is one of the most frequent sources of leakage, whether it's from the equipment housing or damages caused by personnel servicing the equipment. When possible, place equipment on the ground next to the building, or on elevated platforms adjacent to the building. Service lines can then be run through the wall into the building. This greatly reduces the number of penetrations in the roof, thereby reducing the potential for related leaks.
• Consider the use of a penthouse or other structure to enclose rooftop equipment. If the equipment requires frequent maintenance, has sensitive components, or has an extensive amount of service lines, erecting a structure to enclose the equipment may be an effective means of ensuring watertight service. A structural engineer should be consulted regarding the feasibility of erecting a penthouse or other structure.
• Structural capability is usually the primary factor for the method selected for mounting equipment. However, just as important can be the watertight integrity of the equipment. Manufacturers of HVAC equipment give very little regard to the watertight integrity of equipment housing. Built-in leaks are often a result of flat laps in horizontal sheet metal, fasteners without gasketed washers, lack of water-shedding louvers, etc., which are all too common on modern equipment. Most manufacturers rely on a simple steel pan to collect condensate and rain water that leaks past the primary housing. A steel pan can rust out or overflow, causing more leakage into the building's interior.
• The roofing industry generally does not recommend the use of "sleepers" and pitch pockets. Sleepers are wood members (such as 4 x 4 treated lumber), that are placed on the roof's surface on top of which equipment is set. This is not good practice, since it causes compression of the roof insulation, and can lead to rupture of the membrane. In addition, the sleepers and equipment are not secured and offer no wind uplift resistance.

Pitch pockets are not recommended since the filler will shrink over time, causing collection of water and eventual leaking. Pitch pockets require frequent inspection and maintenance. When there is no other alternative, design improvements are available that use non-shrink grout, better performing pourable sealers, and rain collars to enhance the performance of pitch pocket details.

By carefully planning for, implementing and documenting modifications to a roof system, building owners can protect their investment in the roof, while accommodating the functional needs of the facility.