11 More Helpful Design Tips for Low-Slope Roof Systems

February 01, 2005 |

BD&C asked a panel of roofing experts for their advice about what design and construction professionals should do to ensure a successful low-slope roof project. The panel consists of: Tom O'Connor, FAIA, VP and director of building technology for Detroit's SmithGroup; Richard Koziol, AIA, senior consultant with Wiss, Janney Elstner Associates Inc., Northbrook, Ill.; and Greg Doelp, associate, Simpson Gumpertz & Heger, Waltham, Mass. Here is their advice:

  • Coordinate, coordinate, coordinate. Coordinate the building design with expected construction activities to minimize construction traffic from trades other than the roofers on the newly installed roof system.

  • Don't turn the roof into a staging area. During construction a newly installed roof should not be permitted to be a staging area for other trades. However, if this is necessary, consider installing a new roof in stages. Install the first ply to weatherproof the building and to provide a surface for others to work from and to take construction activity abuse. When those activities are done, patch the first ply and add the second ply to the roof system to complete it.

  • Make room for maintenance. Where roof-mounted equipment is specified (e.g., HVAC equipment, cooling towers, satellite and other antennas, etc.), use a two-step roofing system to accommodate construction traffic.

    Design a functional layout of mechanical and electrical systems and include step bridges as required for easy maintenance and use of controls. Construct equipment frames high enough above the roof surface to allow roofing personnel to get underneath the equipment to maintain and replace the roof. Follow National Roofing Contractors Association (NRCA) guidelines for this — they have a good chart showing recommended clearances in their Manual of Roofing and Waterproofing. For more, see

  • Design for future use. Design the roof system for future growth and adaptation of communication antennas and dishes to allow for easy replacement and mounting without damage to the roof.

  • Take a look at LEED. If you're shooting for LEED certification, your choice of roofing system may be limited. Green roof system selection and detailing (for white or vegetated roofs) should be conducted by an experienced professional. If you're not expert in this area, hire a consultant.

  • Conduct flood tests. Flood testing of certain areas may be warranted for high-risk installations and should be mandated for all green roofs — any system with significant overburden or critical internal areas requiring protection.

  • Consider rising walls. Address leakage from walls that rise above the roof — walls of adjacent buildings, penthouse walls, and rising walls often seen on hospital projects.

  • Think about the people in occupied buildings. On roof replacement projects on an occupied building, consider the impact of the roofing work on building occupants and building operations. These include noise from rooftop traffic, demolition, or installing fasteners; odors from kettles of hot asphalt, adhesive fumes, and solvent fumes; and dust from debris attached to the roof deck, such as old, crumbly spray-on fireproofing, old, crushed insulation, or roofing that falls through joint holes and openings in the metal or wood roof deck.

  • Consider interference from electrical conduit attached to the underside of the roof deck if you plan to fasten into the existing roof deck.

  • Build to code. Make sure your new roof design meets the requirements of the local building code. Review code requirements, functional and client needs, and incorporate these into the design. Consider such factors as:

    • drainage (function and capacity)

    • slope to drain (¼ inch per foot in most codes)

    • emergency overflow drains/scuppers

    • wind uplift loads

    • dead and live loads

    • fire-resistance ratings and fire protection

    • energy code requirements

    • thermal insulation needs

    • reflectance and emissivity of membrane

    • whether UL or Factory Mutual requirements need to be met.

  • Use cover boards. On fully adhered roof systems, use cover boards. Don't adhere directly to polyisocyanurate foam insulation. NRCA has published a technical bulletin on this issue at

For 10 additional roofing tips, see the September 2004 issue of BD&C (p. 55), or

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