Trent Cotney, PA, FRSA LEGAL COUNSEL
Ponding water can be a problem on roof systems and a routine justification for non-payment. Standing water can degrade roof materials, cause the collection of debris and muck and increase the UV degradation by focusing sunlight through water to the roof system. It is usually caused by problems in the roof deck, lack of or improper roof drains or scuppers, damaged insulation or materials, and improperly flashed roof-topped HVAC units or vents. Ponding water is commonly defined as water remaining on the roof 48 hours after a rain during conditions conducive to drying. Most building codes, manufacturer warranties, and roof association guidelines call for commercial roofing systems to provide positive drainage to allow for water to drain from the roof and prevent the
ponding of water. Ponding water, over time, can lead to an accelerated aging of the roof membrane causing leaks, growth of algae and vegetation, as well as potentially causing a roof to fail from excessive standing water weakening the roof deck.
The International Building Code states that a minimum slope of 1/4:12 is required for membrane roof systems on low-slope commercial buildings. Similarly, NRCA recommends that roof systems be sloped to provide positive drainage for a finished roof system. Proper slope for drainage is achieved when there is no ponding water on the roof 48 hours after a rain during conditions conducive to drying. It is interesting to note that NRCA’s definition is based primarily on Midwest conditions where lower humidity and higher winds may be a factor.
The Florida Building Code has multiple provisions which govern ponding water (special thanks to Mark Zehnal):
2014 FLORIDA BUILDING CODE
SECTION 202 DEFINITIONS
POSITIVE ROOF DRAINAGE.
The drainage condition in which consideration has been made for all loading deflections of the roof deck, and additional slope has been provided to ensure drainage of the roof within 48 hours of precipitation.
1502 DEFINITIONS
POSITIVE ROOF DRAINAGE. The drainage condition in which consideration has been made for all loading deflections of the roof deck, and additional slope has been provided to ensure drainage of the roof within 48 hours of precipitation. [P] 1503.4 Roof drainage. Unless roofs are sloped to drain over roof edges, design and installation of roof drainage systems shall comply with Section 1503 and Chapter 11 of the Florida Building Code, Plumbing.
[P] 1503.4.1 Secondary (emergency overflow) drains or scuppers. Where roof drains are required, secondary (emergency overflow) roof drains or scuppers shall be provided where the roof perimeter construction extends above the roof in such a manner that water will be entrapped if the primary drains allow buildup for any reason. The installation and sizing of secondary emergency overflow drains, leaders and conductors shall comply with Sections 1106 and 1107, as applicable, of Chapter 11 of the Florida Building Code, Plumbing.
1510.1 General. Materials and methods of application used for recovering or replacing an existing roof covering shall comply with the requirements of Chapter 15.
Exception: Reroofing shall not be required to meet the minimum design slope requirement of one-quarter unit vertical in 12 units horizontal (2-percent slope) in Section 1507 for roofs that provide positive roof drainage.
SECTION 1611 RAIN LOADS
1611.1 Design rain loads. Each portion of a roof shall be designed to sustain the load of rainwater that will accumulate it if the primary drainage system for that portion is blocked plus the uniform load caused by water that rises above the inlet of the secondary drainage system at its design flow. The design rainfall shall be based on the 100-year hourly rainfall rate indicated in Figure 1611.1 or on other rainfall rates determined from approved local weather data. R = 5.2(ds + dh) (Equation 16-36) For SI: R = 0.0098(ds + dh) where:
dh = Additional depth of water on the undeflected roof above the inlet of secondary drainage system at its design flow (i.e., the hydraulic head), in inches (mm).
ds = Depth of water on the undeflected roof up to the inlet of secondary drainage system when the primary drainage system is blocked (i.e., the static head), in inches (mm).
R = Rain load on the undeflected roof, in psf (kN/m2). When the phrase “undeflected roof” is used, deflections from loads (including dead loads) shall not be considered when determining the amount of rain on the roof.
1611.2 Ponding instability.
Susceptible bays of roofs shall be evaluated for ponding instability in accordance with Section 8.4 of ASCE 7.
1611.3 Controlled drainage. Roofs equipped with hardware to control the rate of drainage shall be equipped with a secondary drainage system at a higher elevation that limits accumulation of water on the roof above that elevation. Such roofs shall be designed to sustain the load of rainwater that will accumulate on them to the elevation of the secondary drainage system plus the uniform load caused by water that rises above the inlet of the secondary drainage system at its design flow determined from Section 1611.1. Such roofs shall also be checked for ponding instability in accordance with Section 1611.2.
2014 FLORIDA RESIDENTIAL CODE
SECTION R202 DEFINITIONS
POSITIVE ROOF DRAINAGE.
The drainage condition in which consideration has been made for all loading deflections of the roof deck, and additional slope has been provided to ensure drainage of the roof within 48 hours of precipitation.
R903.4 Roof drainage. Unless roofs are sloped to drain over roof edges, roof drains shall be installed at each low point of the roof. Where required for roof drainage, scuppers shall be placed level with the roof surface in a wall or parapet. The scupper shall be located as determined by the roof slope and contributing roof area.
R903.4.1 Overflow drains and scuppers. When other means of drainage of overflow water is not provided, overflow scuppers shall be placed in walls or parapets not less than 2 inches (51 mm) nor more than 4 inches (102 mm) above the finished roof covering and shall be located as close as practical to required vertical leaders or downspouts or wall and parapet scuppers. An overflow scupper shall be sized in accordance with the Florida Building Code, Plumbing. Overflow drains shall discharge to an approved location and shall not be connected to roof drain lines.
R907.1 General. Materials and methods of application used for re-covering or replacing an existing roof covering shall comply with the requirements of Chapter 9 of the Florida Building Code, Residential.
Exception: Reroofing shall not be required to meet the minimum design slope requirement of one-quarter unit vertical in 12 units horizontal (2-percent slope) in Section R905 for roofs that provide positive roof drainage.
2014 FLORIDA EXISTING BUILDING CODE
708.1 General. Materials and methods of application used for recovering or replacing an existing roof covering shall comply with the requirements of Chapter 15 of the Florida Building Code, Building or Chapter 9 of the Florida Building Code, Residential. Roof repairs
to existing roofs and roof coverings shall comply with the provisions of this code.
Exception: Reroofing shall not be required to meet the minimum design slope requirement of 1/4:12 in Section 1507 of the Florida Building Code, Building for roofs that provide positive roof drainage (high-velocity hurricane zones shall comply with Sections 1515.2.2.1 and 1516.2.4 of the Florida Building Code, Building).
2014 FLORIDA PLUMBING CODE
SECTION 1108
SECONDARY (EMERGENCY) ROOF DRAINS
1108.1 Secondary (emergency overflow) drains or scuppers. Where roof drains are required, secondary (emergency overflow) roof drains or scuppers shall be provided where the roof perimeter construction extends above the roof in such a manner that water will be entrapped if the primary drains allow buildup for any reason.
1108.2 Separate systems required. Secondary roof drain systems shall have the end point of discharge separate from the primary system. Discharge shall be above grade, in a location that would normally be observed by the building occupants or maintenance personnel.
1108.3 Sizing of secondary drains. Secondary (emergency) roof drain systems shall be sized in accordance with Section 1106 based on the rainfall rate for which the primary system is sized in Tables 1106.2(1), 1106.2(2), 1106.3 and 1106.6. Scuppers shall be sized to prevent the depth of ponding water from exceeding that for which the roof was designed as determined by Section 1101.7. Scuppers shall have an opening dimension of not less than 4 inches (102 mm). The flow through the primary system shall not be considered when sizing the secondary roof drain system.
Given the many provisions that affect ponding water conditions in Florida, a roofer should carefully review and consider code requirements before responding to a disgruntled customer. The fact that a roof has initially passed building department and manufacturer inspections does not relieve the roofer of liability from failing to adhere to Florida Building Codes. See Florida Statute 553.84 (creating a civil cause of action for building code violations).
The typical commercial roof manufacturer’s warranty requires that the roofs have positive drainage and follow NRCA guidelines, or excludes failure of the roof membrane caused by lack of positive drainage. Other roofing manufacturers have “birdbath measurements” that discuss the allowable surface area for ponding water. Roofing manufacturers who provide warranties that either call for only positive drainage, or refer to NRCA guidelines, can lead contractors to believe that the warranty requirements are all that need to be met. This creates issues when the local building code conflicts with less stringent manufacturer requirements. Contractors may install a roof that is covered by the manufacturer warranty, but that fails a ponding water inspection using Florida Building Code
guidelines.
Ponding water is always difficult to anticipate because ponding is in large part, determined by the deck and overall roof geometry. Repair or replacement of a portion of the roof may change that geometry thereby creating ponding water. To mitigate or eliminate ponding water, there are a variety of techniques that can be used. First, the installation of scuppers, roof drains or gutters to move water off the roof; second, the use of a tapered insulation system, insulation fill, cricket or similar technique to adjust roof geometry to allow water to flow off the roof; and third, adjust or modify the roof deck to eliminate ponding. While there may be other methods to eliminate ponding, including the use of some coatings, these three methods are the most prevalent.
Roofing contractors cannot “contract” away the building code requirements, nor can they rely solely on a manufacturer’s warranty in the event they have ponding water that exceeds allowable tolerances. However, contract terms can be added that provide that ponding water may be unforeseeable and that the roofing contractor’s customer acknowledges that the cost to remediate ponding water is an extra, compensable charge.
Author’s note: The information contained in this article is for general educational information only. This information does not constitute legal advice, is not intended to constitute legal advice, nor should it be relied upon as legal advice for
your specific factual pattern or situation.
Trent Cotney is Florida Bar Certified in Construction Law, General Counsel and a director of the Florida Roofing & Sheet Metal Contractors Association (FRSA), Treasurer and General Counsel of the West Coast Roofing Contractors Association (WCRCA), General Counsel of the Palm Beach County Roofing & Sheet Metal Contractors Association and a member of the National Roofing Contractors Association (NRCA) and several other roofing associations. For more information, contact the author at 813-579-3278 or go to www.trentcotney.com.
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