Mike Silvers, CPRC, Owner, Silvers Systems Inc. and FRSA Technical Director
When answering calls for FRSA, I never know what the primary topic of the conversation might be. Calls come from consumers, engineers, architects, building officials and others but primarily they come from our members: contractors, manufacturers and distributors. Some are easy to address and are repeated often. Others can be complex and may be the first time the question has arisen. I took one of the latter from a contractor a few days ago. He explained that he was about to start a new low-slope roof system installation. During a walk-through, he noticed that the internal roof drainage point didn’t have a roof drain, just a PVC pipe flush with the top of the metal deck. He inquired why this was the case and asked, “where is the roof drain?” The designer said that it wasn’t required and then said, “show me where it says in the building code it’s required.” I get questions about where a specific requirement is located in the building code, often. As those who are
familiar with the code know, it is not presented in a question-and-answer format and only the simplest questions can be answered in a single section. More often, the answer is found by navigating a pathway that leads you to it. That was the case here.
Before diving into specific code sections, a little background information was needed. When an internal roof drainage system is routed through the interior of a building, it needs to be sealed. If there is any chance that the drain could back up, it must be sealed to resist leakage from a head of water or head pressure. The
pressure is created by water building up on the roof and in the leader as well. In cases where the seams in the drain leaders and downspout occur outside the building, a gravity seal or lap is acceptable. This arrangement was used often during mid-century construction that employed what we referred to as "porch tubes." These were typically used in buildings with overhangs and soffits. A porch tube is like a scupper except it flows straight downward – as opposed to a scupper that extends through a wall or mansard. It should be a sealed unit until it extends through the soffit. If the termination is left open and of sufficient size, blockage won’t occur. If it is run into a downspout and blockage does occur, the leakage from the laps will happen outside of the building envelope. It may only take one turn or elbow to eventually create a blockage. In a more typical drainage system routed through the building interior, there can be many reasons for the drain to stop flowing properly that including:
■ Clogging or restrictions from debris
■ Rainfall in amounts that exceed the flow rate of the system
■ Flooding that limits the outflow of the storm drainage system or outlets near the ground
■ A combination of two or more of the above often occur during hurricanes.
Most experienced roofers that provide repair services on low-slope roofs have come across the inverted lead boot or other similar arrangement, stuffed into a roof drain or the roof drain leader or piping. When heavy rain or blockage occurs, head pressure is created in the system and often causes severe water intrusion and interior damage. The drain at its flashing and any connections inside the structure must be sealed to resist this pressure. With a standard cast iron or PVC roof drain, this is accomplished by a clamping ring that uses the flashing material as a gasket between the drain body and the clamping ring. Other arrangements offer a flashing flange that can be stripped-in or heat welded to. The termination of these drains or flashing arrangements inside the leader must be sealed. Some of these use an inner expansion unit that expands through different mechanisms to create a seal to the inner part of the leader. When using these, the inside of the leader must be clean and relatively smooth: again, think of a gasket effect.
In my opinion, the following code sections lead us down a path to answer the question "are drains required?" We will not address all the sizing and
other drainage requirements in the code. They are voluminous. I do hope to demonstrate that drains are required in the circumstances described and they must accommodate the ability to be flashed in compliance with the roof covering manufacturer’s installation instructions. Note: For emphasis, I have bolded some of the text in tech code paragraphs below.
2023 Florida Building Code, Building, Eighth Edition Chapter 15 Roof Assemblies and Rooftop Structures
SECTION 1501 – GENERAL
1501.1 Scope. The provisions of this chapter shall govern the design, materials, construction and quality of roof assemblies, and rooftop structures.
SECTION 1502 – DEFINITIONS
1502.1 Definitions. FLASHING. The roofing component
used to seal roofing systems, where the system
is interrupted or terminated.
SECTION 1503 – WEATHER PROTECTION
1503.1 General. Roof decks shall be covered with approved roof coverings secured to the building or structure in accordance with the provisions of this
chapter. Roof coverings shall be designed in accordance with this code and installed in accordance with this code and the manufacturer’s approved instructions such that the roof covering shall serve to protect the building or structure.
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 the Florida Building Code, Plumbing, Chapter 11.
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 the Florida Building Code, Plumbing, Chapter 11.
SECTION 1506 – MATERIALS
1506.1 Scope. The requirements set forth in this section shall apply to the application of roof-covering materials specified herein. Roof coverings shall
be applied in accordance with this chapter and the manufacturer’s installation instructions. Installation of roof coverings shall comply with the applicable provisions of Section 1507.
SECTION 1507 – REQUIREMENTS FOR ROOF COVERINGS
1507.1 Scope. Roof coverings shall be applied in accordance with the applicable provisions of this section and the manufacturer’s installation
instructions.
2023 Florida Building Code, Plumbing, Eighth Edition
CHAPTER 11 – STORM DRAINAGE
SECTION 1101 – GENERAL
1101.1 Scope. The provisions of this chapter shall govern the materials, design, construction and installation of storm drainage.
1101.6 Fittings and connections. All connections and changes in direction of the storm drainage system shall be made with approved drainage-type fittings in accordance with Table 706.3. The fittings shall not obstruct or retard flow in the system.
1101.7 Roof design. Roofs shall be designed for the maximum possible depth of water that will pond thereon as determined by the relative levels of roof deck and overflow weirs, scuppers, edges or serviceable drains in combination with the deflected structural elements. In determining the maximum possible depth of water, all primary roof drainage means shall be assumed to be blocked. The maximum possible depth of water on the roof shall include the height of the water required above the inlet of the secondary roof drainage means to achieve the required flow rate of the secondary drainage means to accommodate the design rainfall rate as required by Section 1106.
SECTION 1102 – MATERIALS
1102.6 Roof drains. Roof drains shall conform to ASME A112.6.4 or ASME A112.3.1. Roof drains, other than siphonic roof drains, shall be tested and rated in accordance with ASME A112.6.4 or ASPE/IAPMO Z1034.
SECTION 1105 – ROOF DRAINS
1105.1 General. Roof drains shall be installed in accordance with the manufacturer’s instructions. The inside opening for the roof drain shall not be obstructed by the roofing membrane material. 1105.2 Roof drain flow rate. The published roof drain
flow rate, based on the head of water above the roof drain, shall be used to size the storm drainage system in accordance with Section 1106. The flow rate used for sizing the storm drainage piping shall be based on the maximum anticipated ponding at the roof drain.
1102.6 Roof drains. Roof drains shall conform to ASME A112.6.4 or ASME A112.3.1.
ICC Commentary
ASME A112.6.4 regulates the design and construction of roof drains. Roof drains must have either a dome or grate covering the opening. This helps restrict leaves and debris from entering the storm drainage piping and creating a stoppage. Because roof drains are exposed to extreme temperatures, it is common practice to install an expansion joint between the roof drain and the storm drainage pipe.
ASME A112.3.1 provides details for Types 304 and 316L stainless steel roof drains.
Based on these passages, it seems clear that the Florida Building Code assumes that roof drains are required when part of a storm drainage system. Regardless of the type of drain used, it is imperative that the attachment of the drain and the leader prevent undue movement where they intersect with the roof assembly. Most importantly, a pressure seal is required when a head of water could possibly occur in the drainage system. The code says that all primary roof drainage means shall be assumed to be blocked, so head pressure must also be assumed. It is also clear that the roof covering shall be installed according to manufacturer’s installation instructions which include roof drain flashing.
Mike Silvers, CPRC, is Owner of Silvers Systems Inc. and is consulting with FRSA as Director of Technical Services. Mike is an FRSA Past President, Life Member and Campanella Award recipient and brings over 50 years of industry knowledge and experience to FRSA’s team.
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