As roofing contractors, we endeavor to keep water outside of structures. With most roof drainage designs, we direct the water to the outside of the structure, but there are exceptions to this. Sometimes we purposely direct the water towards the inside. Hopefully, all of that water goes into a drain and then a leader (pipe), which keeps the water out of the interior elements. But when one considers that all of the water from the contributing roof area must pass over and through this drain, it often is not given the careful consideration it deserves. I hope to provide you with some specific code requirements and some observations that apply to interior drains, both primary and secondary. I will also cover some other types of drains like scuppers, porch tubes and flashings at the roof edge.
Properly performing roof drainage systems are a collaboration between the designer, the plumbing contractor (if drains are involved) and the roofing contractor. However, after the initial design and installation, most types of roof drainage, except for some of the plumbing components, are addressed primarily by the roofer. During reroofing (recovering or replacement) the roofing contractor is almost always the party responsible for work done to the drainage system regardless of the type.
Let’s answer a couple of general code questions before we start into particular drain requirements.
When performing a reroof, do I have to bring everything that interfaces with the roof covering, including drainage, up to current code? No.
First, a reroof is an Alteration Level 1 and there is an exception and several other provisions that address this based on the following:
Chapter 2 Definitions
Section 202 General Definitions
Alteration. Any construction or renovation to an existing structure other than a repair or addition. Alterations are classified as Level 1, Level 2 and Level 3.
Chapter 3, Provisions for all Compliance Measures
Section 301 Administration
301.1 General. The repair, alteration, change of occupancy, addition or relocation of all existing buildings shall comply with one of the methods listed in Sections 301.1.1 through 301.1.3 as selected by the applicant.
Exception: Subject to the approval of the code/official, alterations complying with the laws in existence at the time the building or the affected portion of the building was built shall be considered in compliance with the provisions of this code
unless the building is undergoing more than a limited structural alteration as defined in Section 907.4.4.
Section 302, General Provisions
302.3 Existing Materials. Materials already in use in a building in compliance with requirements or approvals in effect at the time of their erection or installation
shall be permitted to remain in use unless determined by the building official to be unsafe.
Chapter 5 Classification of Work
Section 503, Alteration - Level 1
503.1 Scope. Level 1 alterations include the removal and replacement or the covering of existing materials, elements, equipment, or fixtures using new materials, elements, equipment, or fixtures that serve the same purpose.
503.2 Application. Level 1 alterations shall comply with the provisions of Chapter 7.
Keep in mind that the actual work you are doing still must comply with the current code. There are also some very specific areas where some of the building elements must be addressed during certain alterations. One example of this is the deck re-nailing and roof-to-wall connection requirements covered under mitigation.
Does that mean that I can address the drainage as I choose? No.
The code has a common theme of not reducing compliance that addresses this, including:
701.2 Conformance. An existing building or portion thereof shall not be altered such that the building becomes less safe or energy efficient than its existing condition.
This provision is extremely important when it comes to drainage. Many of the roof drainage requirements are covered under the FBC Plumbing (P) volume. In particular, the size of roof drainage system is in this volume and is quite complex. If you have been doing any roofing work on new construction over the last 20 years or so, you know that the size of roof drains has greatly increased during that period. This means that drainage systems in buildings built prior to the current code are often undersized in comparison. If you reduce the capacity of the existing drainage system, it will most likely not meet the requirements in place at the time it was designed. This includes drains and scuppers, both primary and secondary, as well as other types of drainage such as porch tubes and edge flashing. You do not want to be the contractor who decided to reduce the ability of a roof to drain properly during a heavy rain, particularly when it causes what
could be a very serious problem.
In the HVHZ a change has been made to help clarify this in the new code:
1514.4 Roof drainage. Unless roofs are sloped to drain over roof edges, roof drains shall be installed at each low point of the roof. If required, roof drains shall comply with the Florida Building Code, Plumbing. Where required for primary 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. Scuppers shall be sized in accordance with the provisions contained in ASCE 7, Chapter 8 with commentary and shall comply with Section 1611 herein.
1514.4.2.1 When overflow scuppers and roof drains are installed, they shall be lined with approved metal or other approved materials set forth herein.
1514.4.2.2 When recovering, reroofing or repairing an existing roof, the existing number or size of required scuppers and/or roof drains shall not be reduced, unless a new drainage system is designed by a registered design professional in compliance with the provisions of this code.
1514.4.3 Sizing and discharge. Roof drains, gutters, conductors and leaders shall be sized and discharge in accordance with the Florida Building Code, Plumbing and ASCE 7, Chapter 8 with commentary.
So how can roofing contractors have a negative impact on the existing drainage system? There are numerous ways.
When you consider these code requirements, several areas come to mind. If you are installing a new tapered insulation system you may be completely changing the way the building was designed to drain. For additional information on this, please see these previous columns in Florida Roofing: Tapered Insulation Considerations - September 2018 and Tapered Insulation Considerations, Part II – October 2018. But back to the drains themselves.
One of the most common areas where we see the size of drains reduced is when a “retrofit” type drain (see picture 1 Read More) is used. Depending on the size of the original drain, a retrofit drain may reduce the effective opening of the drain by as much as 20 percent. This calls into question when they can be used. If the building has had interior drainage added to reduce ponding, it was not part of the original drainage design or it has multiple drains and effective secondary or
overflow drainage and a concrete deck, you may be okay; but if it is an older building with parapet walls, a metal or wood deck and structure with no overflow provisions, it is a different story. So, a contractor must choose carefully where they use these drains. How about using an inverted lead boot or a similar liner in a drain or, worse yet, for a drain? No.
The first problem with this approach is that if the drain is connected to a leader inside the building a “gravity seal” is not acceptable. If the drain backs up for any reason, including an extremely hard rain, the connection will leak. This drainage system must be able to withstand the pressure that will be created from water standing on the roof surface all the way to the discharge. Some liners have an expansion device to put pressure on the liner and against the pipe to
attempt a seal. These devices can also reduce the effective area of the drain.
I referred to a “porch tube” (see pictures 2 and 3 Read More.) earlier. A porch tube serves the same function as a drain, but is usually one piece that discharges or makes its first “gravity sealed” connection outside the building, usually below the soffit.
How do we comply with these requirements and still reroof a building with drains? You have many options.
This comes back to two main concerns; both typically can be addressed by reusing the original drains or with new replacement drains. You can’t reduce the effective area of the drains and you need a watertight connection between the drain and the roof covering or, in the case of replacement drains, between the drain and the leader as well. To reuse the drain as originally intended, you need to achieve several things. It needs to be clean, particularly where the drain and the clamping ring (see picture 4 Read More) create a gasket effect. Just like with any gasketed surface, contamination of these surfaces will create problems. If the drain doesn’t use a gasket, it will usually have a flange. Some drains may use both a gasket and a flange. It is still important that the flange be clean and primed. The clamping ring must be there and match the drain. The bolts, washers and nuts must all function. You must use flashing at all roof drains because it is a termination and is required by the code. Field membrane alone does not satisfy this flashing requirement. In many roof systems, the flashing will be a lead sheet formed to fit the condition (see picture 5 Read More) Other systems may use a flashing membrane or an additional layer of field membrane. A drain should also have an appropriate cap, dome or screen. Being able to identify the manufacturer and model of the drain will be critical if any parts are broken, deteriorated or missing and you plan to reuse the drains. Most drain components will have identifying marks (see pictures 6 and 7 next page Read More.). If not, with some accurate dimensions and pictures, they can usually be identified by specialty
distributors or some plumbing supply warehouses. Often replacement and/or reworking of clamping ring bolts and the threads in the drain is required. This may require the use of drills, easy-outs, heli-coils or taps to save the drain. If this can’t be accomplished, the drain may need to be replaced by a licensed plumbing contractor. This can be the case if the drains use a synthetic rubber insert to seal between the drain body and the leader. You can replace the drains with new
drains that do not reduce the effective opening size to correct any of these conditions.
Another area of concern are scuppers. I have seen both primary and secondary scuppers that have been relined multiple times, sometimes with a new smaller metal scupper or multiple layers of flashing material. All of this reduces the originally designed effective\opening of the scupper. Remember, if you are not redesigning the drainage system (use extreme caution if so) you need to maintain both the ability to drain the volume of water and the intent of the original design.
When recovering and/or adding insulation you will be raising the height of the roof covering. If the roof drains through scuppers, you will need to either raise or widen the scupper to maintain the original size or create a sump in front of the scupper that maintains its original effective opening.
As I stated earlier, the Plumbing volume of the code contains much of the roof drainage information. Among other requirements, it contains the requirements for gutter and downspout sizing. I will address some of what is included there, as well as other drainage considerations, in a future article. Watch this space.
Hopefully, I’ve provided some information that will help you when considering how to address roof drainage during you reroof projects.
Mike Silvers, CPRC is owner of Silver 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 40 years of industry knowledge and experience to FRSA’s team.
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