Replacing a Roof Drain on a Structurally Sloped Steel Roof Deck

Figure 1. Roof drain detail. Photos: Hutchinson Design Group Ltd.

What is the number one goal of any building owner when it comes to the roof? They don’t want water pouring through their ceilings damaging the interior of the building. How do you keep water out of the building? By keeping the water on the exterior of the building and directing it to the roof drains or other drain locations, such as scupper or gutters. The roof drain is, on a basic level, one of the simplest details on the roof, and yet it is flashed incorrectly time and time again. This paper will walk you through the process of replacing a roof drain on a structurally sloped steel roof deck and installing the new roof system and flashing.

Photo 1. The sump pan and drain body have been installed. Photos: Hutchinson Design Group Ltd.

First off, we are going to assume that the current drainpipe is adequate to handle the existing water volume and drain its portion of the roof, and that the drain pipe is in good condition. Our new roof system will meet the current R-30 requirements for continuous insulation above the roof deck in a roof near Chicago. So, our roof system will be composed of a mechanically fastened substrate board on the steel roof deck, a self-adhering vapor retarder, two layers of 2.6-inch insulation mechanically fastened, a 1/2-inch modified gypsum cover board set in bead foam adhesive, and fully adhered EPDM membrane. (See Figure 1.) We will also assume that the roofing contractor is acting as the general contractor for our scenario.

Now that we have our parameters out of the way, what’s first? I have never met a building owner that likes construction debris inside of their conference room or classroom, so the interior needs to be protected prior to the removal of the existing roof drain. This can be as simple as some Visqueen, but the interior protection needs to be installed prior to the removal of the existing roof drain. The one question that seems to come up is, who is installing this protection? The owner? The plumber? The roofing contractor? I like to put this on the plumber. He knows when he is removing the drain and installing the new one.

Once the interior protection is installed, we need to coordinate the removal of the existing roof system and installation of the vapor retarder with the removal of the existing roof drain, as well as the installation of the new metal sump pan, drain body and lead and oakum joint to the existing drain pipe. (See Photo 1.) This all needs to be done on the same day so that the roof can drain properly and that the vapor retarder can be terminated onto the roof drain flange. This part is critical, as with experience this designer has learned that the vapor retarder can be used as the seal between the extension ring and the roof drain flange and that the O-ring can be eliminated. The sump needs to be fastened to the roof deck around the perimeter at 8 inches on center and be centered on the drainpipe. The drain body then needs to be set over the drainpipe and lead and oakum installed between the drain body and drain pipe.

Installing the New Roof

So, now we have the roof drain body and the vapor retarder installed. Now comes the new roof system. To meet our R-30 requirements, we are going to need a base layer of 2.6-inch polyisocyanurate insulation and 4-foot-wide, 1/2-inch-per-foot tapered insulation sump around the roof drain. This sump will get us to the R-30 requirements of 4 feet from the roof drain as required by the current codes. If my math is correct, that will leave 3.1 inches of insulation at the roof drain. We will need a reversible collar and threaded extension ring to accommodate this height. When setting the reversible collar onto the drain bowl, set it in water cut-off mastic. If the drain ever becomes clogged, this will help to keep water from seeping under the reversible collar and into the roof system. Next the threaded extension ring is installed. First, install some water cut-off mastic onto the treads prior to engagement with the reversible collar. Once again, this will help to prevent water from entering the roof system if the drain becomes clogged and backs up.

Photo 2. The extension ring has been set lower than the cover board (yellow) and water cut off mastic has been installed on the extension ring flange. Photos: Hutchinson Design Group Ltd.

One of the main questions that I receive from the roofing and plumbing contractors is, “How high should I set the extension ring?” Well, it varies per roof system, but for our scenario it needs to be set flush with the top of the tapered insulation. We set it here because we have our cover board that has yet to be installed, and when the clamping ring is installed it will be lower than the cover board. Now back to the insulation; the 2.6-inch insulation should be installed as close to the extension ring as possible, chamfered as required to fit under the flange. Next the tapered insulation sump is installed. This should be installed as close as possible to the extension ring flange and chamfered as required to fit beneath the flange. All voids between the extension ring and the insulation should be filled with spray polyurethane foam insulation.

Once we have our insulation installed, next comes the cover board. The number one thing with the cover board and roof drain is having the cover board cut perpendicularly to the roof drain flange. (See Photo 2.) Do notchamfer the cover board. Chamfering the cover board may ease the transition of the membrane onto the extension ring flange, but it creates an unsuitable substrate surface for the bonding adhesive. And in my experience, water seems to end up ponding around the roof drain and not dropping into the roof drain. This will also allow the roof’s drain clamping ring to sit flat and below the roof surface of the roof.

Photo 3. The membrane has been correctly cut in a cloverleaf pattern. Photos: Hutchinson Design Group Ltd.

Now that our cover board is installed, we have the membrane and its transition into the roof drain. Water cut-off mastic is to be installed on the extension ring flange. How much you ask? One tube. Load that flange up. Make two thick beads with it. I have never heard a contractor say, “Man, using all of that water cut-off mastic on the job really set me back.” It’s a small item, but it is worth it.

After the membrane has been installed and the clamping ring is set, it’s time to cut a hole in the membrane to allow the water to get to the drain and off the roof. How big should the hole be? As small as possible is what some contractors might say. I ask a question to you now: what is the goal of the roof drain? If you answered to get the water off the roof as quickly as possible, you would be correct. Then why would the contractor want to cut a small hole in the roof membrane that would restrict the flow of water into the roof drain piping and off of the roof? I am dumbfounded as well. When we detail the roof drain, we call for the membrane to be cut back to within a 1/2 inch of the extension ring in a cloverleaf pattern around the clamping ring bolts. (See Photo 3.) This way there is no confusion on how far back the membrane is to be cut. Set the drain dome and the roof drain detail is complete.

So, there you have it. Now the roof can drain properly with a brand-new roof drain with no problem (fingers crossed).

The Hidden Costs of Workplace Accidents

Asking an employee why he or she wants to be safe is like asking them why they work. Overwhelmingly, every roofer I ask this question to tells me he or she wants to go home at the end of the day. He doesn’t want to lose any time because losing time is losing money. And, believe it or not, money can buy happiness. A New York City carpenter once told me he fell 35 feet and broke multiple bones. He was out of work for two years, during which he collected $57,000 from workers’ compensation insurance. If he worked, he would have made more than $100,000 per year. In his words, “I almost lost my big house on Long Island and my high-maintenance wife.”

In addition to how accidents impact workers’ finances, they can seriously affect a company’s bottom line. A good Health and Safety Program can save a company money by cutting workers’ compensation insurance premiums; heading off needless, expensive and embarrassing OSHA citations; avoiding expensive and embarrassing lawsuits; increasing the efficiency of the workforce; and boosting workers’ morale, which consequently will improve their productivity. A good Health and Safety Program also will give a business owner peace of mind by knowing all his or her employees are working safely.

In my experience, project managers, job-site superintendents and crew foremen are the people who are reluctant to want job-site safety. They believe following safety standards slows the job down. Management is responsible for making money in a business that regularly grapples with close bids, tight schedules and limited job budgets. However, these factors do not take into account the “hidden” costs of workplace accidents. Oftentimes, accidents are more expensive than people realize because of these hidden costs.

Examples of Hidden Costs

Some costs created by accidents are obvious; for example, workers’ compensation claims cover medical costs and indemnity payments for an injured or ill worker. What people often don’t think about are the hidden costs, like the costs to train and compensate a replacement worker, repair damaged property, investigate the accident and implement corrective action, as well as maintain insurance coverage. Even less apparent are the costs related to schedule delays, added administrative time, lower morale, increased absenteeism and poorer customer relations.

Washington, D.C.-based OSHA’s Safety Pays Program states the lower the direct costs of an accident, the higher the ratio of indirect to direct costs. The more accidents that occur in a workplace, the higher the costs in increased insurance premiums and greater indirect costs. According to the Boca Raton, Fla.-based National Council on Compensation Insurance Inc., these include the following kinds of indirect costs:

  • Any wages paid to injured workers for absences not covered by workers’ compensation.
  • The wage costs related to time lost through work stoppage associated with the worker injury.
  • The overtime costs necessitated by the injury.
  • Administrative time spent by supervisors, safety personnel and clerical workers after an injury.
  • Training costs for a replacement worker.
  • Lost productivity related to work rescheduling, new employee learning curves and accommodation of injured employees.
  • Clean-up, repair, and replacement costs of damaged material, machinery and property.

Some of the possible indirect costs not included in these estimates are:

  • The costs of OSHA fines and any associated legal action.
  • Third-party liability and legal costs.
  • Worker pain and suffering.
  • Loss of good will from bad publicity.

The Human Factor

Direct and indirect costs certainly are motivation for preventing workplace accidents. In fact, when I ask roofing company owners why they want their employees to work safely, many automatically default to the money answer. However, in most cases, business owners are generous, caring members of their communities. I once sat across the desk of an owner of a large construction company after his team experienced a fatality. He asked me, “How do I look at myself in the mirror every morning, knowing one on MY guys didn’t go home today?” Even though he did not know this employee personally, he considered this worker one of his guys. Ultimately, it’s the human factor that is the most important reason to ensure safe working conditions on job sites.

My favorite phrase is “To protect my employer, I protect his employees.” I think they’re words to live by.