When it Rains it Pours – Roof Drains Pipe 101

Working on Roof Drains Pipe is Like an Art

I know this may seem like a strange subject to elaborate on but roof drain pipe work is very much a specialty inside the plumbing trade. What could be complicated about roof drains? This article is not about installing roof drains in a new building, that is pretty straightforward. In this article I will explain in detail how to repair and install roof drains in a re-roof scenario.

This is one of those specialties where most plumbing contractors are usually too high to get a job or too low because they don’t know what they’re doing. However if you do know what you’re doing and I’m going to make sure you do by the time you finish this article, you can make very high profit margins performing this work.

The first thing we should to is to define what a roof drain does. A roof drain is installed on a building roof or canopy to convey storm water from the roof or canopy to the storm drainage sewer or retaining area. Storm water can be received in three different ways.

  • From the roof drain to the storm drainage piping to storm sewer, eventually making it’s way to the city sewer system.
  • From the roof drain to the storm drainage piping to a retention pond or reservoir.
  • From the roof drain to the storm drainage piping and the water is left to splash on the ground where it dissipates naturally.

There are occasions where the roof itself is designed to hold water due to limitations in the storm system and/or water retention system.

The first thing you should know about repairing or replacing roof drains is that most often it falls under the roofing contractor’s scope of work. So the first thing you should do is find the roofing contractors that do the most “re-roof” work. There are some roofing contractors that do both new and re-roof work but you’ll find some specialization as well.

OK so you’ve found the roofing contractors to bid the work to now they want you to go look at a project to give them your know how. The very first thing you should be able to identify is what type of deck you’ll will be dealing with. What material the roof drains go into can give you some clues as to difficult the drains will be to repair/replace. Here are the common decking surfaces you’ll run into.

heavy rain on top of roof


Drains are installed in a concrete deck can be done so in two ways. The drains can be poured in place. This means the drains were set and the concrete roof was poured around the drains. In the second scenario the deck is poured first and a hole is cored to except the drain. (We will expand upon both of these installations in a bit)

Gypsum or “Gyp” Deck

Gypsum roof decking was very popular in the 1970s and 1980s and although they are still used today their popularity has waned in recent years. Gypsum roofs usually consist of two layers. The first layer is made of gypsum board usually ⅝” in thickness, the second layer consists of a gypsum slurry mixture with the consistency of lightweight concrete that is poured over the first layer. This layer can be formed to slope to the roof heads to ensure proper water removal. Gypsum roofs are used for their fire retardant properties and they are economical. Drain installation on gyp decks can be done using a sump receiver/pan or the drain can be installed directly on top of the deck. The flange of the drain will rest on top of the decking material.

Techtum Deck

A techtum panel roof is very popular for it’s acoustical deadening properties and it’s robust fire retardant values. The underside of the techtum panels can come finished or prefinished so the exposed ceiling is a finished product. Drain installation on this type of deck is very similar to that of a “gyp” deck. The drain can be installed using a sump receiver/pan or on top of the deck.

Your Bathroom Is a Mess Should You Use A Bath Fitter?

I get a bath fitter question almost every week. Give me some idea on bath fitter costs or do you have a clue about bath fitter prices? Before I get into detail about a bath fitters price I want to talk about what a bathfitter actually does.

Metal Pan

A metal pan roof typically has a lightweight concrete fill for added rigidity and sound deadening. This type of roof is extremely popular in public buildings most likely because it’s economical and fire retardant. Roof drains are installed one way, using a metal sump pan laid on the deck and the drain is set in the pan.

Wood Deck

Wooden decks are rarely used anymore, they are quick and cheap to install but can deteriorate fairly quickly and can be a fire hazard. Roof drains can be installed two ways using a metal sump pan or by installing the drain directly on the deck.

Standing Seam

A Standing Seam roof is a metal roof that is almost always pitched to gutters thereby eliminating the need for conventional roof drains. You can use a parapet drain for these types of installations as well.

Rubber or EPDM Roof

A rubber roof is just that, a rubber membrane is placed over insulation panels which are fastened to the deck. The roof drain is usually set in the deck and the membrane is stretched over the entire roof. The membrane is cut out at each drain and is secured by the drains clamping collar. EPDM roofs are water proof and tend to be expensive. The clamping collar secures the membrane at each drain to ensure a water tight seal.

old sheet roof after rain

To Know the Roof Drain Manufacturers is to Love Them

So now that you know the different types of roof decks its time to familiarize yourself with the different drain manufacturers. Being familiar with the drains produced by the big drain manufacturers is extremely important especially on re-roof and or roof drain repair. Why you ask? A roof drain is a roof drain. Right? Well all roof drains do basically the same thing however not all drain bowls are the same diameter or more importantly have the same bowl depth.

If you are trying to replace the drains with minimal work from below the roof deck you want to have a drain with the same bowl depth or with a deeper bowl depth. If the new drain is shallower you’ll have to get below to change the rise piece to the drain or it will be too short. So onward, here are the different drains and their color (Hot Plumbing Tip : You can figure out 75% of the roof drains you’ll run into by their color.)

J.R. Smith

J.R Smith Manufacturing has been around since 1926 and they are one of the largest manufacturers of roof drains, floor drains, trench drains, fixture carriers, and grease/debris separators in the US. Very recently J.R. Smith has invested heavily in rain water harvesting. You will find J.R. Smith in most MEP Engineer’s specifications. Their bowl color is mustard yellow.

J.R. Smith


Zurn was founded in 1900 and began by making backwater valves, now Zurn is one of the largest manufacturers of plumbing products in the world. Zurn not only manufactures drainage product like roof drains, floor drains, trench drains, grease traps etc., but they also manufacture Wilkins backflow prevention devices, Zurn Flushometers and faucets, Chemical drainage pipe and fittings and a line of commercial plumbing fixtures. Their drain products are blue in color. The styles and patterns of the Zurn products are very similar and their installation is almost identical to that of J.R. Smith drains.



Wade is one  of the oldest manufacturers of drainage product in the US. The company has a rich and storied history. Wade was founded in around 1868 by James J. Wade. James Wade was a Certified Master Plumber in Chicago and  was one of the founders of Chicago Plumbing Contractors Association (PCA) and served as it’s president in 1880. J.J. Wade Construction was one of the largest general contracting firms in Chicago but gradually moved out of contracting and more into manufacturing eventually abandoning contracting all together. In 1963 Wade was purchased by Tyler Pipe and it remains under their umbrella today. Wade drains are also very similar to J.R. Smith and Zurn drains. Wade drains are orange/red.


Josam Drains

Josam was formed in 1914 and has full line of drainage products including roof drains, floor drains, trench drains, fixture carriers, acid waste piping and customs separating equipment. When removing hardware like clamping rings and domes you’ll notice a very different mounting design. Josam up until several year ago used ladder clamps to lock down their drain domes. They have since changed their design to make them similar to other manufacturers. Josam drains are green.

Josam Roof Drains

These next two are the relative new comers on the block but are no less innovative in their design.

Watts Drainage

Watts Regulator Company was founded in 1874 and was the innovator of the pressure reducing valve. In the 1900s Watts designed the Temperature and Pressure relief valve (T&P Valve). Watts continues to innovate in the area of backflow prevention and pressure regulation. Watts is relatively new to the roof drain, floor drain, fixture carrier market. Watts bought the castings and molds used to manufacture the now defunct Ancon Drains.

Watts Roof Drain

So if you’re looking for parts and you think its Ancon, call up your local Watts rep, they may be able to help. One great feature that Watts incorporates in all the roof drains and floor drains is epoxy coating. This is a cost upcharge on all of the above drains but comes standard on Watts drains. Watts drains and carriers are gray.


The last of the full line drainage manufacturers is MIFAB. The company was founded in 1982 and was originally headquartered in Saskatchewan, Canada. MIFAB’s headquarters and main distribution is now located in Chicago. MIFAB manufactures a full line of roof drains, floor drains, trench drains, separators, access panels and doors, customs stainless steel separators and sinks. We’d like to make special mention, despite their tremendous growth the president and owner Michael Whiteside remains accessible and helpful.

Mi-Fab Roof Drain

The company is extremely good at solving drainage problems. We’ve never seen a company take a sketch and some notes, take it to the drawing board and have an engineered working model in less than a week, the product was not made of parts on hand. If you’ve got an unusual project or problem give Mi-Fab a call, they may be able to solve your issues. Mi-Fab drains are red.

The next two are specialty drain manufacturers but are important in the world of roof drain installation and/or replacement.

Marathon Roofing Products

Marathon was founded in 1966 and originally manufactured copper roof drains but as the years went be they continued to expand their product line. Marathon Roofing Products are very popular with roofing contractors. Why? because they can usually install the drains themselves. Marathon’s retrofit drains are made to insert into the existing drain.

Marathon Insert Drain

They are built with an integral flashing pan so when the drains are inserted the flashing pan is sealed by the roofer. It’s a quick economical fix and they work pretty well. Marathon now has a limited line of traditional roof drainage products and the Owner Todd Cislo is friendly and accessible. Marathon is another company that solves problems so put them in your arsenal as a company that makes your life easier.

Froet Industries LLC

Froet Industries began by manufacturing their patented Bi-Functional roof drain. It’s basically a primary roof drain and an overflow combined into one drain. We will provide a diagram to show you how it works. Each bi-functional drain has two outlets, one that is connected to the primary storm drainage piping and one that is connected independently to a secondary storm line or preferably piped outside the building where is splashes on the ground. Froet now offers options on primary drains as well. By using the Froet drain you are eliminating another penetration in the roof saving you labor and another potential spot for leakage.

Froet Roof Drain

**Zurn Manufacturing was the first company with a Bi-Functional roof drain however it never caught on. It was until after Froet popularized the drain the Zurn brought it back into their catalog. Froet does have a patent on some form of the drain.

UPDATE….After having a long and interesting conversation with the Owner and founder of Froet there is no doubt that they were the very first company to manufacture and patent a bi-functional drain. In fact at the time of its development the design was pitched to most of the major drain manufactures and the idea was categorically shot down.

Froet is the only one piece bi-functional drain. All similar drains manufactured by the major drain companies use their standard large body drain and the other pieces are welded on. Our opinion is that the welds just add more areas for a possible leak.

The above are the most popular drain solution manufactures in the US, there are others but these are the ones to know. So now you know how to identify roof drains and can familiarize yourself with their features but what are some tips for installation?

Removing and replacing a Drain with a Cast Iron Piping Lead and Oakum Joint in any Deck but Concrete

We know that’s a real long description but its really the only one that works. The first thing you do if the hardware is still on is remove the hardware (clamping ring and dome). You can remove the lead and oakum two different ways, the first (hard way) is to fire up your torch and melt the lead out. You take a flat head screw driver and flick the molten lead out until you get down to the oakum.

At this time you should be able to take a pair of channel locks and pull out the oakum and remaining lead. If that sounds inefficient and somewhat dangerous you’re right. Please make sure to wear your safety goggle at all times when performing even the smallest of plumbing projects. The second way (easier way) is to get a drill bit that can fit inside the space of the lead joint and start drilling the lead out of the joint going around the circumference of the joint.

Eventually you’ll remove enough of the lead so you can knock out or pull out the remaining,(a lead pick is pretty handy to get under the lead so you can pull it out.) then you take you channel locks and pull out the oakum. You can then just pull the drain up over the pipe, put the new drain in place and re-lead and oakum the joint.

HOT PLUMBING TIP : If you find yourself a on a re-roof project and you’re replacing drains. Try to get an exact replacement, if that isn’t possible attempt to get a drain with a deeper bowl. If the drain spec’d has a shallower bowl the rise pipe will not be long enough to make up the joint therefore you will have to get underneath and change the rise piece. If the bowl is deeper the pipe will stick up out side the joint but that’s an easy fix. Take an internal pipe cutter and or pencil grinder and cut the pipe down accordingly.

Removal of a Cast Iron Drain Poured in Place

This is probably the most difficult removal situation you’ll run across and believe us it took some time for us to figure it out but figure it out we did. If you run into roof drains poured in place take a 5lb or a 10lb sledge hammer and swing away trying to hit the inside of the drain. Trust us you’ll crack the cast iron eventually. When you get enough of the drain removed it becomes pretty easy.

There is another way to remove these drains but it is more expensive than the above. You can cal in you hole coring experts to come in and core around the drain to remove. It’s a pretty painless process but you’ll pay for the coring sub contractor and you better have someone below with scaffolding or an aerial lift to catch a very heavy core when complete.

Drain Removal Tips on the Rest

  • When installing overflow drains the proper way to install is to connect to a separate storm drain line or to splash outside. We have seen engineered drawings showing overflow drains connecting to the same storm line albeit further down the line but still on the same drain. If a blockage occurs after the connection to the overflow drain the overflow is useless and defeats the purpose.
  • Think twice about using a cast iron drain with a threaded outlet with threaded PVC plastic fittings. The expansion coefficient is different between to the two materials and they almost always leak at some point. We been on enough roof to tell you this with some degree of certainty.
  • If you run into an instance that you have a copper roof or a copper trough that needs drains installed call Marathon, they have the right product to help you out.
  • Even if a set of drawings doesn’t call for the drain body and/or piping to be insulated it’s worth it to see if the existing are insulated. Most buildings that have insulation on their roof drains and downspout piping want you to install the new to match existing.
  • Never and I mean never pour a lead and oakum joint while it’s raining. Don’t even do it if it drizzling. We’ve seen one drop of water empty out a lead pot. It’s very dangerous.
  • If asked to bid a roof drain job always ask what is present underneath the roof drains being replaced. Is it occupied office space? Is it a spline ceiling at 8ft with 10ft above the drop ceiling? Is it a dry wall ceiling, does that ceiling need to be torn out and replaced, does it need to be painted? Are your drains in a gymnasium? If so, make sure your lift has non marking tires. Who’s responsible for protecting the hardwood floor in a gymnasium? Believe us it’s an issue and clarification is necessary. If you are working in a library or in a sensitive area who is responsible for protecting those items?
  • If you are asked to provide new hardware on existing drains but you can’t figure out who manufactured the drains measure the distance between the bolt holes that hold the clamping ring in place and measure the diameter of the drain around the flange. This will give you a good head start. Also a few of the drain manufacturers make a Universal Clamping Ring that fix a majority of the drains both old and new. These clamping rings allow you to install a new clamping ring and a new dome from that manufacturer.
  • If under deck clamps are called for you must have access below to install, so this is once again an instance when it is very important to know what is below. Please note Zurn makes a new underdeck clamp that can be tightened from above thereby eliminating the need to go below deck saving you precious labor time. Please note, this feature is fairly new so not all engineers have seen them. This is a good time to show your know how, call up the engineer and ask for an alternate, tell him or her you can save them time and money.
  • When repairing or replacing roof drains look at using only the option for the cast iron dome. Plastic domes come standard but the cast iron domes are heavy and won’t blow away in the event of nasty weather. It’s good plumbing and you won’t lose a job because you have cast iron domes in the bid. We haven’t used anything but cast iron domes in 20 years.
  • If the roof repair or replacement is in a warehouse ask the owners or building engineer if there is any flex to the roof decking. We have seen no-hub drains become disconnected because the roof deck flexes so much with the wind.

Hope you enjoyed, we will give some additional tips on promenade deck drains, planter drains etc. in the future. Please don’t hesitate to leave us a comment or to ask a roof drain related question. Chances are if you’ve run into a problem with a  roof drain we have as well.



  1. What can you tell me about bi-level drainage for rooftop planters? what options are available for draining surface (soil-level) water and draining water that has seeped to the bottom of the planter?

    1. Hey Benn? I’m glad you found us. Is this a new application or are you putting new drains in an existing planter? Here are two drains you can use, I’ve used both and they work great.


      or http://content.zurn.com/web_documents/pdfs/specsheets/58817.pdf

      In either case you want to specify the type of drain model with type of dome. I would order the standard Z poly dome or better yet the ZA Aluminum Dome with the option suffixes SS for the Stainless Steel Mesh screen to go over the dome and the 84 Perforated Stainless Steel Gravel Guard. The drain model should read like this ZA-100 (3″, 4″, 6″ IC/IP or NH for connection size and type) SS-84. So if you were using the Z-100 drain with a 3″ No-Hub connection it would be a ZA-100 3″NH-SS-84. The stainless steel or bronze mesh would filter out an dirt going into the dome and the perforated extension would allow any water in the planter to seep into the drain. Hope that helps. The cast iron dome may deteriorate over time and although the poly dome would hold up to water the standard poly dome may collapse under some weight. We always try to over engineer when it comes to roof/deck/planter drains.


  2. I am working on a nasty restaurant roof which is covered in grease. At first the PVC flashing was installed improper and you could stick your hands under. We corrected this issue and tightened the ring above up on the roof. This last big rain it leaked again this time it leaked at the first joint of the insulation wrapped drainage pipe. 15 ft away from the drains themselves. I crawled up into ceiling and none of the wood deck was wet like it was before so it appears to only be leaking around the drain inserts where they insert into the actual drain pipe then getting the insulation wet and leaking at the first place it can which is the tape joint. There is a clamping ring underneath also. It was loose. We tightened it up and lifted it probably 1 1/4″ up. Do you feel this could be the cause of the leak. If not can I hear your opinions.
    Thank you
    Brian warren
    Raynestorm Co., LLC.

    1. Is the drain bowl and drop insulated? Can you see the connection between the roof drain and the downspout piping? If it’s a threaded joint and you’re using PVC its very possible the threads could be leaking. If it’s a no hub it could be the band has loosened or separated.


  3. i have a problem with a leak on a flat roof. we have a rubber membrane roof. cast iron drain, probably pvc underneath. its just started leaking was wondering if it could be the threads leaking or drain clamp?

    1. Hey Javier,

      Thanks for reaching out. It is very difficult to pinpoint the leak without you being able to replicate the issue. Do you know that you have a threaded drain? You mentioned PVC piping. I can tell you this much. We have found drains that cast iron threaded drains using PVC downspout piping leak more frequently than any other combination of drains and materials. Their expansion coefficient is different meaning the dissimilar material expand and contract differently with extreme temperatures. Can you flood the roof and see where the leak is coming from? That would be the first step. If you do see it leaking from a certain area of the threads I would replace the drain with a no-hub drain and a no-shear Fernco coupling or a plain no-hub coupling. The only issue we’ve ever had with that installation is with a massive roof flexing resulting in the coupling pulling apart. let me say that it is extremely rare.

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