Here we illustrate just how interior drains on flat roofs become clogged, causing rising ponds of water on the roof surface. The roof drain ketch at above left was provided courtesy of Carson Dunlop Associates. The combination of ponding water on the roof around the roof drain and the mechanical disturbance caused by freeze-thaw cycling act to loosen the drain connections, break the roof drain seal, and cause leaks into the building below.
When the through-building roof drain system has become clogged, even if it does not burst and lead to building flooding, it causes other building problems.
The roof structure may sag due to the added weight of ponding water. In the clogged roof drain photo provided by a reader anon.
Watch out : in severe cases of deep ponding water or water and ice and wet snow on a roof with blocked drainage, the weight of the water and ice may conspire with hidden rot or insect damage such as from prior roof leaks to cause catastrophic roof collapse - a very unsafe condition.
It is possible to add new roof drains to relieve ponding on a sagged flat roof, as shown at left. Notice that the new drain extends through the shortest possible route to the building exterior where it is conducted to ground or to a storm drain. When the building is re-roofed, the roofer may install tapered foam insulation to direct water to roof scuppers or to a main or new-main roof drain to prevent future ponding.
Sketch courtesy of Carson Dunlop Associates. I sent some picture to you and really appreciative your expertise on the water overflow in the elevators a while back.
This is the latest picture I have of what took place yesterday while the roof tank was supposedly being cleaned. This particular picture is directly outside of widow where this canopy drain is located However can you please offer me again your expertise on this issue as it is very scary for me to live with this condition that is totally ignored by management. This is all in addition to other picture I have sent you i. BM: There is additional important information that an on-site inspector would have to observe and then consider before offering a confident diagnosis about the roof drain overflow problem that you and your photo describe in your email.
Low slope roof drains are indeed subject to clogging that in turn can lead to serious, even dangerous conditions such as:. While an on-site expert would undoubtedly have more suggestions and could perform a more reliable inspection than anyone can do based on just a photograph, it seems to me that at a minimum your building maintenance people will want to:.
On some buildings it is possible to adjust the roof slope and amend the roof drainage to convert to roof scuppers that drain out through a parapet wall to the building exterior - eliminating a good part of these clog and leak difficulties. Whom do you trust to fix these problems? It is the building owner's responsibility to find and employ knowledgeable, reliable people; you may just aggravate the owner or maintenance staff if you are too directive, and worse, if you try to specify the exact repair then you will own the problem rather than leaving it in the hands where it belongs.
But certainly the solution to roof drainage troubles is not something to leave to an electrician and usually not a typical home inspector. To design a sloped or flat roof drainage system we need to know the anticipated maximum rainfall rate and the flat or projected roof area.
I examined several roof drainage calculators and tables to see what they tell us. Watch out : keep in mind that a design without adequate safety margins risks dangerous structural collapse of the roof or other catastrophes such as a building flood.
Just consider what happens in "real life" when roof drains become clogged because no one remembered to inspect and clear the drains. If you can change to an all exterior drain or scupper drain you will eliminate the risk of clogged or leaky drain piping that bursts and leaks inside your structure. The time to do this is during new construction - which is now in your case. Same side inside kitchen ceiling appears to be small damage beginning.
Could this be clogged drain or what? Have tall tree over building also. Can you advise. I'm sorry I nonymous, but I can't figure out your problem from just the e text.
It sounds as if you need properly sized and properly connected roof drains to repair an improperly installed, disconnected system. When are they ask your roofer for help. I need a new drain but I don't know which one to buy. The 4 inch drain pipe is located right next to my wall. It doesn't quite reach the 4 inch drain pipe below so it leaks. I want to buy a new drain but not sure which one to buy?
Can you please advise me which drain would work. I've been considering 90Degree types. Have a one-story flat roof house. Noticed wasps building a nest in one of the canales and it looked like they had plugged the canale with their nest. Killed the wasps!! However, after inspecting the canale opening on the roof, I discovered that an elastomer material had been applied to the canale on the roof side, effectively disallowing any water flow off the roof through the canale.
How do I re-open the canale, either DIY or would I have to hire a roofing contractor to open the canale? The roof repair was done 5 years years ago shortly before we bought the house. It is possible the roofer did this on purpose or simply made a giant mistake? Have a flat roof on garage with shingle and interior roof drain fitted to it.
A commercial roof can incorporate all four types of drainage systems. How to design the best drain system for any flat roof. Generally most roof drains are poorly designed. Although drains are the most important part of a roof, very little thought is put into their location and design.
The basic function of a drain is to remove water from a roof effectively. To achieve this the following factors must be in place:. It is important that the drain be placed close to the lowest point on the roof. One way to determine the low part of the roof is to string a line across the surface. This will show where water might be pooling. A laser leveler can also be used. There is far too much water on this roof in the picture, which puts too much stress on the structure.
What is amazing is that this is a Modified Bitumen membrane and it has been like this for over 15 years. Now that is proof that water can pool on a roof without causing too much harm. There will always be some pooling of water on many areas on the roof. The best thing to do is to place a drain in those areas where the water is pooling. A roofing contractor installs drains according to the blue print he is given.
Architects and engineers have failed to provide good specifications on where and how drains should be installed. The best drain system is recessed into the substrate.
Besides recessing the drain, this also provides an area where debris can be trapped. Provide a big enough drain grate and the combination is a very well thought of drain system.
In this video we explain how a good drain system is suppose to work. This drain was recessed and a big square area provides for the collection of debris.
We kept the old cast iron grate in place. Although the roof is relatively flat, most of the water flows to the drain area. The video above is a good example of how to design a good drain system.
The most important feature of a drain is to be able to drain water off a roof even if there is debris collecting around the grate or strainer. The picture below shows a drain in the proper location, the lowest part of the roof.
The problem is, debris is still preventing water from draining off the roof. This is why it is important to lower the area around the drain so it will collect debris and allow water to drain off.
Below is another image of a drain that has a recessed area around it. It is critical that the holes or slots be large enough to let small leaves and debris through the grate or strainer.
This is important because too small holes will quickly clog the strainer making it ineffective. The image below shows what happens if a drain is not properly flowing. The pitch of the roof is towards the drain. As a result, water pooled around the drain and compromised the seams and flashing of the roof at the wall, which caused leaks. The video below shows one of the most common problems we find with both commercia l and residential flat roofs. A drain should always be installed lower than the rest of the roof.
A good roofing mechanic will remove the existing plywood and lower the drain to include a square catchment area around the drain. This will help with the collecting of debris. We lowered this drain and added a double membrane for durability for snow shovel maintenance and standing precipitation. It is essential to the design of a new flat roof; provision is made to install a lower roof drain basin. Because of the basin, around the drain area, is much lower than the roof surface, the basin will likely collect debris that has washed from the roof into the basin, allowing room for water to rise above the debris.
When we installed this roof 20 years ago, we created a basin around the drain. You can see that debris collects around the basin catchment and the strainer; however, water was still able to flow over the debris. A Drain that is placed inside a basin makes for the most practical design This Three-D video shows how a flat roof drain should function…. Read More ».
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