Rooftop Gardens: Smell the Roses NOT the Odors!
Every single day I learn something new and different about the overall issues and concepts to consider when planning any form of garden roof. Whether it be a green roof or a rooftop garden for heavy pedestrian use. Today I was exposed to an aspect of the project that warrants consideration and planning. It is all about odors and what is a natural part of a traditional rooftop: vents and stacks. Fortunately for me, I was able to find a knowledgeable professional who was willing to be interviewed on this very subject.
Q. Mr. Barnhardt, the obvious reasons why people use vent filters is to remove sewer or grease odors. In our case we are talking about roof top gardens and people would like to smell a rose than smell sewer gas. Can you tell us why the sewer pipes are there on the roof for those who don’t know why?
A. First, please call me Mack. Every roof that at least has a restroom Linda has sewer pipe(s) on the roof and sometimes a grease vent pipe if a restaurant is in the building. Vent pipes are a direct link or pipe to the underground sewer system. They are used to allow DFU (Drain Fixture Units) like sinks, toilets & tubs to drain faster and to stop clogging in the pipes from backups. A 4” pipe can have up to 500 DFU’s on it which means it moves a lot of water and waste. In this case our small scrubber will not work very well and we need to go to a larger scrubber. At the same time a 4” vent could only have a few DFU’s and our smallest scrubber would be acceptable for this application. We see engineers capping vents all the time to stop the odors but this only causes problems in the building by building up positive pressure that puts sewer odors in the building or negative pressure which causes pipes to back up or not drain properly.
Q. Mack, so how do we know how many DFU a vent pipe has?
A. You can check your building plans Linda or you can just plan for the worse case application which is the best thing to do in my opinion. So if you do have a 4” vent pipe then just use the correct scrubber for this application. If all you need is a scrubber with a vacuum breaker then use it. We also have building codes that need to be considered as well. While most districts don’t allow our type of filtration in this application, using scrubbers on vents, many let us install them because businesses are losing customers. As long as we have a balance between the DFU & the correct scrubber the vent pipe system will perform as designed. You can always contact your plumber or a person like me to help you get the correct scrubber.
Vent scrubber with protective cage.
Q. Why do you call your vent filters scrubbers Mack?
A. I call them scrubbers because they are not filters although some folks will call them filters. A scrubber is defined as scrubbing the air with activated media without adding unnecessary pressure during its service life; the scrubber focus is not removing particles. A filter focus is to capture particles and this will add pressure during its service life. I agree it is a fine line but it is one that we use to help define what we are trying to accomplish.
Q. Can you explain Mack why one building will have odor problems with vents on the roof while another building next door will not?
A. Some buildings have no issues with odors from vents while a building next door may have light to very bad odor problems is caused by pressure. All are connected to the same sewer (if on the city sewer system) and when the main sewer line goes into positive pressure even for a minute odor is released through the manhole covers and sewer vent pipes. Once the system goes negative the odors are not released. Another reason for odors is when the vent pies hold waste in a horizontal line and it sags or bends. This buildup will hold onto odors and release them on the roof vents. I have even seen a large building like a casino roof have odors on one side of the building and the other has zero odor problems. If there is no positive pressure there is simply no odor.
Q. You mentioned Mack about your unique media, can you explain this a bit more for us?
A. When we used “Activated Alumina Engineered Media” that is designed for sewer gases we increase the removal capacity per pound and lower disposal of media waste that is put into landfills. This capacity we have on Hydrogen Sulfide (H2s), as high as 49% per pound, outlast and out performs activated carbon which is as low as 4% per pound of Hydrogen Sulfide (H2s). We use exclusively Purafil ESD Engineered Dry Media because it has the highest removal of H2s and since H2s is neutralized when used media is thrown away there is no H2s being added to the landfills. This is why I call Purafil media a Green Media since it is safe for the environment. Purafil media is also UL-900 tested so it will not contribute to a building fire. Carbon is not UL tested and will burn at a very low temperature. If you are using carbon in an area like Las Vegas where roofs can get very hot using carbon media is like installing match sticks on your roof. Some say this is extreme reasoning but we do have a good reason for concern. It is a chance that some building owners will take and others do not.
Q. What about cost?
A. We offer the solution to control or stop odors using a refillable housing that allows airflow to keep normal sewer vent pipe operation. The replacement media comes in a pre-packaged bag and all you need to do is dump out the old and pour in the new. Our smallest scrubbers cost $24 and I have seen them last up to 2 years but 6 to 8 months is about the average service life.
PVC vent scrubber.
Q. What is the Bottom Line?
A. Bottom line Linda is controlling odor and allowing the sewer vent pipe system to operate as normal as possible. If you are having odors or having drain problems then something is wrong. You should be able to not smell odors when you are on your Roof Top Garden. Grant it we have came across a couple of systems where we had to custom make a scrubber but we have been 100% successful in removing the odors. One point of caution I like to tell everyone is, to use any type of scrubber or filter on vents require that your vent pipe system has to be 100% sealed! Any leak no matter how small will cause odors to leak into the building. These holes or micro cracks in the vent pipe are required to be fixed even if you choose not to use filtration on the roof. You can check out my web page for scrubbers URL: http://afslasvegas.com/products.html, we have some photos of installed odor control scrubbers from our very small ones we sell for $166 to very large ones going for $20,000 or more.
Thanks to Mack Barnhardt from Air Filtration Systems, Corp. in Las Vegas, Nevada for his time in answering all of my questions and hopefully your questions too. I try to think of questions that we all have about our buildings. Look for Mack’s link on our Resources page as well. It is comforting to know that there is such technology available to make our rooftop gardens enjoyable and pleasant.
