Flood to avoid clogging. Dry vents, a method of providing air to a drain to equalize pressure and prevent traps from being suctioned, often have horizontal sections and are not intended for wastewater management. To prevent them from filling with waste in the event of a blockage downstream, horizontal portions of these vents must be at least 6 inches above the flood edge of the highest drained device.
Summary: Often times, when the goal of the code is to create a mess, it is because the cause of the mess can lead to bigger problems if not addressed. Sink blockages, for example, alert a homeowner to the need to resolve a shutdown before litter gets into the vents. The code creates this little “mess” and avoids a bigger one by placing horizontal dry vents a certain distance above the flood edge of a sink so that the sink fills, not the dry vent. Code expert Glenn Mathewson Explains this and other cases where the code inherently creates a mess and makes a problem obvious without damaging the components.
The bottom line of a reputable contractor’s job is clean, tidy, and effective – but sometimes the purpose is to create a mess in order to be effective. There are a handful of Code provisions the goal is to create a mess through design. A mess is palpable; a mess gets attention. A mess is investigated for the cause. If the goal of the code is to create a mess, it is because the cause of the mess can lead to bigger problems if not addressed. The mess is like a circuit breaker in an overloaded circuit. A problem arises (in the case of a circuit breaker, a power failure) to avoid a bigger problem. Sometimes the design of the pollution is up to the code user, which is made clear by the phrase “observable for the occupant” in the code regulations – for example, finding pipes to make the condensate overflow perceptible. In other cases, the clutter is related to a code deployment, e.g. B. installing horizontal dry vents over the edge of the sink so that blockages return to the sink rather than the vent
An overflow is inherently fail-safe. It keeps a system running in the event of a standstill. In contrast to a Circuit breakerAn overflow does not stop the system, but it does indicate that the system needs to be repaired immediately. For this to work the overflow needs to be noticed. The overflow of an AC capacitor and a high powered oven should inherently create a mess. One way the code handles the condensate overflow is that it must be routed to a “suspicious disposal point to alert occupants” (M1411.3.1 in the International Residential Code). How this can be achieved must be determined by the designer based on the code. However, a code worker must agree that the solution does the job: make inmates aware of it.
The trick is to make the problem obvious without damaging the components or causing too much glitch. I’ve seen this in many ways: for example, loft units with overflows that drain outward, through a prominent window, or from the ceiling of the master bathtub (“Hey, what’s dripping on my head?”). These places grab attention but control the chaos. A more frequent installation is in a Utility room in the basement with a floor drain nearby – the primary drains should be routed directly to the floor drain, but the overflows should not or not be noticed. If routed from a unit above, they can drip from the ceiling through the floor drain. If they’re in the same room, let them flow down the floor to the drain.
Another option is the “circuit breaker” approach: in the event of an AC condensate overflow, the code allows a water sensor to be placed directly in the drain or in an external pan that houses the overflow. The sensor is connected to the device and simply switches it off like a circuit breaker. This solution is very noticeable to the occupants as it halts the system.
The trick is to make the problem obvious without damaging the components or causing too much glitch.
high efficiency Ovens Condensate producing devices have similar options for handling the overflow. However, these options are listed in the installation instructions and not in the code because most devices do not have a secondary overflow. The vent opening for the condensate trap can be located under the flood edge of the collecting tray in the device or above it. If down, a blockage in the drain will rise to the vent and hit the floor before flooding the unit – a mess but keeping the unit going. If this mess would damage components, e.g. B. in an attic or on a wooden floor, a pan and drain are required and the drain must be noticeable (M1411.5). When the vent ends above the internal pan, the pan fills with water and triggers a water sensor that shuts off the operation of the device – the circuit breaker.
Shutting down the operation of an AC unit may be more acceptable than turning off an oven. Leaving town for a week in the winter and returning to a stove that has shut down due to a blockage of condensate can lead to a catastrophic loss of property through frozen pipes. In this case, the better option is often to place the vent below the edge of the high water table.
Similar to the condensate overflow, it is discharged from Temperature and pressure limiting valve (TPRV) of a water heater must also be “observable by the residents of the building” (P2804.6.1). In contrast to condensate, there is no overflow when the TPRV is at a standstill. If this valve discharges, it must be repaired immediately. The discharge from the TPRV is likely to be scalding and pressurized. There is a very small space for observing this discharge as it cannot be more than 6 inches above the floor or drain, but not less than 2 inches. Although you want that discharge near the bottom, I’m saying you don’t want it near the drain. It would be better to watch it flow across the concrete floor – if only a foot or two – than to float directly over a drain where it may not be noticed. If you end up outside (an option when the frost lock is fixed) it shouldn’t be in the bushes or behind an obstacle. It needs to be observable, obvious and annoying, but it also needs to be close to the ground (and serviced so that insects don’t clog it).
It is interesting to note that the regulations here use the same concept to get an occupant’s attention without delving too deeply into the Drain / Waste / Vent (DWV) installation codes. All included devices require a vent to admit air and prevent suction. When a drain backs up, the water and solids in the drain and vent system rise up the pipes. This would be problematic for “dry ventilation”, which only moves air and has no way of cleaning solid deposits itself. (Note: a dry vent can hold rainwater.) Dry vents may rotate horizontally, and when drained, the solids are likely to fall out of the flow and remain in the horizontal vent. A clogged vent can cause the P-trap to suck out and sewage gases to enter the house.
The sanitary code provisions are intended to create confusion rather than allow it to be. A horizontal dry vent must be at least 6 inches above the flood edge of the operated device (P3104.4). This way, if the drain is partially clogged, the sink will fill up before the water reaches the horizontal part of the dry vent. If a fill sink is not indicated enough to the occupant to turn off the water, there is an overflowing sink. This concept is basically the same as the amount of vent relative to the ladle in a heavy duty furnace, but with an opposite result. When this happens, we flood the sink to protect the vent. With the oven we flood the vent to protect the oven.
Another scenario that uses 6 inch mode. The rule of horizontal dry venting is when dry venting from a device below is combined with a dry vent from a device above through a horizontal connection (P3104.5). This is a common practice to limit the number of vents through the roof. In this case, the connection must also be 6 inches above the flood edge of the top light. Otherwise, a standstill can rise in the drain of the device to the connection point and then drain through the vent of the device at the bottom.
That discussion turned from AC condensate to drain pipes – evidence that these systems, while very different, are regulated in similar ways. While a professional always wants their work to be visually appealing, a fundamental aspect of code is to design a mess if something goes wrong. On the other side of the coin, chaos should only arise where the code requires one. For example, if overflows are directed into the same drain as the primary drains and the pipes overlap in a messy configuration, no one knows if it’s always a mess or a mess.
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Glenn Mathewson is a consultant and educator at buildingcodecollege.com.
Drawing: Kate Francis
From Fine Homebuilding # 293
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