Plumbing codes expressly prohibit the use of double traps. But what's the problem with this setup? I've been told that this will cause the sink to drain slower, increasing the potential for the trap to get clogged.
In short, whether from steam locking or the lack of discharge synchronization on the second trap, double-trapping leads to water hammer or other serious problems and should be avoided.
Each “P” trap shall have a water seal of not less than 2 inches and not more than 4 inches and shall be set true to its seal. (6) Size. Traps shall be not less than 1 1/4 inches in diameter. A trap shall not be larger than the waste pipe to which it is connected.
No fixture shall be double trapped. Exceptions to the separate trapping requirements are as follows: (1) Fixtures having integral traps. (2) A combination plumbing fixture may be installed on one trap provided one compartment is not more than 6 in.
In all of these cases, water has to pass through two separate traps, called a double trap. But don't confuse this with two separate traps, which is fine. Of course, those corrugated things in the photo above aren't proper, but the configuration is correct. Plumbing codes expressly prohibit the use of double traps.
An individual vent is permitted to vent two traps or trapped fixtures as a common vent. The traps or trapped fixtures being common vented shall be located on the same floor level.
Yes. A vent is required so that the sewer gas can escape the house safely. The vent should always be located after the P-trap, not before it.
Yes, the toilet and sink can share the same vent, as can the shower. It's common to have one main vent pipe for multiple fixtures, although you might need a larger pipe. You should check with local building and plumbing codes to confirm you'll have adequate piping for your home.
P-traps are known for their reliability and efficiency in maintaining a water seal, which helps to prevent sewer gases from entering buildings. Additionally, P-traps are less prone to syphoning and drainage issues compared to S-traps, making them a preferred choice for both residential and commercial plumbing systems.
Do you know the proper way to size a P trap on an HVAC unit? The pull of the water to the drain has to exceed the sucking of the supply fan (“negative pressure”). Rule of thumb… add 2.5” to the static pressure before the fan (return and internal to the unit) and that's the long end (closer to the drain of the unit.
Disadvantages of P-Traps
One common issue is that the water seal can be protected if properly maintained or if there are blockages in the drainpipe. This can lead to the escape of sewer gases and unpleasant odors. The trap is regularly inspected and cleaned to ensure its proper functioning.
Ideally, it should be as close to your shower inlet as possible. The further away the P-trap is from your shower drain, the easier it is for foul smells and drain bugs to make their way into your shower. Also, a P-trap for a shower must be at least 2 inches in diameter.
double trap (uncountable) (shooting) An event in which two clay targets are simultaneously released in front of the shooter.
P-traps, named after their shape, contain a u-shaped bend that filters wastewater as it enters a plumbing system. The trap is connected to a sink, bathtub, and shower with a J-bend on one end and exits into your drainage system. The J-bend is the section of the p-trap that resembles the letter J.
Double trapping of a fixture is prohibited because of the additional obstruction of flow and potential for stoppages. Double trapping will cause air to be trapped between two trap seals, and the "air-bound" drain will impede the flow.
In a residence, a lavatory sink= 1.0 F.U., bathtub/shower= 2.0 F.U. and a toilet 1.6 gallon or less= 3.0 F.U, greater than 1.6 gallon= 4.0 F.U. So, 3-lav sinks, 3-1.6 toilets and 3-tubs/showers could be on one 2" vent. The UPC requires a 2" minimum vent for a toilet, other codes allow 1½".
Surprisingly, some building codes do not require bathroom fans. All municipalities have different requirements, but some do not draw a hard line on requiring exhaust fans. Bathroom ventilation is needed in those areas, but it can be from a window or fan—you choose.
Typically, each plumbing fixture has its drain line connected to the main sewer line. For instance, toilets have dedicated drain pipes, as do showers, sinks, and other fixtures. The idea behind separate drainage lines is to prevent cross-contamination and ensure efficient disposal of specific types of wastewater.
Sewer Gases
In addition to these issues, improper venting of a sink drain can also lead to more serious problems, such as sewer gas leaks. Sewer gas is a mixture of toxic and non-toxic gases that are produced by the breakdown of waste materials.
For standard P-trap repairs or replacements, where the P-trap is easily accessible and no significant complications are encountered, the cost can range from about $150 to $250. This includes the cost of a new P-trap and labor.
If you are using an air handler where the drain is on the negative side, you must have a trap.
Every plumbing fixture needs to have a vent to work properly. Bath tubs, toilets, washing machines and kitchen sinks need the biggest plumbing vents.
A horizontal wet vent could have as few as two fixtures or as many as ten fixtures but not more than two fixtures of any type can be connected to the system.
Based on UPC, 2" pipe can handle 2 DFUs (drainage fixture units). Your laundry tub is 2, clothes washer is 3, and kitchen sink is 2 for a total of 7.