P-traps are an essential part of any plumbing system. Their role is to prevent sewer gases from entering your home, and they do such an exceptional job that they are the only trap type approved in all jurisdictions and for all situations.
However, these traps are bulky, and it is sometimes challenging to fit them in confined spaces.
There is no need to worry, though. There are ways to fix the issue while remaining code compliant.
One of the easiest ways to fit a P-trap in a confined space is by using a short or shallow trap. You could also consider installing a waterless valve or another approved type of trap. Alternatively, you could replace the cabinet, cut a vanity, or even cut the wall to accommodate the trap horizontally.
Do I Need A P-Trap?
Most people would give an affirmative answer to this question. However, the matter is more complex than a simple yes and no.
If you’re wondering whether your plumbing system needs fixture traps, the answer is yes. However, they don’t have to be P-traps specifically.
The reason most people believe that plumbing trap is synonymous with P-trap is that P-traps are the most commonly used. These plumbing elements are so popular because they are the most effective in keeping sewer gases out of a house.
Considering that the plumbing code requires the use of effective liquid seal traps and that a home might not pass an inspection if it doesn’t have them, most plumbers install P-traps directly.
However, there are approved alternatives, especially in situations where your space doesn’t allow a P-trap installation. We’ll cover them below.
What To Do When There Is No Room For P-Trap?
Designing a plumbing system only to find that there is no room for a P-trap can be frustrating.
However, there are a few ways to fix the issue.
1. Use A Short Or Shallow Trap
Fitting a trap under a fixture requires accurate measurements, and sometimes, you might find that a trap that is only slightly shorter or shallower would fit just right.
To measure your space accurately and ensure that the trap really doesn’t fit, you must first learn the sizing requirements as well as the standard size of a P-trap.
According to the Universal Plumbing Code, the maximum distance between the fixture drain outlet and the lowest portion of the trap should be 24 inches.
However, the code requires no minimum distance, which means that you could bypass the tailpiece and connect the longer arm of the trap directly to the drain outlet.
In terms of trap size, the code only mentions the diameter of the pipe. This should be at least 1¼ inches and no larger than the diameter of the tailpiece and wall stub.
There are various specifications for each fixture type, but generally, the smaller the diameter, the smaller the trap.
When it comes to the trap arm – aka, the portion of pipe that goes from the wall stub to the bend – all you have to respect is a minimum distance of eight inches.
However, your building department may approve the installation of a shorter arm in special situations.
Now, the only thing to consider is the actual size of the trap. “Standard” traps generally have a bend that’s five inches tall and five inches wide. However, a shorter or shallower trap is generally smaller.
P-traps come in multiple sizes because the liquid seal can have any depth between two and four inches; many people find that a short or shallow trap fits into their space.
2. Cut The Wall
If a short trap is still too big for your space, but you don’t mind altering the wall behind the fixture, you could cut a hole to make room for the extra bulk.
This solution might not work in all circumstances; for instance, you might find it tricky to cut a concrete wall. However, cutting drywall is easy, and the extra inches are usually enough to make room for the trap.
3. Cut The Vanity
Generally, people find they don’t have enough room for a P-trap in the bathroom because the vanity comes with interior shelves or drawers that get in the way.
Whether you need more vertical or horizontal space (in case the vanity’s trap opening is not large enough), you can solve the problem by cutting the vanity.
If you don’t want to ruin the furniture beyond repair, follow the steps below:
- Grab a tape measure, pencil, and paper. Ask a helper to keep the trap in position and mark the excess material to know where to cut.
- Remove the trap and use a ruler and pencil to draw the rectangle that you have to cut out based on the marks you did earlier. This step is crucial, or you may end up with cuts that are not straight and that have to be redone.
- Remove the vanity shelf or drawer that you have to cut, if possible. If the shelf or drawer is not removable, remove the entire vanity from the wall. Use a saw to cut out the marked rectangle.
- Remove all burrs with fine-grit sandpaper and seal the edges with a waterproof sealant. This step is particularly important if the vanity is made of MDF or other types of engineered wood that could absorb excess moisture.
- Install the trap under the sink and put the vanity, shelf, or drawer back in its place.
4. Replace The Vanity Or Cabinet
Cutting the vanity is an excellent solution if you don’t want to invest in a new piece of furniture. However, altering an existing vanity is not always possible – or you may not want to embark on this DIY project.
If the problem is in the kitchen or a laundry room, you might not be able to cut the bottom of the cabinet.
In these cases, buying a cabinet that’s large enough to fit the P-trap could solve the problem.
5. Use A Waterless Trap
As mentioned above, P-traps are widely approved, but you might be able to use alternatives. If you live in a very small home or in an RV, you might be able to use a waterless trap instead of the traditional P-trap.
HepvO valves are fixture traps that use a system of valves that open to let the water pass through and close immediately after, trapping sewer gases inside the drain lines.
These valves were invented for use in RVs, but more and more jurisdictions now approve them for residential use, too.
However, you should always check with a local licensed plumber, a home inspector, or the building department if these valves are approved for residential use in your area – and whether there are any special conditions that must apply.
6. Install Another Trap Type
Waterless traps aside, you might also be able to use another liquid seal trap type.
Bottle traps, for instance, work in a way similar to P-traps, and many jurisdictions allow homeowners to install them in special conditions.
Again, you’ll have to check with your building department or local plumber about what those special conditions are.
S-traps are generally prohibited from use, but you might be able to use them for appliances that don’t drain into a sewer or septic system. This is usually the case of washing machines draining into a greywater tank that you use for irrigation.
7. Invest In Fixtures With Built-In Traps
Another way to fix the problem when there is no room for the P-trap is to get a fixture with a built-in trap.
When thinking of such fixtures, most people can only name the water closets. However, sinks, showers, tubs, and even floor drains can have built-in traps.
The main advantage is that these traps are generally smaller than a separate P-trap and they are all approved according to the plumbing code.
Finding out that there is no room for a P-trap under a fixture can be frustrating. However, you shouldn’t feel at a loss.
Alternative solutions include the use of a smaller or shallower P-trap, alterations of the wall or furniture, and the use of a different trap type. No matter which solution you choose, we hope this guide can help you find a quick fix.