Are you building a new house or plan a major kitchen remodeling? One of the most important things to take into account is the rough-in plumbing. Even the tiniest mistake during this stage can cost you a fortune to fix, so make sure you get the plumbing rough-in dimensions right.
The standard kitchen sink plumbing has the kitchen sink drain about 28 inches from the floor. However, the height can vary based on the height of the counter and the depth of the sink bowl. That’s why the rough-in dimensions usually place the drain at a height between 20 and 24 inches.
What is Rough-in Plumbing?
Rough-in refers to that stage of a construction project when electrical, mechanical, and plumbing lines are brought in. Thus, rough-in plumbing is the process of installing water lines, sewer pipes, plumbing vents, and connections.
Most rough-in plumbing is done when you’re building a home from scratch, but heavy home renovation projects that involve a change in the original plumbing can include some rough-in.
The entire rough-in plumbing system focuses on bringing clean water into your home and getting wastewater out.
Rough-in Plumbing for Kitchen Sink
As explained above, the rough-in plumbing for a kitchen sink involves laying out all the pipes that won’t be visible once the sink is installed. They include the hot and cold water supply, the drain pipe, and the vent, which is normally part of the drain.
These parts are routed and secured to the kitchen’s framing, then covered with caulk or drywall. All you’ll see after the rough-in is the stub-outs, which are those short pipes sections protruding from the wall, where the sink’s faucet and drain will connect.
When installing rough-in plumbing for the kitchen, it is important to calculate the height of the water lines, but above all, the height of the drain – an improper drain height can lead to drainage issues that are a pain to fix.
Factors to Consider About Sink Drain Rough-In Height
The drain vent of your kitchen sink should be positioned at 6 inches above the fixture’s flood level rim before offsetting horizontally.
The U-bent section of the P-trap should go below the wall drain level, allowing wastewater to go down and then up again as it drains. This layout is important to prevent sewage gases from leaking into your home.
Considering that a standard kitchen has an 8-inch deep bowl with a wall drain located about 28 inches above the floor, you should calculate a height for the bottom of your P-trap of about 16-1/2 to 18-1/2 inches.
An important thing to keep in mind is that this height is always calculated from the floor level, not from the bottom of your kitchen cabinets. If you want to use the space under your sink for storage, remember that the P-trap is located between 14-1/2 inches and 16-1/2 inches from your kitchen cabinet floor.
Type of sink and countertop
Lastly, you should consider the type of sink you want in your kitchen, the type of countertop, and how you plan to install them.
We mentioned already that standard kitchen sinks have a bowl depth of 8 inches. However, considering that all drain plumbing measurements must be based on the sink’s depth, you should tell your plumber the actual depth of the sink you want to install.
For instance, mounting a 9-inch deep stainless steel or granite composite sink under a granite countertop will effectively make the sink 10-1/4 inches deep. Likewise, a 9-inch deep porcelain kitchen will effectively have a depth of about 8 inches if you mount it over granite or hardwood tops.
Kitchen Sink Height
We talked about kitchen sink bowl depth, but another important factor to consider when planning the rough-in layout is the height of the kitchen sink.
There is no set-in-stone standard, with homeowners preferring to decide the height of the sink based on the height of the people living in the home.
Considering the average height of kitchen cabinets, the average kitchen sinks stand about 36 inches high. However, the range can vary by as much as 10 inches, generally between 29 and 39 inches in height.
Standard Kitchen Sink Drain Rough-In Height
Since there is no building regulation for the minimum kitchen sink height, the standard kitchen sink drain rough-in height can also vary, generally from 20 to 24 inches. Slight variations below or above this range are acceptable for sinks installed at non-standard heights.
DIY: How to Rough-in a Kitchen Sink Drain
Roughing in a kitchen sink drain is a plumber’s job because even the slightest mistake can result in disaster. However, if you have good plumbing skills and want to save some bucks, here’s how you can rough the kitchen sink drain yourself.
Tools & Materials
- 2-inch PVC drain pipe
- Sanitary tee
- Sink vent
- 2-1/4-inch drill bit
- 1-5/8-inch drill bit
- Plastic pipe cement
- Tape measure
Step 1 – Plan the layout of your rough-in drain
Considering the sink’s height and sink bowl depth, mark a point on the stud behind the sink that is at least 12 inches below the bottom of the sink. This height will give you plenty of space to install the P-trap when mounting the sink later on.
From this marked point, plan the route of the sink’s drain line to the point where you can connect it with a larger drain pipe, such as a toilet drain or the main sewer line.
Step 2 – Install the drain pipe
Use a saw to cut a length of 2-inch PVC pipe that suits your measurements. Then, drill a 2-1/4-inch hole in the studs and floor plates beneath the sink. When you’re done, route the drain pipe through these holes, maintaining a minimum downslope of 1/4 inch per foot toward the sewer.
When the sink drain pipe meets the larger drain line or the sewer, use a sanitary tee (2 x 2 x 1-1/2 inches) to connect the two pipes. Place the tee so that the 2-inch ports connect the drainpipes, leaving the 1-1/2 port empty (this port will connect to the vent).
Glue the joints with plastic cement and leave them to dry before proceeding.
Step 3 – Determine the kitchen sink drain vent route
The drain vent should rise from the point where the two pipes connect and then connect to the main vent stack. Determine the best route, considering that any horizontal sections must maintain a 1/4-inch-per-foot slope toward the sink.
Step 4 – Install the vent
Use the 1-5/8-inch drill bit to drill holes in the studs and wall plates to accommodate the vent. The number of holes and their location will vary based on the vent routing layout you’ve planned in step 3.
After you’ve drilled all holes, route the vent and connect it to the main vent stack by cutting the vent stack at a point above the highest fixture in your house. Then, connect the vent to the 1-1/2 port on the tee connecting the sewer and sink drain pipe. Seal all joints with plastic cement and let them dry before continuing with your other kitchen plumbing projects.
While the information above can give you a good insight into kitchen plumbing rough-in, you might still have some questions. We’re answering some of them below.
How far from the wall should a sink drain be?
There is no mandated minimum distance you should maintain between the sink drain and the wall. Thus, any distance is okay as long as you can make the connection.
What size are kitchen sink water lines?
Kitchen water lines have two diameters. The main pipes, which are the ones carrying water from the city supply or a well into your house, have a diameter of 3/4 inches. These lines can be made of copper or galvanized steel.
Exterior water lines start as one line from the main water supply that splits into two when it reaches the water heater. One line will carry cold water and the other hot water to your kitchen (or bathroom) sink.
The pipes under the sink, which are actually the hot and cold water hoses connecting to the main lines, have a diameter of 1/2 inches.
What is the standard kitchen sink size?
Most kitchen sinks have a standard size ranging from 30 to 33 inches. However, the range is broader, and you can find kitchen sinks ranging from 24 to 36 inches. Most sinks that are up to 30 inches long have one bowl. Double sinks can have anywhere from 32 to 36 inches.
Knowing the kitchen sink plumbing rough-in dimensions is essential if you don’t want to have drainage problems after installing the sink. Keep in mind, though, that these numbers aren’t set in stone. You must always calculate the right dimensions and pipe layout based on your circumstances, including the sink’s depth, its height, and the height of your under-sink cabinet floor.
Have you ever installed rough-in plumbing before, or is this your first project? Share your thoughts in a comment.