In a stall shower, the plumbing code requires the floor to be sloped one quarter (1/4) of an inch per foot in order to carry the water effectively to the drain. This slope, according to the TCNA Handbook is called “sloped fill” or commonly known as the pre-slope.
For optimal water drainage, it's advisable to ensure that the shower floor maintains a gentle gradient of approximately 2-4 percent. This corresponds to a decline of ¼ to ½ inch for every 12 inches from the shower enclosure to the drain.
The most important bit of obvious advice ever: soil and waste pipes need to be on a downhill gradient! The “fall” or “drop” should be between 1/40 (1cm down for every 40cm across) and 1/110. Too steep (1/10) then the water runs quicker than the solids so doesn't wash them away (ugh!).
Pipes must slope slightly downhill to drain properly. The standard slope is anywhere from ¼ inch to 3 inches per foot depending on the use. An accurate calculation is essential for properly functioning plumbing.
The maximum fall for a waste pipe is 1 in 40. The minimum fall is 1 in 110 (apart from vertical pipes, but that's a different story). So pipes with a gradient between 1 in 40 and 1 in 110 should have adequate flow to prevent blockages from occurring.
Pitch on a sewer line for a building or home
In the cases of a 6″ sewer line the minimum recommended pitch on a sewer line is 1/4″ per foot, or about one foot for a fifty-foot run.
a 1 in 40 drop is 25mm drop in a 1 metre run. To measure that, I have a standard 1 metre long level, and I tape a small bit of 2*1 timber to one end of the level, then set the pipe so the level reads level and you have a 1 in 40 fall.
ADA compliant thresholds for roll-in or transfer showers have a maximum height of ½”. Roll-in showers would then also require at least 48” from the entrance of the shower to the shower drain with a slope of just ¼” per foot between the drain and the shower perimeter (i.e. an inch per four feet, or a 1:48 slope ratio).
This includes tiling and gradients of bathroom floors including shower recesses. The recommended ratio of fall within showers is between 1:60 and 1:80.
But do you know the proper slope? The ideal slope of any drain line is ¼ inch per foot of pipe. In other words, for every foot the pipe travels horizontally, it should be dropping ¼ inch vertically.
When it comes to installing drains, size matters. The recommended pipe size for a shower drain is 2 inches, whereas most tubs use 1.5-inch pipes. Why the difference? Shower pans are shallower than tubs, so there's a higher risk for overflow.
For less than 1l/s, a fall of 1:40 (25mm per metre) is appropriate. For discharge from any WC, a fall of 1:80 (12.5mm per metre) is recommended. Gullies for foul water drainage must feature a 50mm water seal at minimum.
The P-trap has the important job of preventing sewer gasses from making their way into your bathroom. Although you can't really see the shower trap, it is a super important part of your plumbing system. Does a shower drain need a trap? In short, yes, every shower drain in the United States must have a trap or P-trap.
For a compression-style shower drain fitting, the drainpipe should come up to about 3/4 to 1 inch below the lip of the shower drain (follow manufacturer's recommendations). You may have to test-fit the shower base to mark the right height, then remove the base to cut the pipe.
And, the “pitch” (the slope angle you're aiming for so that water will quickly run downhill to the drain from all parts of the shower floor) needs to be at least 1/8-in per linear foot of run (or, to really ensure no drainage dead spots, 1/4-in per foot of run).
The top of the Pipe should be no higher than, and no more than 1/8" lower than, the top surface of the floor on which the base will be set. Hand-tighten Drain Nut, and then tighten the rest of the way (about 1/2 turn) with a wrench.
The code requires that shower drains be installed with a slope of not less than 1/8 inch per foot toward the building drain and be connected to an approved liquid waste receptor, such as a floor drain or drywell. The standard shower drain must be located at least 12 inches above floors which are below ground level.
Note: The industry standard for shower slopes is a range of 1/4″ to 1/2″ per foot. With certain installations, such as ADA barrier-free showers and standard shower stalls with three-dimensional pebble tile and river-rock mosaics, the minimum 1/4″ per foot for a slope may be insufficient.
For example, calculate the fall in a 50 metre section of foul water pipe work if the gradient is to be 1 in 80. Fall = 0.625 metres or 625mm.
In a stall shower, the plumbing code requires the floor to be sloped one quarter (1/4) of an inch per foot in order to carry the water effectively to the drain.
As a general rule, the recommended slope for most plumbing pipes is 1/4 inch vertical drop over every 1 horizontal foot, or about 2 percent. Pipes with a diameter of 4 inches or greater can have a slope of 1/8 inch per foot downhill from the source. What is the right gradient for the main drain of a house?
Venting is necessary for bathroom plumbing systems to prevent blockage. All pipes in your home, particularly for toilets, sinks, and showers, require proper venting. It protects the trap on the drain pipe. In addition, it helps you secure your wallet, fittings, time, and even the pipe itself.
Gradients between 1 in 40 to 1 in 110 will normally give adequate flow velocities. If the gradient is not steep enough i.e. less than 1 in 110, then the pipe could block if the solids slow down and become stranded.
To calculate drainage fall, divide the total length by the fall ratio. For a 1 in 40 fall, divide the length of the pipe by 40.
Regardless of surface characteristics, when it comes to surface drainage, slope is the most important issue to consider. For efficient drainage, paved surfaces should have a minimum 1-percent slope. Turf or landscaped areas should have a minimum slope of 2 percent.