When constructing a new building or renovating an existing one, focusing on the design of the drainage system is as crucial as any other aspect of the project. A well-planned drainage system can help avoid future headaches, including blockages, bad smells, and costly repairs. Here’s a comprehensive guide on what to consider:

MEP Design

Mechanical, electrical, and plumbing (MEP) systems must be designed to allow for easy maintenance and prevent problems. The routes for electrical cables, water pipes, and drains need careful consideration so that faults can be easily found and repaired. Proper design also ensures that repairs can be made without destroying expensive finishes.

Essential Drainage Guidelines

Drain Size: Ensure drains are of adequate size. A typical setup involves a 1.25-inch diameter pipe from a washbasin leading to a 2-inch diameter pipe, with a straight run to the outside of the building. Washbasins and floor drains should be 2 inches, while toilets should have 4-inch pipes.

Slope: Drains must slope sufficiently to ensure a good flow of water and carry solids away effectively. A normal slope for a sewer or grey water drain pipe is 2% (2 cm per meter).

Straight Pipe Runs: Whenever possible, use straight runs of pipe. Pipes under floors should always be straight until they reach the outside of the building.

Avoid Sharp Bends: Steer clear of 90-degree elbows because drainage rods cannot navigate them. Instead, use “slow” bends or two 45-degree bends to turn through 90 degrees. This approach allows for drainage rods to be pushed through the pipes to clear blockages.

Install Clean Outs: Add “clean outs” at critical locations along the pipes. A clean out is a branch off the drain with a screw cap, which allows a plumber to insert drain cleaning rods to clear the pipe. Clean outs are often placed at the ends of straight pipe lengths.

Use Y Connections: Opt for Y connections instead of 90-degree tees when joining pipes. Y connections allow for smoother flow and are less prone to blockages, while also accommodating the use of drainage rods.

Preventing Bad Smells

U-bends: Make sure all drains include U-bends, which create a water trap to prevent foul odors from coming up the pipes. For washbasin drains, choose those with screw fittings to facilitate easy cleaning of the U-bend water trap.

Floor Drain Covers: Ensure floor drains have properly designed covers with a built-in water-filled cup to block odors. If you have a smelly drain, check the effectiveness of the water seal in your pipework. You can install a U-bend outside the house. Ensure it has a 4-inch diameter with a screw cap for easy cleaning.

Additional Tips for Installation and Maintenance

• Consider access points: Design the building to allow access to the back of bathroom and kitchen walls, allowing repairs without having to remove expensive wall finishings.
• Avoid silicone: Keep an eye on the plumber; silicone on pipework may indicate a lack of expertise.
• Conduit for Electrical Cables: Electrical cables should be installed in conduit (plastic pipe) within walls to allow for removal and replacement without breaking the wall.

By incorporating these essential drainage design principles, you can avoid costly repairs, unpleasant smells, and ensure that your building’s plumbing system functions efficiently for years to come.