Bathrooms Basics: 6 Tips to Plan your Bathroom Plumbing and Layout

Aug 14, 2023

Although the design and layout of bathrooms we use nowadays date back millennia, they are still considered as one of the most difficult to design and renovate. During the earliest stages of planning a bathroom, there are plenty of rules of thumb to follow, especially since it involves a lot of association and "pre-planning" with plumbing, electrical circuits, angular or uniquely-shaped fittings, and small floor areas. We will explore the basics of bathroom plumbing and where to allocate each fixture to optimize the bathroom's layout, facilitating your DIY remodel project or creating the space from scratch.

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Throughout history, civilizations have developed their own sanitation systems based on their geographical, cultural, and economic conditions. The use of a toilet seat, for instance, is commonly used in the Western World, whereas most people in Eastern countries use the floor-mounted squat toilet. Despite being one of the smallest rooms inside a house, bathrooms are certainly one of the most challenging and critical to design, featuring several fittings and hydraulic installations that require careful planning. Naturally, the bigger the bathroom is, the more space there is to freely install fixtures and cabinetry, but architects have managed to define minimum dimensions and specific layouts to consider for small bathrooms, ensuring comfort, accessibility, and practicality, especially for children, the elderly, and handicapped individuals.

This article is exclusively about bathroom plumbing and fitting placements and not the different types and dimensions of bathroom layouts, which we have already explored.

The International Plumbing Code (IPC) is a model plumbing code that sets minimum regulations for plumbing systems with the aim of protecting life, health, and ensuring safety of building occupants. The IPC sets minimum regulations for plumbing systems based on prescriptive and performance-related provisions such as backflow prevention, the different types of fixtures and fittings, water supply and distribution piping, heaters, sanitary drainage and venting, traps, grease interceptors, separators, and non-potable water systems, to name a few. While this model is comprehensive, each country has its own set of regulations, so it is important to make sure you follow the guidelines of where you are based. Also, it is ideal that you consult with a licensed plumber or let him/her perform the work and assemble the pipes on site to prevent implacable or dangerous accidents.

DWV Fittings are used for drain, waste and vent applications mostly in plumbing systems with a continuous water flow. These fittings are often available as a glue or gasketed system with a size range of 1.25" up to 24" (3 cm - 60 cm). The most common types of plumbing pipes are copper, galvanized steel, and Polyvinyl Chloride (PVC), whose use varies based on their designated function and the water flow pressure.

Along with the pipes, DWV fittings also include different types and shapes of connectors and vents, each corresponding to a specific function. A "tee" is a fitting connects to the pipe at a 90-degree angle, a "wye" fitting connects at a moderate 45-degree angle, a toilet flange connects to a 90-degree fitting that connects directly to the drain line, a p-trap is a u-bend unit that stops sewer gasses from backing up into your drain while allowing wastewater to pass through at the same time, a closet bend is a 90-degree elbow pipe that has a gradual sweeping corner that allows waste to flow through without clogging, a closet flange mounts a toilet to the floor and connects the closet bend to a drain pipe, and a flush bushing is a piece that connects to a pipe in order to reduce its size progressively.

Using the proper connectors avoids leaks, whereas drain pipes that are not properly vented could eventually release bad odors into the house. For instance, when a branch line connects to a main drain line, the fitting should always be a "wye" to avoid having the wastewater crash against the side of the pipe and go back in the direction of the vent pipe.

Before designing a bathroom, it is important to thoroughly understand what the existing conditions of the bathroom are; where the shaft is placed, the wall conditions and existing finishing, which fixture will be removed / kept, etc. Ensuring proper water pressure is also very important as you might need to replace the existing shutoff valves. If the water pressure is low, you might need to add a booster pump, and if the pressure is too high, you might need to install a pressure-reducing valve.

All homes include a "wet wall", also known as the shaft wall, which is where water lines and the main plumbing drainage pipes are located, and is usually much thicker than a regular interior wall. Installing fixtures on or close to this wall will facilitate the entire plumbing process and minimize the amount of pipes/connections used since this is where all pipes eventually lead to.

Although the rough-ins, or the distance from the pipe in a wall to the fixture depends on the scale of the bathroom and design restrictions, most codes state that fixtures must not be placed too close together. Bathrooms often require a minimum of 6 pipes: 5 water lines - a hot and cold line for each of the shower and sink, and a cold water line for the toilet seat, each draining into one main sewage line. Since it is where all lines converge, the sewage line is wider than the rest of the pipes, ranging between 11 and 16 cm (4.25 and 4.5 inches) compared to 1.25 and 4 cm (0.5 and 1.5 inches) for water lines. All drain lines should also have vents to allow air into the drainage lines, pushing dirty water downwards.

For the lavatory, the center of the unit's drain is located roughly 45 cm (18 inches) above the finished floor level, and centered in the middle of the vanity. The sink's hot and cold water lines (hot on the left, cold on the right) are elevated almost 7 cm (3 inches) above the drain and spaced 21 cm (8 inches) apart, reaching an approximate 53 cm (21 inches) above the finished floor.

Regarding the toilet seat, the center of the closet flange should be placed 30 cm (12 inches) from the finished back wall with a minimum of 76 cm (30 inches) of total clearance between the finished side wall and the side of the vanity. As for the shower area, there are no standard rough-ins since they vary based on the type of shower and drainage system, but typically range between 15 and 45 cm (6 and 18 inches).

To ensure that the water is continuously flowing, most plumbing codes mandate a 0.63 cm (0.25 inch) slope per 30 cm (1 foot) on a horizontal drain pipe, while some specify 1/8 inch slope per foot for larger pipes (larger than a 3 inch-diameter pipe).

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