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Bathroom Design Principles

From minimalism to maximalism and from classic to contemporary, there are plenty of different ways to design your bathroom. But whatever your design preference might be, it still requires careful planning to make most of the space available. In this post we’ll explore the two main bathroom design principles you need to know before planning your design.

Luxury Bathroom Design
FIGURE 1 – Bathtub View


The bathroom layout is affected mainly by two things; existing plumbing system and the recommended clearances for each bathroom fixture (like sink, bath and shower etc). The existing plumbing will largely dictate where the fixtures will be installed. Re-arranging plumbing is usually very difficult, not to mention expensive, because they are often so inaccessible. You will, of course, have more design freedom when designing a new house, but even then you might find that certain layouts are easier and efficient to connect to the plumbing system than others.

The recommended clearances are important for safe and comfortable movement within the bathroom space. These general guidelines are based on extensive studies and are there to help us achieve a more efficient design. By considering these recommended dimensions we’ll have a better chance of avoiding the mistake of designing an awkward and unpractical space. We’ll go through some of these dimensions a bit later, but first let’s wrap our heads around the plumbing system and how it affects the overall layout.

Bathroom Floor Plan
FIGURE 2 – Bathroom Layout


Plumbing can at first seem all complicated and mysterious. And that’s understandable because the pipes are usually installed in a way that you never even see the them! But when you break it down, there’s actually nothing mysterious about them. Basically, you have two networks of pipes in the house – one which is pressurised and brings hot and cold water in (supply), and another system to carry all the dirty water out (drainage).


There are two main types of supply systems – indirect and direct supply. The indirect system supplies water into a storage tank first (a cistern usually located in the attic), and from there the water is distributed to all the fixtures. This system dates back to the days when water shortages were common – and is still the norm here in the UK.

The direct system, which – as the name suggests – supplies cold water directly to the fixtures. This means that all the cold taps supply cold drinking water straight from the mains supply, rather than going through the cistern first. These cold supply pipes are shown in blue in Figure 3 below. The mains water also supplies water to the the boiler (or similar), which heats it up and distributes around the bathroom (red pipes). This system is the standard in Europe and the U.S.

Bathroom Direct Supply Detail
FIGURE 3 – Direct Water Supply

As you would expect, there are building regulations that lay out some ground rules for plumbing. For instance, to figure out supply pipe sizes, we can look at the flow requirements for each fixture. An example of one of these tables is shown in Table 3.1  below. Also remember that if more than one fixture is connected to the same supply pipe, the flow rate needs to be adequate enough to supply them both at the same time.

TABLE 3.1 – Maximum Fittings Consumption (SOURCE)

To give you an idea of the flow rates, a 1/2″ pipe has a flow rate of roughly 25 liters per minute (14 gpm). If we look at our layout, we have three fixtures connected to the same supply pipe. There are two showers and a sink, so we’ve increased the pipe size to 3/4″ instead. A 3/4 inch pipe has a flow rate of 87 litres per minute (23 gpm), which is enough to supply to all three fixtures. So to design your supply pipes, first find out the required flow and then match the pipe to it. The pipes will then be installed to run in the voids inside the walls and/or floors.


Drainage pipes rely on gravity to carry waste water from the house into the main sewage. This means that the pipes need to have a fall (a downward slope). And when the water moves down through these pipes, it creates a positive pressure (a bit like a syringe) which needs to be released or it starts pushing back the waste – which starts causing blockages. Equally, there’s a negative pressure behind that passing water, which can start sucking (siphoning) water from traps at plumbing fixtures if not equalised.

So how do we equalise this pressure then? The key is to make sure that the drain pipes are able to ‘breath’. This means having vent pipes that let air flow through. As well as maintaining neutral pressure, they ventilate the drainage system by allowing foul air to leave the pipes through a vent on the roof. Traps are also used to keep the smelly gases from entering the house. These are the U- or S-shape fittings that ‘trap’ water in order to prevent foul sewage gases passing through.

FIGURE 4 – Single Stack Drainage

The above visual shows a drainage system with several different size drain pipes all connecting to a larger drain pipe. Again, to figure out the pipe sizes and required slopes, we can look the  building code. Below is an excerpt from that building code which gives us an idea of what the recommended slopes are. For washbasins, we can look at the graph which tells us that shorter the length of pipe the grater the required gradient.

DIAGRAM 5 – Branch Connections (SOURCE)
FIGURE 6 – Bath Drain Gradient

So let’s apply these guidelines to our bathroom design – specifically to the bathtub drain. We’ll be using a two inch PVC drain pipe that runs for a distance of 2650 mm. The recommended slope is quite a wide range actually, from 18 mm to 90 mm per meter. We can do the quick math here to find the gradient (fall/distance);

100 mm fall / 2510 mm pipe distance = 39.84 mm per meter.

 This falls within the recommended gradient.


Now that we know a little more about plumbing we can move onto looking at how the recommended clearances affect the design process. Unfortunately there isn’t a single formula you could apply for an efficient bathroom layout – like the kitchen triangle for kitchen design. Instead, the answer lies in knowing the standard recommended clearances for each fixture you’re planning to install. The drawing below shows some of these clearances marked out in blue dotted lines.

Bathroom Layout
FIGURE 7 – Floor Plan With Recommended Clearances

These standards are there to help you design a  space that allows for safe and comfortable movement. They are not building regulations or legal requirements – rather think of them as guidelines. So where can you find information on these standards you ask? Well, you can start by checking out few of the architectural reference books listed on this website.

But for an in-depth understanding of the subject you should get a hold of  The Bathroom. This book includes numerous studies that look at the way we move or position ourselves when using bathroom fixtures. From these studies emerged commonly accepted industry standards. Let’s look at each of the main fixtures to learn more about these standards.


The position of the toilet can be a pivotal factor determining the layout. The reason being because you need a straightforward connection between the toilet and the soil pipe. In other words, the toilet has to be installed where the soil pipe is located.

It’s also nice to have a bit of privacy while conducting your business, so there should be  some sort of separation between the toilet and the rest of the bathroom. In this case, we’ve used a frosted glass wall.

Another common design guideline is to avoid having the toilet as  the first thing you see when you open the bathroom door – although in small bathrooms this can be impossible to avoid. As for the sinks, they are best sited where there is good natural light for shaving and/or putting on your make-up. So let’s look at the standard clearances for the toilet and the sink;

Sink & Toilet Standard Clearances
FIGURE 8 –  Sink & Toilet – Standard Dimensions 

Toilets – standard depth 700 mm plus 600 mm clearance in front

Bidets – standard depth 700 mm plus 600 mm clearance in front

Sinks – standard depth 400 mm plus 700 mm clearance in front and at least 200 mm to either side


Here we have a wet room with two showers separated from rest of the bathroom by a glass wall. We’ve also added a roof window right above the shower, to emphasise the feeling of space and to flood it with natural light. There is just something oddly satisfying about showering under a roof window – especially when it’s raining outside. The standard footprint size for a shower is given as 900 mm x 900 mm with at least 700 mm clearance in front. As shown below, this shower room is quite a bit larger because there are two showers.

Shower Standard Clearances
FIGURE 9 –  Shower – Standard Dimensions

Shower – standard size 900 mm x 900 mm plus 700 mm clearance in front


Bathing has been around since the ancient Egyptians, but it’s probably the Romans that are most famous for building their bath houses. And there is a whole psychological connection  behind our instinct to immerse ourselves in an elemental, natural floating-like state. But psychology aside, the bathtub is often used as the focal point in the bathroom. If it’s a fancy hand carved marble bath (like we luckily happen to have), it can be placed as the centre piece of the bathroom to draw in all the attention.

Bath Section Detail
FIGURE 10 –  Bath Section Detail
FIGURE 11 –  Bath Dimensions

Bathtub – standard size 1700 mm x 700 mm wide; clearance of 700 mm alongside if sited lengthways.

When it comes to designing (or buying) a bathtub, the most important thing for is to be comfortable. It doesn’t really matter how relaxing the atmosphere in your bathroom is if the bathtub leaves you with a sore back. If you ever find yourself designing a bath from scratch, then it should be made to suit the individual user. Also the design can be individual in terms of style, compared to the rest of the bathroom – both in materials and shape. To design a custom made marble bath like the one we have in this example would definitely cost a small fortune. But you can’t put a price on relaxing in your bathtub while watching the sun set behind the horizon – or can you?


So, to draw up a conclusion, bathroom design takes careful planning both in terms of plumbing and spacing of the fixtures. Like always, there are also tons of other stuff to consider, like having enough storage around the bathroom, environmental requirements, ventilation and lighting design as well. At the end of the day, it’s all about integrating all these aspects into one functional and enjoyable space.

Ultimately, a bathroom can be different things to different people and vary in its design and character. And the design process should never feel restricted in terms of creativity and practicality. Like I’ve said many times before, designing should always be an enjoyable journey into creating something exciting.

To help you get your creative juices running, you can check out the following books. Out of the bunch, The Bathroom is the one I’d recommend as it not only presents the findings of all the studies that they conducted, but also talks about the social and psychological aspects of bathroom design. It will definitely be different to most of the design books you’ve read, that I can promise.


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