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Everything you need to know about downstairs toilet building regulations in the UK

If you’re looking to install a downstairs toilet, it needs to meet these legal requirements when it comes to size, ventilation and accessibility.

4 min read

There are many reasons to build a downstairs toilet. You might host regular parties and want to keep nosy guests from upstairs, or perhaps it’s better to be safe than sorry when it comes to your child’s bladder capacity. Whatever your reasoning, if you do decide a new WC is for you, you’ll need to consider one big thing: building regulations.

Thankfully, we’ve put together this resource to help you. It includes everything you need to know about building regs for a downstairs toilet.

What are building regulations?

While planning permission is often concerned with the appearance of your home, building regulations are there to ensure it provides a safe and healthy environment for both you, your family, and your neighbours. This not only means making sure it stays standing but that everything from the air quality to the noise proofing offers the best possible wellbeing for everyone living in the building.

Building regulations cover a whole range of aspects, including building structure, fire safety, hygiene and ventilation. However, because downstairs toilets are usually smaller projects, a lot of regulations don’t apply. Let’s take a look at the ones that do.

Want to learn more about building regulations? Here’s our complete guide.

Building regulations to consider for a downstairs WC in the UK


Bathrooms and humidity are best friends. Consequently, adequate ventilation is a big consideration for any bathroom, especially if you want to avoid hazards like mould forming in the future. Dreaded black mould is not only unsightly, but it could also put your household’s health at risk, which is why this building regulation exists.

Under current UK rules, you either need an extractor fan that can remove 15 litres of moisture from the air per minute or a window you can open more than 15 degrees. However, why not err on the side of caution and have both? If you can fit both a fan and window in your bathroom, we recommend doing so to benefit from maximum ventilation.

Also, more airflow means fewer smells, erm, lingering...


To ensure the plumbing in your bathroom meets UK building regulations, we highly recommend hiring a professional to handle the installation. Getting this right often requires specialist training, and if things go wrong, you’ll likely pay for it in the future, both emotionally and financially.

Aspects your plumber will consider include:

  • Proper drainage
  • Efficient waste disposal
  • Access to working sewage and draining systems
  • Adherence to the Water Regulations Advisory Scheme (WRAS)
  • Making sure your pipes run downhill


Some councils (although not all) insist that, when installing any downstairs bathroom toilet, it’s fully accessible to wheelchair users. This means having a door frame wide enough for a wheelchair and enough floor space for it to park and move around.

If you’re struggling to create enough room to accommodate this regulation, we recommend asking an architect to help. As masters of space, they’ll be able to identify whether your WC design is possible and suggest space-saving solutions you might not have considered.



Do I need planning permission to add a downstairs toilet?

As long as you’re not altering the exterior of your home, you won’t need to apply for a full planning application for most downstairs toilets. For example, you’ll be able to add a downstairs toilet window on the ground floor of your property without permission. However, we still recommend checking in with your council just to be sure. This is because homes in conservation areas or listed buildings have stricter rules about alterations.

Do I need to respect building regulations for a downstairs toilet?

For your safety and the safety of your neighbours, it’s advised you adhere to building regulations for a downstairs toilet. Installation involves plumbing, electrics, and heating, which all need to comply with safety standards and the sign-off of a building control completion certificate.

What’s the minimum size for a toilet under UK building regulations?

Believe it or not, you only need a space 70cm wide and 130cm long to install a toilet – downstairs or upstairs! However, as you can imagine, this doesn't leave much room for anything else, so we recommend building one a bit bigger to make your, erm… experience more comfortable.

Can I install a toilet off of a kitchen?

There was a time two separating doors were required if you wanted to install a downstairs toilet that opened into the kitchen. However, the rules are more relaxed now (but no less hygienic). So, if you want to build a downstairs toilet in 2022, you only need to include a sink to wash your hands.

Does a downstairs toilet need an extractor fan?

Even if you only have a single toilet surrounded by four walls, a window or extractor fan is still required. Frankly, we’d recommend this even if it wasn’t a regulation!

What are the building regulations when it comes to a new build toilet?

Toilets in a new build are still subject to the same building regulations as every other WC. You’ll need a window or fan for proper ventilation, and adequate plumbing, which means placing your toilet waste pipe near your outdoor drainage.

How Resi can help

Whether you’re renovating the whole of your ground floor or just looking to add a new wash closet, our team is here to make your project a reality.

Our services include:

All Resi packages are tailored to your project, meaning you only pay for the things you need.

To learn more about how Resi can help you grow your home, book a free consultation with our team.

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