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Gravity vs. Water: Why an Upstairs Wet Room Is Perfectly Safe (If Done Right)
When clients ask us about installing a wet room on the first floor, they usually have one specific nightmare scenario in their heads:
You turn on the shower upstairs, and ten minutes later, water starts dripping through the living room ceiling below.
It is a valid fear. Water + Gravity + Wooden Floorboards sounds like a recipe for disaster.
However, the reality is very different. At EA Mobility, roughly 50% of the wet rooms we install are upstairs. So, here is exactly how we engineer an upstairs wet room to be 100% watertight on a timber floor.
The Challenge: Concrete vs. Timber
To understand the solution, you have to understand the floor structure.
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Ground floors are often concrete. To make a drain, we simply dig a hole.
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Upstairs floors are usually Timber Joists with floorboards on top. You can’t just “dig,” and—crucially—wood moves. Floorboards creak, expand, and contract with heat.
If you tile directly onto floorboards, the grout will crack, and you will get a leak.
So, how do we fix this? We don’t use a standard shower tray. We use a Wet Room Former.
The Secret Weapon: The “Wet Room Former”
In the past, builders would try to build a slope using plywood. This was risky because wood warps.
Today, we remove your floorboards and install a Structural Former.
Former vs. Shower Tray: What’s the difference?
| Feature | Standard Shower Tray | Wet Room Former (What We Use) |
| Installation | Sits on top of the floor | Sits flush inside the floor joists |
| Step Height | 100mm – 150mm Step | 0 mm (Level Access) |
| Strength | Can crack if unsupported | Structural (Replaces the floor) |
| Leak Risk | Relies on silicone sealant | Tanked (Sealed System) |
Think of a Former as a hidden tray that replaces your floorboards. It is precision-engineered with a pre-set gradient (slope), guaranteeing that water flows away instantly and never pools.
How We Install It: The 4-Step “Leak-Proof” Method
To get a wet room upstairs, we follow a strict structural process. Here is what happens under the tiles:
Step 1: Structural Reinforcement
We lift the existing floorboards in the shower area. If the joists (wooden beams) need strengthening to take the weight of a wheelchair or heavy user, we reinforce them (“noggins”) to ensure the floor is rock solid rigid.
Step 2: Installing the Former
We screw the structural former directly into the joists. Because it sinks into the floor rather than sitting on top, the finished level is perfectly flush with the rest of the room. No ramp, no step.
Step 3: The “Tanking” (Waterproofing)
This is the most critical part. Before a single tile is laid, we apply a liquid waterproof membrane to the entire floor and the walls.
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We use waterproof tape on every joint (where wall meets floor).
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We paint the floor in a rubberised liquid.
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Once cured, your bathroom is effectively a sealed watertight tank. Even if you left the shower running all day, the water cannot physically reach the ceiling below.
Step 4: Drainage & Pumping
If gravity allows, we run the waste pipe between the joists to your soil stack.
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The Problem: Sometimes the joists run the wrong way, and we can’t get the pipe to the wall.
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The Solution: We install a Digital Waste Pump. This smart pump sucks the water from the drain and pushes it quietly to the waste pipe, meaning you can have a wet room anywhere upstairs, regardless of joist direction.
Flooring Choices for Upstairs
Since timber floors move slightly with central heating, your choice of flooring is critical.
1. Safety Vinyl (The Safest Bet)
Vinyl is flexible. If your house moves slightly in winter, the vinyl moves with it. It is also heat-welded at the corners (“Cap and Cove”) to create a seamless bucket effect.
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Read more in our Ultimate Guide to Wet Room Flooring.
2. Tiled Floors (Possible with Care)
You can have tiles upstairs, but we must use flexible adhesive and grout. We often lay a thin plywood layer (Overboarding) first to rigidify the floor.
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Looking for inspiration? Check our 25 Stunning Wet Room Ideas.
Why Keep the Bathroom Upstairs?
If you are debating between a stairlift/upstairs wet room combo or moving a bed downstairs, here is why keeping the bathroom upstairs makes sense:
- Privacy: Most people prefer bathing near their bedroom, away from the main living areas.
- Space: Upstairs bathrooms are often larger than downstairs cloakrooms, allowing for better turning circles for wheelchairs.
- Resale Value: Keeping the layout “traditional” (bedrooms and bath upstairs) is better for resale. (Does a wet room devalue a property? Read more here).
Frequently Asked Questions (Upstairs Installations)
Q: Is a wet room too heavy for my ceiling joists?
A: No. In fact, removing a cast-iron or steel bathtub full of water reduces the load on your floor! A shower is much lighter than a full bath.
Q: Will the floor be higher than my landing carpet?
A: No. Because we sink the former into the floor, the transition from your landing carpet to the bathroom floor is usually completely level.
Q: How long does an upstairs installation take?
A: Exactly the same as a downstairs one. Our specialist teams typically complete the full transformation in 3 to 5 days.
Get a Technical Assessment
Every wooden floor is different. The direction of your joists determines exactly how we install your drain.
Don’t guess with structural safety. At EA Mobility, our surveyors inspect your floor structure during the Free Home Assessment. We can tell you immediately if gravity drainage is possible or if a pump is needed.
