Buying Guide: How to Build a Steam Room using XPS Foam Components

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Build your own steam room using XPS boards

Buying Guide: How to Build a Steam Room Using XPS Foam Components

Introduction: XPS Cement-Coated Boards & Steam Room Benches

When building your own steam room, choosing the right construction materials is critical. Steam rooms operate in extreme conditions — constant heat, high humidity, and direct water exposure — so standard building boards simply won’t last.

XPS cement-coated boards are the industry-preferred solution for steam room walls, ceilings, and seating structures. Made from extruded polystyrene (XPS) with a reinforced cement coating, these boards are 100% waterproof, rot-proof, mould-resistant, and highly insulating. They provide a stable, tile-ready surface that won’t warp, swell, or degrade over time, even in continuous steam environments.

For seating, steam room benches built using XPS boards as a structural core offer the perfect balance of strength, insulation, and longevity. When finished with tile, stone, or specialist steam-room materials, XPS-based benches stay warm to the touch, resist moisture ingress, and maintain their shape and integrity for years.

In this guide, we’ll show you how XPS boards can be used to confidently build your own steam room — from walls and ceilings to durable, comfortable benches — using professional-grade materials designed specifically for wet heat environments.

Designing and building a steam room using XPS foam parts is one of the most reliable, efficient and professional ways to achieve a long‑lasting, fully waterproof steam environment. XPS (extruded polystyrene) systems are widely used in commercial spas and high‑end residential projects because they combine insulation, structure and tile‑ready surfaces in one solution.

This buying guide explains what to buy, why you need it, and how the components work together, using the XPS foam materials available from Oceanic Saunas.

Why Choose XPS Foam for a Steam Room?

Steam rooms place extreme demands on materials. High heat, constant moisture and vapour pressure mean every component must be waterproof, stable and durable.

XPS foam systems are ideal because they are:

100% waterproof – they do not absorb moisture
Excellent thermal insulators – helping steam rooms heat efficiently
Lightweight yet strong – easy to handle and install
Tile‑ready – designed to accept tiles, stone or mosaics

Unlike traditional plasterboard or cement board, XPS foam does not degrade in steam conditions when correctly installed and sealed.

Core XPS Components You’ll Need

1. XPS Foam Backer Boards

XPS backer boards form the structural shell of the steam room. They are used on:

Walls
Ceilings
Floors (over a suitable base)
Bench bases and steps

These boards provide both insulation and a stable, waterproof substrate for your final finish.

2. XPS Steam Room Benches & Seating

Pre‑formed XPS steam room benches simplify construction and ensure consistency. Oceanic Saunas offers XPS seating components in both flat‑back and solid styles.

Flat‑pack benches are ideal when seating is fixed directly against walls, providing a clean, space‑efficient profile.

Solid benches offer a more substantial appearance and are often used in larger or commercial steam rooms.

Why choose XPS benches:

Fully waterproof construction
Designed to be tiled over
Lightweight but structurally sound
Easy to cut and adapt on site

Using pre‑formed benches reduces installation time and avoids common waterproofing issues associated with timber seating.

Fixings: Screws, Washers & Adhesives

3. Screws & Washers

Correct fixings are crucial for long‑term performance.

Recommended:

Galvanised screws & large washers to spread load and prevent pull‑through
Galvanised mechanical fixings for connecting to brick or concrete walls
Plastic screws are recommended for connecting XPS board to XPS board

Boards should be fixed securely to framing or substrate at appropriate centres to minimise movement.

Essential Waterproofing & Jointing Materials

While XPS foam itself is waterproof, steam rooms require a continuous vapour‑tight envelope. This is achieved by correctly sealing all joints, corners and penetrations.

4. Fibreglass Mesh Tape

Fibreglass mesh tape is used over all board‑to‑board joints before waterproofing.

Purpose:

Reinforces seams
Prevents movement cracks
Creates a strong base for tanking tapes or membranes

Mesh tape is applied directly over joints and embedded into adhesive. Our P8 versatile sealant can be used to bond XPS panels to floors and walls, seal and waterproof fixings, joints and floor-to-wall intersections in steam rooms, and adhere XPS panels to cement, wood, metal, and various plastics.

5. Waterproof Membrane Tape, Corners and Sleeves

Waterproof tanking tape is essential in steam rooms and is used at:

Board joints
Corners
Wall‑to‑floor transitions
Around pipe penetrations, lights and steam inlets

Why it matters:
Steam will always find weak points. Tanking tape ensures a vapour‑tight seal at every change of plane or junction.

Tools:

We supply both flat and corner putty knives; durable, sharp-edged scrapers designed to apply sealant neatly and evenly to flat surfaces and right-angled joints..

6. Liquid Waterproofing Membrane (Recommended for commercial application)

Many installers apply a liquid waterproof membrane over taped joints and in commercial applications across the entire surface.

Benefits:

Creates a continuous waterproof barrier
Adds redundancy in high‑use steam rooms
Particularly useful for commercial or daily‑use installations

7. Tile Adhesives & Grouts

Your final finish depends on adhesives and grouts suitable for steam environments.

Choose:

Flexible, cement‑based tile adhesives rated for wet and high‑temperature areas
Epoxy or high‑performance grouts that resist moisture and mould

These materials protect the integrity of the tiled surface under constant steam exposure.

Steam Generators

Choosing the Correct Steam Generator Size

Selecting the right steam generator is essential for performance, comfort and longevity. An undersized generator will struggle to reach temperature and run constantly. An oversized unit will cycle inefficiently and waste energy.

The correct size is determined primarily by:

The internal cubic volume of the steam room
The type and thickness of wall finish (tile, stone, glass, etc.)
The intended usage (domestic vs commercial / frequency of use)

Step 1: Calculate the Room Volume

Measure:

Length (m)
Width (m)
Height (m)

Basic calculation:

Length × Width × Height = Cubic Metres (m³)

Example:
2.0m × 1.5m × 2.2m = 6.6m³

This gives you the base room volume.

Step 2: Adjust for Wall & Ceiling Finishes

Dense materials such as porcelain tile, ceramic tile, natural stone, marble, or thick slate absorb more heat and require additional steam capacity.

As a general guide:

Standard ceramic/porcelain tile: add 10–15%
Natural stone or marble: add 15–25%
Glass walls or large glass areas: add 25–30%
Thicker tile beds or heavy substrates: add toward the upper end

Example (ceramic tile at 15%):

6.6m³ × 1.15 = 7.59m³ adjusted volume

You would then select the next generator size that comfortably covers this figure.

When in doubt, it is usually better to go slightly higher rather than undersized.

Step 3: Consider Usage

Domestic (1–2 sessions per day): Choose a domestic steam generator or a light duty commercial steam generator for larger size steam rooms.
Frequent or back-to-back use: Choose a light duty commercial steam generators.
Commercial settings: Always select a heavy duty commercial steam generator with auto descale fnctionality.

Locating the Steam Generator & Drain

The steam generator itself should be located:

Within the recommended distance of the steam room
In a dry, well-ventilated area
With easy access for servicing

Drain Position

All steam generators require a drain for automatic flushing and maintenance.

Best practice:

Install a dedicated tundish and gravity-fed drain where possible
Avoid long horizontal waste runs
Ensure the drain location allows safe discharge of hot water
Make sure it remains accessible for inspection

Planning the drain early in the build stage avoids costly retrofitting later.

Hard Water & Limescale Protection

Hard water is one of the main causes of reduced efficiency and shortened lifespan in steam generators.

If you are in a hard water area, we strongly recommend:

1. Installing a Water Softener

A properly sized whole-house or dedicated softener will:

Reduce limescale build-up
Improve performance
Extend the life of heating elements
Reduce maintenance frequency

2. Regular Descaling

Even with softer water, periodic descaling is advisable.

We recommend using:

Citric acid descaling crystals
Follow the dilution and flushing guidance
Always isolate power before servicing

Regular maintenance dramatically increases reliability and keeps steam output consistent.

Ventilation

Proper ventilation protects the structure and improves comfort.

Recommended setup:

Steam inlet: Low on the wall (near floor level)
Vent outlet: High on the opposite wall or ceiling
Vent should lead to:
- An external wall, or
- A mechanically extracted area

Key points:

Vent openings must be steam-room rated
Avoid direct drafts over seating
Ventilation helps the room dry out after use, preventing mould

Putting It All Together: Buying in the Right Order

When planning your steam room purchase, it helps to think in layers:

Structure & insulation – XPS backer boards
Seating & features – XPS benches and niches
Fixings – screws, washers and adhesives
Joint reinforcement – fibreglass mesh tape
Waterproof sealing – tanking tape, corners and sleeves + liquid waterproof tanking membrane
Finish materials – tiles, grout and accessories
Steam generator - home or commercial

Buying a complete system ensures compatibility and reduces the risk of installation issues.

Product-Specific Applications

How to apply XPS flat steam room construction boards

Before starting:

Ensure the room is structurally sound
All framing is rigid and square
A suitable steam generator and drain location have been planned
Suitable ventilation has been planned

1) Installing XPS Boards on a Stud Wall

Steps:

1. Frame the wall

Studs should be spaced at 400–600mm centres
Ensure framing is level and securely fixed

2. Fix the boards

Position XPS boards vertically or horizontally
Screw directly into studs using corrosion-resistant fixings
Use large washers or specialist XPS fixings to avoid crushing the board
Fixings at approx. 300mm centres

3. Seal joints

Tape all board joints with mesh tape or membrane tape
Apply a waterproof cement-based adhesive or sealing compound over joints
Seal internal corners and transitions carefully

2) Installing XPS Boards on a Concrete Wall

Steps:

1. Prepare the surface

Wall must be clean, flat, and free of dust or loose material
Fill any major voids or cracks beforehand

2. Bond the boards

Apply a cement-based tile adhesive or XPS-compatible fixing compound
Use a notched trowel for even coverage
Press boards firmly into place
Once bonded, add glvanised mechanical fixings for extra security

3. Seal joints

Tape all board joints with mesh tape or membrane tape
Apply a waterproof cement-based adhesive or sealing compound over joints
Seal internal corners and transitions carefully