Underfloor heating has quickly become one of the most popular choices for modern homes and commercial spaces – and for good reason. It offers consistent heat distribution, improved energy efficiency, and a much cleaner finish compared to traditional radiators.
But what really makes the system perform at its best is the screed layer that sits above it.
At Q Mix Concrete, we’ve seen first-hand how the right screed installation can significantly improve both the efficiency and lifespan of an underfloor heating system. Done properly, it not only protects the pipework or cables but also ensures even heat distribution across the entire floor.
In this guide, we’ll walk you through how to install screed for underfloor heating step by step.
Why Screed is Important for Underfloor Heating
Screed plays a crucial role in underfloor heating systems. It:
- Encases the heating pipes or cables
- Distributes heat evenly across the floor
- Protects the system from damage
- Provides a smooth, level surface for final flooring
Without a properly installed screed layer, you may end up with uneven heating or reduced system efficiency.
Step 1: Install Insulation (Essential First Step)
Before installing the heating system, insulation must be added to the subfloor. This ensures that heat is directed upwards into the room, rather than being lost into the ground.
For Electric Underfloor Heating:
- Use lightweight foam insulation boards
- Typically between 3mm to 20mm thick
- Ideal for retrofit or smaller spaces
For Water (Hydronic) Systems:
- Use thicker insulation (usually 50mm or more)
- Helps retain heat and improve efficiency
- Screed thickness above pipes: typically 65–75mm
Getting this step right makes a noticeable difference in long-term energy performance.
Step 2: Prepare the Floor
Once the heating system is installed, proper preparation is key before pouring screed.
For Electric Systems:
- Ensure the subfloor is clean and dry
- Repair cracks or uneven areas
- Test the heating system and connections
- Confirm thermostat setup
- Install a vapour barrier if required
For Water Systems:
- Clean and level the subfloor
- Pressure-test the pipework
- Ensure pipes are filled with water before screeding
- Check thermostat and controls
- Install vapour barrier if needed
From experience, skipping proper checks here can lead to serious issues later—especially once the screed has set.
Step 3: Choose the Right Screed
For underfloor heating, not all screeds perform equally.
👉 The best option is usually a self-levelling (liquid) screed with good thermal conductivity.
Why?
- Flows easily around pipes/cables
- Minimises air gaps
- Improves heat transfer
- Creates a perfectly level finish
Step 4: Pouring the Screed
Once everything is in place, it’s time to apply the screed.
Process:
- Pour the screed evenly over the heating system
- Ensure full coverage of pipes or cables
- Use tools to level (if using traditional screed)
- For liquid screed, allow it to self-level naturally
- Lightly tamp or agitate to remove air pockets
The goal here is a consistent thickness across the entire floor.
Step 5: Drying and Curing
This stage is critical and often rushed—but shouldn’t be.
- Leave the screed to dry for at least 7 days (minimum)
- Avoid walking on it too early
- Protect the surface during curing
Gradual Heating Process:
After the initial drying period:
- Turn on underfloor heating at a low temperature
- Gradually increase it over 7–10 days
This prevents cracking and ensures long-term durability.
Underfloor Heating Layout Tips (Efficiency Matters)
The layout of your heating system directly impacts performance.
For best results:
- Keep pipes/cables evenly spaced
- Reduce spacing near walls (to offset heat loss)
- Maintain at least 100mm distance from walls
- Avoid placing under fixed units (kitchens, etc.)
- Use a back-and-forth (serpentine) layout
Typical spacing:
- 50mm → high output (200W/m²)
- 75–100mm → lower output systems
Electric vs Water Underfloor Heating
Electric Systems
Best for:
- Small areas or renovations
Advantages:
- Quick installation
- Lower upfront cost
- Thin profile
- Works well with renewable energy
Water (Hydronic) Systems
Best for:
- Larger spaces or new builds
Advantages:
- Lower running costs
- Better for whole-house heating
- High efficiency over time
- Works with multiple heat sources
Final Thoughts
Installing screed for underfloor heating isn’t just about covering pipes—it’s about creating a system that performs efficiently for years to come.
At Q Mix Concrete, we always recommend:
- Using the right screed type
- Following proper preparation steps
- Allowing sufficient curing time
A well-installed screed layer ensures even heating, protects your system, and delivers a clean, professional finish.
If you’re unsure about the right screed or need reliable supply for your project, it’s always worth getting expert advice before you begin.
FAQs – Screed for Underfloor Heating
- What is the best screed for underfloor heating?
Self-levelling (liquid) screed is usually the best option due to its excellent thermal conductivity and smooth finish. - How thick should screed be over underfloor heating?
Typically, 65–75mm for water systems, but this can vary depending on the system and specification. - How long should screed dry before turning on heating?
At least 7 days before starting the system, then gradually increase the temperature over time. - Can you use traditional screed with underfloor heating?
Yes, but liquid screed is generally preferred for better heat distribution and ease of application. - Do you need insulation under underfloor heating?
Yes, insulation is essential to prevent heat loss and improve efficiency.