Why are expansion joints essential in underfloor heating?
Designing an underfloor heating system does not end with selecting system panels, insulation, or installation parameters. Equally important is the correct planning of expansion joints, which allow dimensional movements and deformations occurring in the screed layer to be controlled, both during the curing process and throughout subsequent operation.
The screed layer is subject to continuous dimensional changes resulting from material shrinkage during curing as well as thermal expansion and contraction. The behaviour of the floor is also influenced by the geometry of the room, the arrangement of structural elements, and the location of expansion joints.
This means that a heated floor is not a static element. The purpose of expansion joints is to create controlled zones that accommodate these movements and deformations. This prevents excessive deformation from accumulating in random locations, helping to eliminate the risk of screed cracking, damage to edge zones, and damage to tiles or panels.
Where do movements and deformations in the floor come from?
A common mistake is to consider expansion joints solely as a means of accommodating thermal expansion. In reality, a heated floor is subject to dimensional changes from the first days after installation:
- Technological shrinkage of the screed: during cement hydration and moisture evaporation, the poured screed naturally tends to reduce its dimensions. This shrinkage can result in cracking if the movement is not properly accommodated.
- Thermal cycles: regular heating and cooling of the system cause the screed to repeatedly expand and contract, resulting in continuous thermal movement.
- Geometry and architecture: large open areas, narrow sections, passageways, recesses, and changes in room geometry can lead to localised deformation and increase the risk of uncontrolled cracking.
The absence of properly designed expansion joints can lead to screed cracking, damage to floor coverings, and costly claims that negatively affect both the supplier’s finances and reputation.
Four key types of expansion joints, an overview
Proper protection of the floor requires components suited to the location and type of movement occurring in the screed.
1. Perimeter expansion joint – LDPE edge strip
The foundation of every system. The edge strip is installed around the perimeter of the room: along walls, columns, stairs, and other vertical structural elements. Made of flexible, foamed LDPE, it creates a separation layer between the screed and the vertical elements of the building. This allows the screed to expand, contract, and deform freely without transferring movement to the building structure. The available movement should be at least 5 mm.
2. Intermediate expansion joint – expansion profiles
When the screed area is large, elongated, or irregularly shaped, a perimeter edge strip alone is not sufficient. Expansion profiles are used to divide the screed into smaller working fields, allowing individual sections to move independently and reducing the risk of uncontrolled cracking in the central areas of the floor. The expansion joint should extend through the entire thickness of the screed, from the insulation layer to its surface. Its purpose is to accommodate dimensional changes and thermal deformation of the screed, which is particularly important in underfloor heating systems.
3. Threshold and transition expansion joints (T-shaped profiles)
Used at room boundaries, door thresholds, and between independent heating zones.
They provide complete separation between screed sections that may operate at different temperatures or be exposed to different loads.
Expansion joints limit the transfer of movement between adjacent screed fields and allow each section to expand, contract, and deform independently.
4. Contraction gaps
Contraction joints should also be taken into account. These are controlled cuts made while the screed is setting and hardening. They create a deliberate weakened section in the screed, causing shrinkage-related deformation to concentrate along a predetermined line. This makes it possible to control the location of potential shrinkage cracking rather than allowing cracks to form randomly anywhere in the screed.
The Role and Use of Expansion Joints
| Component | Location | Type of expansion joint | Basic function |
| LDPE Edge Tape | Perimeter of the room, columns, walls | Peripheral | Decoupling the floor from the building structure, vibration damping, and thermal expansion compensation. |
| Expansion joint profile | Large heating zones, narrowings | Zone-based | Dividing large pouring surfaces into smaller, independent work areas. |
| T-shaped expansion joint profile | Door thresholds, underfloor heating zone boundaries | Threshold / Zone | Separation of adjacent zones with different temperatures or loads. |
| Contraction gap | Large screed areas, areas where shrinkage must be controlled | Contractile / Controlled | Deliberately reducing the thickness of the screed to control the location where a crack or shrinkage crack forms. |
Expansion joints as part of a complete system
One of the most common mistakes is treating expansion joint components as secondary installation accessories. In reality, they are an integral part of the complete underfloor heating system and its warranty protection.
Edge strips, expansion profiles, and T-profiles are designed to accommodate physical phenomena that cannot be eliminated. Material shrinkage and thermal expansion and contraction will always occur.
Why introduce your own OEM expansion joint product line?
For distributors and manufacturers in the HVAC and construction industries, introducing expansion joint components under their own brand offers tangible business benefits:
- Higher margins across the entire project: expansion accessories can generate significantly higher percentage margins than pipes or manifolds while being required with virtually every underfloor heating installation.
- A complete system and fewer claims: contractors can purchase everything from a single supplier, from panels and pipes to edge strips and expansion profiles. Providing a complete system reduces the risk of installers using low-cost substitutes that may contribute to cracking and warranty disputes.
- Your logo on the construction site: an edge strip printed with your branding provides visible brand exposure wherever installers are working.
Create your own expansion joint product line – what we provide as an OEM Partner
As a manufacturer of components for the underfloor heating industry, we believe that informed product decisions should be based on sound technical knowledge. We provide the technology, quality, and manufacturing capabilities while putting a refined private-label product under your brand into your hands:
- Technical customisation: we select the appropriate LDPE foam thickness and density, use high-performance self-adhesive layers, and add polyethylene foil flaps to facilitate installation.
- Custom branding and packaging: we print your logo directly on the products and prepare labels and packaging according to your design.
- Reliable supply and quality: we ensure consistent material quality, full compliance with applicable construction standards, and reliable product availability.
Would you like to develop your product portfolio with us? Contact our team: export@tia.com.pl.
