Boost Thermal Efficiency with Cement Board: Design & Material Tips 

9th Jul 2024 -

Maximising thermal efficiency is crucial for reducing environmental impact. While many focus on insulation and HVAC systems, the choice of construction materials also plays a significant role. Cement board continues to gain traction for its ability to enhance thermal efficiency when used in building design.

This article explores how cement boards are used to boost thermal efficiency. We explore the properties that make cement boards an excellent choice for thermal management. Also, we offer practical tips for selecting and installing the right cement board products.

What are the Thermal Properties of Cement Board?

Cement board holds unique thermal properties that contribute to its effectiveness in enhancing building thermal efficiency. To fully understand its potential, we look at these properties in detail. 

Thermal conductivity 

Cement board typically has a thermal conductivity (k-value) ranging from 0.18 to 0.35 Watts per metre-Kelvin (W/mK). Compared to concrete (1.0-1.8 W/mK), this relatively low thermal conductivity allows cement boards to provide some insulation value. The exact conductivity varies based on factors such as fibre content and density. 

Thermal mass

A key thermal benefit is its high thermal mass, referring to a material's ability to absorb, store and release heat. A cement board's density, typically between 1,300-1,700 kilogram per cubic metre (kg/m³), contributes to its thermal mass. This allows it to absorb heat during warm periods and release it slowly when temperatures drop. It helps to stabilise indoor temperatures and reduce heating and cooling loads.

Specific heat capacity

The specific heat capacity generally ranges from 0.84 to 1.0 kilojoule per kilogram (kJ/kgK). This indicates how much energy is required to raise the temperature of 1 kg of the material by 1 Kelvin. The cement board’s relatively high specific heat capacity contributes to its thermal mass effect. It allows it to store more heat energy per unit mass. 

Thermal diffusivity

Thermal diffusivity measures how quickly a material conducts thermal energy relative to its heat capacity. This is typically low for cement boards. While a cement board absorbs heat, it transfers it slowly through its thickness, contributing to its effectiveness in thermal management.

Surface emissivity

Cement boards generally have a high surface emissivity, typically around 0.9. Surface emissivity refers to the material's ability to radiate absorbed heat. High emissivity allows cement boards to effectively release stored heat, contributing to its thermal regulating properties.

Thermal expansion

Overall, cement boards have a low coefficient of thermal expansion. This means it expands and contracts minimally with temperature changes. It reduces the risk of thermal bridging and maintains the integrity of the thermal envelope.

Temperature tolerance

Cement boards withstand a wide range of temperatures without degradation, typically from -40°C to 100°C. This tolerance allows it to maintain its thermal properties in diverse applications, from cold storage facilities to direct sunlight areas.

Thermal bridging resistance

When properly installed, cement boards help reduce thermal bridging. Thermal bridging is the transfer of heat through more conductive materials in a building's envelope. Its relatively low thermal conductivity and ability to be used in continuous insulation systems contribute to this benefit.

Shop our superb range of cement boards with great thermal capabilities. 

Are Cement Boards Waterproof?

A fibre cement board is highly water-resistant but not waterproof. It can withstand moisture exposure without degrading, but it is not completely impermeable. This distinction is crucial for understanding its thermal performance. With a perm rating (water vapour permeability) of 1.5 to 5 perms, they resist water damage but allow some moisture transmission.

The water-resistant nature of cement boards impacts thermal efficiency. Boards maintain consistent thermal properties even when exposed to moisture. This prevents thermal bridging by resisting water absorption and preserving insulation effectiveness. 

Also, its resistance to mould growth helps maintain indoor air quality and long-term thermal performance. The durability of cement boards ensures these thermal properties remain consistent over the life of the structure.

To enhance water resistance and improve thermal efficiency, several measures can be taken. Applying waterproof membranes, sealing joints and fastener points and integrating the cement backer board with drainage systems are important steps. Using vapour barriers where appropriate and choosing breathable exterior finishes further boost performance.

Installing cement boards varies across different areas of construction, each with its considerations. In wet areas like bathrooms and kitchens, added measures like waterproof membranes alongside tile backer boards are often needed. For exterior cement board cladding, it aids moisture management in exterior insulation and finish systems (EIFS) or rain screen systems. 

In basements, it helps maintain a thermal barrier in potentially damp conditions. Cement boards are even used as roof underlayment, protecting the thermal insulation of the roof structure.

How to Maximise Thermal Cement Board Performance

Maximising the thermal properties of cement boards requires more than just selecting the right product. Proper installation is crucial to achieving optimal performance. The following section key installation practices that enhance the cement board's thermal efficiency. 

Continuous insulation approach

Introduce cement board as part of a continuous insulation system. Apply it over the entire exterior surface of the building, including studs and framing members. This method minimises thermal bridging through structural elements. It creates a uniform thermal barrier and enhances the overall R-value (measure of thermal resistance) of the structure.

Providing an unbroken layer of insulation reduces heat transfer and improves the building's overall energy efficiency.

Proper sealing and jointing

Ensure all joints between cement boards are properly sealed to maintain thermal integrity. Use appropriate sealants or tapes, applying continuous beads of sealant along all edges before installing adjacent panels. 

After installation, tape all seams with fibre mesh tape and embed in thin-set mortar. This sealing process prevents air infiltration and moisture penetration. It preserves the thermal performance of the wall system and enhances its long-term durability.

Integrate other insulation materials

Combine cement board with high-performance insulation materials to maximise thermal resistance. Install rigid foam insulation between studs before applying cement board. Spray foam insulation in cavities also creates air-tight seals. 

This layered approach leverages the strengths of multiple materials. It creates a highly effective thermal barrier that significantly reduces heat transfer through the building envelope.

Attention to thermal breaks

Incorporate thermal breaks at critical junctions to boost thermal performance. Use insulated fasteners or washers to secure cement boards, and install foam gaskets between the cement board and framing members. 

Apply a layer of insulation at floor edges and roof-wall intersections. This effectively reduces heat transfer through fasteners and framing, enhancing the overall thermal efficiency of the building envelope.

Proper thickness selection

Choose the appropriate thickness of cement board based on specific thermal requirements and project needs. Thicker boards like 12mm or 16mm offer better thermal mass effects than 6mm cement board options. 

Consider the local climate and building use when selecting thickness. Balance thermal performance with practical considerations like weight and cost to achieve top results.

Exterior finish considerations

Apply exterior finishes that complement the thermal properties of the exterior cement board. In hot climates, light-coloured finishes reflect solar heat and reduce cooling loads. Use breathable finishes that allow moisture vapour to escape, preventing trapped moisture that may degrade thermal performance. 

Consider textured finishes that increase surface area for better heat dissipation (transferring thermal energy). These finish choices greatly enhance the overall thermal regulation capabilities. 

Ventilated façade systems

Install cement board as part of a ventilated façade system to improve thermal performance. Create an air gap between the cement board and the primary wall structure using vertical furring strips for air circulation. 

This enhances thermal performance by creating a buffer zone that reduces heat transfer. It allows for effective moisture management and prevents thermal degradation. 

Structural considerations

Ensure proper structural support to maintain the thermal integrity of the cement board. Use appropriate framing spacing and install additional support at corners and openings. Account for the weight of the cement board in the overall structural design. 

Proper support prevents sagging or separation that could compromise thermal performance. Also, it ensures the long-term effectiveness of the thermal envelope.

Edge treatment

Properly treat all exposed edges of cement board to prevent moisture ingress that could affect thermal performance. Seal cut edges with an appropriate primer or sealant. This attention to detail ensures that cement board thermal integrity is maintained even at its most vulnerable points. 

Fastener selection and application

Choose and apply fasteners carefully to maintain the thermal integrity of the cement board installation. Use corrosion-resistant fasteners suitable for cement boards. Avoid overdriving them as this can crack the board and create weak points. Proper fastening ensures long-term stability and maintains the thermal performance of the cement board. 

Accommodation for thermal movement

Allow for thermal expansion and contraction to prevent damage compromising thermal performance. Leave appropriate gaps at joints (typically 3-5mm) and use sealants that can accommodate movement. 

Overall, this prevents cracking or separation that could create thermal bridges or allow air infiltration. It ensures that the cement board continues to perform despite temperature fluctuations.

Building systems integration

Coordinate cement board installation with other building systems to maintain overall thermal efficiency. Plan for penetrations like those required for electrical and plumbing systems to minimise thermal bridging. 

Use insulated boxes or wraps for electrical outlets and switches. This approach ensures that the thermal benefits are not compromised and creates a cohesive and high-performing thermal envelope.

How Do You Maintain Cement Boards? 

Proper maintenance of cement boards is important for ensuring their long-term thermal efficiency. While cement board is known for its durability, regular care extends its lifespan and preserves its thermal properties. Here is a comprehensive guide to maintaining cement boards across common applications. 

1. Exterior cladding maintenance

• Visual inspection: Check for cracks, chips or signs of water infiltration.
• Cleaning: Wash with a low-pressure water spray and mild detergent annually to remove dirt that can degrade thermal performance.
• Resealing: Every 3-5 years, reapply sealant to joints and around penetrations to prevent water ingress.
• Repaint: Every 7-10 years, reapply exterior finishes to maintain water resistance and reflectivity (for light colours in hot climates).
• Vegetation control: Trim plants away from the cement board to prevent moisture retention and potential biological growth.

2. Interior wall maintenance (dry areas)

• Visual inspection: Look for signs of damage particularly around joints and fasteners.
• Dust removal: Regularly dust or vacuum surfaces to avoid particulate buildup that may affect thermal properties.
• Repair: Quickly address any cracks or damage to maintain the thermal barrier integrity.
• Repainting: When repainting, use vapour-permeable paints to maintain the breathability of cement boards.

3. Wet area maintenance (bathrooms, kitchens)

• Moisture check: Use a moisture meter to detect any hidden water issues that could affect thermal performance.
• Grout and sealant inspection: Check and replace grout or sealant as needed to prevent water penetration.
• Ventilation: Ensure proper ventilation to reduce moisture levels and maintain thermal efficiency.
• Cleaning: Regularly clean surfaces with appropriate cleaners to avoid mould and mildew growth.

4. Basement and below-grade applications

• Water intrusion checks: Look for signs of water seepage or efflorescence.
• Dehumidification: Use dehumidifiers to control moisture levels.
• Drainage inspection: Ensure exterior drainage systems are functioning properly to divert water away from the foundation.
• Waterproofing renewal: Reapply waterproofing coatings every 5-7 years.

5. Roof underlayment maintenance

• Loft inspection: Check for water penetration or condensation from the loft side.
• Roof inspection: During roof maintenance, check the condition of any exposed cement board underlayment.
• Ventilation check: Ensure proper attic ventilation to prevent moisture buildup that may compromise thermal performance.

6. General maintenance practices

• Fastener inspection: Regularly check and tighten any loose fasteners to maintain the integrity of the thermal envelope.
• Thermal imaging: Consider a thermal imaging inspection every 3-5 years to identify any hidden thermal bridging or insulation issues.

7. Climate-specific considerations

• Cold climates: Pay extra attention to thermal bridging issues during annual inspections. Check for ice dam formation in roof applications.
• Hot climates: Increase the frequency of mould and mildew checks. Consider applying antimicrobial treatments every 2-3 years.
• Coastal areas: Increase the frequency of inspections and cleaning because of salt exposure. Reapply protective coatings more frequently.

8. Repair techniques for thermal performance

• Small cracks: Fill with a waterproof sealant compatible with cement board.
• Large damage: Replace the damaged section to maintain thermal continuity.
• Joint repairs: Use appropriate tapes or compounds to reseal joints.

9. Upgrading thermal performance

• Insulation addition: When possible, add external insulation during major renovations to enhance overall thermal performance.
• Reflective coatings: In hot climates, consider applying reflective coatings during repainting to improve thermal efficiency.
• Smart home integration: Install smart sensors to monitor temperature and humidity levels, allowing for proactive maintenance.