Thermal Movement in Buildings: Design Considerations and Failure Prevention

Thermal movement is one of the most underestimated causes of building failures, yet it affects every structure exposed to temperature variations. As materials heat up, they expand; as they cool down, they contract. While this fundamental principle seems simple, the reality of thermal movement in complex building systems can lead to significant structural problems, costly repairs, and ongoing maintenance issues. Our forensic investigations regularly reveal thermal movement as a primary or contributing factor in building failures across Australia.

Understanding Thermal Movement

All building materials expand and contract with temperature changes, but the amount of movement varies significantly between different materials. The coefficient of thermal expansion determines how much a material will change in dimension for each degree of temperature change. Understanding these differences is crucial for preventing thermal-related failures.

Typical Coefficients of Thermal Expansion (per °C)

• Steel: 12 × 10⁻⁶
• Concrete: 10-14 × 10⁻⁶
• Aluminum: 23 × 10⁻⁶
• Timber (along grain): 3-5 × 10⁻⁶
• Timber (across grain): 30-70 × 10⁻⁶
• Masonry: 5-8 × 10⁻⁶
• Glass: 9 × 10⁻⁶

These seemingly small numbers can result in significant movement over the length of a building. For example, a 50-meter long concrete structure experiencing a 40°C temperature change will expand or contract by approximately 20-28mm.

Common Thermal Movement Problems

Differential Movement

Problems arise when different parts of a structure experience different temperature changes or when materials with different expansion coefficients are rigidly connected. Common scenarios include:

• Roof structures exposed to direct sunlight while walls remain in shade
• Different materials connected without allowing for movement
• Long structures without adequate expansion joints
• Cladding systems with inadequate movement accommodation

Restraint of Movement

When thermal movement is restrained, significant stresses develop that can exceed the material's capacity, leading to:

• Cracking in concrete and masonry
• Buckling of steel elements
• Failure of connections and joints
• Distortion of structural elements

Case Study: Office Building Curtain Wall Failure

We recently investigated a modern office building where the curtain wall system was experiencing widespread failures, including cracked glazing, failed sealant joints, and water ingress. The building featured a steel frame with aluminum curtain wall panels and large glazed areas.

Our investigation revealed that thermal movement was the primary cause of the failures:

The Problem

• The building's east and west facades experienced extreme temperature variations
• Dark-colored aluminum panels reached temperatures exceeding 70°C in summer
• The curtain wall system lacked adequate provision for thermal movement
• Rigid connections between the aluminum frame and steel structure prevented movement

The Consequences

• Aluminum panels expanded significantly, causing buckling and distortion
• Glazing units cracked due to frame distortion
• Sealant joints failed as movement exceeded their capacity
• Water ingress caused internal damage and mold growth

The remediation required complete replacement of the curtain wall system with proper movement joints and flexible connections, costing approximately $3.2 million. Proper consideration of thermal movement during the original design could have prevented this failure entirely.

Design Strategies for Thermal Movement

Movement Joints

Expansion joints are the primary method for accommodating thermal movement:

• Spacing: Joints should be spaced to limit movement to manageable amounts
• Location: Joints should be located at natural break points in the structure
• Design: Joints must accommodate the calculated movement while maintaining weather resistance
• Maintenance: Joint sealants require regular inspection and replacement

Flexible Connections

Connections between different materials or structural elements should allow for differential movement:

• Sliding connections that permit movement in one direction
• Flexible gaskets and sealants
• Slotted bolt holes to allow adjustment
• Bellows joints in piping and ductwork

Material Selection

Choosing materials with compatible thermal properties can minimize differential movement:

• Using materials with similar expansion coefficients
• Selecting light-colored finishes to reduce heat absorption
• Incorporating insulation to reduce temperature variations
• Using composite materials designed for thermal stability

Specific Applications and Considerations

Concrete Structures

Concrete structures are particularly susceptible to thermal cracking:

• Early-age cracking: Rapid cooling after placement can cause thermal cracking
• Long-term movement: Daily and seasonal temperature cycles cause ongoing movement
• Reinforcement restraint: Steel reinforcement can restrain concrete movement, causing cracking
• Joint spacing: Expansion joints should be provided at 15-30m intervals

Steel Structures

Steel's high coefficient of expansion requires careful consideration:

• Connection design: Connections must accommodate movement without failure
• Bracing systems: Thermal movement can affect the stability of bracing systems
• Fire protection: Thermal movement during fires can cause connection failures
• Composite construction: Different movement rates between steel and concrete must be considered

Masonry Construction

Masonry is relatively brittle and prone to thermal cracking:

• Control joints: Vertical control joints should be provided at regular intervals
• Bed joint reinforcement: Can help distribute thermal stresses
• Cavity walls: The cavity can accommodate some differential movement
• Thermal bridging: Should be minimized to reduce temperature variations

Cladding Systems

External cladding experiences the greatest temperature variations:

• Panel size: Smaller panels reduce individual movement amounts
• Joint design: Joints must accommodate movement while maintaining weather resistance
• Fixing systems: Must allow movement while maintaining structural connection
• Color selection: Light colors reduce heat absorption and thermal movement

Calculation of Thermal Movement

Accurate calculation of thermal movement is essential for proper design:

Basic Formula

ΔL = α × L × ΔT

Where:

• ΔL = change in length
• α = coefficient of thermal expansion
• L = original length
• ΔT = temperature change

Design Temperature Ranges

Australian conditions require consideration of extreme temperatures:

• Air temperature: -10°C to +50°C in most locations
• Surface temperature: Can exceed 70°C for dark surfaces in direct sunlight
• Structural temperature: Usually less extreme than surface temperature
• Installation temperature: The temperature at which the structure is built affects subsequent movement

Monitoring and Assessment

For existing structures showing signs of thermal movement problems:

Visual Inspection

• Cracking patterns that suggest thermal movement
• Failed sealant joints
• Distorted structural elements
• Gaps or compression at joints

Instrumentation

• Temperature monitoring to understand thermal cycles
• Displacement monitoring at critical joints
• Strain gauges to measure thermal stresses
• Crack monitoring to track movement over time

Remediation of Thermal Movement Problems

When thermal movement problems occur, remediation strategies include:

Joint Installation

• Cutting new expansion joints in existing structures
• Installing flexible joint systems
• Upgrading existing joints with higher movement capacity

Connection Modification

• Converting rigid connections to flexible ones
• Installing sliding bearings
• Adding flexible elements to existing connections

Thermal Control

• Adding insulation to reduce temperature variations
• Installing shading systems
• Changing surface colors to reduce heat absorption
• Improving ventilation to reduce temperature buildup

Maintenance and Long-term Performance

Thermal movement accommodation systems require ongoing maintenance:

• Joint sealants: Regular inspection and replacement every 5-10 years
• Movement monitoring: Periodic measurement of joint movement
• Cleaning: Removal of debris that could restrict movement
• Adjustment: Modification of systems as building performance changes

Conclusion

Thermal movement is an inevitable aspect of building performance that must be properly addressed in design, construction, and maintenance. Failure to accommodate thermal movement can lead to significant structural problems, costly repairs, and ongoing performance issues.

At AZTA Engineering, our forensic investigations of thermal movement failures inform our approach to both problem diagnosis and prevention. We understand how thermal stresses develop and use this knowledge to help clients design effective solutions that accommodate movement while maintaining structural integrity and weather resistance.

Remember: thermal movement never stops. Buildings that don't accommodate this movement will eventually develop problems. Proper design and maintenance of movement accommodation systems is essential for long-term building performance.