Thermal Performance: Controlling Heat Transfer
Understanding R-values, U-factors, and how building envelopes manage thermal energy flow
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Section 2 of 5Thermal performance is the ability of a building envelope to resist heat transfer. This is measured through R-values (thermal resistance) and U-factors (thermal transmittance). Higher R-values and lower U-factors indicate better thermal performance.
Heat transfer occurs through three mechanisms: conduction (through solid materials), convection (through air movement), and radiation (electromagnetic waves). Building envelopes must control all three to maintain comfortable indoor temperatures and minimize energy consumption.
Heat Flow Through Wall Assembly
Indoor
Outdoor
Performance Insights
• Higher R-values dramatically reduce heat transfer through walls
• Temperature differences drive heat flow - greater differences = more transfer
• Good insulation can reduce heating/cooling costs by 30-50%
• Air leakage around insulation can reduce effective R-value by 20-30%
Key Thermal Concepts
R-Value (Thermal Resistance)
Measures how well a material resists heat flow. Higher R-values = better insulation. Typical wall R-13, high-performance walls R-30+.
U-Factor (Thermal Transmittance)
Rate of heat transfer through a material. Lower U-factors = better performance. Typical windows U-0.35, high-performance U-0.15.
Thermal Bridging
Areas where heat bypasses insulation through highly conductive materials. Can reduce effective R-value by 20-40%.
Air Leakage
Uncontrolled air movement through gaps and cracks. Can account for 20-30% of total heat loss in buildings.