Architecture
Thermal Mass Guide
Thermal mass materials absorb heat during the day and release it at night, reducing temperature swings. Use this guide to compare materials and understand passive solar design applications.
Passive Solar Design Rules of Thumb
1.
Position high-mass materials (concrete, brick, water) where they receive direct winter sun — south-facing walls and floors in the Northern Hemisphere.
2.
Mass should be 6–18 inches thick for optimal heat storage. Thicker mass has a longer time lag before it releases heat.
3.
Glazing-to-mass ratio: for every 1 sq ft of south-facing glazing, provide 5.5–6 sq ft of thermal mass floor area (or 2–3 sq ft of mass wall).
4.
Darker surfaces on mass walls absorb more radiation. Avoid carpeting over thermal mass floors — it acts as insulation against heat storage.
5.
Insulate the exterior of mass walls, never the interior, to maximize the mass's thermal buffering capacity.
6.
Water has the highest volumetric heat capacity of any common building material — water walls, cisterns, or Trombe walls with water can store 2–3× more than concrete per cubic foot.