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Decide where thermal mass goes and how much

Thermal mass (concrete, stone, brick, earth, water) soaks up heat and releases it later. It helps a lot in climates with big day to night swings and can hurt in hot humid climates.

How

1. Use the swing you found in design-3 to choose low, moderate or high mass.
2. Place mass where winter sun lands directly, usually the ground-floor slab of sun-facing living rooms, about 50 to 150 mm thick for most materials (Your Home).
3. Insulate mass on the outside, never leave it exposed to outdoor air. Thick earth walls still need insulation in cold climates (Your Home).
4. Do not cover sunlit mass floors with carpet (DOE fact sheet).
5. In multi-storey homes put heavier construction downstairs and lighter construction upstairs, especially in temperate climates.
6. In hot humid climates prefer lightweight, well-ventilated construction unless you plan mechanical cooling.
7. Heavy earth or masonry mass adds earthquake load. In seismic zones, mass walls and heavy heaters must be engineered and restrained (design-11, design-26).

Sources

1. Thermal mass. Your Home, Australian Government, accessed 2026-11
2. Passive heating. Your Home, Australian Government, accessed 2026-11
3. Construction systems. Your Home, Australian Government, accessed 2026-11
4. Passive Solar Design (Technology Fact Sheet DOE/GO102000-0790). US Department of Energy and NREL, accessed 2026-11
5. A review of local construction practices applied on unreinforced adobe buildings in South America (Cocco, Brando and Spacone, Frontiers in Built Environment 8, 2022). Frontiers in Built Environment, accessed 2026-11

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