Climate

Thermal mass where days are hot and nights are cold

27 July 2026

Heavy materials inside the insulation smooth out large swings between day and night - if the house is lived in every day.

In a continental climate the temperature can move by fifteen degrees between the afternoon and the early morning. A heavy floor or wall absorbs heat while the air is warm and gives it back when the air cools, so the rooms swing much less than the weather.

Where the mass has to be

Mass only works on the warm side of the insulation, in contact with the room air. A brick wall insulated on the inside is thermally light; the same wall insulated on the outside becomes a battery for the room.

• Concrete or stone floors uncovered by thick carpet
• Internal masonry walls that the winter sun can reach
• Exposed ceilings rather than suspended ones
• Night ventilation in summer, so the mass is cooled before the next hot day

When it does not help

A weekend house that is heated from cold on Friday evening will take a long time to feel warm if it is heavy, because the heating has to warm the walls first. For occasional use a light, well insulated construction is the better choice.