Why it works
Why houses stay hot after sunset
Short answer
Building materials absorb heat during the day and release it later, so indoor temperature can peak after outdoor temperature starts falling.
The simple explanation
- ✓Roofs and sunny walls store heat.
- ✓Heavy materials release it slowly.
- ✓Night ventilation helps only once outside is cooler.
Why it works
This advice follows UK Health Security Agency guidance and the underlying principles of thermal mass and time lag.
Important exceptions
Safety, health, weather and the design of your home can change what is appropriate. Stop if an action makes conditions worse.
Related guides
Sources & evidence
Reviewed 2026-08-21
- UK Health Security Agency: Beat the heat: keep cool at home checklist ↗
Supports: Shading, ventilation, reducing indoor heat and protecting people at higher risk.
official guidance · Accessed 2026-08-21