How to Stop the Sun Heating Your Rooms Through the Windows

Sun on glass is one of the quickest ways a house heats up. The fix is simple and costs little: block the sun before it gets in, and time it so you are shutting out heat while the air outside is hotter than the air inside. Official guidance from councils and the NHS is consistent on this. Shade or cover windows exposed to direct sunlight and keep those windows closed during the day¹. Close blinds and curtains to keep out the sun². Close curtains in rooms that face the sun³.

The order matters as much as the kit. Open windows early in the morning or overnight when the air is cooler, then close windows, blinds and curtains during the hottest part of the day, especially in rooms exposed to direct sunlight⁴. While it is hotter outside than inside, keep blinds or curtains closed at windows that are exposed to the sun⁵. When the air outside feels cooler, for example at night, open up again and try to get air flowing through the home⁶.

What you put on the window decides how well it works. Shades or reflective material outside the window are best; if that is not possible, use light-coloured curtains kept closed, because metallic blinds and dark curtains can make the room hotter⁴. Pale reflective linings keep heat out better than ordinary fabric⁷. And whatever you fit, do not seal a room completely: close curtains and blinds on sun-facing windows to block radiant heat, but make sure this does not completely cut off airflow⁸.

Shade the window from outside if you can, inside if you cannot

The single most effective place to stop solar heat is outside the glass, before it passes through. Official guidance is clear that shades or reflective material outside the windows are the first choice, with light-coloured curtains kept closed as the fallback⁴. The UK Health Security Agency's heatwave advice for broadcast during a power outage says the same: keep your home cool by closing windows, blinds and curtains that are in direct sunlight during the day, and close external shutters or shades⁹.

If you have external shutters, roller blinds or awnings already, use them. The government's Beat the Heat checklist suggests considering internal blinds or curtains, and notes that external shutters, roller blinds or awnings are also very effective¹⁰. For south-facing windows in particular, consider solar shading or reflective window blinds³.

Most households will be working from the inside. That is fine, provided you choose the right material. The difference between a pale curtain and a dark one is not cosmetic: dark fabric absorbs heat and radiates it into the room, and metallic Venetian blinds can do the same. Lancashire's civil contingency guidance puts it plainly, advising curtains rather than metal Venetian blinds for rooms that get a lot of sun¹¹. Leicestershire's heatwave booklet adds that curtains with pale reflective linings are better at keeping the heat out⁷.

A simple way to think about it:

Blinds and thermal curtains you can put up yourself

You do not need a builder to make a difference. Official guidance lists stick-up or removable blinds and thermal curtains you hang yourself as valid options, alongside mounted external shutters, awnings or fixed blinds for those who can fit them¹². That covers most renters and most households on a budget.

The choice between them comes down to your circumstances rather than brand:

• Removable or stick-up blinds suit rented homes and windows you cannot drill, and come away when you leave. They are the option official guidance names for people who cannot fit permanent shading¹².
• Thermal curtains you hang yourself suit anyone with a curtain rail already in place. Choose pale or reflective linings, since these keep heat out better⁷, and keep them closed on sun-facing windows during the day³.
• Fixed internal blinds or curtains are the everyday option where you can fit them, and the government checklist suggests considering them¹⁰.
• External shutters, roller blinds or awnings are the most effective, and the government checklist describes them as very effective, but they need fitting and, in a rented home, permission¹⁰.

Whichever you choose, the same rules apply. Close them while it is hotter outside than inside, and on windows exposed to the sun⁵. Do not let the covering cut off airflow completely⁸. And if you are relying on open windows at night for cool air, think about safety: official guidance suggests keeping windows closed when it is hot, or installing window restrictors or grilles so windows can stay open safely at night¹².

Which windows to shade first, and when to open up

You will get the most benefit by working through the house in a sensible order rather than covering every window at once.

1. South-facing windows first. Official guidance singles out south-facing windows for solar shading or reflective blinds³.
2. Any window in direct sun. Shade or cover windows exposed to direct sunlight and keep them closed during the day¹.
3. Rooms that get a lot of sun. Close curtains or blinds in these rooms, using pale reflective linings where you have them⁷.
4. Bedrooms. Move to cooler parts of the house, especially for sleeping, and keep the bedroom shaded through the day⁴.
5. Rooms you are not using. Turning off lights and electrical products that are not being used helps keep the house cooler⁴.

Timing is the other half of the job. Open windows early in the morning or overnight when the air is cooler, then close windows, blinds and curtains during the hottest part of the day, especially in rooms exposed to direct sunlight⁴. Close doors and windows in the heat of the day to keep it cooler inside¹³. Keep your home as cool as possible: shading windows and shutting them during the day may help, and you can open them when it is cooler at night⁶.

Where to check for heat health alerts

Shading your windows is part of a wider response to hot weather, and knowing when a hot spell is coming lets you close up before the house heats. Heat-health alerts are provided by the UK Health Security Agency in partnership with the Met Office¹⁴. The Met Office monitors regional daytime and night-time maximum temperature forecasts, and when certain temperature thresholds are reached it assesses potential impacts and likelihood¹⁴. During the summer, UKHSA works with the Met Office to issue alerts alongside the weather forecast if the weather is so hot that it has the potential to affect people's health¹⁵.

You can sign up to receive heat-health alerts and updates from the Met Office⁴. To receive both heat and cold alerts, register using the Weather-Health Alerting system registration form¹⁶. Your council will also point you to the Met Office for the latest information about heat alerts¹⁷.

Thresholds vary by region. In the North West, for example, the trigger for a heat health alert is 30°C on successive days with an intervening night temperature no lower than 15C¹⁸. That regional variation is why the alerts are issued by area rather than as a single national warning.

Alongside the alerts, the practical advice from councils is to stay hydrated, avoid the hottest part of the day, keep indoor spaces cool where possible, and check on vulnerable people¹⁷. If you are shading windows for someone else, older people are a particular priority: close curtains in rooms that face the sun to keep indoor spaces cooler, and close doors and windows in the heat of the day¹³.

Keeping the room cool once the sun is blocked

Shading is the main lever, but it works best alongside a few other habits. Close windows, blinds and curtains in direct sunlight during the day, close external shutters or shades, and only open windows when the air feels cooler outside than inside, for example at night⁹. Sit and sleep in the coolest part of the home, and go outside at cooler times of the day⁹.

If you are inside on a very hot day, close curtains, close windows if it is hotter outside than in your home, and turn off electrical equipment and lights that get hot²⁰. Keep the home cool by closing the curtains in rooms that face the sun and ensure there is plenty of ventilation²¹. In London, the advice adds that it may be better to keep windows closed during the hottest parts of the day to keep the heat out, opening them when the air feels cooler outside, and trying to get air flowing through your home⁶.

For the wider picture, our guide to keeping your home cool in hot weather covers fans, cool rooms and the rest of the routine, and how to sleep and cool a bedroom on hot nights deals with the room where shading matters most. If you are shading a room for a baby, see what temperature a baby's room should be.