Keeping Cool in a Heatwave

With climate change we expect to have more frequent, more severe heatwaves

Shade Your Home 

Reduce direct sun on your home, particularly windows & skylights

  • Draw curtains or blinds on windows that let the sun in
  • External Shades are even more effective, stopping the sun reaching your windows. Options include:
    External shutters – traditional in southern Europe for a reason →
    External blinds – can be operated with a remote control
    Blinds inside double-glazing – can be tilted with a magnet
    Awnings: retractable or DIY: see PDFvideo. Can’t be used if it’s too windy
    Shade Sails are increasingly used to shade homes and gardens.
    Look here for a wide selection of solutions.
  • Rooflights angled towards the sun are a special problem: Velux windows can have external awning blinds  retro-fitted. Their Internal blinds can help too.  Other rooflight manufacturers have their own blinds
  • Internal curtains or blinds, especially reflective ones, can help reduce the effect of sun coming in a window, but not as well as external shading that keeps it right out.
  • Trees that shade your home really help. Deciduous trees let you benefit from winter sun
  • Solar-control film on window glass reduces the sun’s heat coming in, but it cuts some light too.  You can fix it yourself: See video
  • Low-G glass is good to specify for new or replacement sunny windows. It also lets in much less radiant heat from the sun, with a small reduction in light transmission. But both film and low-G reduce solar gain in the winter too, which would otherwise help warm those rooms.
  • Paint it white – not really shading – but white or light-coloured walls and roofs absorb less heat from the sun. White-painted brick walls can be 7.5°C cooler than identical plain brick walls.

Controlling your Home

Ventilation:

    • On a hot day: close all doors, windows and vents that let in hot air. These may vary with the time of day and the wind
    • Cool off at night to let you sleep better and cool your whole home before the next hot day, possibly with the help of fans:Let hot air out by opening windows or skylights at the top of the house.  Draw in cool air by opening ground-floor windows or vents where the air is cooler outside. Many windows can be part-opened in secure ways that won’t let a burglar in. For example restrictors like these or these can be fitted to wooden sash windows, letting them only open 100mm when you want.
      If your home is only on one floor, purge the hot air at night by opening windows or vents, to give through-ventilation, if possible.If your flat only has windows on one side, try to open them at the top and at the bottom. A fan can really help, if you put it near the bottom of the window to blow cool air along the floor, away from the window. This will create a circulation, pushing hot air out of the top of the window.

Avoid unwanted heating from appliances, lighting, etc

    • Choose low-energy appliances, computers, lights etc. Use them only when really needed
    • Is your hot water system well insulated?
    • Is your fridge or freezer in a hot place? It will be inefficient and make that place even hotter. Fridges and freezers work best in cool places, although check the user-guides for operating ambient temperatures: a garage may be too
    •  cold in the winter.

Thermal Mass from brick, concrete or stone stabilises temperatures and reduces uncomfortable, hot peaks. External wall insulation, with the thermal mass of the walls inside, keeps those rooms cool in heatwaves, especially if night time ventilation can cool the walls, ready to hold down temperatures the following day.  Rooms with internal wall insulation have low thermal mass and will heat up or cool down quickly. This might be be better for a west-facing bedroom that you want to cool quickly after the evening sun. You can benefit from the thermal mass of solid floors by covering them with tiles (or nothing), rather than thick carpets.

Insulate walls and roofs, especially those that get hot in the sun.
In general insulation for winter warmth helps you keep cool in a heatwave too. Reflective, silvery insulation (eg: multifoil) is particularly effective in reducing heat radiating down from a hot roof. Heat can’t travel down by convection, which is driven by hot air rising, so radiation dominates in this situation.
Draught-proofing is important too.

Cool yourself

    • spray or sponge yourself with water
    • Put a cold pack around your neck or under your arm
    • Have a part-filled ‘hot’ water bottle ready in the freezer…
    • Take a cool shower
    • A fan can help you stay comfortable, providing the air temperature is below 35°C, without using much electricity
    • Cover yourself with loose, thin light-coloured cotton clothing. Wear a hat and sunglasses outside/li>
    • Avoid going out or exerting yourself in the heat of the day. Plan ahead with a weather forecast
    • Air movement from a fan can help you stay cool, but keep hydrated. Spraying yourself with water is good too. If it’s really hot (> 35°C) fans can make you hotter.
      If you have high ceilings (>2.8m), consider fitting ceiling fans
    • Don’t get dehydrated. Have cold drinks regularly
    • Avoid heat exhaustion See NHS advice

     

    Other Choices

    • If your home’s too hot, is there anywhere you can go that’s cooler?
    • Could you sleep in a cooler room – on the north side or ground floor?
    • Avoid air-conditioning, if possible – it’s energy-intensive and blasts heat at your neighbours. If you need it, consider turning up the temperature at which it comes on and stay cool by following other advice here.

    Health Risks

    The 2003 heatwave is estimated to have caused 2,000 deaths in the UK and 35,000 in Europe.  Overheating can be much more serious than discomfort, especially if air temperatures go over 30°C.

    See NHS advice on staying safe in hot weather, plus:

    Beat the Heat and Covid-19
    Heat exhaustion and heatstroke

    Older people and young children are most at risk from over-heating.

    Some people, like those in sunny, single-aspect flats have few options to stay cool and suffer badly in heatwaves. It’s a scandal that UK Building Regulations don’t yet require building design to prevent overheating in new buildings.

    Being Neighbourly

    • Do you know people in hot homes you can invite to cool off in yours?
    • Could you offer them advice or practical help, as above?

    Hoping that you can all stay comfortable and enjoy the hot weather,
                    Tom Bragg,  Cambridge Carbon Footprint

    Download this article ‘Keeping Cool in a Heatwave’ as a PDF