How to keep cool in summer

Some people say that modern energy-efficient homes are more prone to over-heating in summertime but in fact over-heating can be a problem with any age of house. Over-heating is worse in the city partly because towns are generally warmer than the surrounding area (the heat island effect) and partly because they are often noisy which is annoying if we open the windows.

What will work for you depends on you and your home. Here are some tips for how to keep cool.

Strategies

  • Mimimise heat generated inside the building eg. turn off unnecessary appliances; when cooking use an extractor
  • Minimise heat coming in from outside e.g. block off windows from the sun with blinds or shutter; apply reflective paint to dark flat roofs
  • Ventilate to remove the heat e.g. open windows to create a through draught (but only when it is cooler outside than in)
  • Use evaporative cooling e.g. fountains, sweating
  • Make use of overnight coolness by ventilating overnight and closing windows during the day

Yourself

Dress for the weather

Dress for the weather! Modern synthetic fabrics, especially those designed for sports or adventure, can be even better than cotton. The material must be light but breathable.

Sweat

Take cool drinks and allow your body to sweat - the is the main way our bodies adapt to the heat. (However some people sweat more than others and older people often sweat less). Use a fan if necessary to create air flow. Wear clothes that allow the sweat to evaporate.

Use ice or a damp towel

It will not look cool but if you find you are really suffering from the heat try wrapping some ice cubes (or a small pack of frozen peas) in a tea towel and applying that as an ice pack for the head. Or, we know someone who uses damp towels overnight to keep their feet cool. This works by evaporation, the same principle as sweating.

Your garden

Trees and shrubs keep the air cool

Trees and deciduous shrubs help keep the air cool because water evaporates from their leaves. Green roofs are good in the same way, especially the deeper ones as they store more water.

Trees for shade

Trees also provide shade which keeps the air at ground level cool.

Trees for shade against windows

Windows facing east or west get morning and evening sun which is low and shines straight through. These windows can be even worse for solar gain than south facing. So shrubs or trees shading these windows make a big difference. Ideally use deciduous plants because then in winter time when you need more light you will still get it.


I like to wear light clothes in the summer like these. They are 'adventure' clothing and they wick really well so I don't feel sweaty. Also here you can see our apple tree that shades the south-facing kitchen window.

Appliances and cooking

Leave the washing and hoovering until later

Any electricity you use - from TV, dishwasher or whatever - puts heat into the building. So turn things off when they are not needed. Avoid hoovering or running the tumble dryer on hot days if you possibly can - or do it in the early morning when it is not so hot. Large screen TVs can also give off a lot of heat.

When cooking, use an extractor

Older ovens that are not well insulated are terrible for heating up the kitchen so avoid using the oven if you can. If you are cooking on the hob make sure you use your extractor to remote the hot steam.

Lag hot water pipes

In some homes, usually flats with communal heating, hot water pipes stay warm most of the day. Make sure these are well lagged.


We have external blinds on the Velux windows on the south side. They keep the direct sun off and by opening the windows here at the top of the house, as well as in the kitchen below, we get a good draught all the way through.

Windows

Close the blinds to keep the sun out.

South, East and West facing windows bring heat in from the sun if you let them so cover windows with blinds or shutters when the sun is on that side. Curtains can help, especially if they are light coloured on the outside, but reflective blinds or shutters are better. Internal blinds are almost as effective as external blinds as long as they are shiny and reflect the sun back out through the window - the window itself does not absorb much heat.

Roof lights angled towards the sun are the worst. Velux windows can be fitted with external blinds, operated by a string or electric (as shown in the picture).

Eaves, awnings and brise soleil

Rather than taking the trouble to open and close blinds and shutters during the day you can have fixed shading. Trees can be very effective. Also deep eaves keep the high sun out on south-facing upper floors - they are not so effective on east and west sides where the sun shines in from low down. Where you haven't got eaves you can fit awnings - you can do this DIY if you are handy - CCF tell you how here. Or you can fit brise soleil which are permanent slatted shades, usually made of aluminium.

Open windows top and bottom to create a chimney effect

Hot air rises. The best way to create a cooling draught through the house is to open windows at the top and bottom of the house. The air has to have somewhere to come in as well as somewhere to go out. Unfortunately this may be impractical as open windows can be a security risk.

Keep the warm air out

When it is warmer outside than in, opening the windows can do more harm than good. It lets the warmth in. Unless you need it for ventilation, keep windows closed in the hot afternoons.

Night time cooling

It is usually cooler at night and most homes take a while to warm up the next day. It is a good idea to get the house as cool as possible overnight by opening windows as much as possible. Hopefully it will stay cool through most of the day. To store you heat you need materials with a high thermal mass such as brick or stone. If you have solid walls and you want to insulate them, external insulation will keep your thermal mass. If you put insulation on the inside then there is no way coolness stored in the walls to connect with the room.

Some modern constructions are low in thermal mass. One way to fix this is by laying ceramic floor tiles or wall tiles.


Tom & Anne Bragg made their own DIY awnings - Download their instructions here (from Cambridge Carbon Footprint)

Flat roofs

Flat roofs with black bitumen tops absorb a lot of heat from the sun. Consider a green roof (if the structure is strong enough) or make the roof more shiny with a mineral coating or reflective paint.

Use underground coolness such as cellars

If you have an underground cellar you will probably find it is cool even during hot days. You can use this as a source of cool air and circulate it around the house. However it is important that the area is clean. You do not want to circulate dust or mould spores at the same time.

Fans and air conditioning

If the weather is not too humid fans can be effective without using a lot of power. Fortunately, Cambridge is generally pretty dry, though not always. When it is dry enough a gentle flow of air encourages evaporation. If you have high ceilings, a central fan can be effective. However, fitting them is a hassle.

Free standing fans can also help. An evaporative cooler (known in the US as a swamp cooler) blows a fan over a store of water that evaporates for extra cooling. You have to fill them up every now and again.

Evaporative cooling is not the same as air conditioning. The only power in the evaporative cooler is for the fan whereas an A/C unit uses much more. It works like a fridge, cooling the room instead of the fridge. However it dumps the heat into the environment which makes the problem worse! So A/C should only be used as a last resort.