Strategies to avoid overheating

What were you doing in the longest heat wave in 42 years? Luxuriating in endless days of brilliant sunshine? Or getting increasingly frazzled from sleepless nights in your overheated home?

Chances are that the older and less modernised your house, the more comfortable you were. Why? Because until late into the last century most homes were exceptionally leaky. Gaps under doors and skirtings, between suspended floorboards, in ill-fitting windows and uninsulated attics all ensured that warm air had much less opportunity to accumulate than in a modern house.

Unfortunately the same things had the completely opposite effect when temperatures dropped. Which is why we have spent much of the last generation packing our homes with insulation, fitting double glazing, banishing draughts and generally ensuring that as much heat is retained as possible.

Curiously, however, even though the official reason for these measures was to combat climate change, the likelihood that that would involve higher temperatures doesn’t seem to have been considered. In fact, overheating, or its avoidance, isn’t mentioned at all in the current Building Regulations. Nor are there any recommendations, let alone requirements, for maximum internal temperatures.

So, how can you ensure your energy-efficient dream home won’t turn into a sauna every summer?

Strategy one:

Stop the heat entering

External barriers, such as awnings, brise soleil, pergolas or balconies are effective ways of keeping the summer sun at bay, particularly for south-facing facades. Leafy shade from nearby deciduous trees can have a similar effect and conveniently disappears in winter when solar warmth is welcome.

Internal barriers, such as blinds, curtains and interior shutters, are useful but tend to be less effective because heat has already entered the building fabric. East- or west-facing windows should have vertical blinds to deal with the sun at lower angles.

The ultimate external barrier to solar heat is external insulation on a house with high thermal mass; that is, one built of blockwork, brick or stone. The heavyweight material both absorbs and releases heat slowly. Once it’s warmed up in winter, the outside insulation keeps the heat inside. But in summer a cool interior stays cool much longer.

In addition, paint the outside of the house white to reflect solar heat. A white roof would be even more effective, though this may not convince your local planning department.

More likely to be approved is a green roof, which will provide both insulation and a cooling effect from the vegetation.

Strategy two:

Minimise internal warmth

Summer doesn’t require central heating but hot water will still be running throughout the house. Ensure all pipework is well insulated to avoid unnecessary heat leakage – and improve the energy efficiency of your white goods.

Think about confining heat-producing items such as the washing machine, tumble dryer, central-heating boiler and hot-water cylinder to a dedicated utility room. This will also help clothes drying in that space and, if you have one, add to the efficiency of a heat pump tumble dryer. Internal walls painted white or pale colours will help to reduce heat absorption. Opt, too, for cooler floor surfaces, such as wood or tile, rather than carpet.

Strategy three:

Ensure effective ventilation

Simply opening a window is always effective, but more so is cross-ventilation where a second window in the same room, or in another wall of the house, creates a through draught.

But there are limits. According to the Chartered Institute of Building Engineers, the maximum distance for effective cross-ventilation is five times the floor to ceiling height.

Mediterranean-style external louvred shutters are a good way of excluding solar radiation while allowing fresh air to enter. They also provide security for windows left open.

Hot air rises so a route to roof level, or close by, provides a useful exit for excess heat. A clear central chimney will achieve this, as will an openable roof light above a central staircase.

A dedicated passive ventilation system works in a similar way. Here, warm stale air from kitchens and bathrooms rises naturally up near-vertical shafts to a rooftop vent. More common, however, are mechanical whole house ventilation systems (MVHR). A continuously running fan in the attic draws stale air through ducting and expels it outside, while simultaneously drawing in fresh air, which is distributed throughout the house via more ducting. In winter the warmth from departing air can be extracted by an integral heat exchanger and used to heat incoming fresh air.

In warmer months the heat recovery capability can be turned off. Some systems automatically boost the intake of fresh air when the outside temperature is lower than the internal.

Strategy four:

Introduce cooling

Air conditioning with ducting to all or most rooms is generally only feasible for new builds. The cost of installation, running and maintenance is unlikely to make it widespread until heatwave summers become the norm. However, individual wall-mounted units for living areas and a main bedroom are much easier to retrofit. Currently all residential air conditioning carries a reduced VAT rate of five per cent.

So, incidentally, do heat pumps. These are effectively reverse refrigerators which extract heat either directly from the outside air, or from the ground via buried, liquid-filled piping. This is then used to run central heating and hot water systems.

Heat pumps are expensive, can be noisy and produce only low-temperature heat. They work best in well-insulated properties using low-temperature heating systems, typically underfloor heating. Under the government’s Renewable Heat Incentive, however, heat pumps attract a tariff designed to recompense householders for the extra cost they incur above that of a standard fossil fuel system.

Even better, air source heat pumps can be reversed to provide cool air. That ability alone is likely to increase their popularity as summers continue to scorch.