When Emma Taylor was offered a two-bedroom apartment in an award-winning block of flats, she couldn’t wait to move in.

Newly built, she was informed the building had been constructed to such high eco-standards that it would cost just £1 a week to heat. Unfortunately, as she’s discovered to her extreme discomfort, keeping warm is the least of her problems.

Because unlike most Britons, 23-year-old Emma has come to dread the summer months. Her ground-floor flat in Coventry is so well insulated that when the sun shines the temperature inside rockets — regularly over 25c, a point at which experts say health can suffer.

New government rulesover green homes that are turning modern houses into ovens

‘The winter was fine and I never needed the heating on,’ said Emma, who has an eight-month-old son. ‘It was great because I saved on bills and never ran out of hot water.

‘But in good weather the flat turns into a greenhouse and there’s no way of controlling the temperature. It’s an absolute nightmare at this time of year.

‘It’s so oppressive, we struggle to breathe. It’s ridiculously hot.’

Even opening the triple-glazed windows and turning on two fans she has bought makes little difference. In the recent hot spell, when it was 20c outside, it was 26c in her son’s bedroom. He suffers from eczema, which Emma is convinced is made worse by the sweaty, stifling conditions.

When the heatwave hit last Wednesday, temperatures exceeded 31c, forcing her to stay with her mother.

She’s not the only one feeling the heat. Over the past three summers, scientists from Coventry University have been monitoring temperatures inside the £2.8 million block, which was built by a housing association to Passivhaus standards — very high requirements for energy efficiency developed in Germany.

They found the flats were at ‘significant risk’ of overheating in the summer, with almost three-quarters registering internal temperatures that often rose above 25c.

It’s not just this development. Experts warn the Government-sponsored drive to construct ever-more ‘green’ homes has created an unforeseen, but potentially lethal, problem.

For while they may help cut carbon emissions and reduce winter heating bills, they can pose a genuine health risk in summer.

As the population ages and summers get hotter because of climate change, it’s feared heat-related deaths will more than triple to 7,000 a year by the 2050s.

Clare Swift lives with her children Yasmin, 7 and Eleson, 3 lives in a hot newly built, two-bed housing association flat in Romford, Essex

The elderly, obese, infants and those with chronic illnesses are most at risk.

‘If you wear a thick coat in winter that makes a lot of sense,’ explains Professor Li Shao, of Reading University. ‘But if you wear the same thick coat in summer you will overheat. It is very, very obvious.

‘The message is clear — if you super-insulate houses, then you’ll create over-heating issues where people will suffer.’

To understand the impact heat can have on mortality rates, turn the clock back to 2003.

That August, much of Europe sweltered under a heatwave, with temperatures in northern France exceeding 40c.

The result was 15,000 heat-related deaths, the vast majority among older people. Research later revealed at least half could have occurred due to exposure to heat in people’s homes.

We struggle to breathe - it's ridiculously hot

Britain also suffered — in just ten days 2,000 more deaths than usual were recorded. Again the worst affected were over-75s. If climate change causes more heatwaves, the consequences could be made worse by the new generation of super-insulated, eco-friendly homes.

The building of such properties has been driven by the Government as it seeks to drastically reduce carbon dioxide emissions.

Various regulations are already in place setting energy efficiency standards for new-build houses, including minimum requirements for thermal insulation in walls and roofs and making homes more air-tight to reduce drafts.

Next year they’ll be further beefed up with the introduction of the Government’s zero-carbon homes target, with its ever-more stringent building standards and energy-saving devices including solar panels — all important steps in a country where it’s estimated some 25,000 people die from cold each year.

Now there’s concern these measures have led to overheating in the summer, something the National House-Building Council first highlighted in a 2012 study.

Eco measures such as fitting double glazed windows and fitting insulation in the roof is good at keeping in heat in winter but doesn't let it out in the summer (file picture)

And just last month the Zero Carbon Hub, a non-profit organisation responsible for achieving the Government’s target of delivering zero carbon homes, published its own investigation with a 96-page report entitled ‘Overheating in Homes — The Big Picture’. It says: ‘As we get better at building and retrofitting [bringing older buildings up to standard] to prevent heat losses in the winter, we may inadvertently increase the risk of overheating in warmer months.

‘Throw in likely increases in the number of unusually hot summers as the climate changes, more frequent and intense heatwaves, and continuing construction in dense cities, then more people could find they are living in homes which reach uncomfortable or excessive temperatures.’

It’s something 30-year-old Clare Swift, a part-time administrator and mother-of-two, knows from experience. She lives in a newly built, two-bed housing association flat in Romford, Essex.

The flat has the second best energy efficiency rating possible. As a result, her heating bills are low, little more than £5 a week. The trouble is the heat in summer.

Living on the first floor, she has to be careful about opening windows in case her toddler son tries to climb out.

Whatever I did, I couldn't get rid of the heat

‘The nights are worst — it feels like an oven,’ she says. ‘I’ve bought fans for the bedrooms, but even so there’s sometimes no escaping it.

‘Everyone in the block complains. I stay outside as long as I can to avoid it, sitting in the park for a breeze. I’ve always loved new-builds and hoped if I bought a place of my own it would be new. But having lived in one, it’s put me off. It’s just too insulated.’

Her complaints are not uncommon. Because new-builds are often in built-up locations, residents may not be able to open windows because of noise, pollution or fears about security. Even if they do, the draught may be insufficient to dissipate any heat, whether from the sun or cooking or electrical items.

In other instances, the cause of the problem can just be bad design. Lucy Rigley, 23, moved into a privately rented, top-floor apartment in the centre of Sheffield last February.

The four-storey block had been built in 2010 and her flat boasted west-facing, floor-to-ceiling windows in the living room and bedroom.

‘It was beautiful, with great views,’ said Lucy, an assistant clinical psychologist. It also promised to be cheap to run, boasting the highest possible energy efficiency rating.

But while she never had to turn on the heating in winter, summer was a curse.

‘Whatever I did, you just could not get rid of the heat,’ she said. ‘You could open the windows or draw the blinds, it didn’t make any difference. It was like a greenhouse and would be unbearable.

Experts warn drive for ‘green’ homes created a potentially lethal problem during the hotter summer months

‘Sometimes I had to work shifts and sleeping in there during the day was impossible. If you had more than one person in the flat, the heat they generated made it even worse.’

Unsurprisingly, her stay there was brief — Miss Rigley moved out last autumn into a less eco-friendly home.

With growing awareness of the problem, there are calls for more attention to be paid to the issue during the design process.

Solutions may include changing the orientation of the building or simply fitting external shading or shutters to the windows.

Some will wonder how it is that no one predicted this problem in the first place. It’s a question I put to Neil Smith, head of research and innovation at the National House-Building Council.

‘It is not entirely unexpected,’ he says. ‘I think the extent to which it occurs in certain types of dwellings sometimes takes people by surprise.

‘You might think improved insulation would tend to keep heat out. But the reality is that the gains from solar and other sources tend to be trapped by the insulation.

‘We are satisfying the Government’s ambitions for zero carbon and I think it is an unintended consequence. I think we are bound to find our way with this agenda. It now seems highly obvious, but perhaps it didn’t at the time.’

And he adds: ‘What we are trying to do as a nation is to improve energy efficiency in terms of heat loss without creating situations where you have to use air conditioning to keep heat down. That would be perverse.’