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  • Writer's pictureKate

How to Keep Your Cool: Reduce summer overheating through your roof

Today we're looking at a more difficult area of the home to deal with- but one that can be really important. People wanting to improve roof performance will need to do some research beyond the scope of this blog- but we will still be looking at the options for different kinds of roof within this post and providing useful links.

Once again we can look at how hot countries deal with roof heating:

In really hot dry places, roofs are often flat and pale coloured- and used as living space in the evenings when they catch the breeze. In places which are hot but rainy, homes still often have sloping roofs - but the whole building design and ventilation are so different from our homes here that a quick adaptation of UK homes isn't going to work- and nor would we want to do it, as we need to keep heat in our homes for a lot of the year. So we have to work with what we have and our year-round conditions.

If you're living in a 2 (or more) storey house, you've probably noticed that upstairs gets a lot hotter than downstairs in the summer. That's generally because of heat coming in through the roof, plus top floor windows and walls getting less shading from nearby buildings and trees.

Most house roofs in this country are pitched (they slope) and are dark colours- often grey, black or red tile or slate. As we already talked about with window coverings, dark colours absorb the heat and light energy from the sun really well, and get hot. Then they radiate that heat into your house (and out of it too- but it's the into the house bit we're concerned about). If you've been into a storage attic on a summer afternoon, it's usually scorching. Loft extensions are often little better.

Flat roofs are often covered in black waterproofing similar to asphalt- which also gets really, really hot in the sun. If you're in a top floor flat with a flat roof, you're likely to get too hot on sunny summer days. If you're lower down a block of flats, you're protected from the sun on the roof by the flats above you- just as the ground floor of a house is usually cooler than higher floors.

The main solution to too much heat getting into your home through the roof in the summer is exactly the same as the solution to too much heat getting out of the house through the roof in the winter: You need good insulation.

Using roof insulation to reduce overheating

Often people think this sounds silly: Insulation is meant to keep you warm, right?

But insulation works both ways. Try putting a cold drink in an insulated mug or flask: The drink will stay cold for ages, just like the flask would keep tea hot for ages. Insulation simply stops energy getting through in either direction- great for summer AND winter.

If you have an accessible attic space, improving your roof insulation is reasonably simple.

Here is advice from B&Q on how to install loft insulation in a dry, accessible loft space- make sure you follow the safety advice and leave eaves gaps: To really ensure you can't block ventilation from the eaves and cause damp issues, you could use eaves vent trays.

It's also important to remember the loft hatch and any other access points into the attic - our airing cupboard used to open directly into the attic space- the cupboard door used to rattle in the breeze because so much air passed through it, which was not at all good for staying warm or cool!

If your loft space is damp or more difficult to access, you will need to seek professional advice- but check online first with reliable groups such as the Energy Saving Trust and Association for Environment Conscious Building to make sure that whoever you ask is taking a sensible approach and won't cause problems with your roof.

If you have a flat roof, installing insulation is complex and will need to be done professionally- especially as flat roof insulation should usually be done on the outside to avoid causing damp problems which can result in structural problems if joist rot.

On the plus side, insulation can be extremely effective on a flat roof and it can also be a good time to install a green roof as many flat roofs are ballasted (weighed down with gravel or slabs) anyway- the green roof can just go on instead of the gravel.

Green roofing is really good because the plants help protect the roof waterproofing from changes in heat and from sunlight and weather, meaning the roof will last much longer. They also give a good layer of insulation to the rooms below, cooling the roof in summer with transpiration from their leaves and with the soil layer reducing heat loss in winter- and they're great for biodiversity too: Here are forget-me-nots blooming this week on our (DIY) green roof- it changes colour all year as different plants flower!

In fact, green roofs have even more benefits: Many countries across Europe and increasingly across the rest of the world are using green roof strategies to improve cities as they help reduce the urban heat island effect and reduce flooding by catching lots of rainwater. For example, all German states have green roof strategies in place and as a rule all new flat roofs need green roofs and/or solar panels- here is Hamburg's information (available in English).

Back to insulation:

Insulating a loft space which has already been converted (badly, given that it wasn't insulated properly when the job was done...) into living space is a very complex option. If you're able to approach the roof from outside- as in, if the roof needs retiling anyway- and there are nice big joists able to take extra weight, you may be able to insulate between joists or even put insulating panels on top of the existing roof before retiling on top.

If you're unable to get to the joists and there is enough headroom inside, using a multilaminar foil or insulation-backed plasterboards could be an option for improving insulation.

Obviously, neither of these options are at all simple- both are expensive and would require professional builders- and potentially planning permission to externally insulate the roof. Putting baking foil on the sloping ceilings inside to reflect away some of the heat from the sunny side(s) of the roof may make some difference to the temperature inside- though it won't look very pretty and will take a lot of foil (see yesterday's post on paper-backed foil blinds if you want to try this).

Using roof colour to reduce overheating

The less common (in this country) option for reducing heat coming through roofs is to paint them a pale colour. This can have quite a big effect on how much heat comes in through the roof, and is reasonably easy to do on a flat roof- obviously taking precautions for working at height, and ensuring your roof is safe to walk on or using appropriate measures (the HSE has helpful guidance). If your roof is pitched and you want to paint it, you will need to contact your planning department as visible alterations to homes may need planning permission- and it's worth checking planning or permitted development for painting flat roofs too if they're visible from the road. Planning departments are usually helpful if you email or phone and there is guidance on permitted development available online too. Winter condensation risks from painting mentioned in the BBC article above are very low in this country as we generally use different roof structures from those in Delhi (the main article example location) due to our much colder climate and the need to heat homes here in winter.

A further option for roofs which will provide some roof shading and reduce roof heating by converting some of the sun's energy into electricity before it hits the roof is installing solar PV (or solar hot water panels). Obviously, the big advantage of this is that you get the electricity to use- and with the smart export guarantee, panels will pay back their installation costs.

So, in summary, there are two main and one little option for reducing roof overheating:

If you're in a leasehold or rented flat which overheats, you could consider approaching your building owner or maintenance provider to ask about possibilities for roof insulation, painting or green roofing as a measure which is likely to make your building much more comfortable and safer to live in. While there are no building regulations on overheating at present, overheating does cause many deaths in the UK, and landlords do have a duty of care to tenants- so if there is evidence that your home overheats badly, discussing this issue and possible solutions with your landlord could perhaps be a first step towards getting the building appropriately insulated.

You could collect evidence of overheating in your home by using a thermometer and recording temperatures in a diary regularly in the morning, evening and middle of the day. If you're also able to record the weather forecast maximum temperature for the day that would give useful information too.

It's worth knowing that there are various natural and renewable insulation materials available including paper, wool and wood fibre based insulations which are often nicer to work and better for the environment than the foam or mineral wool insulations, but they do tend to be more expensive and may need thicker layers to achieve the same insulation values than other insulations. Many non-renewable insulations are recyclable- and they're all better in terms of energy than not having insulation!

While none of the options for improving roofs are particularly easy (unless you have a flat roof of your own and a tin of white paint...), they are definitely worth looking into if you have the opportunity- particularly insulation, because that will pay dividends all year round for your comfort, money and health.

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