Passive Solar: the low-tech way to heat your home

Whether you’re giving your house a new lease of life with a refurb or planning your brand new dream home, getting the most bang for your buck will be a priority.

Good design can save you money on your bills, create a healthier indoor environment and also reduce your carbon footprint. This article is about a particular design principle called passive solar. So, what is it, how does it work and how can it benefit you?

What is passive solar?

passive solar

Diagram illustrating how passive solar works. Wikipedia Commons.

When hearing the word ‘solar’ most people think of solar panels. But that’s not the only way to harness the sun’s energy. Passive solar is simply optimising the sun’s natural light and warmth through low-tech design features such as large south-facing windows and good insulation.

Making the best use of this passive solar energy is an affordable, sustainable and pleasant way to light and heat a building.

How it works

The three key ingredients to passive solar design are orientation, heat-retention and air-flow.

The best orientation is south-facing, or within 30 degrees of south-facing (in the northern hemisphere). Large, often floor-to-ceiling, double or triple glazed windows bring in as much sunlight as possible and warm the inside via the greenhouse effect.

Shades or louvres at the top of the windows can be used to prevent overheating. They block out the high summer sun while allowing the lower morning and winter sun to warm the building. A west-facing orientation is prone to overheating because the late afternoon sun is too low to be blocked with louvres.

An east-facing or north-facing orientation on the other hand is likely to be cold. If possible, arrange the layout so the living and dining rooms, kitchen and bedrooms are towards the south where they’ll benefit from sunlight, and place the hallways, utility room and bathrooms on the opposite side.

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Floor-to-ceiling glazing on south side of a zero-carbon house.

Once the sunlight is brought into the building and trapped as heat, it needs to be retained. Double-glazing helps to do this, but insulation is the most important feature.

Insulation acts like a blanket around the building, minimising heat-loss and also spreading heat more evenly around the building. Unlike a blanket, it can also reduce overheating in the summer because it regulates temperature rather than maximising it.

Insulation comes in a few different types, divided into roof insulation and wall insulation. The costs and savings will vary widely depending on the building, but you could cut your heating bill by as much as 30% with proper insulation.

Interestingly, natural wool-based insulation can actually be the cheaper option. Thick walls also add ‘thermal mass’ – helping to absorb heat when it’s sunny and slowly release it at night.

To make the most of passive solar you also need to control air-flow and make sure the building is very air-tight, so heat isn’t lost through tiny gaps around windows, doors and other openings.

However, once you get twice as air-tight as the building regulations demand you run into another problem – in the form of ventilation. If your house is super air-tight then just opening a window now and again will not be enough to guarantee healthy ventilation.

You can get around this by installing a low-energy ‘MVHR’ system (mechanical ventilation with heat recovery), which chucks out stale air and brings in fresh air. If you are planning a retrofit rather than a new home, you can improve heat-retention quite cheaply with draught-proofing around doors and windows.

How passive solar can benefit you

There are a range of benefits to using passive solar for homes. These can roughly be divided into economic, environmental and aesthetic benefits.

Economic

Passive solar design significantly reduces energy bills. The actual reduction depends on many factors such as the local climate, size and location of the building and the behaviour of you and your family or housemates.

To get a picture of what’s possible, a building that uses top-of-the-range passivhaus standards needs just a third of the energy used by a conventional building. Most people don’t achieve the pure passivhaus standard, but still make big savings.

passive solar

Sliding glass doors provide fresh air and cooling on hot days and warm the inside in colder weather.

As mentioned earlier, insulation alone can cut bills by 30%. The Whole Building Design Guide writes that modest passive design features can achieve a saving of 5 – 25% on heating bills. If you are planning a new home and have an architect experienced with low-energy design, it is possible to heat a house entirely through passive solar energy – although most people prefer to have a heating system for backup.

A key economic benefit of passive solar is the low cost of installation. If designing from scratch it needn’t cost you any extra at all, and if you’re doing a retrofit the payback period will be considerably shorter than renewable energy technologies.

A further consideration is that greener and more energy efficient houses have enhanced property value. A study published by PassivHausPlus reports 82% of homebuyers surveyed would pay more for a sustainable home.

Environmental

In the UK, energy used in buildings accounts for 43% of carbon emissions, and the majority of energy is used for space heating. This means using the sun for heating and lighting can have a dramatic effect on carbon emissions.

Successfully tackling climate change will require all sections of society, including individuals and households, to do their bit.

To find out how much carbon you could save by using passive solar design, start by finding out the carbon intensity of your energy. That means the amount of carbon dioxide and other greenhouse gases that are emitted per unit of energy, usually kilowatt hours. Then, armed with this knowledge and your energy bills, talk to one of the experts linked at the end of this article.

Aesthetic

Finally, buildings designed or retrofitted with passive solar principles are just nicer to live in.

They are flooded with natural light, the large windows and open-plan layouts add a spacious expansive feel, they stay warmer in winter and cooler in summer and they benefit from natural ventilation with fresh air.

Research also shows that indoor spaces rich in natural light and fresh air are good for the health and wellbeing of the occupants.

Learn More

There are so many variables when it comes to using passive solar and other green building techniques, that it’s not possible to give accurate estimations on cost and carbon savings that will be applicable to everyone.

If this article sparked your interest, use these links to find out more:

And if you’re interested in using passive solar for business premises, see our guest post on the ORB blog


We routinely incorporate passive solar principles into our designs. Take a look at our services page to find out more about what we do.

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