Designing a positive-energy home

The near future of eco-friendly homes lies in designing a positive-energy home—one that generates more energy than it consumes. In today’s climate crisis context, building regulations are increasingly focusing on mandatory net-zero consumption and energy self-sufficiency in our homes.

It is truly reassuring to receive constant emails and calls from people motivated to have an efficient, healthy home and, while many of the arguments may be economic—such as seeking energy savings—more and more clients embrace a lifestyle philosophy in harmony with the planet and believe that an eco-friendly home can be their small contribution to change.

Whether it is because in the future you want to stop paying electricity, water, or gas bills, or simply because an eco-friendly home aligns with the lifestyle you want to live, the reality is that today many architects can no longer conceive of a home that not only consumes no energy but, if possible, generates more energy than it uses—with the aim of disconnecting from the grid, becoming self-sufficient, and living in a radically sustainable way.

This concept is already becoming known as designing a positive-energy home: a home that generates surplus energy not only for the family’s day-to-day life but even to charge an electric car.

What is a positive-energy home?

So, how do we define the design of a positive-energy home? A positive-energy home is a dwelling that generates more energy than it consumes for its upkeep and day-to-day operation. In other words, through renewable energy sources, we can obtain more energy than we need to heat and cool, light, and run our home. The reality is that many positive-energy homes are already operating around the world, and they are improving every day by reducing construction costs and becoming affordable for the average family.

Designing a positive-energy home is possible today, and it is something we should consider if we want to build an eco-friendly home, because the near future no longer envisions only net-zero passive houses; homes will be small, highly efficient machines capable of meeting all a family’s needs without any external input.

Designing a positive-energy home

Let us look in detail at what designing a positive-energy home involves, and what its features and requirements are.

1. Orientation and shading

The first step in designing a positive-energy home is always to orient it correctly. This point is essential and can largely determine the energy efficiency of the dwelling.

To do so, the first step is to have a suitable plot of land.

In the Northern Hemisphere, ideally the house should face south, where we have more natural light throughout the day. In winter, it will be essential to capture solar radiation that can warm our daytime living areas without relying on heating systems. The house must be designed according to its orientation, but also according to the available sun exposure.

We must avoid obstacles—such as trees, nearby mountains, or neighbouring buildings—that could prevent sunlight from reaching the home for most of the day. Of course, we cannot remove buildings, but we should position the house to capture as much light as possible, especially in winter.

In the same way that we want the sun’s warmth to reach us in winter, in summer we will need some form of solar protection to prevent excessive heat in the home. We are talking about porches, pergolas, or movable elements that can be opened or closed depending on the time of year.

A positive-energy home should be designed to capture the maximum heat from the sun on the south-facing side, which in summer receives high, vertical sun that we can easily block with an overhang or pergola, and in winter receives lower, more horizontal sun that enters to warm the daytime areas.

In addition, we must consider the placement of rooms to the east, west, and north. In this regard there are different theories: east-facing rooms receive the first morning sun and are ideal for waking up, but on the other hand, west-facing rooms receive the last rays of afternoon sun, which is especially useful in winter to warm the bedroom just before going to sleep.

Sometimes there is no choice but to place bedrooms to the north. In that case, the north façade must be very well insulated—more than is conventional—to ensure that heating is efficient and does not lose heat. North-facing rooms, however, are very cool in summer, and if we also achieve cross-ventilation through courtyards, they can work very well, especially in warm climates such as the Mediterranean.

2. High levels of thermal insulation

The second point in designing a positive-energy home is to have high levels of thermal insulation.

Although the CTE (Spanish Building Technical Code) currently requires a minimum level of insulation, this is not sufficient if we aim to reduce energy consumption for heating and cooling. While a conventional home typically uses around 10 cm thickness, when it comes to designing a positive-energy home, we will likely be talking about thicknesses of around 15 to 20 cm.

In addition, we must avoid discontinuities in the insulation throughout the house. These discontinuities are what are known as thermal bridges, and they occur when a construction detail has not been properly resolved. This lack of insulating material in certain areas can undermine the effort we have put into the rest of the house and not only cause heat loss, but also lead to damp and condensation when extremely cold points in the structure come into contact with the home’s interior heat.

It is also important to pay attention to the type of windows we install. As with thermal bridges, there is no point in installing good insulation if we then use windows with poor thermal performance.

We should install double- or triple-glazed windows, depending on each case, and frames with thermal break, which, in addition to reducing cold, will also prevent condensation and damp.

When necessary, there are also low-emissivity windows that work by mimicking the greenhouse effect, trapping heat indoors and preventing losses. These windows work very well in winter to capture heat, but it is important to protect them from direct radiation in summer.

In any case, the most important thing is to ensure equivalence between the insulation level of the windows and the walls to avoid the much-feared condensation and damp.

3. Reducing air leakage

In the same way that we want to avoid thermal bridges, we must also reduce potential air leakage.

Sometimes wind barrier membranes are installed: they are airtight but vapour-permeable—allowing the wall and insulation to gradually release excess moisture that may build up from daily use of the home. This largely prevents air leaks that can alter the indoor temperature of rooms.

But beyond these membranes, the joints between materials and between the different elements that make up the façades and roof must be very well resolved. Materials should be installed with staggered joints, meaning that the joints of the different façade layers do not align at the same point. This way, air will not have a direct path into the interior, making it much harder for it to enter.

4. Energy generation

We now move on to the fourth point. Of course, in designing a positive-energy home we must include systems that allow us to generate energy to keep the house comfortable and healthy. At domestic level, the most common and efficient options are solar thermal collectors, photovoltaic panels, and wind turbines.

– Solar thermal collectors

Conventional solar thermal collectors are used to produce hot water. We can include them in the design of a positive-energy home, but we will need to generate electricity through another system, such as photovoltaic panels or wind turbines.

What solar thermal collectors will allow us to do is save the electricity or other energy we would otherwise use to heat DHW (domestic hot water) used for showering, cooking, or simply washing our hands.

– Photovoltaic panels

Photovoltaic panels allow us to obtain energy in the form of electricity. These panels generate current from the solar radiation they receive. Efficiency is increasing all the time, making it easier to run a home with a relatively small number of panels.

In addition, today panels are manufactured in different formats, such as sheets or façade panels, tiles, or, in recent years, flexible elements that adapt to a wide range of surfaces.

The energy we obtain from photovoltaic panels will be used to run appliances, cook, and light and heat our home.

– Wind turbines

There is another option for generating electricity: wind turbines. They work in the same way as large windmills, but on a smaller scale.

These are turbines that can be installed on the roof of our home and convert the kinetic energy of the wind—energy of movement—into electrical energy, which is essential in a dwelling.

5. Integrated battery system

So far, so good—but what do we do with the surplus energy? Of course, we cannot waste it and let it go to waste; we must store it so we can use it when there is no daylight or when the wind is not blowing.

We will need a battery system to store the energy we are not consuming at the moment it is generated. There are home batteries designed to store electricity generated in the home itself. They do not require much installation space and can store enough energy for an entire day.

Perhaps the best known are Tesla batteries, although brands such as Mercedes, Nissan, and Solar Rocket also manufacture this type of battery.

Another way to store the remaining energy we generate is by accumulating it as heat in water, for example, in a continuously operating underfloor heating system in winter, or by means of a simple hot water tank.

6. Efficient electrical and HVAC systems

Finally, the design of a positive-energy home must also include the installation of efficient electrical and HVAC systems.

Reducing consumption is an essential part if we want to cover all our electrical needs through renewable energy sources. If we use heating or air conditioning at all hours, use inefficient appliances, or leave lights on, it will be very difficult to cover all our consumption and generate surplus energy.

In any case, when designing a positive-energy home it will be very important to calculate the consumption your family requires and size the home and its efficient systems according to use.

Passivhaus Plus and Premium certifications

Just over 20 years ago, what is known as the Passivhaus standard was created in Germany. It is a certification awarded to homes with reduced consumption.

Three years ago, two new Passivhaus certifications appeared that include not only a home’s low consumption, but also energy generation through renewable sources.

These new certifications include references to the design of a positive-energy home, in the sense that to obtain the label it is necessary not only to achieve near-zero consumption, but also to generate extra energy beyond what is consumed.

– Passive House Classic / Classic Passive House:

The Classic certification sets maximum demand thresholds and does not require generating any type of energy. The Classic Passivhaus label is awarded when a home meets the following characteristics:

– Primary energy demand ≤ 60 kWh/m² ± 15 kWh/m² deviation
– Renewable energy generation: not required.

– Passive House Plus / Passive House Plus:

There is also the label for a Passive House Plus, which further limits consumption and requires renewable energy systems. Specifically, it requires:

– Primary energy demand ≤ 45 kWh/m² ± 15 kWh/m² deviation
– Renewable energy generation ≥ 60 kWh/m²

– Passive House Premium / Passive House Premium:

The Passive House Premium label involves the greatest restrictions:

– Renewable primary energy demand ≤ 30 kWh/m² ± 15 kWh/m²a deviation
– Renewable energy generation ≥ 120 kWh/m²

These certifications ensure that our home has certain characteristics—depending on each certification—which represent not only energy savings, but also financial savings.

The design of a positive-energy home follows fairly clear guidelines, but you need to know how to combine them all properly to achieve a comfortable, pleasant home tailored to each family and each climate.

At our architecture studio, we have been designing passive houses for years, tailored to each family’s needs, respectful of the environment, and built, as far as possible, with healthy materials.