What is a high performance home?

Sustainability is becoming an ever more relevant and desirable factor in everything we do, including building. Creating a new home that includes sustainable and recycled materials in its construction is great, but that's just one part of the equation. Once the building is complete, how sustainable will everyday living in it be?

There are many methods to make a home healthy and warm in a sustainable and energy-efficient way, and this is the goal of all high performance homes.

Here's what you need to know about high performance homes.

While there’s no official definition or set of standards that define a high performance home, aside of course from ratings such as Passive House or Homestar, there are a few generally agreed-upon ideals or principles that a high performance home should embody. In a sentence, you could say 'a high performance home excels at efficiently providing a safe, healthy and comfortable environment for its occupants to live in.'

Think of it like this: what are homes designed to do? What is their function? Well, they have many: they provide shelter; they keep you warm; they are a space in which to live your life. A high performance home is therefore one that does exceptionally well at all the things a home is designed for and, crucially, does so without requiring a lot of energy.

The principal benefit of a high performance home is a comfortable and healthy interior climate that doesn’t require much energy to achieve and maintain an ambient temperature year round.

High performance homes are warm in winter, cool in summer, and dry all year round. This makes them much healthier, as there's less chance of damp and mould developing.

What makes high performance homes different is that they can achieve this dry and ambient internal climate without having to rely heavily on heaters, air conditioners, or other mechanical methods, and if they do use energy they often generate much of it locally using rooftop solar. This can end up saving money, because the costs of heating and cooling the home are minimised.

Finally, there is the fact that a high performance home can play a role in lowering an individual's carbon footprint. Homes that are low energy or even net-zero require fewer carbon emissions over their lifetime to sustain than buildings with poor thermal envelopes. Beyond the day-to-day energy use, buildings that are designed well with durable materials don't require as much maintenance over their lives to upkeep.

There are many design, building, and material choices available for making a home an energy-efficient high performer. They all, however, aim to contribute to at least one of four key performance characteristics: insulation, ventilation, solar gain and heating.

Insulation

The central pillar of a high performance home is having great insulation. Whether it's hot or cold outside, a house with high thermal resistance is better able to maintain it's interior temperature compared with one that's poorly insulated.

While cladding materials and framing have an influence on the thermal envelope of the building, the most important part is the insulation used. Insulation products come in many varieties, including glasswool, polyester and mineral wool, and can be installed in walls, ceilings and under subfloors.

The other element to consider in a building's thermal envelope is the window and door joinery, as well the glazing itself. Any elements of the home that aren't covered with insulation are potentially weak links where heat can escape the building. Double and triple glazing for windows is particularly effective for ensuring maximum performance.

Whatever the exact combination of insulating techniques and products used, aim to achieve the best thermal envelope possible with your budget.

Ventilation

Ventilation is key for the air in a home to stay healthy. The air in a home with no ventilation would soon become stale, as the concentration of moisture, odours, dust and other pollutants slowly built up.

Ventilation in a high performance home is all about control. The goal is to minimise airflow in and out of the building aside from the channels you have decided to use as ventilation. This could be through an HRV system that filters air and retains heat or maybe through specially placed windows where fresh air can enter down low, while warmer, moist air is released near the top of the space. Either way, the ventilation is happening through chosen channels, not via hundreds of small pockets for air to escape all over the house.

A big part of creating this controlled ventilation is having as near to an airtight a seal around the building as possible. When you do so, you're able to achieve both goals of having adequate insulation as well as sufficient air recycling through the building.

Heating and Solar Gain

A high performance home is able to maintain its interior temperature far better than other homes. Depending on the geographic region, some high performance homes don't really need any mechanical method of heating—the insulation and ventilation solutions keep the home at a pleasant temperature without anything extra, because they make the most of the most abundant source of heat and energy there is: the sun.

Harnessing the sun to service a high performance home starts with considering the geography of the site, how light hits it and the local climate changes throughout the day and the seasons. Is it sheltered and sunny all day? Do winds come in at a certain time of day, or in different seasons? Orienting the house on the site where it will collect the most sunlight during the day is an excellent way to minimise the need for extra heating capabilities.

This positioning factor can be assisted by installing materials in the home that have a high thermal mass, such as exposed concrete floors. During the day, these kinds of materials absorb a lot of the sun's heat, acting as a kind of energy bank. Then, at night, all the heat that's been stored during the day is slowly released.

As with ventilation, the specific nature of the site will influence how best to take advantage of solar energy. For instance, in the warmer and sunnier parts of the country it's often necessary to design ways to limit the sun coming in, even if only for certain rooms. However, with heat transfer systems or well designed ventilation and air flow patterns, hot rooms can supply the areas of the house that might not get as much sun, and balance things out.

Solar energy isn't limited in usefulness to passive heating; it can also provide some or all of your home's electrical energy needs if photovoltaic solar panels are installed. Solar panels can be extremely helpful in lowering the net energy use of the house, and in some cases can even turn a high performance home into a net energy producer.

It's important for the insulation, ventilation and heating strategies in a high performance home to work together, with each factor balanced and designed with the others in mind. For example, if you're trying to minimise airflow in and out with strong insulation and an air-tight building wrap, you might rely on a different ventilation solution than a house that uses operable windows for ventilation.

There are a number of certifications in New Zealand that can validate a house as a high performer. While they aren't specifically 'high performance home' ratings, they are all measuring the same kinds of things a high performance home needs to have.

Homestar is an independent tool run by the New Zealand Green Building Council. Homes are rated on a scale from 6 to 10, measuring their health, warmth and efficiency with New Zealand and its climate in mind. A 10 signifies a world-class high-performer, but even a home with a bottom-of-scale ranking of 6 would be one that performs better than the average home built to the minimum standards of the building code.

Assessment takes place at the design stage and again once the home is fully built, to ensure that the plans have been implemented as designed. Points are awarded across seven categories—energy, health and comfort, water, waste, materials, site, home management, (and sometimes innovation, which is optional)—with the final score determining the rating achieved.

The Passive House standard is an international accreditation that aims to increase the energy efficiency and quality of life offered by homes, as well reducing their impact on the environment. Passive House design involves calibrating a home's insulation to the geographic environment it's in, creating an airtight building envelope and then allowing for controlled ventilation of the interior airspace.

The airtightness is checked twice during the assessment process, with the first taking place once the house is fully closed in. A blower door test pressurises then de-pressurises the house, and the amount of air that leaks through the building envelope is measured. Doing a test this early in the build allows those leaky spots to be identified and patched up. A second blower door test takes place once the building is complete, again to identify any gaps and ensure the envelope is doing its job.

If you're aiming to have a new build gain one of these certifications, it's best to understand the standards before planning begins, so you can make sure your whole design process moves forward with them in mind. Talking to an architect or designer who is experienced in this type of building is generally best practice.

While certifications can be valuable, it's important to remember they're not required for a high-performance home. If your net energy usage is low, your insulation is fantastic and your home is comfortable, dry and healthy, then it's probably fair to say your home is a high performer, even though it might not conform to the specific standards of a certification's checklist.

All that said, building towards a certification can add value to your house, because if you ever decide to sell it can be easier to show and prove to prospective buyers that your house really is what you say it is. If you're going to the effort of making your home a high performer, finding a certification that will accredit it as such is usually a sensible strategy to follow.

To find inspiration for your high performance home, browse through Archipro's range of projects, or if you're ready to get started, contact an architecture and design professional to get the ball rolling.

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