Apparently, everyone can build you an energy-efficient home. But are they as energy efficient as you think?
‘Energy efficient’ has become a buzzword. But what does it actually tell you about your future energy costs?
You might be surprised to learn that there’s no single standard for what makes a home ‘energy efficient’. The term can mean different things to different companies. Most often, it’s used to describe a home with a range of energy-saving features.
For most standard new builds, what you’re paying for might include meeting H1 requirements, above minimum insulation, double glazing, a heat pump, LED lights, an efficient hot-water system, and possibly solar panels.
All of these things can help reduce energy use. But they don’t tell you how the house performs as a whole.
Just because a house is brand new doesn’t mean it’s energy efficient.
In 2016, BRANZ studied randomly selected new homes and found that the average new Christchurch home needed 74 kWh/m² of energy per year for space heating. (For a 200 m² home, that adds up to 14,800 kWh/year.)
Meanwhile, a well-designed home used for comparison needed just 36 kWh/m². (For a 200 m² home, that’s just 7,200 kWh/year.) That’s more than double the energy cost.
What’s causing the difference?
The House As A System
A house isn’t a collection of separate energy-efficient features. The insulation, windows, walls, roof, ventilation, and heating all need to work together.
You can pay more for better insulation, but if there are gaps in corners you end up with thermal bridges that lose heat.
You can pay more for windows with thermal breaks, but if those windows aren’t installed properly, the thermal breaks are useless.
That’s why a list of energy-efficient features doesn’t tell you how energy efficient the house actually is. It’s the way all those elements come together that matters.
Ask The Right Questions
When a company tells you a home is energy efficient, don’t just ask what features it includes. Ask what the home is going to deliver.
How much energy will it need for heating?
Ask for the predicted heating demand in kWh/m²/year and how that number was calculated.
How airtight will it be?
Warm air can escape through gaps in the building envelope, wasting the energy you’ve used to heat it – and no one likes a draught! Ask if your home is going to be blower door tested by a certified practitioner.
Where can heat escape?
Ask if thermal bridges have been dealt with. A telltale sign here is being told that these things don’t matter. That isn’t true; it’s the small details that add up.
Will the home manage the heat of summer?
Energy efficiency isn’t just about keeping warm. It’s also about staying cool. No one wants a home to overheat in summer. A comfortable indoor climate is neither an icebox nor a sauna.
Does the home actively manage internal moisture and fresh air?
A well-insulated, airtight home needs ventilation. Ask how fresh air will get in and how moisture is removed. The building code minimum is not enough in this regard.
How will you know it performs as claimed?
Modeling can predict how a home should perform. This verifies the design. But when a house is built, the result can be different. That’s why having skilled practitioners and knowledge on site matters.
New Zealand is exploring ways to give homes energy ratings, so you can see at a glance this key information.
Until we have a simple rating that lets you compare the expected performance of one home with another, it’s up to you to find out what makes a home ‘energy efficient’.
Are you in the process of deciding on the right company to build your new home? Ask us for a free one-on-one presentation and how we can prove our homes perform.
We’ll sit down with you and explain everything you need to know. No gimmicks, no magic. Just systems and processes that work.
You’ll walk away knowing exactly what achieving energy efficiency means – to your health, your comfort, and your future heating bills.
