Have you ever wondered what the difference is between a net-zero house and a passive house? They’re both buzzwords in the green industry. But also even in the mainstream news and during the speeches of politicians these days.
Gaining in popularity, it’s good to be aware of the differences. In some cases, they’re even the smallest of details. But these different approaches to building can have a big effect on cost, comfort, true sustainability and environmental savings, and much more.
In this article, we’ll explain the differences so that you can make an informed decision on which type of green building to pursue when designing or renovating your own home! We’ll also share how we approached our first net-zero solar home renovation project as well, and how we kept costs to a minimum on that.
What is a Net-Zero Energy Home?
A Net-Zero home produces as much energy on an annual basis as it consumes. Design and engineering usually involve energy-efficient technology and renewable energy sources to reach zero net energy use throughout the year.
It may not necessarily be completely engineered to use the lowest energy possible, but if it produces enough to make up for those shortcomings, it could be considered net-zero.
What is a Passive House?
There are many definitions you’ll find on the web. But most agree that a passive house is one of highly engineered energy efficiency and stringent design standards while using environmental factors to keep the energy use as low as possible.
It’s a voluntary standard to be as comfortable, affordable and having the lowest ongoing environmental impact possible.
There are a few prominent organizations in the industry that we look to to drill down on exact definitions.
The Passive House Institute defines a passive house as:
Passive building comprises a set of design principles used to attain a quantifiable and rigorous level of energy efficiency within a specific quantifiable comfort level. “Optimize your gains and losses” based on climate summarizes the approach.Passive House Institute
What Are Some Similarities They Share?
The good news is – both are extremely more energy-efficient and sustainable than an average house. And it doesn’t even have to cost that much more either.
Passive houses and net-zero homes share much in common. Both of these types of homes aim to make sure that their energy consumption is as close to zero as possible.
There are many differences in how they accomplish this, but for the most part, both passive and net-zero houses follow similar principles.
Here Are Some Characteristics of both Net Zero Homes and Passive Houses:
None of these are requirements. However, all energy-efficient homes, regardless of the label, usually aim to have most of all of these characteristics:
- The building envelope should be as air-tight as possible within budget. If you can control the air inside and prevent air leakage, the mechanical systems run less.
- Elimination of thermal bridging when possible. A thermal bridge is a component in the house that acts as a thermal conductor between the inside and outside of the house.
- Use high-performance energy-efficient windows.
- Install thick and continuous insulation through the entire building envelope. Insulation acts like a blanket around your house or your to-go coffee mug that keeps your coffee warm for longer.
- Mechanical ventilation to keep your air healthy and fresh. Since your building envelope is so tight, the air inside your home has nowhere to go. You must move that stale indoor out and bring fresh air in from the outside.
- Efficient mechanical systems and appliances. Things like HVAC, your hot water heater, washer, dryer, refrigerator, stove, dishwasher, and others must be energy efficient. But perhaps more importantly – they must be designed correctly for the home. If systems are too big or small for their actual workload need, they can work overtime and burn out.
- Some use of shading. Ideally, you have some shading on the roof that is optimized to let the warm sun in through the winter (when the sun is lower in the sky) and shade the windows in the summertime.
- Renewable Energy. When you do as many energy efficiency measures as you can and following known passive house standards, you may still need to generate some power. This is where solar energy, small wind turbines, geothermal, or perhaps small microhydropower might come in. We did a whole article on solar alternatives if you’re interested in learning more on that.
How Much Does an Energy Efficient Home Cost?
Many factors contribute to the total cost, so it’s hard to say exactly. The best graph we’ve found is from RMI’s The Economics of Zero-Energy Homes report from 2019, showing that net-zero homes only cost about 6-8% more than traditional homes.
And according to PHIUS, a passive house typically costs between 5-10% more than a typical home.
For the net-zero home renovation we did (see below), the efficiency measures and solar energy costs equate to 6.8% of the final appraised home value, so nearly dead-on with RMI’s findings.
When Was The First Passive House Built?
The first passive house was launched in 1988 by Wolfgang Feist and Bo Adamson, who also wrote the book “Building Physics Basics for Heating Buildings” which helped establish a new way of building homes that consumed less energy. Their research evolved into what would become known as Passivhaus.
When Did Net Zero Homes Come On The Scene?
While now becoming ever more popular, the concept of a zero energy home is still very young. According to the Pembina Institute, the Canadian Housing and Mortgage Corporation developed a pilot program in 2004, which led to the first net-zero project built in Edmonton, Canada. Construction was completed in 2007 and was dubbed the Riverdale House. You can see it featured here in this Net-Zero 101 video:
A Case Study – Our Attempt at a Net-Zero Home Renovation
As part of launching the company here, I wanted to create the most affordable net-zero home renovation I could muster. The goals were clear and deliberate:
- Keep the total cost under the median average home price of the area.
- Ensure that it can rent out for 10-15% above all ownership costs, including long-term maintenance. This is so that you can rent it out if things change in life, so you’re not forced to sell in perhaps a down-market.
The passive house concept was known before starting the project, but the goal was getting to net-zero as affordably as possible.
The reality is, unless you’re building from the ground up, the passive house design will be limited because the house already is what it is.
The interesting and fun (at times) part of the project was using financial models to go after the lowest hanging fruit possible. This creates the freedom to let the spreadsheets tell you what to do on the project. It’s also house-specific, and each one will be different.
Going After The Lowest Hanging Fruit – A Quick Example
The house here has a 2007 13 SEER HVAC system. So naturally, I thought that I must replace this to achieve net-zero. As it turned out, while doing the financial modeling, this wasn’t the case.
In this location, at least on this house, with these electric rates, and this Florida climate – adding more solar panels to the system cost less than upgrading to a new higher SEER HVAC system.
By going after the cheapest and more effective energy-saving measures possible, the overall project will be a success and not be as big a hit on your wallet.
And with this approach even being my first renovation ever – the total efficiency and solar energy costs equate to 6.8% of the final appraised home value, in line with studies mentioned above.
Power Your Electric Car Too
As a bonus – the 9.38KW solar system was designed to produce enough power to drive the Tesla Model 3 for 10,000 miles per year. At the rate that the current system is producing – it looks like more like 12-14,000 miles per year or more.
Passive House Standards And Resources
For some more in-depth information, here are some different acronyms and additional resources for passive house standards:
- PHIUS – Passive House Institute United States
- PHI – Passive House Institute
- PHPP – Passivhaus Planning Package – a certification mark granted by the Passivhaus Institut to indicate compliance.
- Passiv.DE – Passivhaus Institut Germany
Common Net-Zero Energy Home Labels Used
Some different acronyms and standards used for net-zero homes include:
- NZE – Net Zero Energy – acronym
- ZNE – Zero Net Energy – acronym
- ZERH – Zero Energy Ready Home – U.S. Department of Energy and the Office of Energy Efficiency & Renewable Energy
- nZEB – Nearly Zero Energy Building – Europe, India and other countries use this.
There are many differences between passive house and net-zero home standards. But the end goal is nearly the same – to use as little energy as possible on a net basis.
The exciting thing is that it’s growing so much in popularity, and with world government behind the concept to boot. Technology is getting cheaper, the building science is getting better, and the overall economic picture makes it much more affordable to build or renovate homes more efficiently on a grand scale.
While there are so many variables with all of this, just know that there are plenty of ways to meet the goals of using less energy and building more efficiently, whether it be passive house, net-zero, or any other way you are able to get there.