Net zero homes explained (with 7 beautiful examples)
With solar panels, serious amounts of insulation, and energy efficient appliances, these gorgeous homes generate as much electricity as they use.
A net zero house is one that generates as much energy as it uses. Seems amazing, right? Even better: these homes look fantastic too.
Think of all the things in your home that need power, from top to bottom: lights, cooking appliances, washer and dryer, heating and cooling, hot water, and lots of electronics.
These things require a lot of electricity, but you probably have some appliances powered by fossil fuels: natural gas, heating oil, and propane are common heating fuels, depending on where you live.
A net zero home does away with fossil fuel use entirely, and instead uses electricity to power everything. This is accomplished with the help of an extra tight, highly-insulated building envelope that requires minimal energy for heating and cooling. Finally, a solar array and often solar hot water collectors allow the building to generate all of its own power.
What exactly are the features that allow a net zero home to do this? Many of these homes are have customized designs, but there are a few building techniques that are common to all net zero homes.
A net zero home is made to be extra-efficient so that it uses as little energy as possible - and that includes heating and cooling, which tends to be the largest energy consumers in a home.
In a conventional home, the energy usage is usually higher than the amount of energy that could be generated by the number of solar panels that would fit on the roof or backyard. But by reducing the energy usage as much as possible, a net zero home can supply all of its own energy with a feasible number of solar panels.
Solar photovoltaic panels are considered active solar because they are systems that generate electricity. Passive solar, on the other hand, is a type of building design that takes into account the position of the sun to maximize natural heating or cooling. It’s considered passive because it doesn’t require any machinery to work - just the daily rising of the sun.
For example, in a hot climate, passive solar design might involve extra large overhangs on windows to provide shading. Meanwhile, in a cold climate, passive solar does the opposite: big south-facing windows to help the building gain free heating from the sun in winter.
Insulation is a key part of the design of any net zero home. It doesn’t matter if you live in a cold or hot climate: insulation will help maintain the desired inside temperature of your house and reduce the energy needed for heating or cooling.
How much insulation you need is dictated by the climate zone that you live in. Here’s a map of the zones:
The table below lists the minimum insulation that a conventional (not net zero) new home should have for its corresponding climate zone:
Minimum insulation for new homes
|1||R30 to R49||R25 to R30||R13|
|2||R30 to R60||R25 to R38||R13|
|3||R30 to R60||R25 to R38||R20|
|4||R38 to R60||R38||R20|
|5 to 8||R49 to R60||R38 to R49||R20|
A net zero home will need to exceed these minimums - often by a lot. Getting an exact number requires an engineer to do a comprehensive modelling of the energy use of the home. However, as a rough guide, you can expect to see these numbers doubled in a net zero home. For example, a net zero home in a cold climate might have R40 walls and R80 attics.
To achieve this, special building methods are often used - for example, double thickness walls to allow a greater volume of insulation.
Insulation stops the conduction of heat through walls and ceilings, but conventional homes also lose a lot of heat through air leakage. This leakage can happen in obvious places, such as gaps around doors and windows, but also in ways that are not obvious. For example, the OSB or plywood sheathing used in the walls of a conventional home can actually be porous enough that a significant amount of air loss can occur straight through the wood.
A net zero home requires fanatical attention to the air tightness of the “building envelope”, measured in units called ACH50 (air changes per hour at a pressure of 50 Pascals).
A pretty good home might have an ACH50 value of 3, but an extremely tight net zero home might go as low as 0.5.
That’s extremely tight, which means sealing every gap and even paying attention to the porosity of the wall construction.
It’s great to make your house extremely airtight, but the humans living inside still need to breathe. Ventilation is also important to get rid of excessive moisture and prevent the growth of mold. To bring fresh air into an airtight net zero home, mechnical ventilation is used.
A ventilation system brings outside air into the home and vents stale air outside. But that also means wasting energy, because the inside air has previously been heated or cooled. It recover that energy, a system called a heat recovery ventilation (HRV) or energy recovery ventilation (ERV) system is used.
HRV and ERV systems are heat exchangers. This means that if the outside air is cold and the inside air has been warmed,the heat exchanger will recover some of the heat from the inside air before venting it outside. This allows occupants inside to constantly have fresh air without wasting energy.
Heating and cooling with electricity
In cold climates, natural gas is the most common heating fuel, but heating oil and propane are also common. With net zero, the goal is for a home to be energy self-sufficient.
This means switching to an electric heat pump so that solar panels can supply the electricity for home heating and cooling. Heat pumps are highly efficient units that can use the air or ground as a source of heat. Another great thing about heat pumps is that the same unit can work as an electric furnace in the winter, and as an air conditioner in the summer.
With a net zero home, electric resistance heating (the type used in a space heater or hair dryer) is only used in an emergency when the temperature outside is too cold for heat pumps to work efficiently.
Examples of net zero homes
Blue Zero South Carolina home
You might think that a net zero home, being such a different type of home in its technical design, must also look radically different too. This beautiful example of a custom-designed net zero home in South Carolina proves that a net zero home can look completely ordinary - even traditional - on the outside.
This house was built by Blue Zero Homes.
In contrast to the Blue Zero house, here’s an example of a net zero home in Portland with a radically contemporary design. Built by Skylab Architecture + Method Homes, this 3,990 sq ft. home was actually prefabricated in a factory and shipped onsite in 6 trucks. Constructed of 28 trigular units, this house was assembled LEGO-like in a single day. This house is solar-powered and 40% more efficient than a home built to standard code. Pretty incredible.
Sustainable Kansas home
Think that a net zero home can’t be affordable? This amazing 2,200 sqft home in Berea, Kansas is on the market for $284,000. Not only is it net zero with 5.4 kW of ground mounted photovoltaic panels and solar hot water collectors, but also has 10,000 gallons of rainwater collection capacity, 8,000 sqft of organic gardens, and a perimeter security system.
Not only is this house extremely eco-friendly, but it could be a great place to hole up in the event of zombie apocolypse. It’s on the market now, so if you’ve been looking for a zombie-resistant compound, this could be the home for you!
Net zero by Lord Contractors
Lord Contractors is a Pennsylvania builder that specializes in net zero homes that are built onsite in the traditional way, but also prefabricated homes that are built in a factory and then assembled onsite.
The mention of prefabricated homes might bring to mind low cost mobile homes, but many net zero home builders choose to build their homes this way. Why? Constructing the main structure of a home indoors has many advantages. It’s climate controlled, which makes it easier on the builders. But also having a factory-type setup makes it a lot easier to do quality control and do construction with the kind of tight tolerances that are required in net zero building.
In this beauiful home, you can see net zero details such as a solar hot water collector and carefully sized window overhangs that are typical of passive solar design.
Series B home by Acre Designs
If you’re into outdoor spaces, this might be the house for you.
The Series B home by Acre Designs features large windows, sliding glass walls, 4 bedrooms, and a wraparound porch.
From a technical point of view, it’s built with structural insulated panels (sip), which are pre-built walls made of an insulating foam core sandwiched between layers of oriented strand board. SIP panels fit together like LEGO blocks, speeding up construction time considerably. And because they’re built in a factory, the quality of construction tends to be much more consistent compared to walls built onsite.
The house also features an ERV ventilation system, a standing seam roof, and can be ordered with a solar array ranging in size from 5 to 10 kW, depending on your energy needs.
The Oaks Zero Energy Community
This is an example of not just one home that’s net zero, but an entire neighborhood that’s been designed ground-up to produce as much energy as it uses.
The Oaks Zero Energy Community built by Green Hammer is a senior living community in Portland consisting of 12 homes that have been designed to be net zero. At the roofline, you can just see the edge of the photovoltaic array mounted on the standing seam roof.
These homes have been designed for healthy living and feature energy-efficient ventilation and accessible design with seniors in mind.
LSR Passive House
Finally, here’s an example of a home that exceeds the energy efficiency of a net zero home. It’s a Passivhaus (passive house), which means that it’s so energy efficient that it doesn’t even need any mechnical heating or cooling systems at all.
With the use of extreme insulation, passive solar features, and thermal mass - thick wall and floors that can absorb heat - this home stays at a comfortable temperature year-round without the need for a furnace or air conditioner. How neat is that? This house by built by ecocor, a company in Maine.