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:
|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.
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.
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.
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!