What is a net zero home?
A net zero home, or sometimes called zero energy or net zero energy, is a building where the total monthly or annual energy usage is approximately equal to the amount of energy created on-site. There are two major components of a net zero home; the first is having an energy efficient home that lowers the overall power cost required by your day-to-day needs. And the second is integrating renewable energy resources and methods that will offset that utility usage. Why would anyone want a net zero home? Well, there are quite a few benefits including lower energy costs, less maintenance, greater long term durability, and they’re just more comfortable to live in.
In this article, I will talk about the different components of a net zero home, what I have experience with, and I will give more details about the real-world benefits.
Types of energy efficient building practices
Net zero homes aren’t necessarily the “off the grid” type of house you may be thinking of; with a number of energy efficient components and appliances, you can significantly minimize the power cost to heat, cool, and maintain your home. This allows you to have a smaller energy producing system that supports a comfortable lifestyle.
Since there are a number of building practices that we can utilize we’ll start with the foundation and work our way up.
An energy efficient foundation?
Yes! You can build your foundation to be more energy efficient, though maybe not like you are imagining. Builders are incorporating insulation into the foundation by (myself included?) pouring concrete slabs over a bed of closed-cell spray foam and encapsulating the edges of with foundation with Insulated Concrete Forms (ICFs). Concrete is then poured into the interior of these forms, creating and insulating your foundation walls. The ICF’s are made of foam insulation that are either pre-formed blocks that interlock, kind of like legos, or foam panels that are connected by ties. When used for a foundation, ICFs turn the concrete into a more thermally efficient structure. In fact, according to the Structural Insulated Panel Association (yes there is such a thing), “expanded polystyrene, in this application, may help provide lower energy costs by up to 50% and noise abatement by as much as two-thirds.” As you might have guessed, you canbuild all your walls with ICF, though this is likely a little extreme for most.
It is important to note that there are some potential drawbacks with using foam as part of your foundation insulation. First, foam can be burrowed into by pests. This problem has been solved by treating the foam blocks, which also helps to improve waterproofing. Second, foam is potentially a fire hazard. Again, the solution is to treat the blocks with a fire retardant solution. Third, ICF installs cost more. There’s no getting around the fact that the materials are more expensive and since you need highly trained and experienced team for the installation, the labor costs more as well. However, the energy savings are significant as I stated above.
Framing and more insulation
Image source: Building Science Corporation
Framing techniques like double-stud walls allow for more insulation, a higher whole-wall R-value, and increased control over air leaks. So what does that mean to you? Little to no air can sneak inside or escape outside, which is critical to maintaining comfortable temperatures without needing your HVAC to turn on constantly.
How can you create an airtight house?
One of the best methods to build an energy efficient house is to create an airtight barrier. New technology has allowed us to combine exterior water, air, and thermal insulators into a wall assembly. Take a look at the video below from ZIP System.
Instead of your standard oriented strand board (OSB) that then has to be covered with house wrap, the ZIP System has combined the two elements. They utilize a more dimensionally stable OSB (higher resin content) with a facer or lamina, an ultra-fine screen that has been impregnated with green latex paint, and added insulation–all in a single panel. I know I sound like a salesman but this is an incredible product that has helped push the limits of energy efficiency.
To take it one step further, we use AeroBarrier to fill any tiny gaps in your building envelope where air will pass. This sealing process targets leaks in floor and wall joints, rough pipe openings, behind electrical housing, and within door headers. The method for applying the sealant is quite incredible; instead of trying to find and caulk the leaks we pressurize the interior of the home and then spray in the sealant. Because the area is under pressure, the AeroBarrier finds all the gaps where air is leaking and accumulates across the surface. Using this technique we can find and seal leaks as small as a human hair and up to ½ inch openings.
All this work to seal and insulate a home isn’t just about saving on energy costs. Taped seams, spray-in foam, aerosolized sealant…these all double as excellent soundproofing. Not only that, these systems also help prevent odors and particulates from entering your home. Overall, these things make for a more comfortable home with the added benefit of lowering your energy needs, yearly costs and maintenance.
As one of the largest energy consumers in a home, the HVAC system plays a significant role in a net zero energy home and energy efficiency. Typically, forced air units (what most people refer to as air conditioning) and gas furnaces have to work harder when it’s really hot or cold out. So they use more electricity or burn more gas to compensate. But there are alternative methods, and one of my favorites to work with is the geothermal heat pump. These systems are not only significantly more efficient, “relative to air-source heat pumps, they are quieter, last longer, need little maintenance, and do not depend on the temperature of the outside air.”
What exactly is a geothermal pump and why should you care?
Geothermal heat pumps utilize the relatively constant and stable temperatures underground to exchange heat. Think of it as being similar to a cave where the ground temperature is colder than the air above it during the summer and warmer during the winter. These systems use pipes to pump fluid through a ground heat exchanger and will heat or cool your home depending on the season. So how effective is this method? “Ground-source heat pumps are among the most efficient technologies available and a cornerstone to achieving net zero energy building,” Mark Stimson of Bosch Thermotechnology said. “Using the ground as the thermal heat exchanger is the most effective way to heat and cool a building.”
Image source: NC Sustainable Energy Association
Let’s put that into the context of dollars and savings. According to the EPA, homeowners save approximately 30-70% on heating and 20-50% on cooling, an average savings of $400 to $1,500 annually. If you are trying to achieve a true net zero home then this method is critical to reducing the overall energy needs of your home without affecting lifestyle or comfort. That also means you can use a smaller solar panel system. That’s the beauty of combining all of these energy efficient components, everything works together so that you need less power. You’ll also find that a net zero home is quieter, more durable, and needs less maintenance because you’re putting less stress on everything.
Integrating renewable resources and methods into your home
The most common renewable energy source for your home is from solar panels and the good news is this technology has been improving each year, becoming both more efficient and cost-effective. Plus, federal and state incentive programs help make solar even more attractive. For example, the net metering program in Ohio which allows you to ‘bank’ extra energy produced during peak hours so that you can use that during times your panels aren’t producing, like overnight. “Your solar panels will often produce more electricity than you need, but thanks to Ohio’s net metering policy, you will be able to sell this back to the grid in exchange for credits on your utility bill. When you need more electricity than your panels are producing, you can use those credits instead of buying electricity from your utility. Duke Energy offers the top utility net metering program in Ohio.”
So how much solar power do you need to produce to cover your day-to-day use? According to the Energy Information Administration, the average electricity consumption for a US home is 867 kWh per month. To produce enough energy to cover those needs you are looking at an approximately 8kW system, with the average solar panel cost being about $2.90 per watt (remember there are 1000 watts in 1 kilowatt).
With a system this size, and still using that average consumption, you are often going to produce more energy than you need. So you can either use a net metering program or you can utilize a storage system like the Tesla Powerwall, giving you seamless backup power whether or not your panels are producing or the grid is down. One of the advantages of Tesla’s system is how technologically advanced it is while still being incredibly easy to use. “[The] Powerwall detects grid outages and automatically becomes your home’s main energy source.” Plus, with their mobile app you can monitor current production, use, and how much power you have stored all from your phone. Of all the solar systems we have installed, we get the most feedback from the clients that integrate a Powerwall, and it has been overwhelmingly positive.
What is the cost of a net zero energy home
A build that utilizes a combination of these components will generally add about 7-10% onto your price. Don’t let that number discourage you because with your yearly cost savings you will recoup that money relatively quickly. The Rocky Mountain Institute performed a study of the economics of zero-energy homes and found the payoff threshold to be approximately 12 years. “This threshold compares the incremental cost to build a ZE and ZER home (compared with an identical home that meets local energy code) with the net-present value of the anticipated energy savings over the typical length a homeowner is expected to stay in the home (which is 12 years)” At which point, these energy efficiencies built into your home are putting money back in your pocket by saving you annually on power costs, maintenance, and general upkeep.
Net Zero Energy is a quality of life improvement
While there are still a number of topics that I haven’t covered yet, I think I’ve given you a good primer and some potential applications to consider. And I want to leave you with this final thought that net zero homes aren’t the type of “off the grid” house many people think of. You don’t have to commit to drastic lifestyle changes like going without electricity if it’s not a sunny day, or living at the end of a dirt road with a composting toilet and a wood stove as your source of heat. Instead, modern net zero homes improve the quality of life by significantly adding to the comfort and ease of your typical day-to-day routines.
Please send me a note if there are additional net zero components you would like me to cover. There is quite a bit more I could talk about for windows and doors or framing techniques. Or if you would like to talk about specific details for building a net zero custom home give me a call.