Ask the Expert: How can I make an existing home closer to net zero?

| by Teena Hammond
Ask the Expert: How can I make an existing home closer to net zero?

With rising energy costs, many homeowners are looking for ways to make their home more energy efficient. The term "net zero" is a popular one, because it means that a home produces as much energy as it uses. This is accomplished through the use of highly-efficient insulation, a tight building envelop with all cracks and crevices sealed, and adding in alternative energy sources such as solar panels or wind turbines.

While it's much more common to build a new home with net zero energy usage, it is possible to bring an existing home closer to net zero standards. The Approved Contributing Experts, or ACEs, at ProudGreenHome share their opinions on how to make an existing home more energy efficient.

luisLuis Imery, principal of The Imery Group

I will address building envelope issues first. Your first move should be fixing these issues. Once you have maximized these effective weatherization measures, then it's time to go with technology. If you don't seal the building first, to create a tight envelope, it's the same as walking around in the middle of winter with an unzipped jacket and buying warm pads to stay warm. The logical thing would be to zip your jacket first, or, in this case, sealing the building envelope.

The most effective way to identify problems with your building envelope and other inexpensive solutions prior to going with fancy technologies is to hire a professional home energy rater. Depending on your area, they will have different names, but most likely you will find them listed as HERS raters or as a building analyst with the Building Performance Institute. Also, don't forget to check with your utility company as they might provide incentives to cover the cost of the improvements.

Now, assuming you have addressed the basics, now it's time to find ways to bring your home closer to net zero. You can either go with geothermal or solar. Although these approaches have a big upfront cost, in general, you can recoup your investment in 7-9 years. If you chose to go with a geothermal HVAC system, then it makes sense to go that same route with your water heater. You are using the heat pulled from the earth to heat your water as well. With the solar option, you can install photovoltaic panels, and add solar thermal. The latter option introduces a renewable energy option that you can also couple up with your geothermal system to try to cut your energy usage as much as possible.

If you opt for solar, first check with your utility company to see if they accept net metering. You do not want to store your generated solar power in batteries, it makes the system cost prohibitive. Keep in mind that if you use geothermal, it makes no sense to go with solar thermal for your water heater. You will be spending too much money to accomplish the same goal.

tedTed Clifton, founder of Zero-Energy Plans LLC and CVH Inc.

Think more of transforming your home, rather than "adding features."

Existing homes pose a number of problems for would-be renovators. It is often assumed that simply adding solar panels to the roof of a house can make it zero energy. However, nothing could be farther from the truth. Most existing homes use so much energy, they simply do not have enough roof area for all the solar panels it would take to get them anywhere near net zero energy.

Tightening up the building envelope is by far the most cost effective measure you can take with most homes, and that could cost as little as a few tubes of caulk and a few cans of spray foam. By itself, however, tightening the envelope can only get you so far, usually not far enough if you are trying to approach net zero energy.

I recommend taking a whole house approach to the building envelope, considering not only the air tightness, but also the insulation levels in the walls, floor and roof, the u-values of the windows and doors (this is the rate of transmittance of energy), and the heating and ventilation system. Depending on your climate zone, you will spend about half of your total energy budget on the heating and cooling of your home. Whatever you are spending today, it is more than likely going to increase by at least 6.33 percent per year (the historical average inflation on energy over the last 35 years). When you do the correct math, a substantial investment may be warranted.

While you could use a layer of XPS insulation on the outside of your existing walls to improve both the thermal efficiency and the air tightness, we have been avoiding the siding attachment problems associated with this approach by using some products from the Structural Insulated Panel (SIP) industry — specifically, a product called Insul-lam, or Retro-fit SIPS. This is a panel consisting of several inches of EPS foam, with a layer of OSBsipsbonded to the outside. We screw it directly to the walls (after removing the windows and siding). Then new building paper can be applied, along with new windows and new siding, just as if we were doing new construction. The big difference is that we do not need to go inside the house to do any of this, it can all be done from the outside. Even the insulation in the existing stud-walls can be up-graded, by blowing more fiberglass or cellulose into the existing stud cavities while the siding is off and the walls are exposed.

On average, we have been able to reduce the energy needed for heating and cooling by more than 50 percent using this technique, along with replacing the windows, adding attic insulation, sealing leaks in the floor and the ceiling, and adding insulation under the floor. Replacing the heating system with a new high-efficiency unit can drop the remaining heating and cooling load by up to two thirds. This will leave you with a total heating and cooling load of just a small fraction of what it was, possibly only 15 percent or so. Do not forget to incorporate the correct ventilation system into your energy transformation plans.

Lighting is one of the easiest ways to reduce energy use, I am sure by now we all know about the savings available by using compact fluorescent bulbs, or LEDs. Appliances are another easy way to save energy, but look beyond the Energy Star sticker, and you will find units that are up to 30 percent more efficient than the Energy Star threshold of 15 percent better than standard. I recently found my customer a refrigerator that used $8 per year less energy than the one they had picked out; it had exactly the same look and features, and cost $4 less. It would have cost about $400 to put enough additional solar panels on their roof to make up for that $8 per year! The lesson here: Energy Savings are far more cost-effective than energy production! Get every energy load as low as possible, before looking at energy production.

Orientation of the home is one of the final obstacles when considering the possibilities for getting a house to near zero energy. If the ridge-line does not run east-to-west (allowing for a good southern exposure for solar panels) then a ground-based system or a wind power system will be the only way to supply the remaining energy load. Even solar hot water heaters can be installed on pole-mounts, so even if your roof is not oriented well, you can have "free" hot water and electricity, as long as you have enough clear area to the south of your intended location.

heatherHeather Ferrier, marketing manager for Ferrier Custom Homes

Improving the performance of our existing housing stock is one of the most important initiatives we can take to create major changes in the amount of energy America's homes are consuming today. For so many of us, improving the energy performance of our existing house is much more feasible than selling our current home and then designing and building a high performance home from scratch. Below are some simple tips you can take to curb your home's energy consumption, focused primarily on shading, air sealing and insulation. While you're reading, remember that great change is made one step at a time, so let's all pitch in to do our part.


In general, passive strategies are always preferred to mechanical ones, so we first look to how the home is oriented & how it interacts with the sun.

  • In our southern climate, the hot summer sun in considered our enemy in terms of energy efficiency. We are therefore always looking at how the sun interacts with our homes. If you have a considerable amount of glazing on the east, south and west walls, it means the rooms along those walls are going to be baking at sunrise and sunset. As opposed to eliminating those windows and doors (and their vistas right along with them), we suggest installing some sort of shade mechanism. One option is to plant deciduous trees (those that lose their leaves in the winter), which allows sunlight into the home during the colder months when you need it, but block it out when you don't during the warmer months.
  • Another shade option is to install overhangs or porches over exposed areas. These can augment your home's curb appeal while reducing your AC's load during the summer. However, pay careful consideration to how deep you make any overhangs. The winter sun sits lower in the sky, and you want to design overhangs in a manner that allows the winter sunlight in (to assist in heating the home), but blocks the summer sun out (when the sun's sitting higher).

Air Sealing

Air leaking in through and around windows, doors and other openings can undermine the performance of even the greatest of energy efficient technologies. Here are some common trouble spots to look for:

  • During the day, perform a visual inspection around your exterior doors and windows. If you see daylight coming through in any area, that means air is coming through as well. Replace weather stripping where damaged at doors, caulk around windows, install foam barrier in any gaps (all very inexpensive upgrades).
  • During the winter, make sure any outside vents to your crawl space are sealed off to reduce the harsh winter wind from leaking into your home. As a larger upgrade, install spray foam insulation under your home's floor and line the crawl space floor with 6 to 9 mil poly to prevent moisture intrusion.


Beefing up your home's thermal envelope is an important step in reducing your energy bills. Your climate will dictate where the most important spots for insulation are, but here are some general guidelines:

  • In warm and hot climates, insulation on the roof of your home can be up to four times as effective as insulation in the walls. This is a result of the sun beating down directly onto your roof for so many more hours each day than it hits the walls. So, to start the insulation upgrade process, look to your attic and roof deck first. One inexpensive option is installing a radiant barrier under your roof deck, which will help deflect most of the heat that enters into your home via the roof. To realize greater energy savings, consider installing spray foam insulation in your attic (we typically install a minimum of 5.5 inches under the roof in our hot climate).
  • In colder climates, the walls are much more important, so consider adding additional insulation there as well.

For more information, see our Green Home Remodeling research center.

Topics: Energy Audits, Heating & Cooling, Rebates / Tax Credits, Remodeling, Solar Power

Teena Hammond
Teena Hammond has published more than 2,000 articles in People and W magazines, Women's Wear Daily, and in dozens of newspapers and books. She also wrote a home improvement, remodeling and decor column that ran in Gannett newspapers nationwide. She's interested in all things green and would love to hear from you with your story ideas.

Sponsored Links:

Related Content

Latest Content

Get the latest news & insights





Social Entrepreneur on the leading edge of best practices for the Tiny Home movement