The Zero-Energy Remodel

New products have this 1860s home producing its own power

September 30, 2004


Vacant for 15 to 20 years, the cottage had a long way to go to become livable. In May 2003, the entire structure was lifted about 3 feet to allow masons to build up the existing foundation by 24 inches.

After photo: Jeff Klein

The old math went something like this: Pre-1930s house + harsh climate = energy hog that wastes big dollars on heating and cooling. This year's Model reMODEL introduces a startling new formula: Pre-1930s house + harsh climate + strategic energy retrofit = house so energy-efficient it generates more energy in a year than it uses.

Working closely with the NAHB Research Center, William Asdal, CGR, and Asdal Builders transformed an 1860s 1,500-square-foot wood-frame cottage into what Research Center engineers believe to be the country's first zero-energy home created through remodeling rather than new construction.

"Bill is in a high-energy cost area, where electric rates can reach 14 cents a kilowatt hour," says Craig Drumheller, a senior energy engineer with the Research Center. "With the amount of photovoltaics on the cottage and the garage, plus the solar hot water system and the energy efficiency [of the retrofitted house], he's expected to net out close to a zero energy bill in one year. That is, the house is expected to generate as much or more energy than it uses."

Energy-efficiency improvements accounted for a 90 percent reduction in energy consumption, according to the initial report on the project, known as SEER (Systems Engineering for Energy Retrofits). The rest of the energy savings came from the photovoltaic system.

Asdal bought the cottage, located in rural Lebanan, N.J., in late 2002 as part of a 24-acre property that also included a five-bedroom, 4,000-square-foot 1898 house built over a 1732 stone bank house; a 4,000-square-foot barn; a shed; and a garage. Asdal planned to convert the turn-of-the-century house into a five-bedroom bed and breakfast and outfit the cottage as the innkeeper's residence.

The Research Center, which had partnered with Asdal before, proposed using the cottage as a case study, because the house's size and lack of energy efficiency was representative of millions of homes built in the United States before the 1970s. SEER thus became part of the U.S. Department of Energy's Building America Existing Buildings Program to develop national energy-efficient remodeling guidelines. The National Renewable Energy Laboratory funded energy design and research, with Asdal covering construction costs with the help of some manufacturer-donated products.

Drumheller and NAHB Research Center senior research engineer Joe Wiehagen, along with solar and geothermal energy specialist Jason Fisher, designed the retrofit using a systems approach. They focused heavily on sealing the building envelope, then moved on to heating, cooling and electrical systems.


Remodeler Bill Asdal bought the property, now the Raritan Inn, as an investment. The main house is a bed and breakfast, while the cottage, at left, is the innkeeper's residence.

Door: Therma-Tru. Windows: Simonton.

Photos: Jeff Klein

Steps up the retrofit ladder

Just to be made livable it needed a new roof and new flooring, wall and window repairs, a new coat of paint and new appliances. These minimal improvements would simply have returned the house to the standard typical for its era: a drafty place with single-pane windows and no insulation. Annual energy load of the major house systems ù heating, cooling, water heating, lights and appliances ù would have averaged 275 million Btu, which translates into 1,836 gallons of oil and 5,739 kWh. The Research Center labeled this level of improvement "existing house."

The next step up is the gut rehab Asdal ordinarily would have undertaken. Labeled by the Research Center as the "base remodel," it called for standard vinyl double-pane windows; wall, attic and floor insulation; new drywall and siding; a basic propane-fueled furnace and water heater; and a standard air-conditioning unit. Just replacing the windows would have cut air leakage by about 40 percent. Annual energy use for this base remodel would average 135 million Btu (1,273 gallons of propane and 7,023 kWh).

The top rung of the remodeling ladder, SEER, was planned to beat the energy savings of the base remodel by at least 30 percent and to use cost-effective products readily available to remodelers around the country. The project team flew past the goal with flying colors. Total annual energy use for SEER is expected to be around 26 million Btu (entirely electric, 7,708 kWh), which betters the base remodel by a stunning 81 percent.

The house now has a HERS rating of 93.1. According to the Research Center's calculations, the money saved through the energy-efficient enhancements will more than offset the additional costs incurred, even with a 15-year loan at 7 percent interest.


A solar preheat bears 57 percent of the water heating load, while a photovoltaic system provides electricity for the entire property.

Siding: Crane.

Solar sytem: AstroPower.

Photo: Jeff Klein

System 1: Insulating walls, ceiling and floors

The existing house had no wall, ceiling or attic insulation. Asdal Builders replaced the original, worn-out siding with house wrap and insulated vinyl siding with an R-value of 3. To insulate the interior walls, Wiehagen and Drumheller opted for dense-pack blown-in R-15 cellulose, plus R-3 foam. Blowing in the insulation meant that the expense of tearing out interior walls could be avoided. Also, a good installer could push the hose nozzle to the top and bottom of the walls, getting insulation into all the nooks and crannies of the old wall cavities. And the dense-pack cellulose would significantly reduce air infiltration in old, irregularly framed walls. Cellulose insulation was blown into the exposed attic floor as well. Because of New Jersey's cold winters, the engineers beefed up the R-value to 38.

The cottage sits in a flood plain, so it was impractical to insulate the basement. That meant that the living spaces needed to be buffered from the unconditioned, often-damp basement. Wiehagen and Drumheller advised Asdal to separate the basement from the living spaces by both air sealing and installing R-30 unfaced fiberglass batts in the floor joist cavity, rather than the R-19 minimum required by code.

System 2: Low-E matters for windows and doors

Originally, Asdal planned to install insulated doors and replace all single-pane, wood-framed windows with double-pane windows in vinyl frames. The retrofit team went one step further, choosing double-pane windows with a low-E surface. "The big difference" in window performance, says Wiehagen, "is going to a low-E coating."

Windows come with hard coat or soft coat low-E film. The soft coat, which admits less solar heat, is best for warm, southern climates. On the New Jersey project, the team chose hard coat low-E, which lets in more solar heat but keeps more heat in the house. The windows deliver an insulating value some three times better than uncoated single-pane units.

System 3: Air sealing everything

Air can leak through any cracks, gaps and loose seams around a house, allowing conditioned air to seep out and making the heating and cooling systems work harder. The retrofit team brought in an air sealing professional to find all the leaks in the cottage. To seal the leaks, Asdal and his subcontractors glued the interior wallboard to the framing; caulked the window frames to the framing; sealed the sill seam and band joist areas with spray foam; and paired that foam with drywall adhesive at all floor and wall penetration points, such as where stairs join walls.

The dense-pack insulation around the house helped block air flow, too. All in all, the air sealing effort slashed the air exchange rate from an estimated 1.0 ACHnat to .25, or once every four hours. The project team estimates that without all these measures to block air leakage, nearly twice as much energy would have been needed to heat and cool the cottage.


Asdal Builders dug the trenches for the 2-ton geothermal system, which serves both homes on the site.

Geothermal system: WaterFurnace International

System 4: Innovative HVAC equipment

Taking advantage of the large site and high water table, the retrofit team replaced the oil-fired gravity furnace with a closed-loop geothermal system. Any system that uses a fossil fuel, including oil and propane, is 50 to 65 percent efficient at best, says Drumheller. The geothermal system was sized to meet the needs of the house on the hottest and coldest days and also maintain a comfortable environment year-round. Compared to using a "base model" heat pump, the geothermal system will cut in half the energy used for heating and cooling the house. It also prevents potential carbon monoxide problems caused by the combination of a tightly sealed house and a furnace that uses fossil fuel.

Asdal placed all the ducts, as well as the compressor and the air handler, in conditioned space inside the cottage rather than in the unconditioned attic, a more traditional choice. Doing so prevented an estimated 20 percent of the heat from leaking. The supply duct runs through the house, next to the central beam. The compressor is in the kitchen hall, where it needs "very short duct runs and can deliver air around the house very efficiently," says Wiehagen. Noise from the compressor is imperceptible, Asdal says.

Passive wall returns between bedrooms and the central return boost the effectiveness by allowing better air flow. Sealing the ducts with mastic improved efficiency even more. In fact, the system is so efficient that a 2-ton compressor ù half a ton smaller than the space might otherwise have required ù is able to handle the load.

System 5: Lighting and appliances

In place of the standard incandescent bulbs, the researchers specified compact fluorescent lighting throughout the house. A 20-watt compact fluorescent bulb provides lighting comparable to that of a 60-watt incandescent, at energy savings of 66 percent, says Drumheller. Compact fluorescents are becoming very common, he adds, with the bulbs lasting five to 10 years and costing about $4 each. (A New Jersey retail program brought Asdal's cost down to $1 a bulb.)

The project team chose Energy Star rated appliances, including the refrigerator, dishwasher and clothes washer. Altogether, these three energy-efficient machines cost $320 more than standard units, an amount typically repaid in lower energy usage in three to four years. The clothes washer is not only energy efficient but also significantly reduces water use, yielding savings in water heating.

System 6: The panelized room addition

Asdal Builders replaced a 180-square-foot room and 120-square-foot porch that had been tacked onto the back of the cottage around 1900 with a 320-square-foot addition built with custom-sized Techbuilt wall and roofing panels that integrate steel framing and foam insulation. The panels cost more than standard structural insulated panels, says Wiehagen, but are lighter and easier to handle.

With the wooden deck in place, it took just five hours for Asdal's three-man crew, assisted by two Techbuilt technicians, to put up the addition. Because the walls pack an R-30 insulating value and the roofing is a whopping R-50, Asdal was able to forgo the vented attic and give the addition a cathedral ceiling without any loss in energy efficiency.


The manifold plumbing system controls hot and cold water separately.

Piping: Vanguard.

Tankless water heater: SETS.
Energy-Efficiency Cost Summary


Asdal expects to "earn back" the costs of upgrading from the base remodel to the SEER remodel over a nine-year period.

System 7: Water heating and plumbing

The geothermal system runs separately from the water heating and plumbing system. "In our experience, geothermal contributions to water heating using a desuperheater are not very impressive," says Drumheller.

The project team mounted a 32-square-foot solar energy collector on the southwest-facing roof of the cottage instead. "We went to a solar preheat that is estimated to provide 57 percent of the water heating load," says Drumheller.

An electric tankless water heater, installed in the basement, supplements the preheat, making sure that the temperature delivered to the fixtures is consistently 125 degrees Fahrenheit and minimizing the standing losses. Ideally the tank would have gone in a conditioned area, adds Drumheller, but could not because of space constraints.

A relatively new method of distributing both hot and cold water helps save energy, too. Separate plastic manifolds draw from the main water supply line and the hot water heater, serving a system of flexible plastic piping called PEX. Its 3/8-inch supply lines mean that there's less water cooling in the hot water lines than in the usual 1/2-inch pipes, so less is wasted when purged to make way for incoming hot water. Big labor savings are a bonus: No copper pipes means no soldering and no elbows.

"You just pull the tubing to where you want it to go," says Drumheller.

System 8: Solar energy and beyond

New Jersey's Clean Energy Program (NJCEP) offers up to a 70 percent rebate to homeowners who install solar photovoltaic systems. "It's the best program [of its kind] in the country," says Drumheller.

With that incentive, Asdal went ahead with an extensive photovoltaic system, installing solar collectors on the southwest-facing roofs of both the cottage and the garage. Thanks to the state rebate, the $50,400 collectors and power generator cost Asdal only $15,120 to buy and install. The two systems, totaling 7.2 kilowatts, are estimated to generate 9,000 kWh each year, about $1,100 worth of energy, and more than enough to fuel the entire property.

"Now we have a Civil War house that's a residential power plant," says Asdal. "We're putting more into the power grid than we're taking. After six months of operation, we already have well over 1,000 kilowatt hours of positive credit."

He's not finished exploring the property's energy-saving potential. There's a millrace on the property, which he is looking into the possibility of using to generate hydroelectric power. He's also obtaining a permit to build a wind tower.

In the United States, Asdal says "buildings consume 70 percent of all the domestic energy we produce. What we have done here could change that. We've shown that the technologies do exist to use the sun, water and wind ù natural resources that we waste now."

The barrier to using energy-smart techniques and products, says Asdal, is that the systems are unfamiliar. "You have to have skilled crews and a certain willingness to try innovative things," says Drumheller. Asdal hopes SEER will help "melt the barrier" away.

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