High-Efficiency Homes: Moving Markets, Updating Codes

Throughout construction, the house was carefully air-sealed. Notice the solid masonry block stem walls on the crawlspace. The hole in the wall is to allow access, not ventilation.

Figure 1: Flow-through walls have no diffusion vapor retarders. Instead of using materials to prevent moisture intrusion, the demonstration house uses constant ventilation. The house is automatically pressurized in summer and depressurized in winter.

Once the unvented crawlspace was built, most of the HVAC equipment was housed within it. The indoor equipment will run more efficiently and have a longer life within the insulated crawlspace.

During construction, Virginia Power showed the techniques used to hundreds of people from the building trades, the financial sector, and the press.

In order to dense-pack the rafters during construction, builder E. Wayne Norman installed netting between the rafters and blew in the cellulose. This method assures installers that there are no voids in the blown-in cellulose.

Ducts were laid within conditioned space wherever possible and was insulated where outside conditioned space. Where round metal duct like this wasn't used, flex-duct was pulled tight to minimize pressure drop.

With the house built, builder E. Wayne Norman (left) joined energy consultants David Dillard (center) and Charles Bowles to check the submetered HVAC system. They found that the two heat pumps on the 3,100 square-foot house cost only $510 to run in the house's first year of operation.

Builder education takes many forms. One of the most effective ways for builders to learn new techniques is to walk a construction site ask questions. When the site turns into a home where residents feel comfortable and save money, the students use the techniques they learned. That's why the demonstration home that Virginia Power built in 1995 has been such a success. Using technology that builders could readily understand and materials that were on the market, they built an innovative, efficient house without substantially increasing costs.

Virginia Power built the house in Hanover County, just north of Richmond, to promote its Energy Saver Home Plus program. They included innovative features such as an unvented crawlspace, flow-through walls, dense-pack cellulose insulation, mechanical ventilation, round metal ductwork, air sealed drywall, and efficient HVAC equipment housed within partially conditioned space. It was the first house in the Richmond area to demonstrate these combined technologies to the building community. It has since become a prototype for energy-efficient home building in the mid-Atlantic states, convincing many builders to start using--and buyers to start demanding--these home performance improvements.

The demo house changed everything about energy-efficient home building in the Richmond area. For example, in 1997, R.E. Collier Incorporated Builder built a Health House that was certified by the American Lung Association. The house's specifications were based on the energy efficiency specs for the Virginia Power house. Similarly, several whole neighborhoods have been built to the Energy Saver Home Plus specifications.

Charles B. Bowles of the Energy Consortium contributed the design criteria and served as energy consultant for the project. Virginia Power's Charles A. Johnson, director of energy efficiency, and David M. Dillard, another energy consultant, teamed up with Bowles and local builder E. Wayne Norman to build the demonstration house. It is a 3,100 ft², two-story brick Georgian. Both during and after construction, it appeared to the untrained eye to be a standard home for the region.

The house is positioned on the property to maximize passive solar heat and daylighting. A stand of existing trees on the northern perimeter of the lot is used as a natural buffer to help block cold winter winds, and trees were left standing on the western perimeter to provide shade against the summer heat.

Pushing the Envelope

Finding a cellulose installer is tough in some parts of the country, but there were already three small-application cellulose companies in the area. At the time, most installations were in high-end custom homes, but since the house was built, installers like Steven Tretreault of All Weather Insulation of Williamsburg Incorporated have seen cellulose "overtake our fiberglass business."

Norman had his crew employ the airtight drywall approach (ADA), extensively air sealing during all phases of construction. The house is sealed with backer rod, polyurethane caulk, and non-expandable urethane foams.

"Without doing this sealing, all the cracks and crevices in a typical newly built 3,000 ft² house average about 2 ft²-3 ft² of leakage," says Dillard. When the forced-air distribution system was tested with a Duct Blaster, it had only 29 CFM at 25 Pascals (Pa) total leakage, including the air handler. Expressed as a portion of the square footage of conditioned floor area, this is less than 1% leakage. Typical homes in the mid-Atlantic region have duct leakage of 15%-25%. Specs for the house required less than 1.5 ACH at 50 Pa (ACH₅₀). The whole-house blower door test showed a leakage of 535 CFM at 50 Pa, or about 1.3 ACH₅₀.

Fancy Mechanicals and Flow-Through Walls

Optimal value engineering (OVE) framing minimizes the amount of wood used in the exterior walls, leaving more room for insulation. There are no T-posts where partition walls intersect exterior walls; two-stud corners were used; and foam board provides thermal breaks in the headers. The house has double-glazed windows with argon fill, thermal breaks, and low-e glass. The forced-air distribution system is sealed with non-toxic duct mastic that has no lingering odor.

The insulation and air sealing allowed smaller heat pumps. Per Energy Saver Home Plus standards, the two air-to-air heat pumps are 12-SEER with variable-speed air handlers. They were sized according to Manual J, resulting in a 2-ton unit for downstairs and a 1.5-ton unit for upstairs. This resulted in cost savings compared to the units that Norman usually used for homes with the same floor plan: 3 tons downstairs, 2 tons up.

The improved airtightness also means that the home requires mechanical ventilation to modify air pressure, to introduce fresh air, and to remove stale air. The bathroom, family room, and kitchen are ventilated by a VanEE Duo 2000 mechanical ventilation system capable of providing 75 CFM of fresh air. It cost $2,000, installed. This energy recovery ventilator (ERV), which is ducted separately from the heating and cooling system, heats incoming air in the winter and cools it in the summer, with a total efficiency of 68%. It can monitor and control humidity levels during the heating season, recovering and transferring up to 80% of the moisture in exhaust air to the incoming air. During the cooling season, the system removes approximately 80% of the humidity from the incoming warm, moist summer air. The ERV also electrostatically filters the air and modifies house pressure.

The house pressure is constantly controlled to work with the flow-through walls to prevent moisture problems. The controls on the ERV are programmed to maintain a 3 Pa negative pressure when it's hotter inside, and a 3 Pa positive pressure when it's cooler. This forces air from the cooler side, with its relatively light load of moisture, into the wall. So far, residents have had no moisture problems, despite the lack of a vapor diffusion retarder.

To help pressure-balance the house, the air handler closet has a louver door, and rooms without dedicated returns have grills on their doors.

Crawlspace Codes

The crawlspace floor and masonry stem walls are completely covered with 6-mil black polyethylene. Over the poly, the insides of the walls are sprayed with at least 3 inches of damp-spray cellulose insulation, for minimum insulating values of R-10. Bowles had already used this technique in several houses, and had found that the crawlspaces stayed dry and temperate. A termite company agreed to warranty the house because of the lack of moisture. All electrical and plumbing penetrations were caulked, and the access door was weatherstripped and sealed.

Unvented crawlspaces have since become popular in the state. Building inspectors "are used to seeing them vented or unvented," says Bowles.

The inside unit of the heat pump, the heating ducts, and the ventilation ducts are all inside the insulated crawlspace. The first floor zone's mechanical components are in the crawlspace and the second floor zone's air handler is in a closet on the second floor.

Standard building practice in Virginia (even today) is to put vents all around the crawlspace perimeter and house the HVAC and other mechanical components there. The 1993 ASHRAE Handbook of Fundamentals (the most current at the time the house was built) recommended crawlspace ventilation to help prevent moisture problems. It said that all crawlspaces should be ventilated to the exterior. Rectangular crawlspaces were supposed to have at least one vent on each wall.

This ventilation strategy isn't necessary, according to Bowles. "The crawlspace for the demonstration house was designed to operate under a positive pressure provided by the mechanical ventilation system. The positive pressure makes the crawlspace push out and prevents the migration of moisture or other pollutants up through the structure," he says. "By making the crawlspace a conditioned space, the mechanical components housed there [the air handler, ductwork for the first floor zone, ductwork for the ERV, and plumbing lines] operate more efficiently, because now they are inside the conditioned envelope." The crawlspace typically remains at 55°F-65°F year-round, making the equipment run more efficiently. "The equipment will also have a longer life in this environment," Bowles says.

Consultant Dillard also notes the advantages of the system. "The energy efficient gains of the HVAC components being in this unvented crawlspace are twofold," he says. "Not only do the air handler and ductwork operate in a buffered zone, but during the heating season, the first floor of the house does not have the cold floor syndrome prevalent in this area with vented crawlspaces. Also, because the square footage of the crawlspace walls are significantly less area than the square footage of the first floor, it is generally less expensive to insulate. This allows the builder to not only to build a better product, but to do it at less cost."

The unvented crawlspace made quite an impact. It was the first of its kind in the area, and was definitely something that most local building inspectors had never seen. Since the demo house was built, area builders have started using unvented crawlspaces. "We have seen an increase in the use of unvented crawls," says Richard Bartell, a building official in Hanover County. "But not to the point where it has become commonplace. We are seeing a lot of these technologies being accepted more readily, especially a lot more in upscale housing."

The 1997 Fundamentals includes significant revisions about vented crawlspaces. It acknowledges that there is no technical basis for requiring crawlspace ventilation. It states that conditioned crawlspaces do not need direct ventilation to the outside, while vented crawlspaces must be completely outside the building envelope and must contain no mechanical services, including plumbing and ducts. The handbook no longer recommends ventilation of unconditioned crawlspaces.

Builders Take Action

The demonstration house created a tremendous response. It was open to the public throughout construction, and builders and tradespeople continually dropped by to view the process first-hand. An open house held at completion was attended by more than 200 area builders and HVAC professionals. In April 1997, a follow-up article appeared on the front page of the Richmond Times-Dispatch "Real Estate" section, noting the marked changes in local construction practices since the house premiered.

For example, Adams Heating and Air Conditioning Corporation, who installed the HVAC system, began installing the same type of system in other houses, and business has continued to increase. "The percentage of our business that uses this type of system has grown, and people are now asking for it," says Bob Adams, president.

Similarly, the chief builder on the project, E. Wayne Norman, has changed his practices significantly since the demo house. He now gets requests for, and builds, houses that incorporate the same systemwide technologies that were used in the Virginia Power house.

And the residents? "It is larger than the last house we lived in, but the bills are cheaper," says Russell Dickinson. "But to tell you the truth, we were not aware that this house was any different until we had pretty much already decided to buy it. I later found out that there were a lot of people who knew more about my house than I did. When I heard about all the things that were in the house, I really just had a `wait and see' attitude. So far, we have not been disappointed. It is definitely the best house that we have ever lived in."

Deborah Rider Allen is a freelance writer in Richmond, Virginia.

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