Energy Efficiency for a Big House

This large home uses about one-fifth the energy of others in its size range.

No home is too big to be energy efficient. Just ask Fairhope, Ala., architecture firm Watershed, which in 2022 completed a grand example of cost effectiveness. 

The “Inspiration Home” is a four-bedroom, 5.5-bath, two-story single-family structure in Fairhope. According to Watershed architect and owner Rebecca Bryant, it is capable of saving its owners more than $5,000 in energy costs compared to a similar-sized home built to the requirements of the 2018 International Energy Conservation Code (IECC). 

In developing the home, Watershed partnered with builder SCC Group and energy rater Keene Living to win its first-ever Housing Innovation Award from the U.S. Department of Energy (DOE)’s Zero Energy Ready Home (ZERH) program in 2022. The judges were impressed enough to also give the builder-architect team a Grand Award in the Custom Spec category. 

The 5,750-square-foot house was constructed for sale on spec, but Bryant decided to keep it as a personal residence and a showcase of high-performance features and DOE ZEHR construction.

Building such an energy-efficient structure might seem like a costly proposal. But Bryant noted that achieving ZEHR certification added less than 2 percent to the total construction costs, and that was primarily for the higher SEER HVAC, ventilating dehumidifiers, resealing of the HVAC ductwork, and energy rating.

Clean Energy Abounds

Builders installed a 5.44-kilowatt (kW) solar panel array and a 10-kW battery. The photovoltaic (PV)-plus batteries cost $31,250 after incentives. According to Bryant, the payback is 9 years for the PV alone and 6 years for the battery. The battery costs $10,000, about the same as a whole-house backup gas generator, which has no payback.

The battery can serve as an emergency generator in the hurricane-prone region. The home’s solar array reports energy usage and consumption in real time to the homeowner and automatically switches into maximum battery charging mode when a storm is predicted. The battery is tied into the electric panel for the main floor and can power appliances, lighting, hot water ignition, and even HVAC when used non-simultaneously in emergency power mode. 

“When people ask about our solar panels and we explain that our solar array is our backup generator, they get really excited,” Bryant says. “We’re in hurricane country. People here understand the need for backup power. That sometimes feels like a more pressing need than energy savings.”

The homeowners hope to expand the solar array to reach net zero in future years. With the current setup, the home achieves a Home Energy Rating System (HERS) score of 20 when counting the PV, or 39 if the solar is not included—far better than the HERS 80 to 90 of typical just-to-code homes.

To achieve this high performance, the builders constructed a highly insulated shell that included 2-by-6 framed walls, with the studs spaced 16 inches on center. The wall cavities were densely packed with 5.5 inches of cellulose. 

The walls included an engineered wood sheathing, which was then covered with a liquid-applied weather-resistant barrier wrapped with a continuous 2-inch-thick layer of mineral wool insulation and synthetic stucco cladding. The mineral wool is part of the synthetic stucco product, which was actually less expensive than a non-insulated, traditional three-coat cementitious stucco.

Thanks to energy efficiencies such as solar power and a battery storage system, the 5,750-square-foot Inspiration Home can save its owners more than $5,000 in energy costs annually compared to other similar-sized homes.

Addressing Wind Resistance

To increase wind resistance, threaded rods are used in the exterior walls to tie the top plate of the second floor down to the top of the concrete basement walls. The stairway is wrapped in plywood sheathing and works with the elevator core inside the house to provide additional shear capacity to the entire home. Locally sourced southern yellow pine was specified for all framing.

The home’s truss roof uses a wind-resistant hip roof design. The unvented attic is insulated with 10.5 inches of open-cell spray foam sprayed to the underside of the engineered wood roof deck to achieve R-38. The spray foam covers the exterior wall top plates and completely encapsulates the roof trusses to minimize thermal bridging.  

A rubberized asphalt underlayment covers the entire roof deck, providing a continuous moisture barrier and “second roof” should any rain get past the asphalt shingle roofing and clay ridge tiles. Plumbing vents and outside air intakes exit through the top of the wall between the rafters to limit roof penetrations, and reduce the likelihood of leaks.

Meanwhile, there are roof shingles made with a polymer-modified asphalt that utilizes recycled plastic from rubber tires and plastic bags. The shingles use smog-reducing granules that chemically react with the air to reduce smog. The air-purifying performance of each roof with these shingles is estimated to be equivalent to two trees.

Building Efficiency from the Ground Up

The home’s lowest level is part carport, part enclosed basement. The basement level consists of 12-inch cast-in-place concrete walls with a 40 percent fly-ash mix. The exterior of the walls was covered with a liquid-applied bituminous waterproofing membrane and 1.5 inches of mineral wool board insulation within the brick cavity and a brick veneer. A 1-inch air gap behind the brick face prevents vapor drive into the walls.

The ENERGY STAR windows are double-pane, argon-filled, fiberglass-framed windows with low-emissivity coatings, a U-factor of 0.3, and a Solar Heat Gain Coefficient (SHGC) of 0.19. All windows have pultruded fiberglass exterior frames and sealed wood (pine) interior frames. The windows and exterior doors are impact rated for the high wind zone locale.

The large home was blower door tested and achieved a whole home air leakage of only 1.5 air changes per hour at 50 Pascals (ACH 50). This was accomplished by using spray foam at the roofline and band joists, as well as canned spray foam around the windows and at all building penetrations. Sill gasket was installed under the bottom plates. All joints and penetrations in the sheathing were completely sealed with a liquid-applied weather-resistant membrane. 

After duct leakage was discovered inside inaccessible floor ceiling assemblies, the duct work was sealed with an aerosolized acrylic sealant procedure.

Two gas tankless water heaters provide hot water through insulated PEX piping that uses a central manifold for faster distribution. A leak detection system monitors water use in real time and will automatically shut off the water supply if a leak is detected.

A central air-source heat pump with a variable speed compressor provides heating with a heating efficiency of 9 HSPF and cooling with an efficiency of 17.5 SEER for the two upper floors. The central systems use hard piped, rigid metal ducts for the trunk lines with flex duct to each register. A mini-split heat pump with a 19.7 SEER services the partial basement. 

Ventilating dehumidifiers were integrated with the heating and cooling ductwork to bring in fresh air and dehumidify it and to manage moisture when there is no cooling load.

All appliances except the tankless water heaters and fireplace are electric, including the induction cook top. The home is also equipped with an electric vehicle charging station.

Making WaterSense

The whole house is certified to the EPA’s WaterSense program, which specifies the use of low-flow fixtures, and moisture-sensing and drip irrigation. To accommodate heavy rainfalls, the backyard is dedicated to a rain garden that captures runoff from the yard, downspouts, and foundation drains, and can percolate runoff from a 6-inch rainstorm in less than 12 hours.

The gardens are planted with fruit and nut trees and edible plants, and the yard is a National Wildlife Federation Certified Backyard Wildlife Habitat, a place that provides food, resources, and shelter for the animals and insects that live in the area.

Natural lighting and views were a priority for this project. All rooms have daylight from at least two sides, except for one windowless bathroom on the basement level. At night, dimming is provided on all lights, so homeowners only use the amount they need. LED lighting with a “warm dim” function was used throughout the first floor, where all primary living spaces are located. These support healthy circadian rhythms by mimicking the color of sunlight at dusk and dawn.

Bryant said the home’s design is inspired by the Arts and Crafts movement and incorporates elements of Cape Dutch and French Colonial traditional styles adapted to a hot-humid climate. The home also includes many aging-in-place and multi-generation options, including a ground-floor flex space and second-floor second master suite that could accommodate aging parents or returning adult children.

So far, the Inspiration Home has lived up to its name. In the past year, more than 1,500 potential home buyers visited the home. Another 1,100 have visited the website, 17,300 have viewed social media posts, and the home has been the subject of local news articles reaching thousands more. 

Watershed and the energy rater Keene Living are monitoring the home’s energy usage, which they will share via the website. They hope to continue to use the home as a location for training activities for homeowners and contractors.

Key Features

Air sealing: 1.5 ACH50; spray foam at top plates, band joists, all attic and floor penetrations; sill gasket under bottom plates. Ducts are sealed with aerosolized acrylic sealant.

Appliances: ENERGY STAR clothes washer, dryer, freezer, refrigerator, ceiling fans.

Attic: Unvented attic, 10.5-inch R-38 open-cell spray-foam on underside of roof deck.

Energy management system: PV app measures usage and production; charges battery if a storm is predicted. Smart thermostats. Leak detection on plumbing.

Foundation: Insulated basement: concrete walls covered with liquid-applied bituminous waterproofing, 1.5-inch mineral wool insulation, 1-inch grout, brick.

Hot water: Tankless gas water heaters, 0.95 UEF; central manifold, PEX pipes.

HVAC: Two heat pumps, 9 HSPF, 17.5 SEER; one mini-split (19.7 SEER).

Lighting: 100 percent LED, warm dimming in evening. Skylight in stairwell.

Roof: Truss hip roof: 0.75-inch engineered plywood, rubberized asphalt underlayment; asphalt shingles with clay ridge tiles. All vents through walls.

Solar: 5.44-kW rooftop panels, 10-kW battery.

Ventilation: Supply only; ventilating dehumidifiers to HVAC ducts. MERV 13 filters.

Walls: 2-by-6, 16-inch o.c., R-28 total: advanced framed, dense-packed cellulose, engineered plywood, liquid-applied weather barrier, 2-inch rigid mineral wool; stucco.

Water conservation: EPA WaterSense-rated fixtures. Rain garden for storm runoff.

Windows: Double-pane, argon-filled,
fiberglass-framed, low-e, U=0.3, SHGC=0.19.

Other: Low-emission products. Recycled-
content concrete, countertops, mineral wool, roofing, cellulose insulation. Electric vehicle charging station installed.