Energy Efficiency Meets Aging-in-Place
Usually when people retire they downsize. We upsized. My wife and I built our retirement home near Knoxville, Tennessee, many hundreds of miles from our children, parents, and siblings. We wanted plenty of space to host family and friends, even if they arrived in bunches or stayed for months.
We hope to live here until our health gives out. As retirees, we live on a fixed income. We knew the cost to build would yield predictable mortgage payments. But maintenance costs, especially utilities, might vary widely. We wanted stable and relatively low monthly expenses.
After we purchased rural acreage on Fort Loudon Lake—part of the Tennessee River system—in 2006, we began designing a house to accommodate these goals. The home would need to be spacious, accessible, and seriously energy-efficient.
Planning & Construction
I have a longstanding interest in residential and commercial energy use—my involvement with ASHRAE goes back nearly two decades. As we brainstormed, drew, and re-drew our house, I planned the HVAC system and other energy-saving components. My wife designed the floor-plan, accessibility features, and general appearance.
Construction began in the summer of 2011, and we moved into the house in April 2012. Our home has almost 3,900 finished square feet on two levels, not including the attached two-car garage and adjacent workshop or the 600-square-foot unfinished room above them. The completed rooms include a large central great room and kitchen, four bedrooms, four baths, a study, playroom, laundry, and a loft.
Insulation & Other Great Things
Our land consists primarily of limestone covered by topsoil. Rather than dynamite the rock to form a basement, the builder dug a crawlspace one foot deep and raised the house elevation two feet. An integral five-foot-deep section was reserved for HVAC equipment.
The sealed, exterior crawlspace walls were built using insulated concrete forms (ICFs) and have an R-20 insulation value. The crawlspace floor consists of four inches of quarry stone, covered with a six-mil plastic vapor barrier. The underside of the main floor is uninsulated to prevent condensation and to make the crawlspace part of the conditioned house.
The house’s exterior walls have two-by-six wood stud framing. Tennessee code for exterior walls is R-13, and our walls’ R-value is about 30. The garage and workshop walls and ceilings contain R-19 fiberglass batt with no spray foam.
We live in a humid climate, and humidity breeds mold, so we have Super Jumbo Tex paper wrapping the exterior walls to drain moisture downward. The 40-inch-wide wrap is overlapped six inches to ensure coverage.
The roof—constructed in place—is made of two-by-tens with OSB sheathing. Titanium Wrap, rather than tar paper, protects the OSB.
Open-cell, water-blown spray foam having 3.81 R per inch fills the spaces between the rafters. Where possible, the installers retained (rather than scraping away) the foam overflow, producing a house-wide average of 11 inches of foam. Beneath the foam, the ceilings are either drywall or 6-inch tongue-and-groove planks.
Importantly, the shingles have a higher-than-normal temperature rating. This type of roof eliminates the air circulation found in a traditional attic. All space below the roof system is conditioned house space. The thick spray foam raises the top-surface temperature. Timberline Lifetime dimensional asphalt, medium-color shingles increase the heat reflectivity of the roof. The roof system’s total R-value is between 40 and 45; code is R-30.
Inside the house, the framing is standard two-by-fours, though some walls contain fiberglass insulation to muffle sounds. All the windows contain low-E glass, with 0.18 emissivity and a 7/8-inch air gap. The house faces southeast, and the front great room has several large windows. A 10-foot-deep roof overhangs a front patio to give this room passive solar protection, and to allow radiant heat absorption during winter when the sun is low.
Air, Water, Power
Two geothermal ground-source heat pumps—one upstairs within the house, the other in the HVAC section of the crawlspace—provide forced-air heating and cooling. Each pump is a two-stage, Bosch high-efficiency system. In our front yard are two wells, each over 300 feet deep. Water circulates between the wells and to both HVAC systems.
Because the house is tightly built and insulated, a Honeywell outside-air heat exchanger augments the air handling system. Outdoor air is brought inside at 100 CFM. The crawlspace, too, has positive air pressure.
The workshop has a SEER 16 minisplit that runs as needed, depending on our current projects.
Our kitchen and laundry appliances are new, energy-saving models. Since natural gas is not available, all of our appliances and utilities are electric except the fireplace and outdoor grill, which use propane.
Our monthly electricity use for the first 20 months averaged 1641 kWh, costing $168.88 per month, or 40.6% of the average Tennesse home per square foot, according to the U.S. Energy Information Administration’s 2009 Residential Energy Consumption Survey.
Planning for the Future
Our other goals—aging-in-place, accessibility, and space for visitors—also required planning. The exterior and interior doors are 3-feet wide to allow for wheelchair passage. Two of the bathrooms include a 5-foot-diameter turning radius for wheelchairs, as well as curbless (roll-in) shower stalls and heavy-duty grab bars.
All of our floors are level with each other and the floor coverings are suitable for wheelchairs or walkers. Two five-by-five-foot closets align upstairs and downstairs, one atop the other, for future elevator installation if needed; elevator wiring already exists. A built-in ramp leads from the house into the garage. The front and back entries have a single step, to which ramps could be added later.
Since we cannot predict our future health needs (or those of our guests), we made choices among many accessibility options. Though we may need to alter them someday, our house is currently as prepared as possible for future challenges.
Costs Versus Benefits
The energy-efficiency and accessibility features in the house added about 10% to the total building cost, or approximately $50,000–$70,000. The payback on our investment may be 25 to 30 years. But as we planned our retirement home, ongoing monthly expenses concerned us more than did the upfront capital cost.
Our choices also increased the square footage throughout the house. So did the total number of rooms and our desire to have all rooms feel spacious. Our home’s overall size far exceeds what we need day-to-day. We joke that we built it big—and on a lake—as a bribe to lure family, friends, and community groups here. Thus far the bribe is working, and we hope our house will always be a welcoming and energy-efficient place.
Tom Werkema participated in the UN Climate Change meetings for over 20 years. He is currently a vice president with ASHRAE and gives talks on climate issues and energy efficiency. In 2012, Tom retired from Arkema, a global, major producer of fluorochemicals used in energy efficiency applications.
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