One of the owners of this classic ranch house had grown up across the street and had many happy childhood memories associated with the house. When it came on the market, they bought the house with the intention of updating it for its next fifty years, while retaining some of the original 1950’s feel. Two requirements were central to their program: making it as energy efficient as possible; making it suitable for aging-in-place.
With their children grown, they didn’t need to increase the footprint of the house, but they did need to arrange the existing space to conform more closely to their lifestyle. To that end, we removed a small back porch, and enlarged the small original kitchen into that space (with a new potting shed for her down below). We glassed in the large screened porch, which had blocked light and views from the interior of the house, and converted it into a breakfast room and sitting area. To protect the new glass from summer solar heat gain, we added a 3’ overhang at the south gabled roof (shown in the drawing at the top of the page). On the interior, we rearranged walls throughout the first floor to provide more openness and flow between living spaces.
The house was our firm’s third deep energy retrofit, and our most ambitious retrofit at the time in terms of its focus upon reduction of energy demand. In this regard we were lucky to work with Cub Run Builders as the general contractor. Having recently completed an extremely low-energy home in Alexandria, they were ahead of the curve in terms of energy work. Their genuine commitment, their knowledge, and their care for detail in these matters made them a great partner. A shared goal of all members of the team throughout was to maximize investment in the relatively inexpensive things —insulation and air sealing—that reduce overall energy demand, in order to minimize investment in the more expensive things —photovoltaics and ground source heat pumps— that provide energy supply.
The building envelope
Sealing and insulating the building envelope is the key to lowering energy demand. We had two choices in how to approach this task: insulate the building on the outside of the existing walls, or insulate it on the inside. In this case, the latter approach made the most sense. We wanted to keep intact the original stone veneer, and insulating the basement walls from the interior was far more economical.
Roughly 40% of heat loss and gain in existing buildings is due to air infiltration. Open cell and closed cell polyurethane foams excel in retrofits because they seal buildings so well against air infiltration. In new construction, there are less expensive and less fossil-intensive ways to seal and insulate, and we typically prefer these methods over the foams in those cases. But when it comes to retrofits, nothing is so effective at sealing a building as the spray foams.
Most of this building’s exterior walls are solid masonry. To insulate them we constructed new 2×4 stud walls set 1” away from the original walls. We then sprayed between and behind the studs with closed cell polyurethane foam. The insulation in the 1” gap behind the studs gave us a completely unbroken thermal envelope, with no thermal bridging through the studs. This may sound like a minor detail, but energy modeling and studies of thermal movement in walls show this to be a significant factor in creating more efficient walls. Equally important, the lack of cold spots on walls in winter, caused by thermal bridges, reduces the potential for condensation and mold.
The wood frame walls in the gables, behind the stone veneer and at the new breakfast room, were filled with open cell foam. While open cell foams have ½ the insulation value per inch of the closed cell foams, we chose open cell in this case because of moisture issues. Because of the way they were originally built, we could not guarantee moisture staying out of the existing exterior stone veneer walls. Non-vapor-permeable closed cell foam could potentially trap any moisture that got in, with the potential for mold and damage to the interior wood. Open cell foam, however, is vapor permeable, allowing moisture to get out if it ever gets in.
We used Weathershield ZO-E 7 triple glazed casement windows for most new windows. The 10% cost increase over the Weathershield double-glazed unit was justified by the increased energy efficiency, and by the increased level of comfort. Because the interior surface temperature of these windows is very close to the surface temperature of the adjacent walls in both summer and winter, there is no longer the feeling of being hot or cold when standing next to a window (associated with radiation from a hot or cold surface). At the front windows, where we used decorative simulated divided lights, we used double glazed windows. Due to the thickness of three layers of glass, the significant gap between the muntins mounted on the interior and the exterior faces of the glass would have aesthetically compromised triple-glazed windows.
With energy demand reduced as much as practicable (over 50%), we turned our attention to designing a mechanical system to fit the decreased energy needs. Wherever possible we opted for simplicity and efficiency. The heating system uses a simple gas-fired boiler to produce hot water. This water is used in both the radiant floor heating system in the breakfast room, and in the central ducted air system. In a standard furnace, the air in the ducts is toasted over flames. In our system the hot water runs to a coil in the duct system. The coil then heats the air as needed. While the furnace-type system is an on-off operation, the “hydro-air” system heat can be modulated to the actual need, with much less drying of the air.
The air conditioning system is similarly modulated to meet varying cooling demands. Standard air conditioning systems are oversized so that they can deal with worst case scenarios. They are on-off operations. All the btu’s that are needed for that 100 degree day in August have to be cranked up every time the thermostat says cooling is needed. On more temperate days, when only a little cooling is needed, this creates a constant on-off cycling which is bad for the equipment and bad for dehumidification of the house. Our system has variable motor speeds in both the compressor and the interior air handlers, so that the system can run at a very efficient low speeds most of the time rather than in short bursts which consume far more energy. Because it is running more of the time but at highly efficient levels, it is continually dehumidifying the house, lowering the chance for mold in summer months.
Because the house is sealed so tightly against air infiltration, we are using an energy recovery ventilator (ERV) to bring in a constant stream of fresh air and to exhaust stale air. The incoming and outgoing air streams cross each other in the ventilator and exchange both heat and humidity, saving considerable energy. Bathroom exhaust is evacuated via the ERV, eliminating the need for separate bathroom exhaust fans and saving the energy they lose.
One of the owners’ strongest concerns at the outset of the project was to bring natural light into what was a very dark and gloomy interior. This was motivated partially from aesthetics and partially from sensitivity to glare. They plan to live in the house through retirement, and want the kind of balanced light levels we need as we age. To address this we opened up the second floor stair, and placed a bank of skylights above, providing light in what was formerly the dark center of the house.
The den had been a very dark and glary paneled room with only two corner windows. We created a skylight well at one end of the room centered on the fireplace to balance the light coming in from the corners. At the other end of the room we used a solar tube to do the same thing.
The dining room and the front entry halls, separated from natural light by porches, also felt quite dark. We added solar tubes here as well to bring lighting levels up and avoid the need for artificial lighting during daytime hours.
Artificial lighting is all by compact fluorescent and LED fixtures, reducing heat build-up in the summer and overall energy use.
• Bricks from demolition were cleaned and reused in the construction of the kitchen addition, front porch, back porch, retaining wall, and as fill in where doors and windows were removed.
• Stones were salvaged from the backyard bar-b-que pit to use as infill where windows and doors were altered.
• 60,000 lbs. (30 tons) of concrete, cinder block, and old mortar were recycled locally. The old concrete was turned into aggregate for new construction.
• 80% of the framing lumber that was torn out during demolition was cleaned and reused. Damaged lumber was burned on site in two woodstoves to provide heat at the jobsite in the winter. Savings included lower costs for dumping fees, less fuel for travel to the landfill, and less cost for propane used to heat the jobsite. The landfill benefits by having less material to fill it up.
• 6,192 pounds (3 tons) of scrap metal was recycled locally. This included cast iron, steel, aluminum, tin, and BX electrical cable.
• All jobsite cardboard is recycled. Approximately 360 cubic feet has been recycled to date.
Energy related design decisions
• Work as much as possible within the existing building footprint.
• Continuous 3’ overhang at new south-facing sunroom and at kitchen addition for summer solar protection.
• Natural light to all living spaces to avoid artificial lighting during daylight hours.
Energy envelope upgrades
• Walls: Existing exterior masonry walls: closed cell foam insulation to R13 .
New exterior wood frame walls: open cell foam insulation to R13/R22.
• Roof: Open cell foam insulation between joists to R-38.
Relatively high reflectivity roof shingles for lower summer solar heat gain.
• Windows: Double-glazed, argon filled wood windows at units with decorative
Triple-glazed argon-filled casements at all other units.
• Breakfast floor slab: foam between sleepers to R-20.
• Properly sized all-sheet metal (no flex) ducts.
• Mastic duct sealing.
• Insulated hot water and refrigerant lines.
• Energy recovery ventilation system by American Aldes. 2 units.
• SEER 15 AC system. Individual units with variable speed motors for modulation to actual cooling load.
• Burnham 206 boiler provides hot water to radiant flooring, and to coils in ventilation (hydro-air) system, and domestic hot water. Size: less than ½ the size of original boiler in the home.
• Wirsbo radiant flooring in new breakfast room.
• Programmable zoned control system.
• EnergyStar ceiling fans circulate air and allow raising set points for thermostats.
Dishwasher, refrigerator and clothes washer are all EnergyStar rated.
• Aquia Dual Flush toilets
• MBA – Hansgrohe Croma E Green 3-jet showerheads, 1.75 GPM
Energy efficient lighting lowers direct lighting energy use and reduces indirect energy use (by producing less heat in summer months, decreasing load on air conditioning system).
• Compact fluorescent lighting in decorative fixtures.
• LED downlighting.
• Halogen lighting for some specialty fixtures where quality of light on art is
• MasterSet central lighting control system.
• Ice Stone counters in two bathrooms. Fabricated from recycled glass.
• New River Concrete counters. The aggregate is from the New River in North Carolina. Sand & gravel is removed to maintain the hydroelectric dam through low impact dredging. A portion of the Portland cement typically used is replaced with fly ash which has a lower carbon footprint. Some of the dyes are of recycled iron oxide.
• Plastic laminate counter surfaces of recycled banana fibers in utility spaces.
• Marmoleum flooring in basement. Fabricated of linseed oil and cellulose.
• Plyboo bamboo panels and cabinetry in first floor living areas. Plyboo bamboo is taken from sustainably managed bamboo forests and is FSC certified. All construction formaldehyde-free.
• We Cork tongue and groove cork flooring in kitchen. From cork oak trees, from which bark is harvested every seven years.
• Zero-VOC paints and finishes throughout.
Percentage of total project budget devoted to energy upgrades: 7-8%
- Date July 25, 2014
- Category Aging in Place, Deep-Energy Retrofits, Remodeling and Additions