An Old House Gets a Superinsulation Retrofit
General Specs and Team
Location: Arlington, MA
Living Space : 3000 sqf
Cost (USD/sq. ft.): $33/sqf
Completed: March 2009
Basement: ceiling insulated with 4" to 8" of low-density spray polyurethane foam (IcyneneOpen-cell, low-density spray foam insulation that can be used in wall, floor, and roof assemblies. It has an R-value of about 3.6 per inch and a vapor permeability of about 10 perms at 5 inches thick.)
Walls: existing cellulose-filled 2x4 studs; 4-in. of foil-faced polyisocyanurate foam outside of sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. (R-39)
Windows: fiberglass frame, double-pane, argonInert (chemically stable) gas, which, because of its low thermal conductivity, is often used as gas fill between the panes of energy-efficient windows. -filled, low-eLow-emissivity coating. Very thin metallic coating on glass or plastic window glazing that permits most of the sun’s short-wave (light) radiation to enter, while blocking up to 90% of the long-wave (heat) radiation. Low-e coatings boost a window’s R-value and reduce its U-factor. (U-factorMeasure of the heat conducted through a given product or material—the number of British thermal units (Btus) of heat that move through a square foot of the material in one hour for every 1 degree Fahrenheit difference in temperature across the material (Btu/ft2°F hr). U-factor is the inverse of R-value. : 0.33, SHGCSolar heat gain coefficient. The fraction of solar gain admitted through a window, expressed as a number between 0 and 1.: 0.29, Pella Impervia)
Roof: rafter bays filled with low-density spray foam (Icynene); 6-in. foil-faced polyisocyanurate foam outside sheathing; seams staggered and taped (R-59 total)
A detailed journal of the project and a complete list of sponsors can be found at Alex Cheimets' blog: superinsulating.blogspot.com
Heating/cooling: oil-fired steam boiler in each unit
Water heating: main boiler in unit 1; on-demand gas water heater in unit 2 (200,000 Btu, Rheem)
Annual energy use: To come
- All lighting converted to CFLs in unit 2
- Aggressive insulation strategies
- Low-flow toilets and showerheads
Indoor Air Quality
- (2) HRVs (Fantech)
- CO sensors on every floor
- Basement ceiling is foamed/sealed to isolate moisture from living areas
- Interior basement access doors converted to exterior insulated doors with weather seals
Green Materials and Resource Efficiency
- Extra materials donated or reused on other projects
- Retained as much of the original structure as possible
A vintage home gets a 21st-century energy overhaul
What started out as a relatively straightforward re-siding project on this 80-year-old duplex in Arlington, Mass., ultimately evolved into part of an ambitious superinsulation pilot program for the Massachusetts Department of Energy Resources (DOER) and the regional utility company, NSTAR.
Upon contacting the state for technical advice, homeowner Alex Cheimets learned that the DOER was in the middle of developing standards for net-zero-energy buildings and agreed to include his home in the research. The state brought NSTAR into the project. NSTAR brought in Building Science Corp. to conduct a study of the building and make recommendations on the overall design and details of the insulation retrofit. Explaining that the project would serve as a model for broader reaching energy-efficiency programs, Alex convinced several sponsors to donate most of the materials, including the rigid foam (Dow), spray foam (Anderson Insulation), roofing (Atlas), and siding (NuCedar). This brought the budget closer to what Alex had initially set out to spend. The hope is that lessons learned on this retrofit could help lower the cost on similar projects in the future.
Save energy before making energy
Rather than adding complex heating systems or renewable energy sources, this project focused on keeping the actual demand for energy to a minimum. More than just minimizing disturbance of the existing home, adding insulation to the exterior would effectively reduce thermal bridgingHeat flow that occurs across more conductive components in an otherwise well-insulated material, resulting in disproportionately significant heat loss. For example, steel studs in an insulated wall dramatically reduce the overall energy performance of the wall, because of thermal bridging through the steel. through the framing. Plus, with 2x4 walls (already filled with cellulose insulationThermal insulation made from recycled newspaper or other wastepaper; often treated with borates for fire and insect protection.), there was no other reasonable way to get the R-values they needed.
Lots of rigid foam
Contractors from Synergy Companies Construction started by stripping the roof. Then they applied two layers of 3-in. foil-faced polyisocyanurate foam, a layer of plywood sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. , a self-adhesive roofing underlayment, and asphalt shingles. Alex chose the shingles for their durability (50-plus years) and their light, heat-reflecting color.
After the roof was complete and the double-pane, fiberglass-framed windows were in, the crew covered the exterior walls with four inches of rigid foam (2 layers of 2-inch) and taped all the seams. Of course air and weather sealing are just as important as insulation in a project like this, so Synergy meticulously caulked and flashed all windows and doors before the foam went on. Regardless of the choice to replace the existing windows, the new flashing was essential because superinsulated walls dry much more slowly than old, leaky walls.
Furring strips screwed through the sufficiently dense foam provided a sturdy substrate for the new, prefinished cellular PVC clapboards. It did take a fair amount of shimming and tweaking to get everything straight, however.
Adjusting the plan
Even though exterior insulation was deemed the best option for most of this remodel, there were some exceptions. The energy consultants at Building Science felt that the ideal way to address the basement was to insulate the interior surface of the foundation, in order to recapture losses from the mechanical equipment and distribution system during the heating season. The project was already many times larger and more complicated than originally planned, and after careful consideration, Alex Cheimets decided that this was one place where he was comfortable scaling back. The good news is that his choice to isolate the space by installing between 4 and 8 inches of open-cell spray foam on the basement ceiling does not prevent him from insulating the walls in the future, should he reconsider.
The same low-density spray foam used below the living space would also give the roof some additional resistance to heat loss (and gain). After stripping a good deal of poorly installed fiberglass from most of the attic, the insulation contractors filled the empty rafter bays completely with foam. This was especially important for bridging the gap where the walls meet the roof.
Although preventing moisture, air, and heat from moving through the building envelopeExterior components of a house that provide protection from colder (and warmer) outdoor temperatures and precipitation; includes the house foundation, framed exterior walls, roof or ceiling, and insulation, and air sealing materials. was the main priority, it wasn’t the only one. New heat-recovery ventilators (HRVs) in each apartment ensure that these now-supertight spaces will have good air to breathe. To further the goal of energy efficiency, Alex converted all the lighting in his apartment to CFLs and switched to an on-demand, gas-fired hot-water heater. One old steam boiler still provides all of the heat for his place, and his downstairs neighbor chose to keep her entire heat and hot water system intact for now. Alex plans to consider upgrading to a more efficient boiler after evaluating a year’s worth of energy data.
With several severe winter storms and a steady flow of reporters, government officials, and product reps, Synergy was still able to wrap up the whole project in about six months. This was far from its first experience with deep energy retrofits, and it only emphasized the company's desire to be a continuing force in environmentally responsible construction.
During the project, Alex had a revelation that should be an inspiration to energy-conscious builders everywhere: "Seemed a shame to rig the house with the best insulation known to man but yet have no idea how much energy the house was using or saving." Data-logging equipment from Onset Computer now tracks his home’s indoor and outdoor temperatures and humidity levels. Two neighbors volunteered to install similar systems in their conventionally insulated homes to collect comparative information. Daily measurements of fuel consumption made by an ultrasonic sensor (from VisiTank) fastened to Alex's oil tank round out the set of data needed to accurately evaluate the home’s performance.
For more information on post-retrofit energy use at this house, see Massachusetts Superinsulation Project Reveals Impressive Results.
Once the ball got rolling, Alex quickly realized that compromises were necessary to keep the project moving— particularly in material choices. If he had had his way, he would have taken more time to evaluate the sustainability and resource efficiency of everything that went into the home.
Exterior retrofits make sense
It depends on the conditions of the particular home, but the consensus seems to be that exterior insulation is the smartest way to boost energy efficiency of existing homes. Other than what Alex describes as a "week of hell" during the basement and attic demolition, the interior remained reasonably undisturbed during the entire process. The place was drafty and cold at times, but that's hardly unexpected when tearing into a house in the middle of a New England winter.
Overachieving doesn't always pay off
Building Science Corp. had specified 4-in. rigid insulation on the roof, but when Alex found out that 6-in. foam was available, he told Synergy, and they decided to go for it. A box of broken, 10-in. screws, a new set of impact drivers, and a week's worth of frustration later, they wonder if it was worth it. In the end, the roof worked out well, but the extra effort and cost were hard to justify.
—Rob Wotzak is associate editor at GreenBuildingAdvisor.com
- Alex Cheimets
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