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Remodel Project: Deep Energy Retrofit

Addressing and Correcting All the Ways a House Uses or Conserves Energy Will Result in Substantial Savings and Reduced Environmental Impact

Energy-use reductions of 50% to 90% are attainable

A deep energy retrofit assesses and remediates all the ways that a house uses, doesn't use, saves, and stores energy. And it radically improves the energy performance of the existing home. Total household energy reductions of 50% to 90% are achieved by addressing all or nearly all loads — space conditioning, hot water, lighting, appliances, and plug loads — and sometimes even transportation. Energy reductions of this magnitude require an intensive and extensive systems approach: The inherent relationships among energy, indoor air quality, durability, and thermal comfort must be honored throughout design and construction. Passive solar design and renewable energy systems are common in these projects.

Careful planning is required for this extensive and invasive green remodel

A deep energy retrofit can significantly reduce household energy consumption, but only as long as nothing is overlooked. Space heating and cooling, hot water, lighting, appliances and electric loads in general should be considered as part of the retrofit. Current energy use is the key to improvements

You can learn how your house handles energy in a number of ways. Studying utility bills covering at least one year, and preferably more, is a good start. Blower-door testing, infrared imaging and duct-blaster testing offer valuable information about current energy consumption. An energy feedback device, such as the Energy Detective, measures electricity usage and can be useful. An assessment of existing conditions also should include a look at how the building envelope gets wet and dries out, and how energy improvements may affect where this moisture goes.

Energy improvements can affect moisture performance

A deep energy retrofit probably will include changes to the entire building envelope as well as heating and cooling equipment. Moisture must also be carefully managed; this may mean adding perimeter drains in the basement. Exhaust fans in the kitchen and bathroom, or a whole-house ventilation system, where those features are lacking play critical roles too. Plants and roots that are too close to the house may have to be cut back to encourage drying outside and open up the house to get more sun. In some cases, both the site and the structure should be examined with an eye toward adding rooftop- or ground-mounted solar-energy installations, solar hot water collectors, or a wind turbine. With a sharp reduction in heating and cooling loads it might be possible to downsize or even eliminate some heating and cooling equipment.

Don’t throw away the old stuff

What about building materials that might be replaced during the project? Cabinets, trim and flooring might be used elsewhere—in a basement or workshop, for example. Wood, gypsum drywall and other processed materials could become soil amendments or a base for a driveway or sidewalk with some planning.

Smart project planning can cut remodeling trauma

The stages of a project can make it easier to live through. Most of the living spaces will probably be involved, so if you're planning to remain in the house while it's being retrofitted, it’s important to figure out what you will need to use and what you can put up with. Disruption is significantly less when the project is tackled starting from the outside of the house. Approaching projects from the outside also makes it easier to keep the insulation and air barrier continuous.

More About Deep Energy Retrofits

The goals of a deep energy retrofit are similar to those of a new green house, but as with all remodels, the difference is that you have to work around an existing structure. What follows is a list of house systems with areas of concentration you should consider

Building envelope

Insulate the slab and foundation walls.
Provide air sealing and moisture management.
Super-insulate existing walls, floors and ceiling or roof with formaldehyde-free insulation.
Install a durable roof.
Replace doors and windows with energy-efficient models, and specify glazing based on the house's exposure to the sun.>


Provide appropriate controls.
Specify high-efficiency mechanical equipment and heat pumps, where possible
Consider alternatives to conventional air conditioning.
Make sure than combustion appliances are vented properly.


Reconfigure plumbing to distribute hot water efficiently.
Insulate hot water pipes.
Choose a high-efficiency water heater.


Increase natural daylighting wneh possible.
Install energy-efficient lighting.


Provide an easy way to turn off equipment to eliminate phantom electrical loads.
Replace old appliances with energy efficient models.

Energy sources

Consider installing photovoltaic modules, solar hot water collectors, or a wind turbine.

Seven Steps to Net Zero Energy Use

In renovating old homes into super-efficient ones, there is a definite path to success. Betsy Pettit, of Building Science Corporation recommends starting where you can get the most bang, and working your way down the list. After you get past item 5, the house will be efficient enough to downsize the mechanical equipment, which you replaced in step 1. If you’re planning to go at least through step 5, keep that in mind before buying a new boiler or HVAC unit.

1. Upgrade the mechanical systems

An old furnace or boiler is often the worst energy user in an old house. Many houses built prior to 1920 still have old coal-fired boilers that were converted to gas or oil. These units are workhorses, but use a lot of energy. A new furnace or boiler can save energy dollars right away. Replacing window air conditioners, which we did in all these houses, with a central system also can save energy right away, as long as the ductwork has been placed in the conditioned space. Solar water heating is a good option to add here if you can afford it, but at the very least, upgrade the efficiency of hot water production by coupling the tank to the boiler.

2. Bring the basement and crawlspace inside the house

Warm, dry basements and crawlspaces can extend living and storage space. Wet basements are the source of high humidity levels and discomfort in the summertime in old houses. They also can be the source of mold growth that gets distributed around the house. Spray foam is a fast, effective way to bring these areas into the conditioned space while sealing the leaks between foundation and floor framing.

3. Super-insulate and air-seal the roof

If air leaks in at the bottom of the house, it leaks out at the top, which makes a house cold and drafty in winter. A poorly insulated roof also can make a house hot in summer. Air-sealing is a by-product of good insulating, so it’s really a one-step process. Using spray foam under a roof also can eliminate the need for roof venting, which is tricky in complicated roofs.

4. Replace the windows

With the bottom and top of the house sealed and insulated, the next opportunity is the walls. And old windows are like big holes in the walls. Old windows often leak both air and water into the house while functioning poorly. They might not open and close properly, and can be obscured with storm windows and screens that diminish the amount of light that can enter. Properly installed, Energy Star (or better) windows seal the holes in the walls to keep out water and weather extremes.

5. Insulate the walls

Filling empty wall cavities with cellulose is a cheap, easy, effective way to warm up an old house. Blowing cellulose into existing wall cavities is an art, to be sure, but there are many contractors who have been doing it for years. In fact, there are now inexpensive ways to check with infrared cameras to make sure that all voids have been filled without disturbing the existing plaster or sheathing on outside walls. Because siding or shingles on old houses might also have worn out, we take the opportunity to install foam sheathing on the outside of the house before re-siding.

6. Buy Energy Star (or better)

fixtures, appliances, and lighting once you have reduced your space conditioning and water-heating loads, the lighting, appliance, and plug load will be your next big energy item. A new Energy Star refrigerator will use 15% less energy than a standard model. Replacing old light fixtures with pin-based compact fluorescent fixtures ensures your electric bill will stay lower (up to 30%).

7. Add a renewable-energy source

Once your energy consumption has been reduced significantly, it becomes reasonable to produce your own energy with systems such as photovoltaics, wind power, or hydro, if you happen to have a stream nearby. Until you slash the energy usage, though, it’s not worth the investment in renewable power sources. Conservation is still the cheapest game in town.

Note to item 5: Go back to Step 1 and reduce the size of the mechanicals. An airtight house with insulation on all six sides of the cube and good windows provides predictable performance, so the mechanical contractor won’t have to guess at the quality of the enclosure. Downsized mechanical equipment can defray the cost of steps 2-5.

Image Credits: Eric Doub, Ecofutures, Inc./REGREEN

Content By GBA

From zero insulation to net zero

In deciding to remodel, the owners of this 1,000-square-foot 1970s ranch in Boulder were seeking to both add space and make dramatic energy improvements. Like other houses in the neighborhood, this one had single-pane windows and no insulation in the walls, making it drafty in the winter and “an oven” in the summer. The family had made some improvements five years earlier, replacing windows, adding insulation, and installing radiant floor heat, but they didn’t have the experience to take it as far as they would have liked. This time, wanting more comprehensive improvements, the family hired a contractor with experience in high-performance building. Eric Doub’s team retrofitted the existing space for energy efficiency and remodeled it to include a home office in the aboveground space and a play area in the basement. Adding 700 square feet gave the owners a new dining area, expanded the kitchen and great room, and improved solar access and lighting.

A project manager knows about best building practices

Super-insulating and air sealing throughout the home improve comfort and passive survivability, allowing the home to stay warm without heating for a few days in 0°F, cloudy weather. A project manager knowledgeable in building science best practice was always on site to ensure that proper detailing, critical to a successful energy retrofit, was accomplished. The increased square footage improves the daylighting as well as the livability of the space. An all-electric design allowed the homeowners to cap their natural gas line, which was of particular importance to them because of local environmental degradation caused by natural gas drilling and distribution. Their efforts to be as green as possible extended from the structure to energy supply and to finishes.

Key Systems

  • Site
  • 90% of construction waste diverted through on-site reuse, salvage, and recycling
  • Recycled-plastic decking
  • Building Envelope
  • Existing:
  • Walls improved to thermally broken R-28: cellulose blown in to existing frame and walls wrapped with new external insulated 2'x4' framed wall
  • Roof improved to R-70 by 8" spray-in-place open-cell ½'- lb. foam (SPF)
  • Below grade improved to R-17: ½" rigid foam and cotton batts in 2'x4' framed wall added to interior
  • Prior installation of 1 ½" gypsum concrete floor with radiant tubes over existing slab
  • All-in-one vapor barrier, bubble wrap and ¼" flexible closed-cell foam added between gypsum and basement slab
  • Addition:
  • R-27 walls: 2'x6' frame, faced with 1½" resilient channel on interior, creating a 7" wall cavity filled with Icynene spray-foam
  • R-42 SIP roof with 3.5" SPF in dropped ceiling for R-50 total
  • U-0.15 overall window rating
  • FSC-certified and engineered lumber
  • 6" core ICF crawl space with dropped joists to break thermal boundary; 12" SPF between joists
  • HVAC
  • Operable windows and motorized skylight for ventilation and cooling
  • Energy recovery ventilator for continuous ventilation during winter and hot summer days
  • Plumbing
  • Dual-flush toilet
  • Direct-from-solar-tank hot water dispenser to reduce energy demand in cooking
  • Lighting
  • Natural daylighting enhanced with four solar tubes, two skylights, and 30% more glazing
  • Compact fluorescent lighting
  • Appliances
  • Existing Energy Star washer and dryer, plus clothesline
  • New refrigerator and electric oven to eliminate use of natural gas
  • Separate switch to eliminate phantom electronic loads
  • Interior Finishes
  • Low- and zero-VOC paints and stains
  • Water-based floor finish
  • Clay plaster
  • Linoleum tile with low-VOC adhesives
  • Formaldehyde-free cabinets
  • Concrete and sorghum-based countertops
  • Oriented-strand board subfloor
  • Natural wool carpet
  • Energy Sources
  • Evacuated tube solar hot water system provides 90%–100% of domestic hot water as well as space heating using in-slab radiant tubes; the system has cloudy cold-snap backup from on-demand 9-kW modulating electric boiler
  • Grid connected solar PV (6.15kW installed on new porch and existing roof)
  • EPA-approved wood-burning fireplace

Project wish list can differ from real-world realities*

In a comprehensive retrofit of this sort, it can be easy to miss some of the ways in which the systems interact; even manufacturers may overlook details of advanced energy systems. For instance, the team learned that the evacuated tubes for solar hot water could overheat and break if the power went out on a sunny day. To prevent this, they installed a single solar panel that provides backup power so that the pump can continue to circulate water through the tubes. Despite of their deep-green objectives, the homeowners also had to make some trade-offs. The cost premium for certified wood led them to forgo using FSC-certified wood exclusively in favor of investing more in renewable energy systems.

Team and Processes

With highly committed homeowners, the team was able to push far beyond typical energy retrofits, and explore new approaches to comprehensive efficiency. At the project outset, the contractor and energy designers worked with the homeowners to calculate electrical loads, and used computer modeling to understand heat and energy flows. This critical step in the design process informed all stages of project development. During construction, the homeowners, designers, engineers, and contractor continued to work closely together to ensure project success. For example, when the homeowners asked about thermally retrofitting the exterior of the building to minimize disturbance, the contractor verified with modern building science resources that this approach would work well to create continuous air and thermal barriers.

  • Location: Boulder, Colorado
  • Homeowners: John and Vicky Graham
  • Architect: Andy Johnson, DA J Design
  • General Contractor: Eric Doub, Ecofutures Building Inc.
  • Area affected: Remodeled existing 1,000 ft2; added 700 ft2


With the intention of building their “dream home,” the homeowners selected high-quality finishes throughout, pushed energy measures as far as possible, and took full advantage of Colorado’s new incentives for renewable energy systems. According to the homeowners, construction costs were comparable to those of other high-end remodels, and with recent reports that local electricity prices may increase by 11% in the next year, the projected return on investment keeps getting better.

  • ASID