Deep Energy Retrofit X10
Deep Energy Retrofits (DERs) are at the cutting edge of the residential building industry. These ambitious projects aim to take existing homes and transform them into extremely low-energy homes. While the exact definition of a DER is not yet clear, most experts consider energy reductions greater than 50% to be readily achievable with existing technologies, materials, and construction practices. These drastic energy cuts are typically achieved using a combination of comprehensive building enclosure improvements, HVAC and domestic hot-water system replacement, lighting and appliance upgrades, and sometimes the addition of renewable energy. In addition to these building system improvements, energy conservation by the occupants plays a critical role in the success of DERs. When you are looking for low environmental impact in housing choices, a DER is a viable alternative to a new home—one that minimizes environmental footprint, maintains historical character, and achieves exceptional energy performance and occupant satisfaction.
The Residential Building Systems group at Lawrence Berkeley National Laboratory (LBNL) recently monitored ten Northern California DERs. The ten homes we monitored were local projects that were undertaken without funding or design support from the research team. This was important, because we wanted to focus on evaluation of current DER practice without the bias of the LBNL research team—either in selecting particular retrofit techniques or components, or in funding improvements that homeowners would not have undertaken otherwise. We chose the retrofitted homes that have the potential to save more than 50% of their site energy and demonstrate successful paths to DER. Six of the homes were remodeled and four underwent less extensive retrofits. This article will describe the remodels.
The Remodels (P1, P3, P4, P5, P6, P10)
DERs require a different mind-set than that required for a home weatherization or typical home performance upgrade. These more common energy reduction delivery models focus on reducing heating, cooling, and hot-water energy use through minor enclosure improvements and/or equipment maintenance and upgrades. Often, cost-effectiveness metrics are used that limit the up-front costs and long-term benefits. This restricts the potential for energy savings. For example, Home Performance with Energy Star suggests an average energy reduction target of only 20%.
The remodeling projects in this study represent the highest level of intervention. When completed, they typically do not resemble the home in its pre-retrofit condition, and they incorporate significant changes in building aesthetics, layout, and floor area. P1 was a home with a ground floor below legal height that was raised during the retrofit. The foundation was replaced, and the ground floor was completely rebuilt to full, legal height. P3 was initially two separate homes joined by a covered breezeway, and these structures were combined into a single home as part of the renovation. P4 was retrofitted in three stages, beginning in 1998; the retrofit included a full aesthetic makeover, a new roof structure, and the creation of business offices on the ground floor. P6 consists of two homes that had been next-door neighbors. The retrofit homes were then moved a few blocks to a shared lot and are now an affordable community housing facility. P10 was a rustic and run-down family cabin on the Pacific coast that was completely gutted and updated, in order to create a comfortable home for the soon-to-retire occupants. All of these homes were significantly altered, requiring the occupants to vacate during the retrofit. These homes now look new, and they perform and use energy in fundamentally new ways.
During the remodeling, contractors exposed major structural systems, in order to upgrade insulation, replace windows, and install new mechanical, electrical, and plumbing infrastructure. Windows in all six remodel homes were replaced or rehabbed, most with high-performance double glazing, and P3 with triple-pane, superwindows. Remodels provide the most potential for external insulation upgrades (as seen in P1, P3, and P5) because the exterior cladding is often replaced. All remodels except for P4 and P10 were insulated well above code levels—P1, P3, and P5 underwent Passive House-style retrofits, and a second internal stud wall was added to P6 to double the insulation. Due to the replacement or improvement of existing air barriers, these remodels significantly reduced air leakage. The most impressive results came from P1 at 1.1 ACH50, P3 at 0.43 ACH50, and P5 at 2.4 ACH50. Building systems in these projects were fully re-envisioned, with little regard for the existing system types or fuels. P1, P3, P5, and P6 were all retrofitted with low-load heating and cooling equipment, with about 1 kW of electric baseboard heaters and wall radiators, respectively, in P1 and P5, a mini-split heat pump in P3, and a single, central gas fireplace in each P6 structure. P4 is currently heated with a high-efficiency gas furnace, and the occupants plan to add solar thermal panels and a biomass boiler in the future. P10 has a solar-assisted boiler that provides underfloor radiant heating.
Remodels can make building enclosures more durable. The building control layers for air, heat, and moisture are exposed, allowing for significant improvements. Rain screens were used in P1, P3, and P5 where exterior cladding was installed over a ventilated air space, which allows the building assembly to remain dry. Fully adhered weather-resistive barriers and meticulously detailed flashing can also be incorporated into project design. The P3 remodel took this strategy the furthest, using a REMOTE/PERSIST system, with a fully adhered membrane tying together the foundation, walls, and roof. The P4 remodelers installed new roof overhangs to protect the walls and the foundation from rain, and for solar control. Some projects did not incorporate these kinds of improvements, which may have been a lost opportunity for improved building durability and indoor air quality.
Most remodels also included upgrades to all the other building equipment, including appliances, lighting systems, and plumbing fixtures. Every remodeling project except P5 included the installation of all new appliances throughout, with Energy Star models used wherever applicable—often the top-performing and lowest-energy models were used. P3 remodelers transferred the old refrigerator to the garage; this is never advisable, but it is particularly damaging in an aggressive DER. Lighting systems were entirely changed, with CFLs and LEDs installed throughout. The P10 remodel incorporated numerous daylighting features, such as light tubes, translucent doors, and skylights, which reduce the use of electric lighting. Low-flow plumbing fixtures were installed in every home. It is revealing that not all of the homes used solar technologies to offset electricity use or to heat water. This shows that a key aspect of DER is reducing load and consumption, not simply offsetting loads with on-site generation. Solar PV was installed on P3, P4, P6, and P10. Solar-thermal systems were used in P3, P6, and P10.
P1 Berkeley Bungalow
This house was built in 1904, and the retrofit was completed in 2007. It has four occupants, three bedrooms, two baths, and a home office. The remodel increased the legal size of the house from 960 square feet to 1,630 square feet. No renewable-energy systems were added. Located in the mild climate of Berkeley, California, the home experiences approximately 2,800 heating degree-days (HDD) per year. P1 reduced its site energy consumption by 28% while doubling both the number of occupants and the conditioned floor area. (For more information on the remodel, see Table 1.)
Even a house designed to be passive in a mild climate like that of Berkeley needs some form of heating. In this home, electric baseboards were selected as an inexpensive option, with the idea that they would be used sparingly only on the coldest days. Even though this is how the heating system is operated, we found that it uses significant energy—457 kWh of electricity in January 2012—and even for this low-use case, there are savings that could easily be achieved using a heat pump, for example. This is particularly true if we take a long-term view and imagine that the home's next occupants might be less willing to put on a sweater, resulting in potentially high electricity consumption in winter.
The owner of this house was a pioneer in Passive House retrofit techniques in the United States, and this posed a series of challenges. (See "First U.S. Retrofit to Passive House Standards," HE Nov/Dec '08, p. 25.) The homeowner described some of these challenges to us. "It [the retrofit] would have been easier to do as part of an experienced team," he told us. "The idea of these [Passive] houses is to figure it all out from the beginning. You have to challenge how things are done and figure out better ways to build. If I were to do it again, I would probably do a similar design if I were doing a DER. If I were doing a Passive House...I would spend more time on the Passive House Performance Package (PHPP) and energy modeling to really understand the energy implications." But he adds, "I am not convinced that reaching the Passive House standard is what is necessary in this climate. If you can get net zero energy without meeting the Passive House standard, it's hard to do better than net zero."
Table 1. P1 Berkeley Bungalow
P3 Sonoma Passive House
Originally built in 1958, this house was renovated in 2011, making it the first certified Passive House retrofit in the United States. P3 was initially two separate structures joined by a covered breezeway, and these structures were combined into a single home as part of the renovation. The house has two bedrooms, two and a half baths, a home office, and only one occupant. Situated in the town of Sonoma, California, the house experiences approximately 3,190 HDD per year. The remodel increased the floor area of this house from 1,937 square feet to 2,357 square feet. Three solar-thermal panels for domestic hot water (DHW) and 2.15 kW of PV were installed as part of this renovation. The design process was truly collaborative; the contractor, architect, and building scientist/Passive House consultant all worked together with the client from the very beginning, and the highest construction quality was maintained in every aspect of the project. (See Table 2 for more information.)
The energy-modeling efforts undertaken in this project are noteworthy. In an attempt to find the best balance between buildability, cost, and performance, 76 full iterations of the home's envelope details were simulated using the Passive House Planning Package (PHPP). This process gave the designers a very good sense of exactly how performance would be affected by the decisions they were making. The home's performance is most impressive in that the hourly average heating load peaked at only 470 watts, and averaged 115 watts for the 2011 heating season!
P4 Petaluma Phased
This house was built in 1940. Located in Petaluma, California, it has two bedrooms, two baths, a home office, and two occupants. It experiences 3,190 HDD per year. The house has been renovated in three phases, each incorporating structural, aesthetic, and efficiency improvements, and increasing the floor area from 1,540 to 2,510—or by close to 1,000—square feet. The first major upgrade was done in 1998, when the present owner purchased the house. New structural elements were added at that time, and numerous efficiency measures were implemented. In 2004, a new roof structure, a new ventilation system, and a 2.5 kW PV system were added. Finally, in 2011, seismic upgrades and additional insulation and air sealing were installed. Performance after each phase informed the next steps toward the owner's goal of a carbon-neutral home. We asked the homeowner what some of the main challenges of phasing the retrofit were. "Looking back, it was done in a silly way," he told us. "With each phase, I was making up for past mistakes, but there were also financial constraints. I didn't start off with a master plan; I was doing the best I could do at the time" He added that it was a big challenge getting the contractors to understand the importance of careful workmanship.
P4 is the first certified Affordable Comfort Thousand Home Challenge project in California. The iterative process in this remodel resulted in one of the greatest energy reductions in the DERs covered by our research. (See Table 3.)
P5 Point Reyes Compact
Originally built in 1920, this house has two bedrooms and one bath, shared by four occupants. This is a small house that got a little bigger during the remodel, going from 800 to 905 square feet. Located in Point Reyes Station, California, the house experiences approximately 3,220 HDD per year. No renewable-energy systems were added during the remodel.
As an affordable-housing, deep energy retrofit, P5 is notable for its use of low-cost, simple strategies and for its use of the Passive House standard in planning. Technologies used require little maintenance and are not prone to malfunction. P5 relies on high insulation values, a tight building envelope, and a small, compact shape to achieve its low energy use. (See Table 4.)
Much like P3, P5 has extremely low heating requirements. It used just 415 kWh in the first year of monitoring—one major advantage of a smaller home.
P6 Davis Double
P6 was originally two homes, built in Davis, California, in 1932 and 1933, respectively. The remodeled homes have a total of eight bedrooms, two baths, and eight occupants, and they experience 2,581 HDD per year. The two houses are 1,462 square feet (north house) and 1,496 square feet (south house). Each house has two solar-thermal panels for DHW. Community volunteers, including the current occupants, provided part of the labor for both design and construction. In-kind donations also played a key role, including a 4 kW PV array that will be installed in 2012. The project is applying for LEED for Homes certification and has created a lot of excitement around DERs in the town of Davis. (See Table 5 for details.)
The occupants of P6 appear to live a very low-energy lifestyle. P6 has the lowest electrical base load of the ten project homes, at 160 watts for the two homes combined.
P10 Pacifica Coastal Cottage
P10 was built in 1934 by the current occupant's father, a couple hundred yards from the Pacific shoreline, south of San Francisco. The original 700 ft2 shack was added onto haphazardly over the years to a total of 1,503 square feet, and it grew to 1,706 square feet in its 2008 DER. It has two bedrooms, two baths, and two occupants. It experiences approximately 3,200–3,700 HDD in Pacifica, California.
P10 is notable for its daylighting strategies, which are especially valuable in a home that is occupied all day, every day. Significant efforts were made to create a well-insulated and airtight building, yet the owners expressed disappointment in the results of blower door diagnostic testing (about 6 ACH50), which had not previously been performed. P10 is an exemplary project that preserved the historical character of a family heirloom while at the same time making huge advances in comfort, energy efficiency, and sustainability. (See Table 6 for details.)
P10 has consistently exported net energy during several months of the year ever since its completion in 2008.
We do not have complete full-year results for all the homes in the study. However, Table 7 shows measured energy use for the homes for which we have sufficient data, compared to a typical California home. In some cases we do not have prerenovation energy use, because the house changed hands and the old bills were not available.
For more information on the REMOTE/PERSIST system, go to www.cchrc.org/remote-walls.
For a good overview of the charette process in building design and construction, see the summary from the online Whole Building Design Guide at www.wbdg.org/resources/charrettes.php.
Here are some other DER resources:
These DERs all started with very different homes, and renovators took different approaches in renovation. However, the six DERs do have certain things in common, and it is useful for anyone who is planning a DER to look at those things. DERs demand a more thorough, whole-house approach than a typical retrofit or remodel. This approach must take into account all the energy uses in the home, as well as the activities of the occupants. In order for a DER to be successful, everyone involved in the planning and construction must understand and use the house-as-a-system approach. Design strategies should be integrated throughout, preferably using the charette process. This holistic approach can allow for a synergy to be developed between building systems, and for every aspect of the home's operation to be rethought and redesigned. These changes can make possible much deeper energy reductions than would otherwise be the case and can simplify building systems, reduce renewable-energy requirements, and reduce costs.
Evaluating energy savings in DER projects is not as simple as comparing before-and-after consumption, and it is not easy to define what qualifies as a DER. DERs can entail substantial changes in the size, occupancy, and even location of the home that make before-and-after comparisons of energy use difficult to interpret. There are alternatives, such as energy use per square foot of floor area, or energy use per occupant, that could be used. In this article, we have simply reported energy use together with significant changes to the home, and we leave it to the reader to decide whether they meet DER requirements. Finally, metrics that convert energy use to carbon equivalents can result in significantly different evaluations of approaches to renovation.
This article is part of a series sponsored by Home Performance with Energy Star, jointly managed by the U.S. Department of Energy and Environmental Protection Agency. The opinions, views, and ideas expressed within this article are those of the authors and do not necessarily reflect the official policy or position of any agency of the U.S. government.
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