HEED-Advised Affordable Housing
A free design tool can help identify the most cost-effective strategies for improving building energy efficiency and occupant comfort.
Designing energy-efficient housing that is also affordable is an especially complex challenge. There is a limited budget available for special features; tight time lines are imposed on the design team; and there are many decision makers whose approval is required.The thermal comfort of the residents is rarely considered; as a result, housing may be affordable, but uncomfortable and expensive to live in. One design software tool, Home Energy Efficient Design (HEED), if used from the very beginning of the design process, can alert architects, managers, and owners to the potential impact of design decisions on occupants’ thermal comfort and energy costs.
The Las Brisas Project
Las Brisas is a 92-unit rental project that the Los Angeles Community Design Center (LACDC) is remodeling into affordable housing, with a particular emphasis on energy efficiency (see “Los Angeles Community Design Center,” p. 33).Tim Kohut works for the architectural arm of the LACDC and is the project architect for Las Brisas. Murray Milne is a consultant on the project.The project is part of a comprehensive neighborhood revitalization plan for the city of Signal Hill, California. The city of Signal Hill used its power of eminent domain to gain control over 23 fourplex buildings, the great majority of which have suffered the ill effects of absentee landlords, who have neglected upkeep at the expense of the residents and the neighborhood.The 23 existing buildings in Las Brisas are identical 40-year-old apartments with stucco over uninsulated wood framing. The ground floor units have slab-on-grade, while the secondfloor units have plywood flooring and an uninsulated attic space.
The LACDC’s projects benefit individuals and families whose incomes fall below 50% of the area median income. At Las Brisas, monthly rents start at $499 for a two-bedroom unit and go up to $645 for three bedrooms. Conscious of the limited income of residents, the LACDC has made it a priority to hold down the tenants’ monthly energy costs and to make the units more comfortable, especially in the summer.
The new Las Brisas is designed to create an integrated residential neighborhood with rehabilitated apartment units, landscaped open space, a low-cost child care center, a multipurpose community center,well-defined public and private spaces, and clear pedestrian and vehicle circulation.This rehabilitation project improves the existing building shells by adding insulation, new windows, earthquake protection, new interior wall surfaces, new furnaces, new water heaters, and other features that enhance thermal comfort. Some units are enlarged with additional bedrooms, stairways, private porches, and storage space.The limited budget eliminated the possibility of including air conditioners.
Affordable Housing, Energy Efficiency, and HEED
During the design process for Las Brisas, the architects were able to use HEED to quickly test many different passive- design strategies with the existing building shells in the specific local climate.The evolution of two selected units helps illustrate how HEED allowed the architects to evaluate the impact of alternative designs on the two issues deemed most important: a tenant’s energy costs and indoor air temperatures.
Instead of telling the developers and property managers generally that the units would be more comfortable and energy efficient, HEED made it possible to quantify how much cooler they would be or how many dollars would be saved. Thus, as the project design evolved and project financing began to solidify, it was possible to evaluate where the owner could get the most bang for the buck.
Once the user gives HEED four facts (floor area, number of stories, building type, and zip code), it will automatically create two initial base case schemes: Meets the Energy Code, and More Energy Efficient.The total yearly cost to operate, excluding cooking and water heating,was $650 and $400 respectively for the two base cases. Next, the architects tested seven different design alternatives: the as-built condition; added insulation; added whole-house fan; additional shading; added insulation combined with the whole-house fan; added insulation combined with additional shading; and finally, added insulation combined with the whole-house fan, and additional shading. (For more on HEED, see “HEED: Home Energy Efficient Design,” p. 34)
Using HEED,we found that the three uninsulated schemes averaged about $800 total yearly costs, while the four insulated schemes averaged about $500 yearly. Because air conditioners were eliminated from this affordable housing project, energy cost alone is not a sufficient measure of design quality. The four schemes that include insulation all use about the same amount of energy for the furnace, lights, fans, and appliances (see Figure 1).The decision on which of the four to use was based on which one provided the lowest peak indoor air temperature (see Figures 2 and 3).
Initially, the architects and owner agreed to remove any materials containing asbestos and lead-based paint. This included all the interior plaster, since there was asbestos in the joint compound.This meant that fiberglass insulation (R-13) could be easily introduced into the walls before the new gypsum board finish was installed. To help meet the construction budget, only the exterior stucco that contained asbestos was to be removed; selective demolition was proposed where new additions met the existing building. Unfortunately, when construction began, extensive termite damage was discovered, and the owner decided to demolish and replace all the exterior stucco.
Uninsulated attics were fitted with R-30 fiberglass batt insulation. The original attic space was also poorly ventilated. New eave venting and dormer vents were added to increase ventilation beyond code requirements. In southern California, enhanced attic ventilation helps alleviate heat buildup—and conductive heat gain—during the hottest months of the year. (Cold months are not very cold— outside temperatures drop only into the 40s.) Where the insulation installed over the second-floor ceiling joists extended above the exterior-wall top plate, insulation baffles were used to ensure that the insulation extended over the walls without blocking the eave vents.
Curiously, neither the general contractor nor the insulation contractor had ever seen an insulation baffle (we used the Raft-R-Mate by Owens Corning). In the first series of buildings, the insulation contractor cut the ceiling insulation 2 ft back from the eave vent, exposing the second-floor ceiling. After the insulation contractor was notified of the problem, and after the architects made a number of visits to the attics, the insulation subcontractor finally got the point and began installing the baffles correctly.
Installing new dualpane windows and adding insulation to the walls and attic spaces helped bring the 23 Las Brisas buildings up to code, and also dramatically reduced annual gas heating costs (see Figure 1).
From the outset,we thought that increasing exterior window shading on the south and west elevations was key to reducing indoor air temperature. However, using HEED, the architects found that in the second-story unit the average monthly indoor temperatures peaked at 88ºF with insulation and exterior window shades, but fell to 84ºF with insulation and a whole-house fan. Perhaps more importantly, the unit with the whole-house fan cooled off more quickly on summer evenings than the unit with the shading. Occupants in the unit with the whole-house fan would feel even cooler because the high air change rates create evaporative cooling that is not measured by drybulb temperature.
We determined that the cost of one 6-ft-wide trellis awning made of wood to fully screen the south- or west-facing 6 ft x 4 ft windows during the hottest months,May to August, from midmorning to midafternoon,would be approximately $1,100. The cost to upgrade the same window to spectrally selective lowe glazing, with a solar heat gain coefficient (SHGC) of 0.4,was about $35.While spectrally selective glass doesn’t accomplish what a shading device would, it does help reduce heat gains. HEED also helped the architects place a dollar value on the cooling created by exterior shading in relationship to other building features.
The building management division viewed the exterior shades as a potential maintenance problem. To alleviate these concerns, the shading devices were constructed of durable materials; the roofs were extended, or wood trellises were built. Complicating the proposed approach, the fire department would not allow fixed awnings below any second story egress window; they felt that the awnings would impede their ability to ladder to the second-story egress window during a fire. Since the existing windows stack, this meant that large bedroom windows (6 ft x 4 ft),many of which faced south, could not be shaded. Where shading devices were not allowed at the first-floor level, low-e, spectrally selective (SHGC 0.4), dual-pane glass was used instead. Elsewhere, dual-pane, aluminum frame windows with an SHGC of 0.7 and a Uvalue of 0.4 were used.
The original buildings are built very close together. In the courtyards, they are 20 ft apart, while in the side yard there is only 8 ft of separation. The architects felt that this would allow for only minimal natural ventilation. In designing and building affordable housing previously, the owner had installed ceiling fans at living rooms and major bedrooms to help make up for the lack of air conditioning.While ceiling fans do help with occupant cooling, especially in our dry climate, they are of no value in flushing the units at night. HEED helped demonstrate that installing whole-house fans would increase indoor air flow and significantly reduce indoor temperatures during the hottest months of the year.
The final overall design used new dual-pane windows, energy code levels of wall and attic insulation, and a whole-house fan.A few units also have additional shading. With this design, the average peak indoor air temperature was 83ºF in the second-floor unit and 76ºF in the first-floor unit. The upper unit behaves like a low-mass building, with very little thermal storage and only a few hours of lag time between the peak outdoor and peak indoor air temperatures.The lower unit, with its slab-ongrade, behaves more like a highmass building, with much more thermal capacity to store up nighttime “coolth,” and a longer lag time between peak outdoor and indoor air temperatures. This longer lag time gives the fan more time to bring in cooler outdoor air to cool down the interior thermal mass, which helps explain why the peak temperatures are much lower in the ground floor unit.
On the worst peak hour of the year, when it was 98ºF outdoors, the second floor unit peaked at 91ºF and the ground floor unit peaked at 86ºF. Nighttime temperatures indoors never exceed the high 70s.While all these temperatures are still uncomfortable, there is a significant temperature difference between indoors and out.Also, the occupants feel an additional cooling effect from the increased air velocity when the whole-house fan is operating.
HEED also allowed the architects to demonstrate that whole-house fans introduce natural cooling very economically— it costs just $25 per year to run this whole-house fan. During the course of bidding and construction, the true cost of the whole-house fan was pegged at roughly $500 per unit. This included the cost of the fan, the wiring, and the construction of a plenum at first-floor units. This cost was competitive with what the owner had spent installing ceiling fans in previous projects.
Traditional whole-house fans vent directly into an attic. While this works at the second-floor units at Las Brisas, finding a whole-house fan that could be used at the ground floor units proved more of a challenge.The architects discovered a Minnesota company, Kool-o-matic, that designs a wholehouse fan that is appropriate for plenum installations (model P2400). In this application, the fan is mounted in a “mushroom” on the exterior face of the building; it connects to an air intake shutter, and then to a plenum that is fed by a grill in the interior hallway.The whole house fan operates independently from the heating and duct system. The fan forces air to exhaust from the interior of the house at a rate of 1,250 CFM on the ground floor and 2,500 CFM on the second floor. The air displaced by the fans is pulled inside from an open window (see figure on page 30).
Placement of the mushroom was also a challenge. Since the buildings are only 8 ft apart (as opposed to the code minimum of 10 ft), the architects did not want to install the mushrooms in the sideyards. They were installed instead at the face of the building, which tends to call attention to them, but at least serves to educate residents and passersby about ventilation.
During construction, the building officials issued a correction notice stating that the fans were too close to bathroom windows at a number of locations. This unavoidable situation was due to the location of existing windows, and the limited opportunities to create a plenum (and a dropped ceiling) to allow the fans to exhaust to the outdoors. The architects were successful in arguing that the provision of the building code cited by the inspector dealt with exhaust appliances, and did not include ductwork and exhaust for cooling devices—that is, a whole-house fan. In the end, the building official allowed the installation of the whole-house fans at the proposed locations.
The architects believe that HEED not only helped them quickly test many assumptions about the impact of each proposed building element, but also helped define the relative value of each element in terms of the residents’ comfort and utility bills. Before using this design tool, the architects thought that exterior window shades were essential to controlling heat buildup for Las Brisas. They thought that insulation was important not only in keeping the building warm, but also in keeping it cool.They thought that whole-house fans were useful but not necessarily essential. Although each of these features proved important, the combination of insulation with a whole-house fan turned out to be the most effective in achieving the goals of affordability, comfort, and efficiency. Window shading (though the architects still included it when possible as a part of the final project) was not essential, as long as insulation and whole house fans were used.The architects felt that it might even be less important than introducing additional mass into the second- floor units—through a lightweight concrete floor covering, for example.
When the project was bid, it came in almost $200,000 over the owner’s budget of $8 million. Together with the owner and the contractor, the architects were able to identify areas in the project that could be value engineered to bring the project within budget without sacrificing quality. Long-term livability was a high priority, and the HEED graphics allowed them to gauge the value of the environmental features. At a cost of $500 per unit, the whole-house fans were deemed too important in the overall equation to merit elimination. Twenty thousand dollars was saved from the budget by allowing the contractor to purchase windows from an alternate manufacturer (low-e glazing at south and west windows was still included). The remaining $180,000 was saved by using alternate finishes, and by simplifying the project’s site work.
Because HEED allowed design optimization at the very beginning of the design process, the architects were able to convince the owner to pursue Energy Star certification for the project, even though it required modeling the existing buildings as newly constructed. HEED’s graphic outputs also supported the requirement to develop a manual that shows tenants how to operate their unit to maximize comfort and minimize energy costs.The manual explains the best way to use the whole-house fan, operable windows, and interior shading. Residents were moved into the first 40 units on December 1, 2003. The remaining 52 families moved in during January 2004.
Beyond Las Brisas
Las Brisas was the first project in which the LACDC used HEED to develop a project’s design and construction strategies. Since then, HEED has become a critical step in evaluating all projects early on to determine what steps should be taken for each new project. In many climates, owners and developers come to the table with assumptions about thermal comfort that stem from poorly designed and constructed models. They generally insist on the need for air conditioning without understanding all of their options. HEED allows the LACDC to challenge these and other existing assumptions about what should be included in a building’s design.
The LACDC recently persuaded another nonprofit developer who thought that air conditioning was required for an affordable housing project they were building in East Los Angeles. HEED graphs demonstrated that such simple things as protecting windows, using low-e glazing, and introducing whole-house fans kept indoor temperatures within the comfort range, even during the hottest days of the year. The owner used the prepared report (with HEED graphics) to convince the lender that the homes could be built and sold without the initial installation of air conditioning.
As architects and owners struggle to keep affordable housing affordable, HEED is one of the few tools available to help them. It is both easy to use and free, and allows for the design and construction of housing that is affordable to build and affordable to live in.
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