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Twelve 50-year-old homes have been renovated by Habitat for Humanity of Montgomery County, Md. — with technical assistance from the NAHB Research Center — to significantly improve their energy efficiency while keeping the construction costs affordable.
Most of the homes are 1950s-era ramblers with block and brick facade construction and basement foundations.
Project goals included enhancing safety, improving durability, lowering monthly utility bills and adhering to a tight schedule and minimal budget — as well as taking into account Habitat’s usual practice of using volunteer laborers working in six-hour shifts.
Energy-efficiency gains ranged from 9% to 38% over the original homes. However, nearly all achieved a Home Energy Efficiency Rating (HERS) index of 100, bringing them up to the energy performance of homes built to the 2004 International Energy Conservation Code, the baseline for the HERS index.
Habitat partnered with the NAHB Research Center through the Department of Energy's (DOE's) Building America program. Its job was to observe the remodeling process and details, recommend additional energy enhancements, help identify the right products and materials for the volunteer laborers, model potential energy savings, verify improvements with before-and-after testing where possible and document the process so it could be repeated in similar kinds of homes.
Habitat trained the volunteers and segmented the work into discrete tasks taking three to four hours each and also made sure that all necessary materials and supplies were ready — ensuring timely delivery for quicker occupancy.
For all the homes, Habitat removed interior wall finishes from exterior walls, adding or increasing insulation in the foundation, above-grade walls and ceiling; upgrading electrical systems, including rewiring; replacing most plumbing and all fixtures; and evaluating HVAC equipment and ducts.
While upgrades to the heating and cooling systems were considered, the cost forced Habitat to leave the original system in place if it was still in good working order.
Following recommendations from the NAHB Research Center to enhance energy efficiency, durability and indoor air quality, the improvements included:
- Replacing windows with the highest efficiency that the budget would allow and taking care to install them according to the manufacturer's recommendations
- Adding air-sealing details at various locations — including roof/wall intersections, crawlspace walls and soffits
- Relocating supply and return ducts from exterior walls to the floor
- Ensuring adequate and simplified return air paths for all rooms
- Installing programmable thermostats
- Ducting kitchen and bath exhaust fans to the outdoors
- Installing Energy Star-rated appliances and light bulbs
- Broom sweeping all areas of the home after demolition to improve the effectiveness of the air sealing, helping to improve worker safety and indoor environmental quality
- Confirming that the downspouts and grading adequately directed rain water away from the house and that sump pumps were operating properly
- Adding exterior insulation where appropriate
The NAHB Research Center found that the most significant gains in energy performance came from improvements to wall insulation.
For the 10 homes constructed of block, the original R-4.7 walls were upgraded to whole-wall R-20 by removing the drywall, attaching 1-inch rigid foam to the block and then constructing a 2x4 wall on the interior of the rigid foam, air-sealing the top and bottom, insulating the 2x4 cavity with R-13 batt insulation and finishing by installing drywall and painting the interior walls.
Wall insulation details were also developed for two homes that were wood-framed. Where the siding was replaced, the volunteers added one inch of exterior rigid insulation to increase the whole-wall R-value from R-11.8 to R-17.4.
The second solution for wood-framed homes was for volunteers to build a 2x4 wall on the inside of the existing 2x4 wall and insulate both walls to R-13 in the cavity, so that the wall was upgraded from a whole-wall R-value of 11.6 to R-20.2.
Another key was air sealing. While the Research Center could find air leakage paths for individual homes through blower-door testing and other measures, the overall goal of the project was to determine common problem areas to successfully air-seal multiple homes without having to test every one.
The Research Center developed a list of good candidates for air sealing, including the intersections of floor and foundation walls and the ceiling and walls; rim/band joist areas; wire and pipe plate penetrations; sloped ceilings; balloon-framed gable end walls and any gable walls adjacent to the main house walls in split-level designs; cantilevered floors; attic hatch covers; chases and chimneys; wall sheathing; and any new openings created by the retrofit.
However, details for air sealing measures were developed and applied throughout the remodels with varying success, the Research Center found, primarily because the details were developed through this work.
“The 12 remodels successfully addressed and installed more insulation in exterior walls to increase the energy efficiency of these homes,” said Amber Wood, the Research Center’s program manager.
“The energy performance shows that meeting current energy code is achievable through whole-house remodeling of 1950s era homes,” she added.
Habitat and the Research Center now are studying best practices, details and training to determine specific ways to increase energy efficiency and durability for each remodeled house.
“A more definitive assessment procedure based on house design and location is needed to improve and simplify the selection of energy performance remodeling upgrades,” Wood said.
Better training for volunteers who do the air-sealing would also improve the results.
In addition, the Research Center wants to develop better guidance to help Habitat determine when to upgrade or replace an existing HVAC system. As part of this work, product options, design details and application details are needed, Wood said.
The purchases of the homes and renovation costs were supported through a special grant program from the county, and Habitat will pay the grant back when it sells the homes.
The costs were kept down because of Habitat’s network of suppliers and volunteers.
The good news, according to Wood, is that “Habitat Montgomery County is planning additional renovation projects that could provide the opportunity to advance the development of energy performance remodeling for affordable homes in Maryland.”