Learn about wall assemblies and retrofits.
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When planning an energy retrofit or replacing damaged and/or deteriorated materials of your building envelope (the components of the house serving as a thermal and weather barrier between the inside and the outside), there are various aspects to consider. Among many things, the main areas are your roof, exterior walls, windows, basement/crawl space, and how airtight your building is. What approach to take depends on the condition of the building and your needs. Click on the items below to view more information on the specified retrofit categories.
- Roofs and Attics
- Exterior Walls
- Windows and Attachments
- Basements, Crawl Spaces and Foundations
- Building Airtightness
Other than exterior walls, the building science advisor is currently not setup to analyze the moisture durability of other types of retrofits. In addition, BSA does not account for air leakage which contributes to energy loss and moisture intrusion in the building envelope. The links provide guidance regarding how best to approach these other types of retrofits together with their associated benefits.
To learn more about the details and construction of the building envelope please refer to additional resources:
Most important, before taking on an exterior retrofit make sure that the demolition and reconstruction follow local, regional and federal code requirements as it pertains to fire, hazardous materials and the impact changes will have on the structure’s performance and surrounding property and neighbors. Make sure to check with local code officials regarding permitting requirements prior to the start of construction.
An exterior energy efficient and durable wall retrofit consists of adding insulation and potentially reducing air leakage
into an existing home, while managing moisture penetration. A retrofit can significantly improve the thermal performance of
the building envelope providing economic benefits to homeowners by reducing energy demand. The National Renewable Energy
Laboratory’s ResStock program estimates that enclosure improvements
such as increased insulation and air sealing can result in significant annual utility bill savings. When done correctly, a
retrofit improves durability, indoor air quality and comfort. In addition, it can lead to environmental benefits such as the
reduction of greenhouse gas emissions and an improvement in the long-term durability of the home.
The residential housing stock accounts for 21% of the energy consumed in the U.S (U.S. Energy Information Administration). A significant portion of the homes, about 68%, were built prior to the Department of Energy’s establishment of the building energy code (American Housing Survey). As a result, these homes are poorly insulated resulting in significant energy loss compared to homes built today.
Studies have shown that there's a strong likelihood that some form of moisture damage will be encountered while doing a retrofit. Knowing the condition of the wall will help guide contractors and remodelers with remediation efforts, design, material selection and installation. Before beginning an exterior wall retrofit, it’s important to know the design and condition of the existing wall. Studies by the University of Florida, the Environmental Protection Agency (EPA), the Partnership for Advanced Technology in Housing (PATH) and the U.S. Department of Housing (HUD) revealed that there is a significant fraction of residential buildings that have been exposed to moisture resulting in damage or durability problems. Using data from 17,000 construction defect claims, the abstract of the University of Florida study, Identifying the causes of moisture-related defect litigation in U.S. building construction, determined that 69% were related to moisture penetration in the building envelope. In the PATH report, Building Moisture and Durability, Past, Present and Future Work, there is an extensive literature review section that includes reports, standards and case studies related to moisture durability in residential housing stock. One fifth of the homes surveyed in the HUD study, Assessing Housing Durability, A Pilot Study, documented various types of moisture damage. Though the HUD study was limited to one area, it does reveal the possibility of encountering moisture durability problems in existing homes.
A general assessment of the home should be done before doing a retrofit or renovation. The U.S. Department of Energy Building America Solution Center provides a comprehensive list of guides that cover all parts of the home from the roof to the basement including the HVAC systems and combustion appliances.
When considering a wall retrofit, a good place to start is with the Pre-Retrofit Assessment for Walls, Windows, and Doors and Hazardous Materials guides. These guides provide a check list format of what is referred to as “Potential Stop-Work Conditions” together with recommendations for remediation. Hazardous materials such as asbestos and lead paint are of particular concern in older homes and should be identified and remediated by professionals before construction begins. Also, older electrical wiring, such as knob and tube, needs to be upgraded by licensed electricians.
| Case Name | Location | % Energy Reduction | Challenges |
|---|---|---|---|
| Millbury Cape Deep Energy Retrofit | Millbury, MA | 58 | Encountered moisture damage of wooden sheathing and studs under the cladding. Removed/repaired to complete retrofit. |
| Two-Family Belmont Residence Deep Energy Retrofit | Belmont, MA | 74 | Height restrictions prevented insulation of basement slab. Used coating and dehumidification to manage basement moisture. |
| Westford Modern Colonial Deep Energy Retrofit | Westford, MA | 29 | To ensure airtightness and eliminate thermal bridging, thermally isolated the home from the garage. |
| Three-Family Triple Decker Comprehensive Deep Energy Retrofit | Jamaica Plain, MA | 48 | Owners wanted to preserve original slate roof preventing installation of exterior insulation from the walls to the roof. Installation of insulation on interior side of unvented roof with air space between deck and insulation to promote drying. |
| 19th Century Small Colonial Second Floor Reframing Comprehensive Deep Energy Retrofit | Lancaster, MA | 50 | Impermeable wall assembly; in this case a mesh was installed between sheathing and insulation to promote drying in case of minor accumulations of moisture. |