BA-1901: Retrofit of Blown Attic Insulation in Existing HUD-Code Manufactured Homes - Needs Assessment Report

Effective Date

The purpose of this report is to disseminate the findings from a needs assessment of issues related to attic insulation retrofits in manufactured homes that meet building codes specified by the U.S. Department of Housing and Urban Development (HUD-code) as installed by DOE’s Weatherization Assistance Program (WAP). The original design for this research was developed by the Building Science Corporation (BSC) Building America team with input from WAP stakeholders. As part of the evaluation plan development, the design team consulted with and received feedback from various stakeholders involved with WAP, the HUD-code manufactured housing industry, and residential building science research. 



This needs assessment was conducted by the Washington State University (WSU) Extension Energy Program and Building Science Corporation (BSC) with support from the U.S. Department of Energy (DOE), Office of Energy Efficiency and Renewable Energy, Building Technologies Office.

The primary goal of this research was to identify moisture durability, energy savings, and savings-to-investment ratio (SIR) research needs related to the retrofit of attic insulation in DOE’s Weatherization Assistance Program (WAP)—specifically, manufactured homes that comply with building codes established by the U.S. Department of Housing and Urban Development (HUD) built after 1976 and sited in colder climates. This project assessed current practices of WAP insulation and/or roof venting solutions that improve attic insulation energy savings and durability. 

WSU and BSC conducted outreach to stakeholders via email, phone, in-person interviews, and group meetings designed to inquire about relevant issues stakeholders might have observed. Needs assessment feedback was provided from stakeholders involved with attic insulation retrofits in existing HUD-code manufactured housing in the colder climates of the United States. The list of more than 50 stakeholders who provided input into this assessment is provided in Appendix A. 

Critical needs were discussed with the following stakeholder groups:

• Residential building science community at the 2016 Thermal Performance of the Exterior Envelopes of Whole Buildings XIII International Conference and 2017 ASHRAE winter and annual meetings. Additional discussions were implemented at the 2017 Westford Symposium. 

• WAP practitioners and management involved in field installations at the 2017 Home Performance Coalition National Home Performance Conference cosponsored by WAP. WSU coordinated and participated in a session on manufactured housing weatherization at the 2017 conference. This provided an opportunity to engage those involved with all aspects of WAP associated with manufactured home retrofits and gain perspectives related to the real and perceived challenges of attic insulation retrofits under WAP. Additional discussions occurred in June 2017 with the WAP Training Consortium to share the current needs assessment findings and solicit ideas to consider when developing the test plan.

Manufactured housing industry stakeholders, including builders, suppliers, and government stakeholders at DOE, HUD, and other organizations involved with implementing and enforcing HUD-code as part of the HUD Manufactured Home Construction and Safety Standards.

The key project objectives and general findings include:

Objective 1: Identify and evaluate the cost-benefit challenges associated with attic insulation retrofits. Targeted Retrofit Energy Analysis Tool (TREAT) and Pacific Northwest National Laboratory energy modeling was used to determine the SIR where attic insulation is cost-effective (e.g., SIR greater than 1.0). Results suggest challenges in milder climates and in locations where lower cost natural gas is available, as expected. Maximum target costs to achieve attic insulation are provided for various climate zones and heating systems/fuel types. These costs vary depending on the climate, fuel type, and attic insulation R-14 or R-20 baseline assumptions. Community Action Partnerships (CAPs) in northern climate states have generally been able to achieve these cost targets except for the natural gas heating case.

Objective 2: Investigate building science-related concerns about why attic retrofits were not occurring as frequently as other measures. These included challenges presented by (1) access to the attic to insulate, (2) inability to meet the SIR in mild climates and/or where lower cost natural gas is available, (3) code conflicts about reducing venting at the eave, and (4) HUD-code homes not specifically addressed in the standard work specifications (SWS), especially for a new innovative gable end wall access insulation approach. Historically, the SWS focused on pre-HUD-code 1976 vintage manufactured homes.

Objective 3: Determine technical resources and future research that would help stakeholders more confidently insulate attics in manufactured homes. The recommendations are to (1) conduct a field evaluation to assess the attics that have previously been insulated by CAPs for moisture issues, (2) evaluate the gable end insulation approach and develop training tools, and (3) address low eave venting requirements through research on the effectiveness of alternative mitigation measures.

Download the complete report here.