Case Study of Envelope Sealing in Existing Multiunit Structures

Research output: NRELSubcontract Report


Envelope air sealing was included in the retrofit of a 244 unit low-rise multifamily housing complex in Durham, N.C. Pre- and post-retrofit enclosure leakage tests were conducted on 51 units and detailed diagnostics were performed on 16. On average, total leakage was reduced by nearly half, from 19.7 ACH50 to 9.4 ACH50. Costs for air sealing were $0.31 per square foot of conditioned floor area,lower than estimates found in the National Residential Efficiency Measures Database (NREMD) and other sources, perhaps due in part to the large-scale production nature of the project. Modeling with BEopt software -- using an estimate of 85% of the envelope air leakage going to the outside (based on guarded tests performed at the site) -- calculated a space conditioning energy cost savings of 15%to 21% due to the air sealing retrofit. Important air leakage locations identified included plumbing and electrical penetrations, dropped ceilings/soffits, windows, ducts and wall-to-floor intersections. Previous repair activity had created significant leakage locations as well. Specifications and a pictorial guide were developed for contractors performing the work.
Original languageAmerican English
Number of pages54
StatePublished - 2012

Bibliographical note

Work performed by ARIES Collaborative, New York, New York

NREL Publication Number

  • NREL/SR-5500-54787

Other Report Number

  • DOE/GO-102012-3583


  • affordable housing
  • air sealing
  • air tightness
  • blower door test
  • Building America
  • enclosure leakage
  • envelope leakage
  • multifamily
  • residential
  • residential buildings
  • shell leakage


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