This paper evaluates dwelling unit undercoverage in the 2017 U.S. Programme for the International Assessment of Adult Competencies (PIAAC), an in-person survey of adult literacy that resulted in 3,660 completed cases. The international PIAAC standard requires that its surveys achieve at least a 95 percent coverage rate. To meet this standard, U.S. PIAAC used traditional listing of dwelling units in areas expected to have poor address based sampling (ABS) frame coverage, and ABS elsewhere. Missed dwelling units were identified and sampled through a missed structure procedure in traditionally-listed areas and through the Address Coverage Enhancement (ACE) procedure in ABS areas. Coverage enhancement procedures may be beneficial in reducing undercoverage bias, but they can be expensive for surveys with small sample sizes, and they can be time-consuming. There are differential cost structures for each coverage enhancement approach. We evaluate the cost-coverage trade-offs and explore options for improving the procedures’ efficiency of reducing the undercoverage of dwelling units for PIAAC.