Effective Floor Cavity and Knee Wall Construction Techniques in Two-Story Homes in Hot Climates

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This article or paper was published in the ASHRAE Thermal Performance of the Exterior Envelopes of Whole Buildings XIII International Conference Proceedings. Copyright 2016 ASHRAE. Reprinted by permission at www.fsec.ucf.edu. This article may not be copied and/or distributed electronically or in paper form without permission of ASHRAE. For more information, visit www.ashrae.org. Requests from third parties for use of ASHRAE published content should be directed to www.ashrae.org/permissions.It is understood that the floor cavity between the first and second floors of residential construction should be isolated from unconditioned space by an effective air and thermal barrier. Although the construction materials utilized likely have reasonable air and thermal resistance, the application may not be applied correctly or some applications may not hold up well over time. A research project of existing homes (Withers and Kono 2015) measured impacts from this problem and identified durable construction techniques and cost-effective repairs. Floor cavity pathways to unsealed attics combined with natural or mechanical driving forces result in air transport between the attic and the floor cavity. Unconditioned air leakage into residential floor cavities has been found to cause elevated space-conditioning costs, increase peak electric utility demand, and cause moisture-related problems.This paper provides new research on measured cooling and heating impacts from floor cavity and knee wall repair. Overall, 56 multistory homes were inspected and had performance tests completed, with 12 monitored for energy savings from floor cavity and some knee wall repairs. This paper describes practical inspection, testing, and dependable construction methods. Construction methods discussed consider challenges such as contractor experience, limited working access, and complex structural geometry. The measured energy savings from floor cavity repairs combined with cost-effective repair methods in 12 homes was found to be able to pay for repairs in about 3 to 4 years. Evidence from one home has shown that significant building moisture damage was eliminated as a result of floor cavity repair.

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