Thermal Performance Characterization of Residential Wall Systems Using a Calibrated Hot Box with Airflow Induced by Differential Pressures

    Published: Jan 1995

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    ASTM E 283 and ASTM E 1424 in conjunction with ASTM C 976 were used to study the effect of airflow on thermal performance of the wall. A typical residential 2 × 4 stud wall was constructed and placed on top of a subfloor, making a 2.44 × 2.74 m (8 by 9 ft) test specimen. This base wall assembly was then covered with two types of XPS sheathing, various housewraps, a 15# felt, and a polyethylene vapor retarder film in 40 different configurations and tested individually per ASTM E 283 and per ASTM C 976. For 24 of the 40 C 976 tests, a differential pressure was induced across the test wall as per and ASTM E 1424. Airflows ranged from undetectable airflow at 0 ∙ Pa ΔP to 1.63 L/s ∙ m2 for the base wall assembly alone. Difference in airflow resistance performance between the ASTM E 283 and ASTM E 1424 test methods were noted. Thermal testing results incorporating both ASTM C 976 and ASTM E 1424 for tests 1–28 produced apparent thermal conductances (C-values) in the range of 0.40 W/m2 ∙ K for a nondetectable airflow level to 1.81 W/m2 ∙ K for an airflow of 1.53 L/s ∙ m2 for the base wall assembly alone with a 20-Pa ΔP. The calculated C-value for this base wall assembly was 0.40 W/m2 ∙ K. Test results reveal that airflow rates as low as 0.2 L/s ∙ m2 could produce a 46% increase in apparent C-value. Similar thermal performance differences were revealed when thicker shiplap XPS sheathing was used. Tests were also conducted using an Air-Tight Drywall configuration showing the effect of “wind washing” on thermal performance. By sealing the gypsum drywall on the base wall assembly tested, the apparent C-value, when exposed to a 12.5 Pa wind pressure, was found to be equivalent to a base wall assembly configuration which allows 0.15 L/s ∙ m2 airflow to penetrate completely through.


    airflow, walls, thermal performance, blower door, housewraps, air retarder, air barrier, hot box, air leakage, infrared

    Author Information:

    Jones, DC
    Research Associate, Tyvek Market & Product Development, Dupont,

    Ober, DG
    Director of Testing Services Division and Project Engineer for Hot Box Testing, Holometrix, Inc.,

    Goodrow, JT
    Director of Testing Services Division and Project Engineer for Hot Box Testing, Holometrix, Inc.,

    Committee/Subcommittee: E06.41

    DOI: 10.1520/STP14698S

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