Phase One Task 5:  Building Envelope Performance Evaluation

Principal Investigator: Louise F. Goldberg
Building Physics and Foundations Research Programs
Co-Principal Investigator: Patrick H. Huelman
Cold Climate Housing Program
Department of Bio-Based Products
Project Manager: Tom Schirber
Amherst H. Wilder Foundation

The research described herein has been performed with funding provided by the
Amherst H. Wilder Foundation.  While this support is gratefully acknowledged, the Principal Investigators assume complete responsibility for the contents herein.


The principal objective of this research project was to experimentally determine the relative thermal performance of a warm-sided SEP-ETTMS panel system (SEPS) compared with a standard Minnesota building code compliant R-19 fiberglass stud framed wall system.  In particular, since the SEPS uses exterior extruded polystyrene insulation with a nominal thermal resistance of R-12.5 in combination with an exterior water separation plane and drainage cavity, there is a concern that the SEPS does not yield actual, in-situ R-values similar or better than batt/stud walls compliant with the building code requirements.

The approach taken was to build four SEPS variants all using R-12.5 extruded polystyrene insulation but with different drainage systems and compare the dynamic, real-time heat transfer performance of these variants against an equivalent fiberglass batt system in a wood stud frame.  To realize this objective, the principal investigators designed and developed a prototype, unguarded hot-plate experimental apparatus that can be attached to any building envelope component and yield the time and area-integrated, apparent relative thermal resistance of that component under transient thermal loading conditions1.  This measurement system utilizes any number of test hot-plates together with a reference hot-plate system that provides a real-time calibration of the test hot plates.  The measurements yield the thermal resistance of the test wall systems relative to the reference hot plate system under non steady-state or transient conditions, that is, with the external ambient temperature varying with time.   These transient data can be compared with steady-state performance data produced by 3-dimensional, thermal conduction only, finite element simulation to determine the impacts of the transient loading as well as dynamic, non-linear heat transfer effects (such as convection) within the test panels.

The 4 SEPS variants, batt/stud system and reference guarded hot-plate were installed in 3 test bays at the Cloquet Residential Research Facility (CRRF) and tested from January through April, 2004.


  1. The prototype unguarded hot-plate experimental apparatus is considered to be University of Minnesota Intellectual Property and its details, currently, are thus confidential.





The following conclusions may be drawn for the SEPS/ETTMS panel variants tested in a cold Minnesota climate:

  1. The SEPS panel with a 0.25" drainage mesh adjacent to the OSB surface can yield superior thermal resistance to a standard, MN building energy code compliant R-19 batt / stud wall under both steady-state and transient thermal boundary conditions if it includes at least 3 in. of extruded polystyrene insulation.
  2. The drainage mesh yields the highest thermal performance of the 4 SEPS panel drainage systems tested.
  3. There is evidence to suggest that conventional R-19 batt / stud wall systems yield significantly lower thermal resistance under transient boundary condition loading than determined by steady-state calculations.
  4. The prototype unguarded hot plate apparatus performed satisfactorily in assessing the in-situ thermal resistance of the SEPS panels.  However, it yielded apparently anomalous results for the batt/stud panel that require further detailed research in order to ascertain whether these results are indicative of real physical effects, a result of systematic errors or a combination of both aspects.


The following recommendations for future work are warranted by the results:

  1. Continued development of the unguarded hot plate apparatus with particular emphasis on determining the source of systematic errors when testing systems with thermal bridges and high embedded air volumes.
  2. Evaluation of a SEPS prototype with the drainage mat located at a mid-insulation position.
  3. Perform transient analyses including air movement of all the test panels in order to further explore the relative impacts of capacitance and convective flows in the context of transient, cold-climate boundary conditions.
  4. Use the experimental and analytic data to develop improved manual calculation methods for ascertaining more realistic R-values for use in building energy code compliance investigations.

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Rev B