Rim Joist and Foundation Insulation Project Final Report

Louise F. Goldberg
Center for Sustainable Building Research,
College of Architecture and Landscape Architecture

Patrick H. Huelman
Department of Wood and Paper Science



The Cloquet Residential Research Facility (CRRF) was constructed in 1997 and is located near Cloquet, Minnesota.  The CRRF is jointly operated by the following university departments:

Department of Wood and Paper Science, College of Natural Resources
Center for Sustainable Building Research, College of Architecture and Landscape Architecture
Cloquet Forestry Center, College of Natural Resources

Additional support has been provided by:

Department of Soil, Water and Climate, College of Agricultural, Food and Environmental Sciences.

The principal investigators may be contacted as follows:
    Louise Goldberg:    e-mail:

                           voice: (612)626-8783
                           fax: (612)821-9237

    Patrick Huelman:   e-mail:

                                voice: (612)624-1286
                                fax: (612)625-6286

Revision date:  2/28/2002



This study investigates the cold-climate moisture transport performance of various vapor retarder configurations for interior basement walls and rim joists using fiberglass batt insulation onlyAs such, it must be stated clearly that this limited scope of research does not constitute an endorsement of interior foundation systems over alternatives.  In particular, the authors recommend the use of exterior or integral foundation insulation systems for basements in cold climates.

The research investigates the moisture transport performance of the vapor retarder systems studied by measuring the psychrometric conditions in the insulation cavities and relating these conditions to the temperatures prevailing in the insulation.  Both wall and rim joist cavities are investigated.  Data were collected for a period of about 600 days spanning a winter and two summers.  The data are pseudo-transient in nature, as each data point comprises aggregations of several individual readings (at least 5) over a period of about 20 minutes.  Thus, on average, 72 readings are stored per day.

The wall vapor retarder configurations studied include the following combinations:

The rim joist vapor retarder configurations without exterior insulation include:

The above configurations were studied on hollow masonry block and poured concrete walls on both north and south orientations.  In addition, the above 4 rim joist vapor retarder systems also were evaluated with the installation of R-10 extruded polystyrene attached to the exterior face of the rim joist sheathing.  Each of these cases was evaluated for one wall type / orientation combination only.

Psychrometric results in terms of time profiles over the entire measurement period of humidity ratio, degree of saturation, and basement/insulation cavity humidity ratio difference are given for all the moisture measurement stations.  A more detailed phenomenology of the rim joist condensation performance is given by adding the condensation plane location ratio (CPLR) and various bounding temperatures to the analytical data set.

The experimental data are summarized in terms of a simplified model of basement wall and rim joist water vapor transport.  The model is applied to the various vapor retarder configurations and the resulting condensation behavior shown.  Finally, all the experimental results are condensed into a set of recommendations for interior basement wall and rim joist insulation systems that include water vapor management only.  These recommendations are given for new and retrofit construction using both masonry block and poured concrete walls and have the following features:

Interior foundation insulation of the kind recommended should not be installed on wet basement walls or on walls that can become continuously wet after the installation is complete.  This includes superficially dry walls, that is:

  1. Wet walls that appear to be dry on the interior surface prior to insulation installation.

  2. Walls that remain dry only because of their ability to continuously evaporate soil-sourced liquid water to the inside.  This is a particular problem for new construction without effective liquid water management systems.  This effectiveness needs to be demonstrated by field-testing before the recommended interior insulation systems are installed.


The research described herein has been performed with the support of a Minnesota Department of Commerce grant.  In turn, this State grant was made possible by a grant received from the U.S. Department of Energy, Office of Building Technology, State and Community Programs, DOE grant no. DE-FG-96R530335.

Additional support was provided by the CertainTeed Corporation, the CRRF sponsor, who supplied the fiberglass batt insulation used in the study and allowed the CRRF data acquisition system to be used to gather the experimental data.

While this financial support is gratefully acknowledged, the Principal Investigators assume complete responsibility for the contents herein.



    D.1    Humidity ratio time profiles
    D.2    Degree of saturation time profiles
    D.3    Humidity ratio difference time profiles
    D.4    Rim joist phenomenology and discussion




We hope that this report will provide improved guidance for interior insulation systems.  However, it is important to once again encourage the use of exterior insulation systems.  Even though (as stated in section C) this report focuses on interior insulation systems, it is important to repeat that the report should not be misconstrued as implying that  the authors or sponsors necessarily support or recommend the interior insulation configuration.  The study was conducted to better understand interior insulation systems owing to their popularity and use in the market and because of growing concerns about moisture migration issues and the resulting potential for biological contamination over time.

It also must be noted that the report recommendations are limited to fiberglass batt insulation with a double vapor retarder,  or extruded polystyrene in a dry wall environment.  This does not imply that other insulation systems are unworkable, but that we simply cannot speculate on their performance because we do not have solid experimental data (gathered either during this study or at the University of Minnesota's Foundation Test Facility) to support their use.  Further, the use of fault-tolerant interior insulation systems that can accommodate some level of persistent wall wetness are possible in theory, but the development of such systems was outside the scope of this project.

In reality, there probably are solutions to this complex problem that would use two different insulation / vapor retarder configurations for the upper and lower portions of the wall.  However, these were beyond the purview of this study and may be difficult to implement in the field due to varying wall depths and sloping grades.

One of the criticisms of exterior insulation has been the concern for proper installation and protection.  From this report, it should be clear that to ensure good long-term performance, interior insulation has demanding installation requirements, as well.


Goldberg, L.F and Aloi, T., 2001.   Space Humidity / Interior Basement Wall Insulation Moisture Content Relationships With and Without Vapor Retarders.  To be published in the proceedings of the ASHRAE Conference on "Indoor Air Quality and Moisture in Buildings", San Francisco.


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