PROPOSED INTERIOR INSULATION CONFIGURATION
FOR BASEMENTS WITH WET WALLS

A.    INTRODUCTION

In the "Rim Joist and Foundation Insulation Project Final Report" (given in section D), it is made very clear that integral and exterior insulation configurations are recommended for basement foundation insulation in a cold climate.  In terms of the research project results given in that report, two interior foundation insulation configurations are described as being suitable for use with dry basement walls only.  The definition of a dry wall given in that report is repeated here for emphasis.

A dry wall has the following characteristics:

  1. It has an effective soil drainage system that does not permit any liquid water to enter the wall and floor slab regardless of basement interior and soil moisture conditions for the life of the building (excluding catastrophic conditions such as natural floods).
  2. It has an internal drainage system that can remove liquid water from sources such as vapor condensation and plumbing failures regardless of whether such failures are caused from within the wall (such as pipe leaks) or inside the basement (flooding from a blocked sewer).

This definition excludes superficially dry walls, that is, walls that appear dry but in fact are not.  Sometimes, such walls are wet to begin with and only appear to be dry on the surface.  More often, superficially dry walls only appear dry because they continuously evaporate soil-sourced liquid water to the basement interior.  Once this drying potential is removed or substantially retarded by the interior foundation insulation system, then the walls become wet very rapidly.

In this context, it has been made clear by builders' associations, code officials and homeowners that there is an ongoing and pressing need for the development of a wet wall interior basement insulation system particularly for application in the retrofit market and for remediation of existing failed interior foundation insulation systems.  The risk in promulgating such a system is that the prevailing economic forces predicate that such a design will be applied to new construction as well, that is, if it works for existing wet walls, why would it not work for new walls as well?  Hence it needs to be reiterated that this research program unconditionally recommends integral or exterior insulation only for new construction with dry walls as defined above.

The wet wall design proposed here is founded on experimental data gleaned at the Foundation Test Facility and the Cloquet Residential Research Facility over a period of at least 14 years.  The design is based on the measured hygric performance of a range of interior foundation insulation systems tested over a broad range of interior boundary conditions ranging from fully heated in winter and dehumidified in summer to no space conditioning at all (that is no heating or dehumidification) throughout the year.  These data clearly show that systems that appear to work under nominal controlled interior conditions (typically, 68 F with nocturnal setback in winter, 50-60% RH in summer) fail under off-design conditions (56 F in winter and 80-90% RH in summer, to name one specific test condition).

It needs to be clearly stated at the outset, that the proposed design has not been tested although it has been engineered to accommodate all the known failure mechanisms revealed by the research data.  As befits an untested design, the proposal is conservatively engineered in the sense that the included materials may in practice prove to be over-specified (and thus needlessly expensive) and the details too meticulous.  However, no apologies are made for this prudence as the proposed design is intended as the starting point for an appropriate testing program, not necessarily as a "production" system.

B.    PROPOSED DESIGN

The requirements for the proposed design are as follows:

  1. Unheated basement in winter (~ 50F) with no dehumidification and an unconditioned basement in summer (no dehumidification or ventilation, ~85% RH).
  2. Wet, unfilled, masonry block walls with continuous seepage into the cores and interior surface rundown.
  3. Cracks (particularly around window wells) that permit the ingress of rain and irrigation water.
  4. No sub-slab vapor retarder.
  5. No exterior drainage, damp-proofing or water-proofing.
  6. A limited amount of wall movement (settlement and cracking).
  7. Retrofit installation.

The design is given in the following three schematics:


Figure 1  Proposed wet wall interior insulation design


Figure 2  Bottom of wall detail A


Figure 3  Top of wall detail B

The effectiveness of this design only can be assessed by an experimental test program that applies the design requirements as boundary conditions.  Satisfactory performance under nominal or average conditions usually encountered in practice offers no assurance at all of acceptable long term (30 or more years) performance.

C.    PROGNOSIS

The proposed design is presented here in the interests of seeding a viable research project that will definitively measure the performance of interior, wet wall basement insulation systems.  The data gathered during such a test program should include the following:

Please contact Louise Goldberg with any questions or any expression of interest in participating in a research project to evaluate the performance of interior wet-wall foundation insulation systems.

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