Long-Term, Hygrothermal Performance of Exterior Insulation and Finish Systems (EIFS)
Authors: Bomberg Mark , Lstiburek Joseph , Nabhan Fadi 
Published: March 2007

To control rain ingress, the Exterior Insulation and Finish Systems (EIFS) can be constructed with one of two design principles

• a drain screen (rain screen, pressure equalized rain screen-PER) approach

• a face sealed (barrier) approach

While the barrier approach has an inherently higher risk for moisture damage, it offers econormc advantages and may be successfully used under a multitude of cli matic and service conditions. Its performance evaluation is carried out in three steps:

1. Examine whether this system can be used for a specific set of climatic and use con ditions

2. Formulate necessary measures for material and field quality control in the design specifications

3. Examine the system for integrity under cycling environmental conditions and long-term performance

Step 1 of this evaluation is based on the moisture control strategy of the whole wall assembly. Step 2 requires the addition of several small-scale material tests, and Step 3 involves full-scale system testing. The full scale testing is necessary to incor porate several parameters that act on the system simultaneously (thermal stress, thermal and moisture originated expansion and contraction, structural movements, material changes caused by weathering and aging, presence of moisture, etc.). The in teraction among these factors may provide conditions with severity significantly in excess of those achieved when these parameters are tested separately.

This discussion paper consists of three parts:

Part 1: Deals with the assessment of constituent materials of the EIFS with a view to ensuring (characterizing) hygrothermal performance of the system (by testing and characterization of the constituent materials, one may limit the range of variation in the hygrothermal performance of the whole system).

Part 2: Postulates a new test for evaluation of EIFS integrity under simulated expo sure to climatic cycling.

Part 3: Recommends EIFS design solutions and construction details for both new and retrofit construction. These details are discussed in the context of specific environmental/climatic conditions. This will be published in a later issue of JTIBE.

Testing EIFS cladding systems for integrity under simulated exposure to climatic cycling involves preconditioning under simultaneous exposure to a water vapor gra dient and temperature gradient followed by exposure to severe conditions of one- sided, uni-directional climatic cycling. The testing and characterization of the con stituent materials (Step 1) coupled with the full-scale test for EIFS integrity under exposure to climatic cycling (Step 2) will increase the reliability of the EIFS systems in North America.

Part 3 fills the gap between the current understanding of moisture control princi ples and construction practices. Many small changes in materials and technology create a compound effect that increases the frequency of inadequate field perform ance. Though most inherent EIFS flaws may be minor, those, when coupled with a number of failures of wall systems involving EIFS, caused an adverse attitude toward EIFS, perhaps more prevalent in some regions of North America. This paper pro vides a fundamental framework to cement many of the previously postulated correc tive measures into a coherent package aiming at the improvement of the EIFS reli ability in North America.