Architectural joints are made by cutting straight grooves cut part way into the rigid foam insulation board of an Exterior Insulation and Finish System (EIFS). When the insulation boards are covered with lamina (base coat and finish), the grooves then simulate the appearance of expansion joints for the purpose of stress relief or thermal movement. Although architectural joints are esthetic in nature, they do provide an additional advantage of being natural stops for application of base and finish materials.

Here are some things to remember about architectural joints:

  • Horizontal joints must have the lower surface beveled downward so that water can flow out of the joint.

  • They should not line up with board joints, sheathing joints, or natural stress lines in the structure such as window corners.

  • A 3/4-inch insulation board minimum thickness must be maintained in all EIFS. Therefore, a 3/4-inch insulation board can not receive architectural joints, and a 1 inch thick board can only have a 1/4 inch deep architectural joint, and so on.

  • Higher density insulation boards, such as polyiso board (Quick-R) or 1.5 to 2 pound density polystyrene are higher modulus materials than standard 1 pound density EPS. That means that the higher density (stronger) boards will tend to transfer more of the stresses to the lamina. This translates to more tendencies for cracks to develop in the architectural joints. The bottom line is to be more careful when using higher density insulation board to avoid architectural joints in those systems when possible.
  • Repair of cracks in architectural joints should be done with low modules (easily stretchable) repair materials. These materials will include low modules sealants, elastomeric coatings, and joint repair strips such as Sil-Span from Pecora or System 1-2-3 from Dow-Corning. The type of repair procedure and materials selected will be determined by the system being repaired and severity of the crack problem.