Shortly after completing the walls on a new two-story office building, we noticed that the insulation in the cavity walls was not taped or adhered to the backup, as required by the project specifications. The walls are 4-inch face brick with an 8-inch concrete masonry backup. The wall system is 22-inches thick with 2 inches of rigid polystyrene insulation. There are several areas where the insulation is not tight against the backup, but instead, is occasionally in contact with the back of the veneer wythe.

We are concerned that the lack of tape on the insulation joints and the fact that the insulation boards were not adhered to the backup may contribute to water leakage problems after the building is completed.

Will this condition likely cause future problems? Should the walls be rebuilt before further money is spent on adding interior finishes?

There is certainly a potential for future problems. Because water penetrates the outer wythe of all masonry walls, it will probably be flowing down the back face of the masonry veneer.

The cavity in this wall system is likely 1/2- to 1-inch wide. As a result, mortar protrusions on the back face of the veneer is probably in contact with the exterior face of the insulation. Water flowing down the interior face of the brick masonry is diverted at these mortar protrusions and can travel down the face of the rigid insulation. This possibility is even more likely if the insulation is in contact with the back face of the brick masonry.

Since the joints in the insulation are not taped, a portion of this water may flow across the horizontal joints in the insulation and reach the face of the concrete masonry backup wall. At this point, water either soaks into the face of the concrete masonry or flows down the wall. This situation can lead to a variety of moisture problems.

Water flowing down within the concrete masonry backup walls may enter the interior at the base. Water that soaks into the concrete masonry can lead to mold problems with some interior finishes. If the interior surface of the concrete masonry backup is furred and covered with gypsum wallboard, condensation likely occurs on this gypsum sheathing during warm weather because the moisture within the concrete masonry evaporates into the furring space.

The resulting high moisture content of the air within the furring space causes condensation to occur on the gypsum wallboard. Depending on the length of time that the wallboard remains wet, mold can grow on its paper. The potential for this problem is greatly increased if vinyl wall coverings or other vapor retarding coatings are applied to the interior face of the wallboard. These coatings restrict the movement of water vapor and slow the drying of the gypsum wallboard.

Recognizing that the exterior walls are completed, I recommend performing water testing to evaluate the potential for problems before considering a rebuild. Because the interior finishes have not been installed, it is possible to inspect the interior face of the walls visually for evidence of water penetration. Any wet spots that develop during the test could indicate problems.

I recommend testing the walls using a water spray rack built in accordance with ASTM E 1105. The spray rack need not cover the entire face of the wall at the test location, provided a sheet of water forms on the exterior face of the wall during the test. Usually positioning a spray rack near the upper portion of the wall is sufficient to develop a sheet of water on the face.

From my experience, this testing should be performed for 1-1/2 to 2 hours. Shorter tests may not identify the potential problems and longer ones may indicate problems that do not typically occur during actual rainstorms. Several areas should be tested to identify potential problem areas.

A moisture meter should be used to evaluate any changes in the moisture content in the concrete masonry before, during, and for 2 hours after the test. There is a potential for mold problems if moisture migration is identified before, during, or after the tests if gypsum wallboard will be used on the interior. Walls should not be closed in for a week or more following the test in order to give them time to dry out. Test the moisture content of the concrete masonry prior to installing interior faces to verify that its level is not elevated.

When these walls are enclosed, I recommend using wall coverings or coatings that are vapor permeable. This approach helps the wall system dry out if water leakage occurs in the future. The furring space should not be insulated since its use would require that a vapor retarding membrane be added on the interior side of this insulation in most climates. A vapor retarding membrane in this case prevents any moisture within the furring space from drying to the interior.