Windows are a common point of water infiltration into a building. Preventing moisture intrusion into building interior spaces near window openings requires proper flashing and careful installation. This is especially true if the windows are installed in masonry veneer cavity walls.
Chapter 7 of the 2009 International Residential Code requires protecting building material products sensitive to adverse weather from moisture damage. Dry wood structural members can expand, twist, distort, and deflect unpredictably when exposed to ongoing excessive moisture. If rainwater infiltrates into wall structural cavities through gaps along the window exterior perimeter, it can provide a continuous and damaging moisture source to unprotected interior materials. The result: Wood and interior covering material decay and rotting.
Window and masonry veneer wall systems have two moisture resistant components: The window flashing system and the masonry wall materials. When properly installed, these two components act together to repel rainwater or other forms of moisture. When damaged or defective, these systems may allow water to infiltrate from the window exterior areas to its interior areas. Usually, the water travels through the exterior masonry wall veneer gaps and holes along the window frame and the into the masonry cavity wall interior spaces. Once inside wall cavity, the water gravity can flow through even the tiniest of holes between the window frame flanges and their supporting wood studs. The resulting damage and decay to the unprotected interior and exterior building materials can be costly.
Properly repairing leaking windows requires a competent mix of flashing, carpentry, and masonry skills. Each trade must coordinate with the other to assure all three skills work together to form a single moister barrier to help keep water out of the building. Unfortunately, there are know known “off the shelf” drawings or details that apply to waterproofing every type of window. Thus, a competent builder or contractor will rely upon the prevailing codes, builder supplied manufacturer’s installation instructions, and applicable system standards to effect a successful repair. Once the window is properly installed and flashed, the stone mason must assure any gaps between the masonry mortar and the window frame are sealed with a resilient water resistive material such as silicone or caulk. The builder or general contractor should then perform a final diligence check of the window to assure its water tightness, while keeping in mind Chapter 7 of the 2009 International Residential Code is a governing code document for waterproofing exterior window openings.