Commercial storefronts are the front line of any retail or office environment, yet they are frequently the most neglected component of the building envelope. When a facility manager calls me about water on the interior floor, they often assume they need to replace windows immediately. However, diagnostics must precede any talk of replacement. Water is a patient enemy; it follows the path of least resistance, driven by hydrostatic pressure, capillary action, and wind-driven rain. To identify where a system has failed, we use a diagnostic protocol that separates the professionals from the amateurs. One of the most effective, low-tech ways to find the source of an ingress is the simple chalk method.
A business owner once called me in a panic because their new high-efficiency storefront was ‘sweating’ and dripping onto their expensive inventory. I walked in with my hygrometer and showed them the humidity was 60 percent. It was not a leak in the traditional sense; it was their lifestyle and the building’s HVAC balance. I used the chalk method to prove to them that the gaskets were perfectly intact. By dusting the exterior glazing bead with finely powdered carpenter’s chalk and then performing a controlled water spray, I demonstrated that no moisture was bypassing the EPDM seals. The ‘leak’ was actually internal condensation because the dew point was being reached on the interior surface of the aluminum frame, which lacked a proper thermal break.
“Installation is just as critical as the window performance itself. A high-performance window installed poorly will fail.” – AAMA Installation Masters Guide
When dealing with commercial window repair, you have to understand the anatomy of a storefront. Unlike residential units, storefront systems are typically center-glazed or front-glazed aluminum extrusions. These frames are designed to manage water, not just block it. This is why the weep hole is the most misunderstood part of the assembly. If a window cleaner accidentally plugs these holes with debris or wax, the water that naturally bypasses the exterior gaskets has nowhere to go but into the building interior. The chalk method helps us determine if the water is entering through the glazing pocket or if it is a failure of the flashing tape at the rough opening.
To execute the chalk method, you start with a dry system. You apply a heavy layer of colored chalk to the gasket lines where the glass meets the frame. Then, using a low-pressure hose, you simulate a rain event starting from the bottom and working your way up. If the chalk remains dry on the interior but the floor gets wet, the leak is likely in the sill pan or the perimeter sealant. If the chalk is washed away and appears on the interior side of the glass, you have a gasket compression failure. This often happens because the gaskets have shrunk over time due to UV exposure, a common issue where the rubber pulls away from the corners, leaving a gap. This is a critical distinction because it tells us whether we can perform a simple gasket replacement or if we need to pull the glass and check the shim placement and the integrity of the thermal break.
In hot, southern climates, the solar heat gain coefficient (SHGC) is the primary metric we track. When I inspect a storefront in a high-sun environment, I am looking at how the heat is affecting the expansion and contraction of the aluminum. Aluminum has a high coefficient of thermal expansion. If the rough opening was not sized correctly or if the installers did not leave enough room for expansion, the frame will bow and break the perimeter seals. This leads to air infiltration that bypasses the glass entirely. A master glazier knows that the Low-E coating on surface number 2 is there to reflect that radiant heat back outside, but if the frame is failing, that expensive glass is useless. You are not just paying for a window; you are paying for a managed thermal barrier.
“Standard Practice for Installation of Exterior Windows, Doors and Skylights requires that the water-resistive barrier be integrated with the fenestration in a manner that ensures water is shed to the exterior.” – ASTM E2112
Often, a facility manager will ask if they should just replace windows when a leak is found. The math rarely favors full replacement for simple leaks. If the aluminum extrusions are in good condition, we can usually perform a window repair by replacing the glazing bead, updating the EPDM gaskets, and ensuring the sill pan is properly weeping. We look at the muntin bars and the sash to ensure there is no structural sagging. However, if the thermal breaks—the plastic or resin separators between the interior and exterior aluminum—have degraded, the system will start to conduct heat and cold so efficiently that condensation becomes an unsolvable problem. At that point, the energy loss justifies the capital expenditure of a new system.
Water management is a science, not a matter of applying more caulk. The ‘caulk-and-walk’ installers will try to seal every weep hole they see, thinking they are stopping the water. In reality, they are trapping water inside the frame, where it will eventually rot the sub-floor or cause mold in the drywall. A proper window repair involves cleaning out those channels and ensuring that the shingle principle is followed: every layer must overlap the one below it. From the head flashing down to the sill pan, the water must have a clear, unobstructed path to the exterior. If you see water on your windowsill, do not just call a window cleaner to wipe it up; call a professional who understands the physics of a glazing pocket.