Commercial Window Leaks During Rain? How to Find the Entry Point
A leaking commercial window may admit water through perimeter sealant, head flashing, masonry joints, glazing gaskets, sill joints, or wall cavities above the window. Start high and work down.
Last reviewed 2026-09-12 · General facility-maintenance information, not a substitute for site procedures, manufacturer instructions, codes, or qualified professional judgment.
Quick answer
Safety boundary
Likely causes
- Failed perimeter sealant
- Head flashing issue
- Masonry joint leak
- Glazing gasket failure
- Blocked or sealed weeps
Symptom → cause → first move
Failed perimeter sealant
Check: Document where water first appears
First move: Repair confirmed sealant failure
Head flashing issue
Check: Inspect exterior sealant
First move: Restore blocked drainage paths
Masonry joint leak
Check: Check intentional weep paths
First move: Repair flashing or glazing system as appropriate
Glazing gasket failure
Check: Inspect wall and flashing above
First move: Repair confirmed sealant failure
Blocked or sealed weeps
Check: Perform controlled water testing if appropriate
First move: Restore blocked drainage paths
What to check first
Bring these
- Flashlight
- Camera
- Rags/buckets
- Moisture meter when available
Before touching anything
- Confirm the exact location and complaint.
- Photograph labels, settings, fault codes, and the original condition.
- Determine whether the failure affects one item or several nearby items.
- Know how to safely isolate the system if the task requires it.
Step-by-step procedure
- 1Document where water first appearsPhotograph the first wet point and record rain direction, intensity, and whether leakage occurs with the window closed.
- 2Inspect exterior sealantInspect accessible perimeter joints for gaps or loss of adhesion; do not assume every frame joint should be sealed.
- 3Check intentional weep pathsIdentify and preserve designed weep openings; remove only loose accessible debris without drilling new outlets.
- 4Inspect wall and flashing aboveTrace staining above the frame and inspect visible flashing or wall defects from safe access; the window may only be the exit point.
- 5Perform controlled water testing if appropriateIf an approved test is appropriate, use controlled low-pressure water on one small area at a time while an observer watches inside; stop at leakage, repair the confirmed path, and recheck during rain.
Routine fixes that make sense here
- Repair confirmed sealant failure
- Restore blocked drainage paths
- Repair flashing or glazing system as appropriate
Stop and call a licensed professional when
- Leak originates inside wall cavity
- Glazing system needs specialist repair
- Access requires lift or fall protection
Common mistakes
- Replacing parts before proving the failure.
- Changing several settings or components at once.
- Failing to photograph the original condition.
- Ignoring whether nearby equipment has the same symptom.
- Crossing into electrical, refrigerant, life-safety, structural, or plumbing work beyond training.
FAQ
What should I check first?
Start by deciding whether the problem is local to one fixture or piece of equipment. Then begin with the simplest safe observation: document where water first appears.
What is the most common mistake?
Replacing parts before proving the failure. BuildingWrench recommends documenting the symptom, changing one thing at a time, and testing after each change.
When should maintenance stop?
Stop when the repair crosses your training or site-safety boundary. In this case, one clear handoff point is: leak originates inside wall cavity.
What should I document?
Record the exact location, model or asset tag, what the equipment was doing, what you checked, what you changed, and whether the fix held through repeated testing.