Commercial Window Leaks During Rain: How to Trace 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.
Likely causes
Do not jump straight to the most expensive possibility. These are the common places to start:
- Failed perimeter sealant
- Head flashing issue
- Masonry joint leak
- Glazing gasket failure
- Blocked or sealed weeps
| Possible cause | How to check | Routine first move |
|---|---|---|
| Failed perimeter sealant | Document where water first appears | Repair confirmed sealant failure |
| Head flashing issue | Inspect exterior sealant | Restore blocked drainage paths |
| Masonry joint leak | Check intentional weep paths | Repair flashing or glazing system as appropriate |
| Glazing gasket failure | Inspect wall and flashing above | Repair confirmed sealant failure |
| Blocked or sealed weeps | Perform controlled water testing if appropriate | Restore blocked drainage paths |
Tools and preparation
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 checks
Document where water first appears
Work through this check deliberately and record what you find before moving to the next one.
Inspect exterior sealant
Work through this check deliberately and record what you find before moving to the next one.
Check intentional weep paths
Work through this check deliberately and record what you find before moving to the next one.
Inspect wall and flashing above
Work through this check deliberately and record what you find before moving to the next one.
Perform controlled water testing if appropriate
Work through this check deliberately and record what you find before moving to the next one.
Routine fixes that make sense here
- Repair confirmed sealant failure
- Restore blocked drainage paths
- Repair flashing or glazing system as appropriate
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.
Controlled water testing
If site conditions allow, test the window in small exterior zones from low to high, pausing between zones. Starting high or spraying the entire assembly at once can make almost any lower joint look guilty because water travels inside frames and walls.
When to stop and hand it off
- Leak originates inside wall cavity
- Glazing system needs specialist repair
- Access requires lift or fall protection
Frequently asked questions
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.
Related BuildingWrench guides
BuildingWrench provides general educational information for commercial-facility maintenance. Manufacturer instructions, applicable codes, site procedures, and required trade qualifications always take priority.