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.
Do not assume the visible wet spot is the failed joint. Water can enter above or beside a commercial window through perimeter sealant, flashing, masonry, glazing gaskets, or the wall assembly and then travel before appearing indoors.
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
- Pin-type moisture meter
- Shop towels
- Exact model manual and phone for documentation
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
Photograph the first wet point and record rain direction, intensity, and whether leakage occurs with the window closed.
Inspect exterior sealant
Inspect accessible perimeter joints for gaps or loss of adhesion; do not assume every frame joint should be sealed.
Check intentional weep paths
Identify and preserve designed weep openings; remove only loose accessible debris without drilling new outlets.
Inspect wall and flashing above
Trace staining above the frame and inspect visible flashing or wall defects from safe access; the window may only be the exit point.
Perform controlled water testing if appropriate
If 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
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.
Tools that fit this task
Use what you already own first. These affiliate links may earn a commission at no extra cost to you. Confirm model and compatibility before buying.
Compare with a dry baseline of the same material; readings indicate moisture, not its cause.
Dry accessible surfaces so fresh leakage is easier to identify; not for hazardous spill cleanup.