A commercial roof rarely stays perfectly flat and uniform throughout its service life. Property teams may notice a round bubble, a long ridge, a loose sheet, a crease near a wall, or an area that changes shape as the day warms.
Those conditions can look similar from a distance while involving different roof layers and causes. Cutting the surface, pressing it flat, or covering it with coating before inspection can destroy useful evidence and create a new leak path.
Start by Naming What You Can Observe
Use plain descriptions before assigning a cause. Record whether the area is round or linear, firm or soft, isolated or repeated, open or closed at its edges, and near a seam, drain, curb, wall, patch, or traffic path. Note whether the surface is cracked, scuffed, stretched, or discolored.
Measure its length, width, and approximate height without stepping on it. Mark the location on a roof plan and photograph it from the same angle with a scale in view. Repeat observations can show whether the condition is stable or growing.
Do not puncture a raised membrane as a test
A knife or probe can turn an uncertain surface condition into an open roof. Any test cut should be planned where it will provide useful evidence and immediately become part of a compatible, documented repair.
Blisters and Bubbles
A blister generally describes a localized raised area where layers have separated or pressure has formed within the roof assembly. It may occur within built-up roofing, modified bitumen, a coating, or between another membrane and its substrate. The exact mechanism depends on the roof system.
Moisture, air, vapor movement, poor adhesion, incompatible materials, trapped contaminants, or substrate conditions may contribute. A surface bubble does not prove which one is present. Moisture mapping and carefully selected verification points can help define what lies below.
Wrinkles, Ridges, and Loose Membrane
A long raised line may follow a seam, insulation joint, deck flute, fastener row, or material movement. A wrinkle can form when a sheet is not lying flat or when movement transfers through the assembly. A loose area may flutter or shift without forming a sealed bubble.
Location matters. A ridge that reaches a seam can place stress on the lap. A loose area near equipment may be vulnerable to service traffic. A wrinkle at a wall or curb can interfere with drainage and flashing. Each condition needs evaluation as part of the surrounding detail.
Why Temperature and Timing Matter
Roof materials expand, soften, and move as surface temperature changes. A raised area may be more visible in afternoon sun than early morning. That change is useful inspection evidence, but it does not establish the cause by itself.
Record the date, time, surface condition, recent precipitation, and approximate temperature when practical. Avoid unsupported conclusions about trapped pressure or water based only on the fact that a condition changes during the day.
Check the Roof Around the Raised Area
The surrounding roof may explain why the condition deserves attention. Inspect nearby seams, patches, drains, penetrations, curbs, perimeter flashing, and traffic routes. Look for punctures, surface cracking, open laps, coating wear, or water that repeatedly collects nearby.
Our guides to commercial roof drainage and commercial roof traffic explain two conditions that can affect how surface defects develop or become damaged.
What a Useful Inspection Should Document
- 01Identify the roof system and map every raised, wrinkled, loose, cracked, or distorted area rather than sampling only the largest one.
- 02Measure and photograph each condition with nearby seams, drains, equipment, walls, repairs, and traffic routes visible.
- 03Compare observations at useful times without assuming that daily movement proves a specific cause.
- 04Use appropriate moisture-screening and verification methods to separate a surface issue from wet material below.
- 05Record which areas need immediate protection, focused repair, scheduled monitoring, or broader roof evaluation.
Repair or Monitor Based on Evidence
A stable condition away from seams and traffic may call for documented monitoring under the applicable roof-system guidance. A growing blister, cracked surface, stressed seam, wet substrate, or vulnerable location may need a focused repair. Broad or repeated distortion can point to a larger assembly issue.
A repair scope should state what will be opened, removed, dried or replaced, and how new material will tie into sound roofing. Coating over a loose surface or wet insulation does not correct the condition underneath.
Frequently Asked Questions
Is every raised spot on a flat roof a blister?
No. A raised area may be a blister, wrinkle, loose membrane, ridge over an insulation joint, trapped debris, displaced insulation, or another condition. Shape, firmness, location, roof type, temperature, and construction details help separate them.
Should a roof blister be cut open to release pressure?
Not without a repair plan from a qualified roofer. Cutting a waterproof membrane creates an opening and may release moisture without correcting wet insulation, poor adhesion, or another cause below it.
Can a commercial roof blister be left alone?
Some stable conditions may be monitored, while others need prompt repair. Size, growth, location, traffic exposure, surface cracking, seam stress, trapped moisture, and manufacturer guidance all affect that decision.
Does a bubble prove there is water under the roof?
No. Moisture is one possible contributor, but air, vapor pressure, adhesive problems, movement, or substrate conditions can also create raised areas. Surface appearance alone does not prove what is underneath.
What should a repair estimate include?
It should identify the roof system and condition, map the affected area, describe moisture findings, state removal limits, name compatible materials, explain how sound material will be tied in, and include final photos and monitoring notes.
Map the Condition Before Choosing the Repair
Platinum Roofing inspects and restores commercial roofs across Grand Rapids, Jenison, Holland, Muskegon, Kalamazoo, and nearby West Michigan communities. Call or text (616) 256-0831 to schedule a free commercial roof assessment.