Membrane Roof Blisters: Causes, Prevention, and Repair


As weather changes from season to season, it’s important to keep up your maintenance plan to keep your roof in working order. With weather changes, roof blisters may pop up on your commercial flat roof. While roof blisters may not need immediate attention, if left unmonitored, they could lead to saturated insulation and a damaged membrane.

Roof blisters are not limited to one type of roof system; they appear in all types of roofing systems – residential and commercial. Roof systems with membranes are more prone to blistering because blisters are formed by gaps between the membrane plies or between the underlying substrate and the membrane.

Read More: Commercial Roof Preventative Maintenance


What is a Roof Blister?

A roof blister is a raised area where there is a loss of adhesion of the roof. This area can fill up with air or water to form a blister – which looks like a bubble on your roof. If left untreated, a blister can grow larger and allow more moisture to get in so that the problem gets worse until more extensive repairs and possible replacement is necessary…unless it pops!

Roof blisters can be caused by any number of problems:

  • Moisture
  • Poor Installation
  • Poor Ventilation


This article will cover the main causes of commercial roof blisters and how they are repaired.

When air or water is trapped in a blister, the weather can cause the blister to grow on a daily basis. Warm weather will cause the water or air to expand during the day then cool temperature will cause the trapped water or air to contract at night.



How to Prevent Roof Blisters


Keep Dry

The number one rule for preventing commercial roof blisters is to use dry materials in dry settings. If your contractor says they need more time for the right weather or for your facility roof to dry out after bad weather, make sure they get that time. Here are some tips to be sure that your roof and materials stay dry:

  • Seal any substrate materials
  • Store roofing materials inside or well-sealed with tarps
  • Verify that the substrate is dry after harsh weather or cleaning before the new roof is installed


Proper Installation

Another blister prevention tip is to make sure that your materials have firm contact between them for the adhesion to work properly.

  • Install the insulation board snugly to substrate
  • Clean the work area of dust and other contaminants
  • Allow proper ventilation for the new roof system


While as a facility owner or manager, you may not have control over the installation process of your contractor. You can ensure that you hire the right contractor and talk to them about installing your roof to the manufacturer’s specifications.

Read More: Roofing Contractor Warning Signs: 4 Red Flags of a Disreputable Contractor


Regular Inspections

Whether you have a new roof or your roof is a few years old, it’s important to have a maintenance contract with a local roofing contractor. A maintenance contract will ensure that your roof will regularly be inspected and any damage will be addressed before it causes major damage to your substrate or facility.

Read More: Roof Inspections


How to Fix Roof Blisters

Generally speaking, roof blisters that contain air are still keeping water out of the substrate. Unless the roof blister falls under this list of characteristics (from you may be fine with leaving your blisters alone:

  • Loss of gravel, granules or another surfacing
  • Membrane deterioration
  • Blisters in seams which have reduced lap coverage
  • Blisters that have breaks that can admit moisture
  • Blisters that have fatigue cracking around the circumference
  • Blisters that occur in areas of high traffic


If your blister needs to be repaired, it’s best to hire a contractor to perform the repair properly. If your roof is still under warranty, call the contractor that installed your roof to see what they can do to help you.

Read More: Roof Blisters by Roofing Contractor

There are a few ways a contractor will repair a blister:

  1. Membrane roof – Cut away the membrane that has lost adhesion, replace any wet insulation with like material, and replace the membrane with overlapping edges at least 6 inches wide.
  2. Bitumen roof – If the membrane is in good condition, your contractor can simply cut an X shape into the blister to access the layer underneath. If the membrane is damaged, your contractor will need to replace the entire damaged area.


Investing in a commercial roofing project can be a daunting task. But by being prepared and asking the right questions, you can find the right contractor to deliver high-quality work for a good price.

Choosing West Roofing Systems as a turnkey roofing company will provide you with highly trained teams and award-winning service. Our services are flexible and diverse; we can recoat, repair or replace your facility’s roof so that it lasts decades.

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Author: Rufus West

Rufus West is a commercial roofing expert! You may see him on the West Roofing website and also on the West Roofing social media pages, giving fun facts and tips about the company and roofing industry.

Just like West Roofing System’s roof solutions, he isn’t bothered by water—it simply rolls off of his back!

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