Should You Repair Roof Blisters?

Whenever we get an order to inspect a residential or business building’s roof, especially when the roof is flat or has a very low pitch, we often find blisters in the roofing material. A blister is a puffed up, curved area of the roofing material. Blisters can occur in all roofing materials, except for rigid clay or concrete tiling, which are not used on flat roofs.

Mostly Membrane Blisters

The most frequent blistering in low-age roofing, is with membrane systems of one ply, such as TPO, PVC, and EPDM rubber roofing. Some blisters will still provide plenty of weather protection, if not cracked and have no gaping hole opened in them. If a blister does provide a way in for the elements, it must be fixed. Yet, often they are intact bubbling of the roof surface, perhaps unappealing, but still functional.

Modern roofing materials are more durable than a traditional single tar-paper layer. Roofing industry experts have grappled with this problem, without any conclusion. It comes down to flat roof architecture and the roofing solutions engineered to clad them.

Blister Sources

Low pitched roofs always develop some amount of blisters as they wear with age. Although the membrane roof types develop them first and usually more of them, even composite shingle roofs can develop blistering in their substrate layer. Blisters are created by voids in the layer between the top membrane and the under-substrate or sometimes between multiple ply layers. The blisters between plys are the result of applying the membrane adhesion incorrectly.

Blister Prevention

The best preventative measure for membrane systems is to properly adhere the membrane to the substrate material. Regular maintenance checks and quickly correcting any problems found can prevent most blisters from ever occurring. Bituminous membranes are especially vulnerable, because of microscopic openings that allow some moisture to gain access.

Blister Repairs

Each roofing company deals with blisters according to their own internal policies. It is a judgement call whether to cut out a blister, apply a patch over it, or leave it be. These are the main concerns that affect the decision to repair a blister:

  • Do the blisters have cracks or holes?
  • Is the roof surfacing or gravel significantly missing?
  • Is a blister in an area that is walked on a lot?
  • Are lap blisters reducing protection?
  • How much has the membrane deteriorated?

Once a decision has been made to repair blisters, each roofer follows some prescribed steps, some of which may be trade-proprietary, to effectively and quickly remove or roof over the blisters.


Each roofing repair foreman must make the call. Depending on the membrane material, blisters could threaten the viability of a roof. A roof maintenance program will eliminate problems with blisters, thus extending the life of your roof. If you are not certain a blister should be repaired, go ahead and fix it.


Leave A Reply

Facebook IconTwitter IconGoogle+Google+