Built-Up Asphalt Roof Deficiencies in Ontario
Built-up roofing systems (BUR), also known as asphalt and gravel roofs or 4-ply roofs, have been installed on commercial buildings across Ontario for decades. Many are still in service today — but as these systems age, common deficiencies begin to appear. Knowing what to look for can help building owners and property managers address issues before they turn into major leak events or full system failures.
Below are some of the most common warning signs seen on aging asphalt roof systems throughout Toronto, the GTA, and across Ontario.
Common Warning Signs
Blistering, alligatoring, bare felt, wet insulation, vegetation growth, flashing failures, and prolonged ponding water are all signs an aging BUR roof may require repairs or replacement planning.
Why It Matters
Older asphalt roofs can hide moisture within the assembly. What looks minor at the surface can sometimes indicate larger issues below the membrane and insulation layers.
Next Step
A proper commercial roof assessment can determine whether the roof is repairable, suitable for retrofit, or approaching the end of its service life.
Common Signs Your Asphalt Roof Is Failing
These are some of the most common deficiencies found on aging built-up roofing systems in Ontario. Not every issue automatically means full replacement is required, but each one should be evaluated in context with the age of the roof, active leak history, insulation condition, and overall building plan.
1. Roof Blistering
Blistering occurs when moisture or air becomes trapped within the layers of a built-up roof system. As temperatures rise and fall, these trapped pockets expand and create raised bubbles in the membrane surface.
Small isolated blisters may sometimes be monitored, but widespread blistering can indicate aging materials, trapped moisture, or long-term deterioration within the assembly. If blistering is severe, traffic can rupture the affected areas and create direct leak pathways.
2. Alligatoring and Surface Cracking
Alligatoring is a common sign of an aging asphalt roof. It appears as a pattern of interconnected surface cracks that resemble reptile skin and usually develops as the asphalt dries out, loses elasticity, and becomes brittle.
Once this condition appears, the membrane has usually lost much of its original flexibility. On older BUR roofs, alligatoring often signals advanced weathering and can be a warning that patching will only provide short-term relief.
3. Ponding Water and Drainage Problems
Flat roofs are designed to manage water, not hold it for long periods. When water remains on a BUR roof well after rainfall, it can accelerate membrane deterioration, increase loading, and contribute to leak development at seams, flashings, drains, and low areas.
Persistent ponding often points to poor drainage design, structural deflection, blocked drains, or long-term settlement. This is one of the most common issues seen on older commercial asphalt roofs in Ontario.
4. Bare Felt and Surface Erosion
Built-up roofs rely on layered protection. When surfacing wears away and bare felt becomes exposed, the assembly is far more vulnerable to UV exposure, moisture intrusion, and premature breakdown.
Exposed felts can be a sign that the roof surface has weathered beyond its intended protection level. On older roofs, this often means the system is nearing the point where repeated repairs become less cost-effective than replacement planning.
5. Flashing Deterioration at Details and Penetrations
Most commercial roof leaks do not start in the field of the roof. They happen at details — penetrations, curbs, parapets, drains, tie-ins, and perimeter transitions. BUR systems often fail first where the roof has to change direction or tie into other materials.
Splits, open laps, dried-out mastics, deteriorated pitch pans, and failing base flashings are all warning signs that a roof is becoming vulnerable. If these conditions are showing up in multiple areas, it usually means the system needs more than isolated patchwork.
6. Wet Insulation Hidden Below the Roof Surface
One of the biggest issues with aging asphalt roofs is that they can hide moisture inside the assembly. A roof may look manageable from above while the insulation below is already saturated and losing thermal performance.
Wet insulation adds weight, reduces energy efficiency, and often spreads further than expected. It is commonly discovered during tear-off or through proper testing and assessment. This is why visual inspection alone does not always tell the full story on an older BUR roof.
7. Vegetation Growth on the Roof Surface
Vegetation growth is one of the clearest signs that moisture has been sitting on the roof for too long. Dirt, organic debris, and standing water can create conditions where weeds, moss, or plant growth begin to develop.
On a commercial asphalt roof, vegetation is not just a cosmetic issue. It usually points to long-term drainage problems, neglected maintenance, or areas of the roof that remain wet for extended periods.
Why These Asphalt Roof Deficiencies Matter
Built-up roofs can often be patched and maintained for years, which is one reason they remained so common across Ontario. But once multiple deficiencies begin appearing at the same time, the roof usually needs a more complete review. Surface symptoms like cracking, blistering, or exposed felt may be signs of larger hidden issues such as saturated insulation, deteriorated deck conditions, or widespread aging across the assembly.
For property managers and building owners, the goal is not just to react to leaks. It is to understand whether the roof is still a good candidate for targeted repairs, whether a retrofit is possible, or whether replacement planning should begin before emergency failures disrupt operations.
Should an Old BUR Roof Be Repaired or Replaced?
The answer depends on the age of the system, the amount of trapped moisture, how widespread the deficiencies are, and whether the building owner is planning short-term repairs or long-term capital improvements. Some roofs can still justify strategic repairs. Others are already beyond the point where ongoing patching makes financial sense.
A proper commercial roof assessment should consider:
- overall age of the roof system
- active leak history
- condition of flashings and penetrations
- evidence of trapped moisture or wet insulation
- drainage performance and ponding areas
- whether retrofit options are available
Book a Commercial Roof Assessment
If your building is showing signs of blistering, cracking, ponding water, exposed felts, wet insulation, or repeated leak activity, the best next step is a proper roof assessment. That allows you to determine whether your asphalt roof is still repairable, suitable for retrofit, or approaching the end of its service life.
Serving Toronto, the GTA, and commercial buildings across Ontario.
