Installing a New Roof Over Existing Shingles: What Edmonton Homeowners Need to Know

When facing the need for roof replacement in Edmonton, many homeowners wonder if they can simply install new roof over old roof to save time and money. While this practice, known as a "roof overlay" or "re-roofing," might seem appealing, there are significant considerations specific to Edmonton's challenging climate that make this approach problematic for most homes.

Understanding Roof Overlays vs. Complete Roof Replacement

A roof overlay involves installing new shingles directly over existing ones without removing the old material. This differs from a complete roof replacement, where all old materials are stripped away before installing new roofing components. While overlays can reduce labor costs and installation time, they come with substantial drawbacks, particularly in Edmonton's harsh climate.

Building Code Requirements in Alberta

According to the Alberta Building Code, only one layer of re-roofing is permitted over existing asphalt shingles. This means if your home already has two layers of shingles, you must perform a complete tear-off before installing new materials. Additionally, local municipalities may have specific requirements that further restrict overlay installations.

Why Edmonton's Climate Makes Roof Overlays Problematic

Edmonton's extreme weather conditions create unique challenges that make roof overlays particularly risky:

Heavy Snow Load Concerns

Edmonton receives significant snowfall, with accumulations that can create substantial weight on roofing systems. Adding a second layer of shingles increases the overall roof weight by approximately 2-3 pounds per square foot. When combined with heavy snow loads, this additional weight can stress the structural framework beyond design limits.

Freeze-Thaw Cycle Damage

The city's frequent freeze-thaw cycles, particularly during chinook events, create expansion and contraction that can compromise overlay installations. The different expansion rates between old and new materials can lead to:

Premature shingle cracking and splitting
Nail backing out and loosening
Increased thermal movement stress
Accelerated deterioration at material interfaces

Temperature Extremes and Material Performance

With temperatures ranging from -30°C in winter to +30°C in summer, Edmonton's climate puts tremendous stress on roofing materials. Overlays create additional thermal barriers that can trap heat and moisture, leading to accelerated aging of both old and new materials.

Hidden Problems That Roof Overlays Conceal

One of the most significant risks of installing new roof over old roof is the inability to identify and address underlying issues:

Structural Damage Assessment

Without removing existing shingles, contractors cannot properly inspect:

Roof deck condition and potential rot
Water damage to underlying structures
Mold growth beneath old shingles
Compromised flashing and penetration seals
Proper ventilation system functionality

Moisture-Related Issues

Edmonton's climate creates ideal conditions for moisture problems. Ice dams, common in the region, can cause water to back up under shingles. An overlay installation cannot address existing moisture damage or improve the roof's ability to handle ice dam formation.

Long-Term Cost Implications of Roof Overlays

While overlays may seem cost-effective initially, they often result in higher long-term expenses:

Reduced Lifespan

Overlay installations typically last 10-15 years less than complete roof replacement systems. The compromised installation surface and trapped heat reduce shingle performance and longevity.

Future Replacement Complexity

When an overlay system eventually fails, the replacement project becomes more complex and expensive, requiring removal of multiple layers and potentially addressing structural damage that developed undetected.

Warranty Limitations

Most shingle manufacturers provide reduced warranties for overlay installations, often voiding coverage for wind damage and reducing material defect protection.

When Complete Roof Replacement is Essential

Certain conditions make complete tear-off mandatory for Edmonton homes:

Existing Multiple Layers

If your home already has two layers of roofing material, building codes require complete removal before installing new materials.

Structural Concerns

Homes with structural issues, inadequate framing, or compromised roof decks cannot safely support additional material weight, especially considering Edmonton's snow loads.

Ventilation Problems

Proper attic ventilation is crucial in Edmonton's climate to prevent ice dams and moisture buildup. Overlay installations can compromise ventilation effectiveness and prevent necessary system upgrades.

Benefits of Complete Roof Replacement

Complete roof replacement offers several advantages over overlay installations:

Comprehensive Inspection and Repair

Tear-off allows for thorough inspection and repair of:

Roof deck integrity and replacement of damaged sections
Proper installation of ice and water barrier
Upgrading ventilation systems for Edmonton's climate
Flashing replacement and proper sealing
Structural reinforcement if needed

Enhanced Performance Features

Complete replacement enables installation of modern roofing technologies specifically designed for Edmonton's climate challenges, including upgraded ice and water barriers and improved ventilation systems.

Professional Assessment and Installation

Given Edmonton's challenging climate and the complexity of roofing decisions, professional assessment is essential. Qualified contractors can evaluate:

Structural capacity for additional load
Existing material condition and compatibility
Local code compliance requirements
Long-term cost-benefit analysis
Proper installation techniques for local conditions

Conclusion

While installing new roof over old roof might seem attractive for cost savings, Edmonton's harsh climate and building requirements make complete roof replacement the preferred choice for most homes. The risks associated with overlays including hidden damage, structural concerns, and reduced performance typically outweigh the initial cost savings.

For Edmonton homeowners considering roof replacement, investing in complete tear-off and replacement provides better long-term value, superior weather protection, and peace of mind knowing your roof can handle whatever Alberta's climate delivers.

Ready to make an informed decision about your roof replacement project? Contact PJ Roofing for a comprehensive assessment of your roofing needs. Our experienced team understands Edmonton's unique climate challenges and will provide honest recommendations tailored to your specific situation and budget.