Many commercial and industrial buildings in Calgary still have older built-up roofing (BUR) systems—tar-and-gravel roofs that have performed for decades but are now showing their age. As these roofs approach end-of-life, property and facility managers face a key question:

Do we replace the roof with a completely new system (like TPO), or can we restore and upgrade it using SBS modified bitumen?

In many cases, SBS is the ideal “next chapter” for an aging BUR roof: it builds on the strength of the existing assembly, adds modern waterproofing performance, and can extend roof life significantly when designed correctly.

This guide explains what SBS modified bitumen is, why it works so well over aging BUR in Calgary, and how to know when it’s the right solution for your building.

For a broader look at system choices, see “TPO vs SBS vs EPDM in Calgary’s Climate: Choosing the Right Commercial Roofing System” on the CMP Roofing blog at Blog, and our full commercial services at Commercial Roofing Services.

How Aging BUR Roofs Fail in Calgary

Classic tar-and-gravel (BUR) roofs have served Calgary buildings well, but time and climate eventually take their toll.

Common end-of-life symptoms include:

  • Membrane cracking and alligatoring
    Bitumen dries out and loses flexibility, leading to surface cracking and openings.
  • Blisters and ridges
    Trapped moisture and movement cause raised blisters and ridges that can split open.
  • Gravel loss and exposed felts
    Wind, snow removal, and weather strip away gravel, exposing felts to UV damage.
  • Persistent ponding water
    Deck deflection and insulation compression create low spots that hold water for days.
  • Frequent leak history
    Patch after patch is applied, but leaks continue in new spots, especially around details.

When these conditions are widespread, continuing with patch repairs quickly becomes false economy. At that point, SBS modified bitumen often becomes a strong candidate—especially when the underlying BUR and deck are still structurally sound.

For more on deciding when it’s time to move beyond repairs, see “Commercial Flat Roof Replacement in Calgary: Costs, Options & Timelines for Property Managers” at Blog.

What Is SBS Modified Bitumen Roofing?

SBS (styrene-butadiene-styrene) modified bitumen is an evolution of traditional asphalt roofing. The bitumen is modified with synthetic rubber (SBS), which improves flexibility, durability, and resistance to temperature extremes.

On Calgary commercial roofs, SBS is typically installed as:

  • A multi-ply system (base sheet + cap sheet)
  • Torch-applied or cold-applied, depending on design and safety requirements
  • Finished with a granulated cap sheet for UV protection and durability

When applied over an aging BUR roof, SBS can be used either as a:

  • Full tear-off and replacement, or
  • Resurfacing/overlay system when existing conditions allow

CMP Roofing designs SBS solutions specifically for Calgary’s freeze–thaw cycles, snow loads, and hail exposure. You can see how SBS fits into our wider services at Commercial Roofing Services.

Why SBS Is a Strong Option for Aging BUR Roofs

1. Compatibility with Existing BUR Assemblies

SBS is closely related to traditional asphalt-based systems, making it highly compatible with older BUR roofs.

Benefits include:

  • Good adhesion to properly prepared BUR substrates
  • The ability to reinforce and upgrade an existing assembly without always removing it entirely
  • Familiar detailing at parapets, drains, and penetrations for contractors experienced with BUR

2. Multi-Ply Redundancy and Robustness

Unlike many single-ply membranes, SBS systems are multi-layered:

  • Multiple plies provide built-in redundancy
  • Granulated cap sheets add surface durability and UV resistance
  • The system is very tolerant of occasional foot traffic and rooftop work around mechanical units

For aging BUR roofs that already have a proven structural “backbone,” SBS adds a modern, resilient waterproofing layer on top.

3. Excellent Performance in Calgary’s Climate

Calgary’s climate can be unforgiving—long cold periods, Chinooks, and frequent freeze–thaw cycles.

SBS performs well because:

  • It retains flexibility at low temperatures
  • It can stretch and recover with building movement and temperature swings
  • Multi-ply construction provides strong protection against minor impacts and hail

For hail-focused discussion, see “Hail Damage to Commercial Roofs in Calgary: Inspection, Insurance Claims & Repair Options” at Blog.

SBS Resurfacing vs Full Tear-Off: What’s the Difference?

When considering SBS for an aging BUR roof, there are two main strategies.

1. SBS Resurfacing/Overlay

In a resurfacing (also called “re-roof” or “overlay”):

  • The existing BUR roof remains in place
  • Loose gravel is removed and the surface is cleaned and prepared
  • Localized saturated areas may be cut out and repaired
  • An SBS base and cap sheet are installed over the prepared BUR

This approach can:

  • Reduce labour and disposal costs compared with full tear-off
  • Shorten project timelines
  • Minimize disruption inside the building

However, it is only appropriate when:

  • The existing assembly is structurally sound
  • Moisture levels are within acceptable limits
  • Code and manufacturer requirements regarding number of roof layers are met

2. Full Tear-Off to SBS

In a full tear-off:

  • The existing BUR, saturated insulation, and damaged materials are removed
  • Deck is inspected and repaired as needed
  • New insulation (meeting current R-value requirements) is installed
  • A new SBS multi-ply system is installed over the new assembly

Full tear-off is typically chosen when:

  • The BUR system is heavily saturated in multiple areas
  • Deck condition is unknown or suspect
  • You want to address structural slope, drainage, and insulation upgrades comprehensively

For more on replacement planning and cost, see “Commercial Flat Roof Replacement in Calgary: Costs, Options & Timelines for Property Managers” at Blog.

When SBS Is the Right Solution for Aging BUR Roofs

SBS over BUR is often the best choice when the following apply:

1. The Roof Is Functionally Failing, but the Assembly Still Has Structure

  • Frequent leaks, patchwork, and surface breakdown
  • Core samples show that not all areas are saturated
  • Deck remains structurally sound

In this case, an SBS resurfacing can restore waterproofing performance and extend roof life significantly.

2. The Building Has Complex Details and Heavy Rooftop Activity

  • Numerous penetrations, parapet walls, and curbs
  • Regular mechanical access and foot traffic
  • Sensitive tenants or operations beneath the roof

SBS’s robustness and detail-friendly nature make it particularly effective in these scenarios.

3. You Want a Familiar Asphalt-Based System

Owners who have had BUR or SBS for decades may prefer to stay within the same “family” of roof systems rather than moving to a single-ply:

  • Maintenance teams are comfortable with SBS/BUR detailing
  • Past performance and repair strategies are well understood

4. You Need a Strong Transition Strategy

For portfolios with multiple buildings:

  • SBS can serve as an intermediate step: resurfacing now, planning upgrades later
  • It can also be used on certain buildings while others receive TPO or EPDM, depending on use and energy goals

For help comparing systems at the portfolio level, see “TPO vs SBS vs EPDM in Calgary’s Climate: Choosing the Right Commercial Roofing System” at Blog.

When SBS Might Not Be the Best Choice

SBS is not always the right solution. It may not be ideal when:

  • The BUR assembly is severely saturated across large areas
  • Code limits have already been reached for the number of roof layers
  • Structural capacity for additional roofing weight is limited
  • Energy and cooling priorities heavily favour white, reflective membranes (such as TPO)

In these cases, full tear-off to a new system (TPO, SBS, or EPDM) may offer better long-term value.

CMP Roofing helps you evaluate these factors through detailed inspections and core sampling. You can request a commercial roof assessment via Contact and confirm service areas at Service areas.

Design and Construction Considerations for SBS Over BUR

Drainage and Slope

Ponding water is a common problem on older BUR roofs.

An SBS upgrade is an opportunity to:

  • Improve slope with tapered insulation or localized structural corrections
  • Rework drainage details at internal drains, scuppers, and gutters
  • Reduce long-term ponding that accelerates wear

For more on drainage issues, see “Flat Roof Drainage Problems in Calgary: Ponding, Freeze–Thaw Damage & Permanent Fixes” at Blog.

Safety and Fire Considerations

SBS can be installed using:

  • Torch-applied methods, or
  • Cold-applied adhesives and self-adhered membranes in sensitive locations

CMP Roofing designs installation methods with safety, building use, and local regulations in mind.

Integration with Future Work

When SBS is part of a broader asset strategy, we also consider:

  • Future mechanical additions or replacements
  • Possible solar installations
  • Long-term phasing of roof sections and other building upgrades

Maintenance and Lifespan of SBS Over BUR

An SBS system—especially over an existing BUR assembly—can deliver long service life when paired with a structured maintenance plan.

A typical maintenance program includes:

  • Semi-annual inspections (spring and fall)
  • Cleaning and verification of drains and scuppers
  • Repair of early-stage cracks, blisters, or detail issues
  • Documentation for ownership, boards, and insurers

This ties directly into “Commercial Roof Maintenance Plans in Calgary: How to Extend Flat Roof Life by 10+ Years” on the CMP Roofing blog at Blog and our maintenance-related services at Commercial Roofing Services.

How CMP Roofing Evaluates SBS Options for Aging BUR Roofs

CMP Roofing specializes in commercial and industrial roofing systems across Calgary, including BUR, SBS, TPO, EPDM, and coatings. When you ask us to evaluate an aging BUR roof, we typically:

  • Review leak history and tenant complaints
  • Conduct a detailed visual inspection
  • Complete core samples to check moisture levels and assembly makeup
  • Assess drainage, slope, and deck condition
  • Provide clear options:
    • SBS resurfacing/overlay (if appropriate)
    • Full tear-off and replacement (SBS, TPO, or EPDM)
    • Interim repairs and maintenance strategies

We then help you align the chosen option with your capital plan, operational needs, and risk tolerance.

Next Steps: Is SBS the Right Upgrade for Your BUR Roof in Calgary?

If your building still has an aging BUR roof and you’re facing recurring leaks, it may be time to explore SBS as a robust, climate-ready upgrade.

CMP Roofing can:

  • Inspect your existing BUR system
  • Determine whether SBS resurfacing or full tear-off is appropriate
  • Compare SBS with other systems like TPO and EPDM for your specific building
  • Design a maintenance plan to protect your investment over the long term

To schedule a commercial roof assessment in Calgary or surrounding areas, visit Contact. You can confirm coverage at Service areas and explore related system comparisons, maintenance strategies, and replacement guides on our blog at Blog and the full Commercial Roofing Services hub at Commercial Roofing Services.

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