The Ultimate Guide to Roofing Tar: Tips and Tricks

A property manager in Transcona was dealing with a persistent ceiling stain in a 1970s commercial building with a flat tar-and-gravel roof. After a wet spring with several freeze-thaw cycles in April, water had worked its way through a failing seam near a rooftop HVAC unit. A handyman was sent up with a tub of cold-applied roof cement to patch the area.

Three weeks later, the stain was back. The cold-applied product had not bonded properly because the underlying substrate had softened from moisture infiltration over several winters. The patch looked solid from the surface, but water was routing around it through the compromised gravel layer below.

All Weather Exteriors was called in for an assessment. The crew found two additional seam failures and a section of membrane that had separated from the parapet wall flashing. A proper hot-applied repair was completed on the affected sections, the flashing was re-secured, and the drainage slope was improved near the unit base. No further leaks occurred through the following winter.

The early patch cost money without fixing the problem. The professional repair costs more upfront but has not needed to be touched since.

Roofing tar has been a staple of the roofing trade for generations. It seals, waterproofs, and extends the life of flat roofs, parapet walls, and low-slope surfaces across Winnipeg. But it is not the right product for every roof, and applying it incorrectly can mask bigger problems or void existing coverage.

This guide covers what roofing tar is, where it works, where it does not, and when a Winnipeg homeowner should call a licensed contractor rather than reach for a bucket.

TL;DR

• Hot-applied tar in a built-up roofing system, installed correctly, can last 20 to 30 years.
• Roofing tar (bitumen) is used primarily on flat and low-slope roofs, not on asphalt shingle roofs.
• It comes in hot-applied, cold-applied, and modified polymer versions, each suited to specific applications.
• Most DIY tar work is temporary. A professional application is required for lasting results in Winnipeg’s climate.
• Signs that your tar roof needs professional attention include cracking, blistering, standing water, and interior leaks.

What IsWhat Is Roofing Tar?

Roofing tar, also called bitumen, is a dark, viscous material derived from petroleum or coal distillation. It is used primarily as a waterproofing agent on flat and low-slope roofs. In Winnipeg, where temperatures range from minus 40 degrees Celsius in January to plus 35 degrees Celsius in July, the formulation of roofing tar matters significantly. A product that performs well in a mild southern Canadian climate can crack, delaminate, or lose adhesion under Winnipeg’s extreme freeze-thaw cycles.

Modern roofing tar comes in four main formulations, each suited to different applications and temperature ranges:

• Coal tar pitch: Traditional tar derived from coal, known for exceptional water resistance. Used in built-up roofing (BUR) systems on low-slope commercial roofs. Less common in new construction due to health and environmental restrictions.
• Modified bitumen: Asphalt-based bitumen enhanced with SBS (styrene-butadiene-styrene) or APP (atactic polypropylene) polymers. SBS-modified products retain flexibility down to approximately -25 degrees Celsius, making them well-suited to Winnipeg’s winter conditions. According to the National Roofing Contractors Association, SBS-modified membranes are among the preferred choices for cold-climate applications.
• Asphalt-based tar: Petroleum-derived product; the most common type used in Winnipeg residential and commercial applications. Available in hot- and cold-applied versions.
• Cold-applied tar cement: Pre-mixed, ready-to-use product applied at ambient temperature. Convenient for small repairs but limited in adhesion performance below 4 degrees Celsius.

SBS-modified bitumen outperforms APP-modified bitumen in cold climates because it remains flexible at low temperatures rather than becoming rigid. For most Winnipeg flat roof applications, SBS-modified products are the correct specification.

The bottom line: roofing tar is a category, not a single product. The right formulation depends on your roof’s slope, substrate, climate exposure, and what is already installed. A licensed contractor can confirm which product is appropriate for your specific situation.

Applications of Roofing Tar

Roofing tar serves different functions across different roof types. Its primary applications in Winnipeg are on flat commercial roofs, low-slope residential structures, and targeted repair scenarios.

Flat and Low-Slope Roofs

On flat roofs and low-slope commercial and residential structures, tar is often the primary waterproofing agent. A built-up roofing (BUR) system layers hot-applied bitumen with reinforcing felts to create a membrane that handles standing water and heavy snow loads. BUR systems have been standard on Winnipeg commercial buildings for decades. When installed and maintained correctly, a hot-applied BUR can last 20 to 30 years.

Repair and Maintenance

Roofing tar is commonly used for targeted repairs on flat roofs, including:

• Sealing active leaks around roof penetrations, such as plumbing vents and HVAC curbs
• Reinforcing flashing at chimneys, parapet walls, and roof-to-wall transitions
• Patching small areas of surface deterioration before they allow water infiltration
• Sealing gutter seams and downspout connections on older commercial buildings

Waterproofing Elements

Beyond the main roof surface, tar is also used to waterproof specific roofing components:

• Parapet wall cap flashing and coping joints
• Roof-to-wall transition points on low-slope additions
• Downspout and drain connections on flat commercial roofs
• Base flashing at HVAC curbs and penetration sleeves

Where Roofing Tar Does Not Belong

Roofing tar should not be applied as a coating over asphalt shingles. Tar traps heat beneath the shingle surface, accelerates granule loss, and shortens shingle life by restricting the natural water-shedding function of the shingle. If a sloped residential roof leaks, the correct repair is shingle replacement or flashing repair, not tar application over the surface.

The bottom line: roofing tar works on flat and low-slope roofs and in targeted repair situations. It is not a solution for sloped residential shingle roofs.

Key Roofing Tar Terms Defined

These terms appear frequently in roofing assessments and contractor quotes. Understanding them helps you evaluate proposals accurately.

Built-Up Roofing (BUR)

• What it is: A flat or low-slope roof system made by alternating layers of hot-applied bitumen with reinforcing felts or fibreglass mats.
• Why it matters in Winnipeg: BUR systems provide redundancy against ice and water infiltration, making them a long-standing choice for Winnipeg commercial buildings.
• What it causes or prevents: A properly installed BUR prevents water penetration through the flat roof membrane and can last 20 to 30 years with maintenance.

Modified Bitumen

• What it is: Asphalt-based bitumen enhanced with SBS or APP polymers to improve flexibility, tensile strength, and temperature performance.
• Why it matters in Winnipeg: SBS-modified bitumen retains flexibility to approximately minus 25 degrees Celsius, which is critical for Winnipeg’s freeze-thaw cycles.
• What it causes or prevents: Modified bitumen membranes resist cracking and delamination under the thermal stress that would damage standard asphalt products.

Cold-Applied Tar Cement

• What it is: A pre-mixed, ready-to-use bitumen product applied at ambient temperature without heating equipment.
• Why it matters in Winnipeg: Available at most hardware stores and commonly used for DIY repairs, but adhesion fails below 4 degrees Celsius.
• What it causes or prevents: Cold-applied tar can seal minor surface openings temporarily, but does not bond adequately to wet or cold substrates, making it a short-term measure in most Winnipeg conditions.

Flashing

• What it is: Sheet metal or membrane material installed at roof transitions, edges, and penetrations to direct water away from vulnerable joints.
• Why it matters in Winnipeg: Ice dam formation puts extreme pressure on flashing at eaves and at roof-to-wall transitions during freeze-thaw events.
• What it causes or prevents: Properly installed and sealed flashing prevents water from entering at the most common leak points on any flat or low-slope roof.

How Roofing Tar Is Applied: Professional Methods

Most roofing tar work in Winnipeg should be left to licensed contractors. The following overview helps homeowners and property managers understand what a proper application involves and what to ask when reviewing a proposal.

Preparation

Proper preparation is required before any roofing tar application. Skipping preparation steps is the most common reason DIY repairs fail.

1. Clean the surface completely. Remove all debris, standing water, loose material, and vegetation. Power washing may be necessary on larger areas.
2. Confirm the surface is dry. Any moisture beneath the tar will prevent bonding. In Winnipeg’s wet spring and fall seasons, allow additional drying time.
3. Repair the substrate. Replace rotted wood or deteriorated decking before applying tar. Surface repair over a failed substrate will not hold.
4. Prime porous surfaces. Concrete, masonry, and aged gravel surfaces benefit from a compatible primer to improve adhesion.
5. Gather proper safety equipment. Gloves, safety glasses, appropriate footwear, and respiratory protection for hot applications.

Hot Application

Hot-applied tar is the standard method for built-up roofing systems and large-scale flat roof work. A kettle heats bitumen to between 175 and 230 degrees Celsius (350 to 450 degrees Fahrenheit). The material is transported to the roof and spread with mops or mechanical equipment before the reinforcing fabric is embedded while the tar is still hot. This method requires trained crews, proper equipment, and strict fire and safety protocols. It is not appropriate as a DIY application.

Cold Application

Cold-applied tar products are the only realistic option for homeowner DIY minor repairs. They are applied with a trowel, brush, or putty knife and require no heating equipment. They must be applied to a clean, dry surface at temperatures above 4 degrees Celsius. In Winnipeg, this limits cold-applied work to approximately May through September. Applying cold-applied tar to a wet or cold substrate results in adhesion failure within the first winter.

Apply in layers of approximately 3 mm (1/8 inch). Do not apply in a single thick coat. Allow 24 to 48 hours of cure time between layers. Total thickness should not exceed 6 to 10 mm.

Safety Considerations

Working with roofing tar requires specific safety precautions at every stage.

• Adequate ventilation is essential, particularly with hot applications. Hot-applied bitumen releases volatile organic compounds (VOCs) that are harmful when inhaled in enclosed or poorly ventilated spaces.
• Hot tar causes severe burns on contact. Appropriate protective clothing, gloves, and footwear are non-negotiable.
• Never leave heating equipment unattended on the roof. Open flame equipment is a fire risk on roofs with dry debris.
• Cold-applied products require ventilation as well. VOC release is lower than in hot applications, but still requires fresh-air conditions.
• Temperature extremes affect application quality. Do not apply below 4 degrees Celsius or above 35 degrees Celsius.

Key Numbers: Roofing Tar Performance in Winnipeg

Data Point	Figure	Source / Context
Hot-applied BUR lifespan (properly installed and maintained)	20 to 30 years	National Roofing Contractors Association (NRCA) general estimates for maintained BUR systems
Cold-applied tar: typical useful life before reapplication	3 to 5 years	NRCA maintenance guidelines; shorter under high freeze-thaw exposure
SBS-modified bitumen: minimum flexibility temperature	Approximately -25 degrees C	Manufacturer specifications for SBS-modified membranes; critical for Winnipeg winter performance
Standard hot tar application temperature	175 to 230 degrees C (350 to 450 degrees F)	Industry standard for kettle-applied bitumen and coal tar pitch
Cold-applied tar: minimum application temperature	4 degrees C (40 degrees F)	Manufacturer guidance: adhesion fails below this threshold
Winnipeg’s average January temperature	-16.4 degrees C	Environment and Climate Change Canada 30-year climate normals (1991 to 2020)
Winnipeg’s annual freeze-thaw cycles	Approximately 40 to 60 per year	Environment and Climate Change Canada’s historical climate normals are the primary factor in membrane wear
Tar application thickness per layer	Approximately 3 mm (1/8 inch)	Standard industry application guidance: total thickness should not exceed 6 to 10 mm
Attic ventilation’s impact on roof longevity	Up to 20 to 25% longer shingle life with adequate ventilation	According to the Canada Mortgage and Housing Corporation, proper attic ventilation extends shingle and membrane life in cold climate zones

When to Use Roof Tar Patch Products

Cold-applied tar patch products are available at most Winnipeg hardware stores and are appropriate for a specific, limited set of repair scenarios. Understanding the boundaries of DIY tar work saves money and prevents situations where a surface patch conceals a deteriorating substrate.

Emergency Leak Repairs

When facing an active leak, specially formulated roof tar patch products can provide temporary relief until professional repairs can be scheduled. These products are designed for rapid application, and some formulations are rated for wet-surface use as an emergency measure only. They form a flexible temporary seal, and many contain reinforcing fibres. They are not a permanent repair.

Preventative Maintenance

Regular inspection and targeted tar maintenance can extend the service life of an aging flat roof by addressing small failures before they become large ones:

• Check and reseal around roof penetrations annually, particularly around HVAC curbs and plumbing vents
• Inspect flashing laps and edge terminations for separation; reseal with compatible tar product
• Address surface blistering or minor cracking before the freeze-thaw season begins
• Apply reflective coating over exposed tar surfaces to slow UV degradation

Limitations of DIY Tar Applications

Cold-applied tar products are widely available, but there are clear limits to what DIY application can accomplish in Winnipeg’s climate.

Situation	DIY Appropriate?	Why
Single small blister or surface crack, dry weather, above 4 degrees Celsius	Yes, with caution	A cold-applied patch can seal the area if the surface is clean and dry
Active leak during or after rain or snowmelt	No	Wet substrate prevents proper adhesion; professional assessment needed
Multiple leak points or a recurring leak at the same location	No	Pattern indicates systematic membrane failure; temporary patch delays necessary repair
Any application in the fall or winter	No	Temperatures too low for reliable adhesion; patch will fail before spring
Flashing separation at the parapet wall or chimney	No	Requires compatible materials and proper lapping technique
Substrate showing softness, rot, or delamination	No	Surface repair conceals structural failure; professional assessment required
Previous DIY patch that has already failed or lifted	No	Indicates a deeper substrate problem; the second patch will repeat the failure

The bottom line: if a repair has been attempted once and failed, or if the leak involves more than one location, a professional assessment will cost less in the long run than repeated temporary patches.

When to Call Professional Roofers

Contact a licensed roofing contractor when any of the following conditions are present on your Winnipeg flat or low-slope roof.

• Multiple active leaks or water stains appearing in different areas of the building
• A leak that has returned after a previous repair attempt
• Visible bubbling, surface separation, or widespread alligatoring across the membrane
• Standing water that does not drain within 48 hours after rainfall or snowmelt
• Any flashing separation at a chimney, parapet wall, HVAC curb, or vent penetration
• A roof more than 20 years old with no documented maintenance or inspection history
• Visible softness or deflection in the roof deck when walking across the surface
• An insurance claim involving storm or hail damage to a flat or low-slope roof

In Winnipeg’s climate, professional expertise ensures that repairs hold through extreme temperature cycles, heavy snow loads, and spring thaw conditions. A contractor who inspects the substrate before applying surface treatment is doing the job correctly. One who patches without lifting the membrane to assess what is beneath it is not.

Why Choose All Weather Exteriors for Roofing Tar Applications

When it comes to professional roofing services in Winnipeg, All Weather Exteriors brings 18 years of local experience, more than 6,000 completed residential and commercial projects, and a BBB A+ rating held since 2009. The company is fully licensed and insured in Manitoba.

Every flat roof assessment includes inspection of the substrate condition, membrane type, drain function, flashing integrity, and surface wear before any repair scope is recommended. This approach prevents the common outcome of surface repairs that fail within one season because the substrate problem they were masking was never addressed.

• Climate-specific expertise: 18+ years working exclusively in Winnipeg’s freeze-thaw conditions
• Substrate-first assessment: underlying issues are identified before any surface treatment is applied
• Product selection: materials are specified by formulation and temperature rating, not by convenience
• Written estimates: Every project scope is confirmed in writing before work begins
• Financing available for qualifying repair and re-roofing projects

Maintenance Tips for Tar Roofs in Winnipeg

Regular maintenance extends the life of a tar roof and reduces the cost of eventual replacement. These practices apply to built-up and modified bitumen roofs on both residential and commercial properties in Winnipeg.

1. Inspect twice a year. Spring and fall inspections catch damage from ice, snow, and summer UV exposure before it becomes serious. Spring inspections should follow the last significant freeze-thaw cycle, typically in late April.
2. Keep drains and scuppers clear. Flat roofs accumulate debris from the cottonwood season in late May, summer storms, and fall leaf drop. Standing water for more than 48 hours adds structural load and accelerates membrane wear.
3.  Inspect flashing at every penetration and wall transition after each winter. Look for separation, cracking, or gaps at termination bars and lap seams.
4. Monitor for surface cracking, blistering, or alligatoring. These are early signs that the membrane is aging and that moisture may be working into the layers below.
5. Apply reflective coating on exposed tar surfaces. Dark tar surfaces absorb heat, increasing cooling loads in summer. Reflective coatings reduce surface temperature and slow UV degradation.
6. Address small repairs before the freeze-thaw season. Water that enters a seam or crack before freeze-up expands during the first hard frost, widening the gap significantly.

Canada Mortgage and Housing Corporation notes that periodic roof inspections and regular maintenance help spot developing problems before they cause costly damage and can help prolong the life of the roof.

Frequently Asked Questions (FAQs) About Roofing Tar

Book a Free Roof Assessment

All Weather Exteriors provides a free comprehensive roof assessment for all flat roof repair, maintenance, and re-roofing projects in Winnipeg. With 20+ years of experience in Manitoba’s climate, a BBB A+ rating since 2009, and work completed on more than 6,000 homes and commercial properties, the company offers the credentials and local knowledge to give you an honest assessment of what your roof needs.

Call (204) 510-2959 or email info@allweatherexteriors.ca to book your inspection. Financing is available for qualifying projects through a Canadian finance partner.

Editor’s Note: This post was originally published on March 14, 2025. The last update was made on May 30, 2026, to reflect new information and insights.