Replacing a flat roof in Calgary typically costs about $11–$25 per square foot installed, depending on the membrane: roughly $15–$25 for two-ply SBS modified bitumen, $12–$18 for TPO and $11–$17 for EPDM rubber. That puts a 400 square foot detached garage at roughly $4,500–$10,000 and a 1,200 square foot flat-roof house or infill at roughly $13,000–$30,000, before insulation upgrades, drains or deck repairs.
This guide compares the three membranes used on most Calgary flat roofs, lists the extras that show up in a quote, covers old tar and gravel roofs, and explains when a repair is enough and when it is time to replace.
Table of Contents
- Flat roof replacement cost at a glance
- SBS vs TPO vs EPDM for a Calgary flat roof
- What else goes into a flat roof quote
- Tar and gravel roofs: repair or replace?
- Flat roof repair or replacement?
- Snow, chinooks, ponding and hail
- When to replace a flat roof in Calgary
- Storm damage and insurance
- Why Calgary homeowners call Total Exteriors
- Frequently Asked Questions
Key Takeaways
- Two-ply SBS typically costs about $15–$25 per square foot installed, TPO about $12–$18 and EPDM about $11–$17.
- Small roofs such as garages cost more per square foot because set-up, flashing and edge metal are spread over less area.
- Removing tar and gravel, replacing wet insulation and repairing a soft deck are the most common additions to a quote.
- Isolated leaks can usually be repaired. Several leaks, widespread blistering or wet insulation usually mean replacement.
- In Calgary, drains, slope and snowmelt matter as much as the membrane you choose.
Flat roof replacement cost at a glance
The table uses typical 2026 installed ranges. The garage and house columns simply multiply the per-square-foot range by the roof area, so treat them as a guide rather than a quote.
| Membrane | Installed cost per sq ft | 400 sq ft garage | 1,200 sq ft house roof | Typical service life |
|---|---|---|---|---|
| SBS modified bitumen (two-ply) | $15–$25 | $6,000–$10,000 | $18,000–$30,000 | 20–30 years |
| TPO (single-ply) | $12–$18 | $4,800–$7,200 | $14,400–$21,600 | 20–30 years |
| EPDM rubber (single-ply) | $11–$17 | $4,400–$6,800 | $13,200–$20,400 | 25 years or more |
Estimate ranges only. Roof size, height and access, the number of drains and penetrations, parapets and what is found under the old roof all move the final price. An on-site inspection gives the real number.
SBS vs TPO vs EPDM for a Calgary flat roof
SBS modified bitumen
SBS is a two-ply system: a base sheet plus a granulated cap sheet, torch-applied, heat-welded or self-adhered. The rubberized asphalt stays flexible through temperature swings, the two layers give redundancy, and the granulated surface handles foot traffic and hail well. It is a common choice for Calgary houses, garages and low-rise buildings. Our guide to SBS roofing explains how it is installed.
TPO
TPO is a single-ply thermoplastic membrane with heat-welded seams. It is usually white or light grey, so it reflects summer heat instead of absorbing it, which suits roofs over living space. Seams are strong when welded correctly; the details at drains, curbs and walls are where workmanship shows.
EPDM rubber
EPDM is a single-ply synthetic rubber that stays flexible in deep cold. On a small roof such as a garage or addition it can often go on in one sheet with very few seams. The seams and flashings are the parts that need the most care, and they are where most EPDM repairs happen.
No membrane is the right answer for every roof. A rooftop deck, a roof with lots of equipment or a roof you walk on often favours SBS; a large, simple roof over living space may suit TPO; a small, low-traffic garage may suit EPDM. See our residential flat roof page for the systems we install.
What else goes into a flat roof quote
The membrane is only part of the job. These items are common on Calgary flat roofs and explain most of the gap between two quotes:
- Tear-off and disposal: about $2–$4 per square foot, more for heavy tar and gravel or more than one old roof.
- Deck repairs: about $2–$5 per square foot where the sheathing has gone soft.
- Insulation: adding or upgrading roof insulation can add roughly $2–$8 per square foot. Tapered insulation also creates slope toward the drains.
- Drains and scuppers: replacing a roof drain commonly runs several hundred to about $1,500.
- Parapet and edge metal: new cap flashing on parapet walls is priced by the linear foot.
- Penetrations: vents, skylights, plumbing stacks and equipment curbs each need their own flashing.
Need a flat roof priced properly? Total Exteriors can inspect your roof, check for wet insulation and quote SBS, TPO or EPDM side by side. Call (403) 313-4932 or contact us online.
Tar and gravel roofs: repair or replace?
Tar and gravel, or built-up roofing, is layers of asphalt and felt topped with gravel. It is still found on older Calgary houses, garages and commercial buildings. Isolated leaks at flashings, blisters or penetrations can often be repaired by clearing the gravel, patching and re-graveling the area.
When a tar and gravel roof is older, leaks in several places or holds water, replacement is usually the better investment. Tearing it off is heavier and messier than removing a single-ply roof, which shows up in the price, and most owners replace it with a modern membrane such as SBS. For apartment blocks, retail and industrial buildings, see our commercial flat roofing page.
Flat roof repair or replacement?
Many flat roof leaks can be repaired: a split seam, a failed vent flashing, a hail puncture or a lifted corner. If the rest of the membrane is sound, a repair costs far less than a new roof and can buy years of service.
Replacement is usually the better call when:
- The roof leaks in several places, or the same leak keeps coming back
- Blistering, cracking or open seams are spread across the roof
- Thermal imaging finds wet insulation under the membrane
- The deck feels soft or spongy underfoot
- The membrane is near the end of its expected life
Patching a roof in that condition tends to move the leak rather than stop it. When both options are realistic, we price both in writing. Our article on roof repair versus replacement in Calgary goes into more detail.
Snow, chinooks, ponding and hail
Ponding. Water that sits long after rain speeds up membrane wear and adds weight. The usual causes are a blocked drain, a sagging deck or insulation that was never sloped toward the drains. Fixing slope during a replacement is one of the best investments you can make.
Snow and chinooks. Snow sits on flat roofs, and a chinook can melt it in an afternoon. If the water refreezes at a drain or scupper overnight, it backs up under seams and flashings, which is why many flat roof leaks appear in mid-winter. Our guide to how much snow a roof can hold covers the weight side.
Hail. Large hail can puncture or bruise a membrane, especially over soft insulation. A granulated SBS cap and a firm cover board under the membrane both help. Our flat roof maintenance tips cover what you can safely check after a storm.
When to replace a flat roof in Calgary
Spring through fall is the easiest time to replace a flat roof, because many membranes, adhesives and sealants need moderate temperatures to bond properly. Some systems can be installed in cooler weather with the right products and precautions, and emergency or temporary repairs can be done year-round. Our post on replacing a roof in winter explains the trade-offs.
Book inspections in spring and fall, and plan a replacement for the warmer months when the signs start to stack up. Waiting for a winter leak usually means paying for a temporary fix first.
Storm damage and insurance
If hail or wind damaged your flat roof, the repair may be covered by your home insurance, less your deductible. Age-related wear, ponding from a sagging deck and neglected maintenance usually are not. Photograph the damage, check your policy with your insurer or broker, and have the roof inspected before the next rain. See hail damage repair and our insurance claims process.
Why Calgary homeowners call Total Exteriors
Total Exteriors has repaired and replaced flat and low-slope roofs on Calgary-area homes, garages, additions and infills since 2016, and we have been BBB accredited since 2017 with an A+ rating. Our HAAG-certified inspectors use thermal imaging to find wet insulation, and every estimate is written and itemized.
We serve Calgary, Airdrie, Cochrane, Chestermere, Crossfield, Irricana, Beiseker and Rocky View County, and we offer 24/7 emergency call-out service when a roof is actively leaking.
Flat roof leaking or near the end of its life? Get a written quote for repair or replacement. Call Total Exteriors at (403) 313-4932 or contact us online.
Conclusion
A flat roof replacement in Calgary usually costs about $11–$25 per square foot, with two-ply SBS at the top of that range and EPDM and TPO a little lower. What sits under the membrane, how the roof drains and what has to come off drive the rest of the price. Repair isolated leaks early, plan replacement for the warmer months, and choose the membrane that suits how the roof is used.
Frequently Asked Questions
How much does it cost to replace a flat roof in Calgary?
Most flat roof replacements cost about $11 to $25 per square foot installed, depending on the membrane: roughly $15 to $25 for two-ply SBS, $12 to $18 for TPO and $11 to $17 for EPDM. Tear-off of a tar and gravel roof, wet insulation, deck repairs and new drains add to the total.
How much does it cost to replace a flat garage roof?
A detached garage roof of about 400 square feet typically costs roughly $4,500 to $10,000 to replace, depending on the membrane and the condition of the deck. Small roofs often cost more per square foot because set-up, flashing and edge metal are spread over less area.
Which is better for a Calgary flat roof: SBS, TPO or EPDM?
All three can perform well here when they are installed properly. Two-ply SBS is tough and handles foot traffic and hail well, TPO reflects summer heat and has heat-welded seams, and EPDM stays flexible in the cold with few seams on small roofs. The right choice depends on the roof size, how you use it and your budget.
Can a tar and gravel roof be repaired?
Often, yes. Isolated leaks at flashings, blisters or penetrations can be repaired. When a tar and gravel roof is near the end of its life or leaks in several places, replacing it with a modern membrane such as SBS is usually the better investment.
How long does a flat roof last in Calgary?
A well-installed SBS, TPO or EPDM roof typically lasts about 20 to 30 years, and EPDM can last longer. Ponding water, blocked drains and skipped inspections shorten that, so have the roof checked in spring and fall.
Sources: RenoQuotes, Flat Roof Cost in Canada (2026); RenoQuotes, Elastomeric Membrane Flat Roof Cost (2026). Prices are typical ranges that vary by home, not Total Exteriors quotes.
