Replacement
Flat Roof Replacement in Ottawa
When a low-slope roof has reached the end of its useful life, replacement is a chance to fix drainage, upgrade insulation and choose the right membrane for the building.
The short answer
Flat roof replacement removes the existing roofing down to a sound layer — often the deck — and installs a new assembly: any needed deck repairs, vapour control, insulation, tapered insulation for drainage where required, cover board, membrane and new flashings. It is the right choice when failures are widespread rather than isolated.
What this service covers
- Tear-off of existing membrane and wet or failed insulation
- Deck inspection and repair of damaged sections
- Insulation and tapered systems to improve the designed drainage slope
- New TPO, EPDM or SBS modified bitumen membranes
- New flashings at parapets, walls, curbs, skylights and penetrations
- Drains, scuppers, edge metal and transitions to adjoining roofs
Signs it's time for an assessment
- Recurring leaks in different locations
- Large areas of blistering, cracking, shrinkage or exposed reinforcement
- Ponding water across broad areas that drainage repairs can't fix
- Soft or spongy areas suggesting wet insulation or deck damage
- A roof whose age and repair history suggest it is near end of life
- Plans for a renovation, rooftop unit or deck that would disturb the roof anyway
How the process works
- Step 01
Assessment
We review the roof's condition, drainage, edges, penetrations and — where possible — what's beneath the membrane.
- Step 02
System options
We explain suitable membranes and assemblies for your building, with the trade-offs in plain language.
- Step 03
Written proposal
Scope, materials, inclusions and exclusions are written down so quotes can be compared fairly.
- Step 04
Preparation
Scheduling, protection of the property, material delivery and any permit questions are handled before work starts.
- Step 05
Installation
Removal and installation are staged to keep the building protected from weather throughout.
- Step 06
Close-out
A walkthrough of what was done, plus maintenance guidance for the new roof.
What shapes the scope
Every roof is different, so we don't publish flat prices. These factors drive the scope of work — see what affects flat roof cost for more detail.
- Roof area and shape
- More corners, levels and penetrations mean more detail work.
- Layers to remove
- Multiple existing layers or wet insulation add removal and disposal.
- Deck condition
- Damaged sheathing or decking must be repaired before new roofing.
- Drainage correction
- Tapered insulation, crickets or new drains change materials and labour.
- Insulation target
- Thicker or higher-performance insulation affects cost and edge heights.
- Membrane choice
- TPO, EPDM and SBS differ in material, method and detailing.
Ottawa conditions to consider
Replacement is the best moment to address drainage. A 'flat' roof is designed with a slight slope toward drains or scuppers; where an older roof has sagged or was built nearly dead-level, tapered insulation can restore that fall so meltwater leaves the roof instead of sitting through freeze-thaw cycles.
Insulation and vapour control matter in Ottawa's heating-dominated climate. Moisture moving up from a heated interior can condense within a poorly designed assembly. The National Research Council's Energy RCI resource is a useful technical reference on roof insulation thresholds and calculations.
Re-roofing can trigger permit requirements depending on scope, structural work or changes to the roof. Check the City of Ottawa's building permit guidance, and expect your contractor to raise any scope items that need a closer look.
Useful references: the City of Ottawa's “Do I need a building permit?” page and the NRC Energy RCI resource on roof insulation.
Frequently asked questions
How long does a flat roof replacement take?
It depends on size, access, the number of layers being removed and weather. A small residential roof might be a matter of days; larger commercial roofs are planned in phases. Your written proposal should give an expected schedule.
Can a new roof go over the old one?
Sometimes a recover over an existing roof is possible, but only if the existing insulation is dry, the deck is sound and the added weight and edge heights work. Wet or deteriorated layers should be removed.
Which membrane is best?
There is no single best choice. TPO, EPDM and SBS each suit different buildings, details and budgets. See our roofing systems comparison for a factual overview.
Can replacement happen in winter?
Some work can proceed in cold weather with suitable methods and precautions, but many owners schedule replacement for spring through fall. If a roof is failing in winter, temporary repairs can bridge the gap.
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