Burnaby Roof Expansion Joints: Where Flat Roofs Leak
Burnaby Roof Expansion Joints: Where Flat Roofs Leak
If a flat roof on a Burnaby commercial or strata building keeps leaking along one straight line, the expansion joint is the first thing to check. A roof expansion joint is the planned gap where two parts of a building are allowed to move independently, and the waterproofing across that gap has to move with them. When it can’t, the membrane tears, and no amount of patching holds for long. Below we cover what these joints do, why they fail on Burnaby buildings, what a proper detail looks like, and what the City of Burnaby expects before anyone touches one.
TL;DR
- An expansion joint is a structural movement gap, not a membrane detail. A membrane-only patch over a moving joint will usually tear again.
- Joint curbs should rise at least 200 mm (8") above the finished roof surface, and nothing should drain through the joint.
- In Burnaby, altering a commercial or strata roof, joints included, needs a City building permit, sealed drawings from a Registered Professional and, for strata, a signed Consent to Construction.
- Fix a joint by having it measured, designed and prefabricated for your building, not by cutting and patching in the field.
- Look at joints at every roof inspection, especially after our wet October to March season.
Table of Contents
What a roof expansion joint actually does
Buildings move. Concrete and steel expand and contract with temperature, long wings settle at different rates, and a building in a seismic region like ours also moves in ways you can’t see on a quiet day. Designers split a large structure into sections with a structural separation, and the roof has to cross that separation without letting water in.
SOPREMA describes an expansion joint, also called a movement joint, as the element that keeps the junction between two roof elements, walls or decks fully waterproof. Think of it as the elbow in a garden hose: the hose has to bend and stretch there, and that is where it fails first if it’s built cheaply.
Two terms get mixed up constantly:
- Membrane control joint: a detail in the roofing membrane meant to relieve stress within the roof system itself. Older ones assumed roofing materials behave elastically, which is why many have split.
- Building expansion joint: a true structural separation that the roof must accommodate. The National Research Council of Canada has long cautioned that a membrane fix can’t absorb structural movement, and that if the structure is shifting, a membrane-only repair will almost certainly tear.
That difference decides your repair. If the leak is at a building expansion joint, the answer is a properly engineered joint, not another strip of membrane.
Why joints fail on Burnaby buildings
Burnaby’s mix of low-rise commercial roofs along Kingsway, industrial buildings and strata complexes around Metrotown and Brentwood means a lot of long, low-slope roofs with joints running across them. In our experience the same handful of problems show up.
The joint was an afterthought
SOPREMA’s design team points out that many failures start when the joint is treated as a late detail. Roofers get to the separation at the end of a re-roof, fold the membrane into the gap and carry on. It looks fine on handover day and starts leaking in the first heavy fall rain.
Field patching over a moving gap
A bead of sealant or a cut-and-patch strip is a thrifty move that rarely pays off. Sealants harden and crack, and a patch glued across a joint that opens and closes is pulled apart twice a year. SOPREMA’s guidance warns against exactly this: patching in the field creates weak points, particularly in a wet climate like Metro Vancouver’s.
Curbs that are too low
A joint sitting flush with the roof surface is a gutter for ponding water. The Alberta Roofing Contractors Association standard calls for double curb or plate construction fastened to the structure on both sides of the separation, with the top at least 200 mm (8") above the finished roof. On older Burnaby roofs we often find curbs that were built lower, or that were buried when the roof was re-covered and the surface level crept up.
Drainage running through the joint
Industry standards forbid drainage openings through expansion joints. It still happens when a drain or scupper was added close to a separation and the water path was never checked. Water that is directed at a joint will eventually find a way in.
Shear movement nobody designed for
The most damaging movement is often not up-and-down or open-and-close but sideways shear, where one building section slides past the other. Joints designed only for simple opening and closing can tear under this. Modern EPDM-based monolithic joints, such as the SOPRAJOINT PLUS system, are designed to take horizontal, vertical and shear movement at the same time, and use a vulcanized assembly rather than adhesives or sealants that can degrade.
Signs your roof joint is failing
You don’t need to be on the roof to notice early warning signs. Property managers and strata councils can watch for:
- Staining on ceilings or walls that follows a straight line , usually matching a joint on the roof above.
- Water in the same stairwell, corridor or parkade corner after every heavy rain.
- Ponding beside the joint that lingers more than a couple of days after the rain stops.
- Visible splits, lifted edges or hardened sealant at the joint cover.
- Torn or displaced walk pads where foot traffic crosses the joint.
- Repeated repairs in the same spot. If the same line has been patched two or three times, the detail itself is wrong.
If you spot any of these, book an inspection before the next wet season stacks up. For an active leak, our emergency roof leak repair page explains how we respond.
What a proper repair or replacement looks like
Every building is different, and the detail for a concrete podium roof is not the detail for a steel-deck warehouse. But the sequence below applies to most of the commercial and strata roofs we look at.
- Find out what kind of joint it is. Is it a true structural separation, or a membrane control joint? Building drawings help, and so does a site visit.
- Measure the movement. The joint’s width, the direction of movement and how it behaves across the seasons all affect the product choice.
- Involve a Registered Professional when the structure is involved. Designers need to coordinate with a structural engineer so the joint matches the full range of anticipated movement, shear included.
- Specify a prefabricated, purpose-made joint. Custom measurements taken on site let the transition pieces at corners, walls and parapets be made before they reach the roof, instead of improvised there.
- Build the curb and flashings correctly. Minimum 200 mm curb height, secure fastening on both sides, and a membrane tie-in that suits the roof system, whether that’s torch-on, EPDM or another.
- Keep the joint clear. On roofs with vegetation or ballast, leave a 300 mm (12") zone free of soil and vegetation around the joint so it can be inspected and maintained.
- Test and document. Photographs of the work before it’s covered, and written confirmation from the reviewing professional, protect the owner later.
Expansion joints also meet other weak spots. Where a joint runs into a parapet, the corner is among the most leak-prone details on a flat roof, so see our notes on Burnaby parapet leak examples. Where it passes near rooftop units, the HVAC curb flashing guide applies.
Permits and paperwork in Burnaby
This is the part that catches owners off guard. A joint can look like maintenance, but in Burnaby it is treated as an alteration to the building.
- Building permit. The City’s guidance says that altering an existing commercial or strata roof needs a formal Building Permit, with sealed drawings by a Registered Professional.
- Strata consent. For strata buildings, a Consent to Construction form signed by the strata corporation is required, because the work affects common property. Missing it commonly stalls the application at review.
- Current code. Applications made on or after March 10, 2025 must comply with the 2024 BC Building Code, which includes seismic requirements under Subsection 4.1.8 that can affect how structural elements on a roof are designed and anchored.
- Letters of Assurance. Field-reviewed projects need Schedule B letters from a Registered Professional (a P.Eng. or architect). The City’s commercial building permit submission checklist shows how heavily the process leans on engineer-signed documents.
If you are a landlord or manager, it helps to understand how these obligations sit alongside tenancy and compliance questions. This list of questions landlords should ask about commercial buildings is a useful reference when you are deciding what to confirm before work starts.
Requirements shift, and some projects fall under different permit streams, so confirm your case with the City of Burnaby and your consultant. We’ve put together a plain-language walkthrough in our Burnaby roof permit application guide.
Who should be at the table
A joint repair that works usually involves several people, and the owner or strata council coordinates them:
| Role | What they contribute |
|---|---|
| Strata council or property manager | Approves scope and budget, signs the Consent to Construction, keeps records |
| Registered Professional (engineer or architect) | Designs for structural movement, seals drawings, provides Letters of Assurance |
| Roofing contractor | Builds the curb, installs the joint and ties it into the membrane, flashing and drains |
| City of Burnaby | Reviews the permit and inspects the work |
Strata councils in particular should avoid starting with a quote for “fixing the leak” and instead ask for an assessment of what the joint is and what movement it has to handle. That one question tends to separate a lasting repair from a repeat visit.
Our perspective
We see Burnaby flat roofs where the membrane is in decent shape and the leak has come back three times, always at the same joint. In those cases, the roof isn’t worn out. The detail was never right for how the building moves.
Our advice is plain. Don’t treat a movement joint as a sealing job. Work out whether it is a true building separation, bring in the right professional where the structure is involved, and have the joint made and installed as a proper assembly with correct curb height, clear drainage paths and a tidy tie-in to the rest of the roof. It costs more thought up front and far less than the fourth patch.
We also encourage owners to look at joints during routine inspections, not only after a leak. Burnaby’s long wet season is hard on any weak seam, and a joint caught while the membrane is only starting to lift is a small job.
— Harman
How Paragon Roofing BC can help
We work on commercial, strata and multifamily roofs across Burnaby and the rest of Metro Vancouver, from inspection and repair to full reroofing. If you suspect a joint is behind a recurring leak, we can look at the roof with you and help you work out the next step, including what a consultant needs to review. See our commercial roofing services or our strata and multifamily roofing services, or get in touch through paragonroofingbc.ca.
FAQ
Can I just reseal a leaking roof expansion joint?
Sometimes a temporary seal buys time, but it rarely lasts, because the joint keeps moving and the sealant keeps cracking. Industry guidance warns that cut-and-patch repairs create weak points. A lasting fix usually means a properly designed and prefabricated joint.
Do I need a permit to repair an expansion joint in Burnaby?
On a commercial or strata roof, altering or installing a joint generally means a Burnaby building permit with sealed drawings by a Registered Professional. For strata buildings, you also need a signed Consent to Construction. Check with the City before work begins, since the answer depends on the scope.
How high should a roof expansion joint sit above the roof?
The ARCA standard asks for the top of the joint curb to extend at least 200 mm (8") above the finished roof surface, with double curb or plate construction fastened on both sides of the separation. Your designer will confirm the details for your roof system.
Can a drain or scupper discharge near an expansion joint?
The joint itself must not have drainage openings through it. Drains should be placed and sloped so water moves away from the joint, which is one reason we check the drainage layout whenever a joint is being repaired.
How often should we inspect the joints on our roof?
At least once a year, and after major storms. Strata corporations and property managers often fold it into a scheduled roof inspection before the wet season starts.
Sources
- Alberta Roofing Contractors Association, BUR Section 2: Control Joints, Perimeters and Penetrations
- ARCA Modified Bitumen Manual, Vegetative Roofing
- SOPREMA, Expansion Joint Design Service
- National Research Council of Canada, publication on roof joints
- City of Burnaby, Home Improvement Permits
- City of Burnaby, Tenant Improvement Permits Informational Guide
- City of Burnaby, Submission Checklist for New Commercial Building Permit
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