When it comes to flat roofs, timing is everything—especially when rain is in the forecast. Imagine scheduling a long-awaited roof installation only for the skies to open up halfway through. For homes and commercial buildings in Burnaby, where rainfall averages over 1,100 mm annually, this is more common than you might think.
Rain during installation can disrupt work, damage materials, and even void warranties. In this blog, we’ll explore exactly what happens when it rains on flat roofs mid-installation—and what you or your contractor can do to minimize the risks.
Why Rain Is a Big Deal for Flat Roofs During Installation
Unlike sloped roofing, flat roofs lack natural water run-off. That means any rain can linger and pool, especially if the drainage system isn’t in place yet. This standing water can seep into insulation, delay curing times, and lead to structural issues.
Certain roofing materials like EPDM roofing and torch-on roofing are particularly sensitive to moisture. If not installed on a dry surface, their performance—and lifespan—can be compromised from day one.
In regions like Burnaby, where weather shifts rapidly, ignoring these concerns can cause long-term consequences for both residential and commercial roofs. Flat roofs require a more controlled environment during installation compared to traditional pitched systems.
7 Major Issues Caused by Rain During Flat Roofing in Burnaby
1. Water Traps in Insulation Layers
When rainwater seeps into the exposed underlayers of flat roofs, it can get trapped in the insulation. Over time, this moisture leads to mold, rot, and drastically reduced energy efficiency. Moist insulation also creates a breeding ground for bacteria and fungi—especially dangerous in buildings with HVAC systems that circulate indoor air.
Many flat roofs use layered insulation systems that can hide moisture damage for months before any signs appear indoors. Left unchecked, this hidden moisture can compromise structural integrity and require a full tear-off for proper remediation.
2. Adhesion Failure on EPDM Roofing
EPDM roofing relies on adhesives to bond the membrane to the surface. If it rains before the adhesive sets, bubbles and gaps form underneath the material. These weak points often go unnoticed until water damage appears inside the building months later.
This is a major concern for flat roofs, where a single weak point can compromise the entire surface. Adhesion failure can also result in air pockets that allow water to travel beneath the membrane, increasing the area affected by leaks.
3. Improper Sealing of Torch-On Roofing
Torch-on roofing requires a clean, dry surface for the bitumen sheets to bond properly. Rain interferes with the torching process, causing uneven heating and poor adhesion. The result? Higher chances of leaks and significantly reduced roof life.
On flat roofs, where pooling is more likely, even a minor leak can lead to expensive repairs. Improper sealing can also invalidate manufacturer warranties, forcing property owners to shoulder full replacement costs down the line.
4. Project Delays and Cost Overruns
Rain delays mean contractors must halt work, protect exposed areas, and return at another time. These delays can increase labor costs, extend rental periods for equipment, and delay inspections. For large commercial roofs, this can mean thousands of dollars in added costs.
In some cases, installation teams must remove and replace partially installed materials to maintain quality, further increasing project expenses. This is why many professionals prefer scheduling flat roofs in drier months to avoid unnecessary setbacks.
5. Structural Damage to Roof Decking
If rainwater reaches the roof deck—especially when plywood or OSB is exposed—it can cause swelling or warping. This makes it harder to achieve a smooth, level surface for membrane application. Warped decking also compromises roof stability.
In the worst cases, the deck may need to be replaced entirely before roofing can resume, leading to even longer delays. This is particularly risky for older buildings where decking materials may already be weakened or uneven.
How Roofing Experts Protect Commercial Roofs During Rain in Burnaby
Experienced roofers monitor forecasts closely using tools like The Weather Network. Still, even the best planning can’t always stop a sudden downpour.
Here’s how seasoned professionals protect in-progress flat roofs:
- They tarp exposed sections as soon as rain is expected.
- Work is scheduled in weather-safe phases to reduce exposure.
- Contractors use quick-setting products when needed.
- Roof materials are stored off the ground and covered until needed.
These tactics are especially vital in large-scale commercial roofing jobs where unfinished sections span wide, flat surfaces prone to pooling water.
How You Can Prepare for Rain During Flat Roofing in Burnaby
If you’re a homeowner or property manager, don’t leave everything to your contractor. Be proactive.
Here’s what you can do:
- Ask upfront: What happens if it rains during installation?
- Confirm your roofing contractor’s rain protocols and material handling practices.
- Review your contract—look for clauses about weather delays or damage responsibility.
- Choose spring or early summer for projects, when Burnaby sees less rainfall.
And if your building uses EPDM roofing or torch-on roofing, make sure your roofer specializes in those materials. Not every team is skilled in handling weather-sensitive installations.
Professionals who work on flat roofs regularly will have clear plans and waterproofing procedures to keep your structure safe, even during wet surprises.
Long-Term Tips: Flat Roofs and Weather-Ready Maintenance
Once your flat roof is installed, make maintenance a priority—especially in rainy areas like Burnaby. Regular care helps you catch small issues before they turn into expensive repairs.
Here are a few simple but powerful tips to extend the life of flat roofs:
- Clear debris from drains and scuppers monthly to prevent ponding.
- Schedule yearly inspections before and after winter to catch damage early.
- Apply reflective coatings to combat UV and temperature swings.
- Check for blisters, cracks, or standing water after every major storm.
For a complete checklist of preventative steps you can take, explore these 10 Essential Tips for Maintaining Flat Roofs. They’ll help you stay ahead of costly repairs and ensure your roof performs at its best year-round.
Maintenance is often overlooked, but for flat roofs, even small oversights can lead to major damage if water isn’t managed properly.
Final Thoughts: Why Smart Planning Matters for Flat Roofing in Burnaby
Installing flat roofs in a city like Burnaby isn’t just about labor and materials—it’s about timing, weather strategy, and experience. Rain might seem like a temporary nuisance, but when it strikes mid-installation, the ripple effects can last years.Whether it’s a small garage roof or a sprawling commercial roof, never underestimate the importance of preparation. Ask questions. Choose experienced roofers. And don’t rush the job—because for flat roofs, a dry start leads to a durable finish.
