7 Serious Risks Rain Brings to Flat Roofs During Installation (And How to Prevent Them)

Why Rain Is a Big Deal for Flat Roofs During Installation

Flat roofs don't naturally let water run off like sloped roofs do. That means any rain can stay there and pool, especially if the drains aren't set up yet. This water can seep into insulation, which can slow down the healing process and cause problems with the structure.

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 the 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 gets into the exposed layers of flat roofs, it can soak into the insulation. Over time, that moisture causes mold, rot, and makes the building less energy-efficient. Wet insulation can also lead to bacteria and fungi, which is risky for buildings with HVAC systems that move air throughout the space.

Flat roofs have layers of insulation that can hide water damage for months before you notice anything inside. If ignored, this trapped moisture can weaken the structure and may even require a full tear-off to fix the damage.

2. Adhesion Failure on EPDM Roofing

EPDM roofing uses glue to stick the membrane to the surface. But if it rains before the glue dries, bubbles and gaps can show up underneath. These weak spots are hard to notice and often don’t show problems until water starts leaking inside the building, sometimes months later.

This is a big problem for flat roofs because even one small weak spot can mess up the whole surface. If the glue doesn't hold well, it can also make air spaces where water can get in and spread under the membrane. That means that even more of the roof could leak.

3. Improper Sealing of Torch-On Roofing

For bitumen sheets to adhere correctly to torch-on roofing, the surface must be dry and clean. Rain disrupts the torching process, resulting in poor adhesion and inconsistent heating. The outcome? Significantly shorter roof life and increased likelihood of leaks.

Even a small leak might result in costly repairs on flat roofs, where pooling is more prone to occur. Additionally, improper sealing may void manufacturer warranties, requiring property owners to pay for future replacements in full.

4. Project Delays and Cost Overruns

Because of weather delays, contractors had to stop working, cover any open areas, and come back later. These delays could mean greater labor costs, lengthier equipment rental times, and inspections that are pushed back. This can cost big businesses thousands of dollars more.

To keep the quality high, installation workers often have to take out and replace parts that have already been put in place. This makes the job even more expensive. Because of this, many professionals prefer to arrange flat roofs during dry months to avoid unnecessary delays.

5. Structural Damage to Roof Decking

Rainwater can cause swelling or warping if it gets to the roof deck, particularly if plywood or OSB is exposed. This makes it more difficult to apply membranes on a flat, smooth surface. Additionally, warped decking jeopardizes the stability of the roof.

In the worst situations, even lengthier delays may result from the deck needing to be completely replaced before roofing can start again. For older structures, where the decking materials may already be deteriorated or uneven, this is especially dangerous.

How Roofing Experts Protect Commercial Roofs During Rain in Burnaby

If you're a homeowner or property manager, don't leave everything to your contractor. Be proactive.

You can do the following:

• Ask right away: What happens if it rains while the job is being done?
• Check with your roofing expert about how they handle materials and how they handle rain.
• Go over your contract again and look for parts that talk about weather delays or who is responsible for damage.
• For projects, spring or early summer are better times because Burnaby gets less rain at those times.

 Also, if your building has EPDM or torch-on roofing, make sure that the roofer you hire is experienced with those types of materials. Not every team knows how to handle projects that are sensitive to weather.

Professionals who work on flat roofs all the time will have clear plans and sealing steps to keep your building safe, even if it rains unexpectedly.

Long-Term Tips: Flat Roofs and Weather-Ready Maintenance

After installing your flat roof, it's important to keep it in good shape, especially if you live in a rainy place like Burnaby. Small problems can be found and fixed before they get too big and cost a lot to fix.

Here are some easy but effective ways to make flat roofs last longer:

• Every month, clean out the drains and scuppers of garbage to keep water from pooling.
• Plan to check your home once a year before and after winter to find damage early.
• To fight UV rays and changes in temperature, use materials that reflect light.
• After every big storm, look for blisters, cracks, or water that is still there.

Check out these 10 Essential Tips for Maintaining Flat Roofs for a full list of steps you can take to keep your roof in good shape. They will help you avoid expensive fixes and keep your roof in good shape all year.

A lot of people forget to do maintenance, but on flat roofs, even small mistakes can cause big problems if water isn't handled 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.