Why It’s So Important to Properly Clean and Prep a Roof Before Installing New Material 

If you’re managing a commercial building, one of the most frustrating (and expensive) surprises you can run into is when a brand-new roofing system fails early—not because of the materials, but because the surface wasn’t cleaned or prepped correctly before installation. 

We get it. When there’s a leak or visible roof damage, you want it fixed fast. But skipping steps in roof prep to save time can cost you much more in the long run. At Weather Shield Roofing Systems, we’ve been helping businesses protect their commercial roofing investments for over 40 years. One of the most common causes of premature roof failure we see? Inadequate prep work. 

Take a look at the before and after photo below. The left image shows a roof drain area before proper cleaning and prep. The right side shows the same area after thorough cleaning and new membrane installation. The difference isn’t just visual—it’s structural, functional, and long-term. 

Let’s break down why cleaning and preparation matter so much before applying new roofing material. 

What happens if you skip cleaning before roof installation? 

Think of your roof like a paint job. If you paint over dirt, rust, or grease, the paint won’t stick well, and the same goes for roofing membranes or coatings. If dirt, debris, or leftover adhesive is left under new material, it can cause: 

• Poor adhesion: New roofing material won’t bond properly, especially single-ply membranes like TPO or PVC. 

• Trapped moisture: Moisture left behind can cause blistering, mold, or corrosion under the new layer. 

• Punctures and wear: Debris beneath the new roof creates pressure points that can wear through over time. 

• Drainage problems: As shown in the “before” photo, clogged or obstructed drains can cause pooling water and roof leaks. 

• Shortened roof lifespan: You might only get half the life expectancy you paid for. 

What does proper roof prep involve? 

Good roof prep goes beyond just sweeping the surface. Here’s what a thorough cleaning and prep process typically includes: 

1. Removing debris and loose material 

All dirt, leaves, insulation, and broken materials must be completely removed. Leftover roofing pieces or drain screens like those in the “before” photo can create weak spots in your new roof. 

2. Cleaning oil, grease, or contaminants 

Commercial roofs, especially near HVAC systems, can accumulate oils and contaminants that prevent adhesion. These must be cleaned with proper solvents or degreasers. 

3. Inspecting for water damage 

Before new roofing is applied, the existing deck should be inspected for moisture. Wet insulation or decking can rot from the inside out. 

4. Checking drainage systems 

Drains, scuppers, and gutters must be cleared and repaired as needed. In the after photo, you can see how much cleaner and structurally sound the drains look, which helps prevent future ponding issues. 

5. Priming and prepping the surface 

Depending on the type of roofing material, a primer or bonding agent may be needed to ensure full adhesion. 

Proper roof prep saves you money 

It may feel like an extra step, but proper cleaning and prep actually protect your roof investment. Here’s how: 

• Fewer leaks: A well-prepped surface helps prevent common leak sources. 

• Longer roof lifespan: When materials adhere correctly and the roof drains properly, you get the full life out of your commercial roofing system. 

• Warranty protection: Manufacturers often require proper prep as a condition of their warranties. Skipping this can void your coverage. 

• Avoid costly repairs: Poor prep often means costly rework within a few years—or even sooner. 

Is prep different depending on the type of roofing system? 

Yes. Each roofing material has specific prep needs: 

• TPO/PVC Roofing: Requires a clean, smooth surface and often a primer for full adhesion. 

• Modified Bitumen: Needs a level, dry surface and secure base sheet. 

• EPDM: Extremely sensitive to dirt, dust, and oil—cleaning is critical. 

• Metal roofing overlays: Often require special insulation or barriers to reduce condensation and improve adherence. 

No matter the system, proper prep is never optional if you want long-term performance. 

How do I know if my roofing contractor is doing proper prep work? 

Great question. Ask these before any roofing job: 

• What’s your cleaning and prep process before installation? 

• Do you inspect the substrate and deck for water damage? 

• Will you photograph and document the condition before and after prep? 

• Are your methods approved by the manufacturer for warranty purposes? 

At Weather Shield, we make this process transparent. We show you exactly what we’re seeing, explain our process, and never skip steps that protect your roof. 

Skipping surface prep might save a little time upfront, but it can cost a lot more in repairs, replacements, and headaches down the road. Your commercial roof is a long-term investment. Give it the foundation it deserves. 

At Weather Shield Roofing Systems, we believe in doing things right the first time. Our commitment to proper roof inspections, prep, and installation helps you avoid emergency roof repairs, extend your roof lifespan, and protect your building and budget. 

Need help with a roof inspection or repair? Contact Weather Shield today to schedule a visit. We’re here to help you get the most out of your commercial roofing system. 

Sir Maximus Shield

Sir Maximus Shield is the noble protector of rooftops far and wide—a knight forged from Weather Shield craftsmanship and unwavering integrity. From the battlements of factories to the towers of office parks, he stands guard against leaks, storms, and time itself. His quest is simple: to defend every commercial roof with honor, precision, and lasting strength. When he’s not patrolling the skyline, Sir Maximus shares his chronicles of durability, innovation, and the noble pursuit of maximum protection. One roof at a time.