Flat Roof Trouble? Here’s Why They Go Bad (and What a New One Costs)

If you own a rowhome in Philadelphia or the surrounding areas, there’s a good chance you have a flat roof. And if you’ve ever dealt with leaks, ponding water, or bubbles in your roof membrane, you already know how tricky these roofs can be.

At BMG Exteriors, we’ve been working on flat roofs since 1988. We know what causes problems, how to spot issues early, and—most importantly—how to install a flat roof that lasts.

Here’s everything you need to know about why flat roofs fail and what you can expect to pay for a new one.

Why Flat Roofs Start to Fail

Unlike pitched roofs, flat roofs don’t naturally shed water. That means proper installation, drainage, and maintenance are critical—or problems show up fast. Here are the top reasons flat roofs go bad:

1. Ponding Water

Standing water is a flat roof’s biggest enemy. If the roof isn’t pitched properly or the drains are clogged, water collects—and over time, it eats away at seams, penetrations, and membranes.

Tip: After a heavy rain, check your roof. If water sits for more than 48 hours, it’s time for an inspection.

2. Sun Damage & Dry Rot

Flat roofs take a beating from the sun. UV rays dry out roofing materials, causing them to shrink, crack, and split. One common sign is alligatoring—a pattern of surface cracks that looks like reptile skin. Once you see this, your roof is already deteriorating.

3. Poor Flashing & Seams

Flat roofs rely heavily on edge flashings and seam seals. If these aren’t installed correctly—or if they dry out and split—water finds its way in fast. Even a small gap can lead to leaks and interior damage.

4. Foot Traffic & HVAC Units

Most flat roofs in Philly rowhomes have HVAC systems, satellite dishes, or service access. Constant foot traffic and vibration around curbs, pipes, and supports can weaken the membrane and create puncture points over time.

5. Old, Layered-Over Roofs

In Philadelphia, it’s common to find multiple layers of old torch-down or modified bitumen roofing stacked on top of each other. While layering may seem cheaper at first, it often hides existing problems and adds weight your structure wasn’t designed for. If you’ve already got two or more layers, a full tear-off is usually the safest solution.

How Much Does a New Flat Roof Cost?

The cost of a new flat roof depends on several factors:

• Square footage and roof size

• Existing roof condition and number of layers

• The roofing system you choose (modified bitumen, silicone, EPDM, or TPO)

Here’s a general cost breakdown for Philadelphia rowhomes and similar properties:

Flat Roof Type	Estimated Cost
2-Ply Rubber Roof (Tear-Off & Replace)	$6,000 – $10,000
Silicone Restoration (If Eligible)	$3,500 – $6,500
TPO Single-Ply (Tear-Off & Replace)	$10,000 – $15,000+

Pro Tip: We always inspect first to see if a silicone restoration or repair makes sense before recommending a full replacement. We’ll never upsell you on something you don’t need.

What’s Included in Your New Flat Roof

When you hire BMG Exteriors, your project includes:

• Full tear-off (if needed)

• Dumpster & cleanup

• New membrane (modified bitumen, silicone, TPO, or EPDM)

• Flashings, pitch pockets, and vent boots

• Proper drainage solutions

• Full warranties for long-term protection

  
  

Signs It’s Time to Repair or Replace Your Flat Roof

You don’t have to wait for a major leak to call us. Look for these warning signs:

• Ponding water that takes days to drain

• Bubbles, cracks, or seam splitting

• Leaks during heavy rain

• Roof is 15+ years old

• HVAC curbs or pipes leaking at the base

If you’re seeing these issues, it’s time to schedule a free inspection.

Why Homeowners in Philly Trust BMG Exteriors

We’ve been serving Philadelphia, Bucks County, and the tri-state area for over 30 years, and we know flat roofs inside and out. Homeowners choose BMG because:

• Local expertise: We know rowhome flat roofs and city drainage challenges

• Honest assessments: We’ll tell you exactly what’s going on—no gimmicks

• Transparent pricing: No hidden fees, no surprise bills

• Quality workmanship: Installed right the first time, every time

Most of our business comes from referrals, and that speaks for itself.

Don’t Wait for a Leak to Wreck Your Ceiling

Flat roof problems often go unnoticed until it’s too late—and by then, you’re dealing with interior damage, ruined ceilings, and mold.

At BMG Exteriors, we’ll come out, inspect your roof, and give you a no-BS assessment. If a repair or coating will get the job done, we’ll recommend it. If you need a replacement, we’ll show you your options and walk you through every step.