Flat roof vs pitched roof on a South Philly rowhome: which materials win?

The two-system reality of South Philly rowhomes

A typical South Philadelphia rowhome built between 1890 and 1925 has two roof systems on one property:

• Front pitched roof — sloped, visible from the street, typically covered in asphalt shingles (since the mid-20th century re-roofs replaced original slate or wood shake). This handles the front 30-50% of the roof area.
• Flat or low-slope rear roof — covers the rear addition built behind the original house, holding a kitchen, bathroom, or back room. Pitched at 1-3 degrees, drains to a scupper or downspout. Covered in membrane material (EPDM, TPO, or modified bitumen). This is where most leaks start.

Pitched front roof — material options

Four materials are common on South Philly pitched front roofs. Costs are roughly per 100 sq ft installed:

• 3-tab asphalt shingle ($150-$250 per 100 sq ft) — cheapest, 15-20 year lifespan. Functional but not premium. The kind of roof a flip-and-sell renovation uses.
• Architectural asphalt shingle ($300-$500 per 100 sq ft) — the standard South Philly upgrade. Thicker, longer warranties (30-50 years available), better wind resistance. This is what 80% of South Philly replacements use.
• Slate ($1,500-$3,000 per 100 sq ft) — premium, 75-100+ year lifespan, but rare on South Philly. A few Queen Village and Bella Vista properties still have original slate; restoration runs $25,000-$50,000+ for a full roof. Replacement with new slate is dramatically more expensive than re-shingling.
• Standing-seam metal ($800-$1,400 per 100 sq ft) — premium aesthetic, 50+ year lifespan, increasingly popular on Graduate Hospital and Point Breeze infill builds. Heavier than shingle, requires confirmed deck support.

Flat rear addition — material options

Flat-roof membrane choice matters more than pitched-roof shingle choice because the flat section is where most leaks happen. Three systems dominate:

• EPDM ($400-$700 per 100 sq ft installed) — black rubber membrane, 20-30 year lifespan, durable and forgiving of detail work. The South Philly default for rear additions. Good for shaded properties where heat reflection doesn't matter much.
• TPO ($500-$900 per 100 sq ft installed) — white heat-welded membrane, 20-30 year lifespan, reflects summer heat. Better if your top-floor bedroom bakes in summer. Slightly more sensitive to installer skill (heat-welding seams correctly matters).
• Modified bitumen ($300-$500 per 100 sq ft installed) — torch-down or peel-and-stick membrane, 12-18 year lifespan. Cheaper upfront but shorter-lived. Common on older South Philly installs but being phased out in new work.

Which combination works for your property?

Three common pairings:

• Architectural shingle + EPDM — the South Philly default. Reliable 25-30 year combined system, ~$14,000-$22,000 installed on a typical 1,000 sq ft rowhome. Right for 80% of properties.
• Architectural shingle + TPO — same upgrade tier with better summer thermal performance. Adds $500-$1,500 to the rear-addition cost. Worth it if your top-floor faces south or west and gets uncomfortably hot in summer.
• Metal standing-seam + TPO — premium pairing for new builds and gut-renovated properties. Both systems reflect heat, both last 50+ years. Total cost on a typical rowhome: $28,000-$40,000.

Getting both replaced together

The transition between the pitched front and the flat rear is where most leaks originate after a piecemeal replacement. Doing both sections in a single coordinated project ensures the transition is flashed properly the first time.

If your budget only allows one section now, replace the one that's actively leaking or visibly failing. Most of the time that's the flat rear addition. Defer the front by 1-2 years if it has more remaining life. Just don't expect the contractor to give you a discount on the second job when you come back — pricing is roughly the same either way.