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Philly Roof Decks

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Roofing under a roof deck in Philadelphia

A roof deck is only as good as the flat roof underneath it. If the roof is near the end of its life, replace it before the deck goes on, not after.

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Why the roof comes first

Once a deck is built, the membrane underneath is hard to inspect and expensive to reach. Philly Home Collective’s cost breakdown includes roofing and waterproofing upgrades of $3,000–$15,000+ as part of a typical project. If your roof is older or has been patched repeatedly, ask the builder whether it should be replaced first.

Philadelphia flat roof costs

ItemAngi, Philadelphia
Average flat roof replacement$4,098 (most pay $2,384–$5,813)
1,000 sq ft flat roof$3,000–$12,000
Materials$4–$12 per sq ft
Labor$3–$8 per sq ft
Tear-off of the old roof$1.50–$5 per sq ft
Structural engineer$350–$690

Membrane types

Angi lists these installed costs per square foot in Philadelphia: EPDM (rubber) $8–$12, TPO $5.50–$7.50, and modified bitumen $3.50–$7.50. Ask the roofer which membranes the deck system’s maker approves, and how the deck’s posts or pedestals will sit on it without puncturing it.

Permits

L&I’s fee schedule lists a roof covering replacement permit for one- and two-family homes at $69. The deck itself is a separate building permit. In historic districts, the City lists “roofing and flashing” among the work that needs Historical Commission review.

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