Coastal Re-Roof System Selection
A three-story 1920s masonry building two blocks from the Atlantic is being re-roofed. The main roof is framed at 5:12 with 2x10 rafters at 16 in. o.c.; a rear porch roof is 1:12. The owner wants a 30-year appearance, minimal maintenance, and a budget of $48,000 for 4,200 sf. The existing roof is 20-year-old three-tab asphalt with corrosion at galvanized drip edges and many exposed fastener heads. Local code requires a Class A assembly and a 130-mph ultimate wind design. Hail is rare, salt spray is persistent, and the building has no attic ventilation. The contractor proposes architectural asphalt shingles on both roofs with standard galvanized accessories.
1. Which roof areas cannot use the same system, and what performance differences drive the choice?
Read the worked answer
- The 5:12 main roof is steep-slope and can accept a range of shingles, tiles, or metal. The 1:12 porch roof is below the steep-slope range for standard asphalt shingles, so it needs a low-slope membrane such as mod-bit, TPO, EPDM, or an approved specialty product.
- Both roofs still need a Class A assembly, but the porch needs a membrane with positive drainage and membrane-compatible edge metal.
- The transition between the 5:12 and 1:12 areas is a critical flashing condition; do not simply run shingles onto the low-slope roof.
- Selection must be based on slope, wind uplift, salt exposure, and maintenance, not only on the 30-year appearance request.
2. Evaluate the proposed architectural shingles and galvanized accessories. Recommend a practical system and explain the trade-offs.
Read the worked answer
- Architectural shingles can meet Class A and the budget on the main roof, but a generic 30-year shingle is not enough. Specify a manufacturer-approved high-wind installation with enhanced fastening, starter course, and hip/ridge details, and verify the assembly against the 130-mph ultimate design using project uplift pressures.
- Standard galvanized accessories are a weak choice near salt spray. Use aluminum, stainless, or other coastal-rated metals and compatible fasteners; avoid dissimilar-metal contact.
- The $48,000 budget is about $11.43/sf. That may cover tear-off, deck repairs, shingles, and upgraded metals, but not a full standing-seam metal roof. A metal roof would better meet the minimal-maintenance goal but likely exceeds the budget.
- Recommended scheme: high-wind architectural shingle on the main roof with coastal-rated edge metal and fasteners; low-slope membrane on the porch; include deck repair and ventilation allowances in the bid.
3. What project-specific information must be verified before the bid is finalized?
Read the worked answer
- Verify deck condition and attachment: sheathing thickness, rot, fastener pull-through, and whether the 2x10 rafters can receive upgraded fastening.
- Obtain the actual wind-uplift design pressures and confirm manufacturer approvals for the selected assembly, not just a generic wind rating.
- Confirm whether the building is in a historic district and whether visible profiles or materials are restricted.
- Check attic ventilation and whether adding ventilation is feasible; the no-ventilation condition affects moisture performance and shingle warranty.
- Verify disposal, lead paint or asbestos assumptions, and the cost of replacing corroded edge metal and flashings.