PROJECT RUNDOWN
Due to its deteriorating condition, the asphalt roll roofing on this ADU required replacement before the Fall rains. Asphalt roll roofing generally lasts only 5-10 years, leading to ongoing maintenance challenges. The original 1×10 sheathing showed significant sagging in several spots, resulting in standing water not suitable for asphalt. Additionally, there was a complete absence of ventilation after improper installation of R-21 fiberglass insulation, leaving no air gap between the sheathing and insulation. A noticeable hump along the center of the roof indicated that the load-bearing wall had been supporting that section since construction, contributing to light sagging between the walls.
OUT WITH THE OLD
The old roof was completely removed down to the joists, revealing a solid base for the new installation. The central hump was eliminated by shaving the high point along that line. 2×6 beams were ripped in half then nailed on top of the existing joists, creating a 1.5″ gap for insulation and providing strong attachment points for the OSB sheathing, which was secured with screws to prevent any potential issues with nail heads popping through over the roof’s expected lifespan of over 50 years. The EPDM membrane was then adhered using glue and contact cement along the edges of each sheet, with the ends folded over the roof edges and secured with termination bars. Drip edge flashing was added and taped to ensure a water-tight seal, and EPDM-safe caulking was applied over the seams for additional protection. Finally, all exposed wood was primed and painted.
OLD VS NEW
The new roof features a 60mil commercial-grade EPDM rubber membrane, offering a lifespan exceeding 50 years, in stark contrast to the 5-10 year lifespan of asphalt roll roofing.
Using two sheets of EPDM for installation streamlined the process, resulting in one single seam across the entire roof, compared to the asphalt roll’s dimensions of 3 feet wide by 33 feet long, which created 8 vertical seams and 9 horizontal seams—significantly increasing the risk of leakage and failure. Wrapping the rubber over the edge of the roof effectively addressed concerns about water infiltration at the edges, an issue prevalent with the asphalt and drip edge interface.
Another benefit to removing the splitting 1×10 decking and replacing it with OSB sheathing is the increase in structural integrity, moisture resistance, longevity and consistency.
AT THE END OF THE DAY
The project successfully transformed the ADU’s roof from a maintenance-prone asphalt roll system to a highly durable 60mil EPDM rubber membrane. By addressing critical structural issues, including sagging sheathing and inadequate ventilation, the team ensured that the new roof not only offers superior water resistance and longevity but also meets higher performance standards for insulation and durability. The replacement process eliminated common weak points, such as numerous seams and poor edge sealing, which were vulnerabilities in the old roofing system. The result is a streamlined, secure installation that provides peace of mind and long-term value, with a lifespan extending well beyond the original roof.
