CSLB C-39 Roofing ContractorSafety and RepairMedium
A roofing crew is performing a reroof on a residential building with a complex roofline that includes several valleys. To ensure proper water drainage and prevent leaks, what is the correct sequence for installing the valley underlayment and flashing?
- AInstall shingles, then valley flashing, then valley underlayment.
- BInstall valley underlayment, then valley flashing, then shingles.
- CInstall valley flashing, then valley underlayment, then shingles.
- DInstall shingles, then valley underlayment, then valley flashing.
Show answer & explanationAnswer & explanation
Correct answer: B. Install valley underlayment, then valley flashing, then shingles.
The valley underlayment provides an initial layer of waterproofing and protection to the roof deck in this critical area. The valley flashing, typically metal, is then installed over the underlayment to create a smooth, durable channel for water to flow. Finally, the shingles are installed, overlapping the flashing.
Why the other options are wrong
- A. This sequence is completely incorrect, installing shingles first and underlayment last offers no protection.
- C. Installing flashing before underlayment incorrectly places the primary waterproofing membrane on top of the flashing, compromising protection.
- D. Installing shingles first would cover the area where underlayment and flashing are needed, making proper installation impossible.
Valley Installation Sequence
The correct order of materials installed in a roof valley to ensure effective waterproofing and drainage.
- Underlayment first for deck protection.
- Flashing second for water channel.
- Shingles last, overlapping flashing.
Memory trick: Underneath first, then shine, then cover, and it's fine.