Flashing, Penetrations, Valleys, and Edge Metal Details
Flashing is the test's detail domain: valleys, sidewalls and headwalls, pipe penetrations, and edge metal. The examiner wants the layering sequence and the reason for it, not a memorized sketch.
Core rules
- Water must flow over, not into, a joint. Underlayment goes under counterflashing and over step flashing; step flashing goes under the shingle above and over the shingle below.
- Valley metal should be wide enough for the design flow and secured with cleats or fasteners outside the water path. Shingles are cut back from the valley centerline per the manual.
- Sidewall step flashing is one piece per course, woven with the shingle. Headwalls need a backer or kick-out to divert water.
- Pipe boots must have a flange that laps over the underlayment and under the upslope shingle, with a collar sealed to the pipe. Sealant is a backup, not the primary seal.
- Drip edge at the eave goes under the underlayment; at the rake it goes over. Fasten per schedule and avoid crushing the hem.
Worked example
A 2-in. plumbing vent on a 5:12 roof: install the underlayment, set the boot flange over it, slide the flange under the shingle above and over the shingle below, fasten the flange at its edges, then seal the collar with the approved sealant. The reasoning: the shingle above sheds onto the flange; the flange sheds onto the lower shingle; the collar handles the pipe.
Traps
Relying on sealant instead of layering; fastening through the valley pan; cutting shingles too far back; omitting step flashing at a sidewall; using dissimilar metal; not allowing movement at a headwall.