Lifting a shingle course you find the shingles nailed directly to the wood structural panel deck, with no underlayment of any kind between them. What is the correct finding?
- AAccept it; underlayment is required only on slopes below 4 units vertical in 12 units horizontal
The slope threshold changes the number of underlayment layers, from one on steeper roofs to two on shallow ones. It does not remove the requirement for a steep roof.
- BAccept it; self-sealing shingles form a continuous membrane once the tabs seal in warm weather
A sealed shingle field is not a membrane. Water routinely gets behind shingles in wind-driven rain and at every fastener, which is what the underlayment is there to handle.
- Reject it; underlayment is required beneath the roof covering, so this work has to be lifted and redone
- DReject it; the deck must be covered with an ice barrier over its entire area before shingles are applied
Ice barriers are required in specified climates along the eaves and at other vulnerable locations, not over the whole roof. Requiring full coverage confuses a targeted requirement with the general underlayment rule.
Why C is correct
Underlayment is required under the roof covering at all slopes. What changes with slope is the number of layers and how they are applied, not whether underlayment is needed. The shingles already laid must come off and be reinstalled over underlayment.
What this question is testing
Whether the candidate knows underlayment is required at all slopes, understands what changes with slope, and does not confuse the general requirement with the targeted ice barrier provisions.
On the job
This is rare but it happens on small jobs and owner work, and it is caught by lifting a course at the rake. Once caught, the conversation is unpleasant because the correction means removing shingles that are already fastened and, in warm weather, already sealed. Where only a portion is done, catching it early is the difference between one square and the whole roof.
Memory technique
One layer steep, two layers shallow, never none.
Exam tip
Underlayment is always required. Slope decides how many layers, not whether.
Where to look it up
IRC Chapter 9, roof coverings, the underlayment requirements for asphalt shingles.