Hi. Joe D.
This appears to be a roofing installation epidemic, it has been to Ontario and now headed out toward the Ohio Valley. 
:mrgreen: :mrgreen: 
Marcel
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Underlayment is a must and is required by all asphalt shingle manufacturers. From what I understand, the main reason for an underlayment is to help prevent the shingle from “drying out”. It keeps a barrier between the sheathing and the shingle.
Looks like it has felt to me like Ralph said, but Joe sounds sure it’s bare wood. Must be plywood stained from getting wet. We always have shingles falling off roofs here in Ga since the roofers keep nailing them high. Always wanna have felt. Usually you won’t see it on the bottom 4 inches at the gutter line on steep pitched roofs though. This is where they put a toe board on bare decking and start running the felt above it.
Underlayment is usually standard installation procedure and is also required for roofing over bare deck, and is required for a UL Class A fire rating in most cases.
Use “breather type” materials such as Asphalt Saturated Felt or Shingle Underlayment classified by UL as a Prepared Roofing Accessory to assure a Class A fire performance and watertight performance from wind driven rain.
Drip edge is the first thing that is installed at the roof eaves, and then coverd with ice and water shield to within two feet of the exterior wall line. This is suggested in ice back up areas. The drip edge should also be installed over the membrane at the rake edges.
Use of 4 fasteners in normal wind areas.
Use of 6 fasteners in mansard construction or high wind areas.
Fasteners should not be driven into or above the adhesive strip on the shingle.
Hope this helps.
Marcel
Good information from everyone. Thanks.