Alex, I am very much “down to earth”
Roofers, Roofing Contractors do their trade every day. Very seldom they will measure, read Codes and engineering specifications. They just do what they know how to do. And the lead roofer or contractor is not overlooking all the atrocities that his crew does on-the-job. They are usually in-and-out in ONE day and that is IT…! Whatever you know is way, way more technically supported than what these people do…! Yeah! You may be lucky and you hire the PERFECT academic roofing contractor, but 80 to 90+ % of the time, That is not the case.
So take all this specifications that your InterNACHI peers are giving you and seat down with this fellows and have them understand that you will not give them the final check ($) if they do not listen to you. You are their customer and a Licensed PROFESSIONAL Home Inspector with 100s of Experience inspectors behind your back at InterNACHI.
Take a look at this picture and make an evaluation of the poor quality of a task done by roofing contractors. Another thing to consider is your Gutter/Downspout contractor. If those two contractor do not work in harmony, the will defeat the whole purpose of protecting your home’s roofing and exterior envelope. The height of the gutter in relation to the shingles edge is critical, if too close/tight… it will not fall by gravity and will fly over the gutter and the gutter will not be able to catch the water to take it down the downspout were it should be directed 6 to 10 feet away from the foundations. In a nut shell… You need a contractor with attention to details and with good communication skills that can provide for a harmonic holistic integration of your gutter, downspout, drip edge, fascia, shingles, underlayment, and so on…!
In this picture you can see how critical is the engagement of the drip edge, the underlayment of the roof, the shingles and the gutter.
The shingles are within the 2" per code, but if it rains hard, the storm waters will overshot the gutter. Usually most 100% contractor use the less expensive gutter. A wider gutter will ensure the roof running storm water does not fly over the gutter. Depending on the overall surface (sq2 feet) of the roof, the water collected during astorm may or may not exceed the volume that the gutter can handle. If the installer of the gutter or roofer does not carefully install each part of this system properly, out of plumb, for example, not sufficient retainers, the weight of the water itself will separate the gutter from the fascia que the drip edge will loose all purpose.