Here's the thing, once the contractor decided to violate their contract, they lost whatever leverage they acted like they had over you. Now they have none.

In over 30 years as a home inspector and P.E. my father has done expert witness testimony and inspections/reports on dozens of cases where homeowners were scammed, taken advantage of a defrauded of their money. Coincidentally, he used to run a roofing company that specialized in torch-down, flat roofs (mostly commercial because they were located in where there are few residential flat roofs). So when we bought a home with a torch-down flat roof he was really concerned and helpful and gave me a lot of information and things to look for. Also, one of my best friends runs a roofing company. So when we bought our row home I had the privilege of some really helpful people like your uncle.

From your write up it appears Kelbie Roofing ripped you off and possibly perpetrated a breach of contract and potentially fraud. Specifying materials to be used in a contract, and then not using those materials is a breach. If they did that willingly and attempted to conceal it, they potentially defrauded you. If those materials do not meet code, they are in violation of the permit they supposedly pulled.

I don't want this to be misconstrued as I'm wagging a finger at you so please don't take it that way. I understand how these experiences can make you feel humiliated and extorted; that is because you were humiliated and extorted. And this is NOT a reflection on you, it is a reflection on Kelbie Roofing's dubious business practices. You absolutely deserve the proper roof that matches what you paid for and is installed completely to code. And you have the power to make that happen. Regardless of how little leverage they made you feel like you had.

To anyone else reading this; this may be typical of unethical businesses, but it is not and should not be typical of a home improvement/repair contractor.

OSB or particle board is not appropriate for roofing underlayment. But specifically, it's not in your contract.

Other people have pointed you towards Maryland's Home Improvement Commission and I encourage you to talk to them. Before we bought I read the cases involving the GC who did the work on our house. They are there to assist you, the homeowner. Using the improper (and not to code) roof underlayment could mean you or a potentially new owner, will have to replace that roof much sooner. Worse, if you know you have the wrong underlayment you now have to disclose that upon the sale of your home. And that could mean a new buyer requests you replace the entire roof (again) to bring it up to code.

Again, I'm not trying to make you feel worse. You did nothing wrong here. The roofing contractor is in the wrong. It is absolutely worth fighting them over this. Because your new $40,000 roof could end up being $53,000 roof prematurely. I know it all sounds like a giant pain in your ass, but it is well worth it.

Sorry if I went off a bit here but in addition to growing up with a father "in the business" and friends in the business and a BIL in the business of home repair and improvement I've also spent several years doing work for a few different larger home foundation repair contractors with very good reputations. So I understand that good companies doing good work and doing right by their customers are out there. But over the last few decades I've also seen way too many contractors take advantage of decent people by getting them to pour their money into dubious home repairs and improvements. Too often people don't have something like MHIC or they just let it slide. This is definitely worth you taking to the Commission.