Litigation is best avoided if possible (there is a distinct chance that everybody except the lawyers will be worse off at the end of it), but you could politely point out that the following questions would almost certainly have to be answered at some stage:
Have you studied the manufacturer’s recommendations for installing the type of roof shingles fitted to Mr X’s building, in particular the use of special corrosion resistant roofing nails and the minimum dimensions for nail length, nail head diameter and nail rod diameter?
Have you inspected the installation of roof shingles carried out by your sub-contractor at Mr X’s premises?
Do you agree that your sub-contractor failed to use the manufacturer’s approved fixings and methods when installing the roof covering to Mr X’s building?
Prior to agreement of the contract, did you inform Mr X in writing that work might be carried out using methods contrary to the manufacturer’s published recommendations?
Did you inspect the work during construction to find out whether your sub-contractor was installing the roof covering in accordance with the manufacturer’s recommendations?
Did you at any time instruct, advise or permit your sub-contractor to use any method contrary to the manufacturer’s recommendation?
Have you ever instructed, advised or permitted any sub-contractor to use any methods contrary to the manufacturer’s recommendation?
Have you contacted the manufacture of the roof shingles to inform them of the methods used by you sub-contractor and seek their advice on rectification of the work in order to re-validate the normal warranty?
I suspect his subby was not his normal one, found hurridly to satisfy a customer....id also suggest you make all your communications in writing, phone calls unless recorded are hard to argue what was said.
You need to find a lookalike company and get someone who looks like Matt Alright to go sniffing around their showroom
Joking aside , it sounds like the Director is on your side. At the end of the day, he has a good product that was installed in a rush by muppets who don't care.
You can have the best product in the world, but unless it is installed correctly then its not worth anything. Yes, he will replace the shingles if they come off, but what about any incidental losses ? Will he cover those if the rain comes in and damages stuff inside. You need to keep on his case about getting the roof correctly installed , using the correct fixings.
In my business, I have steelwork fabricated by various companies, then installed by another company ( who do 95% of my installations). If the product is wrong , then its corrected. If the installation is not up to the customers satisfaction ( very very very rare) then its corrected. The customer wouldn't have to justify themselves to me. It would be put right , no questions. This game is all about reputations. People make mistakes ( mostly fabricators ) , but its about what you do to put things right that counts.
My neighbour had his house extension done by a bunch of cowboys. They made their own scaffolding out of the timber they salvaged from wrecking the house and nailed it to my row of trees! When they put the Marley roof tiles on, they didn’t stagger the tiles and laid all the perps in a line because they thought they looked better. I pointed out to the owner that it wasn’t right and may leak. Marley refused to guarantee the tiles unless they were correctly laid. They had to redo the whole roof. When they fitted the staircase the wall was so far out there was a bow of an inch along the stringer.