contract responsiblity question

I hired a contractor to put in a cathederal ceiling in my house. He hired a structural engineer, pulled the permit, removed the old ceiling and put the new cieling up to the ridge line of my roof After it was done the inspector said that the LVL beam that was put up is blocking the ridge vent now and roof venting is needed.
When I called the contractor he tells me that since my contract with him was just for the framing he is not responsible for putting in the new ventilation.
My question is since the venting was fine before the cathederal was put in and he pulled the permit shouldn't he be responsible for fixing the problem identified by the building inspector? btw this is Massachusetts if it matters.
Thanks in advance for any help
Mike McCarthy
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