Can a Massachusetts condo HOA be held responsible for inside mold remediation due to suspected water seepage of a roof?
How great of a burden would it be on the home owner to prove it came from the exterior?
1) That all depends on your lease contract or ownership contract with the HOA. You need to carefully read it, or find legal representation who can read it and advise you on if the HOA may or may not be liable. Ask a lawyer, or check Mass Legal Services to see if you qualify for legal aid.
2) You will probably need to have a third party examine the roof, i.e. one or more licensed (bonded and insured) roofing contractors who can make written determinations. But that course of action will depend on the advice of your legal representation, who can tell you what will be useful in a legal action (if you go that route); and if the HOA even allows third party contractors to evaluate the property, as they may require their own contractors to be used.