Any legally nonconforming building or structure damaged by fire or other accidental or natural cause to the extent of not more than 3/4 of its value at the time of damage, as determined by the Inspector of Buildings, may be reconstructed if rebuilding is commenced within one year and completed within two years from the date of the occurrence, or else such reconstruction must comply with this bylaw. Any change or expansion in total square footage, footprint, or dimensions will require a special permit (or variance, if the proposed change or expansion does not comply with the zoning bylaws) from the Zoning Board of Appeals, upon a finding that such change or expansion will not be substantially more detrimental to the neighborhood than the existing structure.