ALTON — School District voters here approved a $4.2 million plan for renovation, repairs and an addition to the Alton Central School by a 611-340 vote Tuesday. The proposal, which required 60 percent approval, earned 62 percent of the vote. But an article which would have appropriated $500,000 for a $1 million metal roof at Prospect Mountain High School, with the other half of the money coming from Barnstead, fell short of the required 60 percent even though it was supported by a 526-427 majority. Voters did approve a new two-year contract with the Alton teachers by 575-359 vote. The contract adds $96,472 in salary and benefit costs in the first year and $95,599 in the second year.