A.Mark Snyder, a builder who works in Massachusetts and Vermont, responds: Installing new backprimed clapboards over a rainscreen will almost certainly solve the problem of premature paint failure, regardless of whether the house has an interior vapor barrier. If you think an interior vapor barrier is important, you could paint the interior walls with a vapor barrier paint. In addition, the homeowner should know that every house needs adequate mechanical ventilation, both to maintain indoor air quality and to reduce the chance that interior humidity could migrate into the walls.

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