Keep the Water Out
The most significant threat to the longevity of any house is preventing the incursion of water inside. Consider the house in its immediate environment: It’s connected to the ground and exposed to heat and cold, humidity and dry air, and rain, sun, snow, and wind. It’s protected by an envelope that starts at the roof with shingles, flashing, and gutters, and continues down vertically with siding, windows, and downspouts. The house continues to shed water in its immediate surroundings through surface drainage, and beneath the house with systems that control the entry of water. Signs of water infiltration can be as obvious as water damage to the ceiling (check the roof), or as subtle as a consistently damp basement. Let’s start at the top.
Stains or moss on wood shingles are a sign of trapped moisture. Solutions include better ventilation underneath, or a replacement roof laid over battens that permit air circulation.