The roof is a topic of much discussion during the home inspection process, and understandably so. If you think of the home as a system made up of many components, then the roof plays an important role – it protects everything else below it! What’s worse is that the roof can often be partially or completely out of view of the homeowner, making it difficult to assess the condition and make decisions on repair or replacement. In this post I share some information on roof performance, its components, and some of the common conditions we find on older roofs.
Roof Design and Performance
What’s important to understand about roofs is that they are not meant to be waterproof. This may come as a surprise, but in fact they are designed to be “shedding” system, as opposed to a watertight membrane. Think of this like duck feathers, the water lands on the feather and beads off, but the duck would still get wet if it were completely submerged! Shingles are generally laid over felt paper and a plywood backing. They start at the bottom and each subsequent row overlaps the lower one by a few inches. This allows water to fall on the roof and run down to the soffit or gutter, but stops it from backing up under the shingle above. If water sits or pools on the roof in any location, then it will likely run up under the shingles and into the plywood sheathing or attic space.