Attics and roofs that don’t work and why

Taking building investigations and turning them into building science puzzles is fun and informative. In "Attics and roofs that work and why," we learned how to configure high performance attics and roofs. What can we learn from roofs and attics that have had problems? We can learn about tolerances attics and roofs have for heat and moisture management and quite a bit about how to and not to retrofit existing attics and roofs.