Lack of building science when building a home or addition can create real horror stories. This home addition has had its share of problems. Outdated wiring, interiors, and fixtures. However, the big problem is water damage, as you might expect from the flat roof and sloping landscape.
Here you can see the overhang has rot caused by lack of gutters and water running over the surface for years. This is amplified by the overhang never getting direct sun to dry it out.
A flat roof does not guarantee a roof leak, but certainly raises the possibility. However, pooling water on that flat roof makes it very likely. As you can see, this home has experienced some neglect that has led to rot, termite, and moisture damage.
To learn more about how building science affects your home, read this blog post.