When stripped down to its most fundamental purpose, architecture is about sheltering people from the elements. From this point of view, perhaps the most important part of any building is its roof.

Roofs, on average, last only about half of their designed lifetime. 40% of all building-related problems are due to water intrusion--and water usually intrudes through roofs. Most startling, though, is the fact that, while roofs only make up about 2% of construction costs, water intrusion accounts for more than 70% of construction litigation; roof failures and related fallout are often at the root of the issue. So what's going wrong?

"The most common thing that leads to roof failures is improper installation," says Stan Graveline, vice president of technical services at Sika Sarnafil, a global manufacturer of roofing and waterproofing systems. "The contractor doesn't put the materials on properly and ultimately the roof begins to leak at a joint or seam."

Karen L. Warseck, AIA, president of Building Diagnostics Associates (BDA), a Florida-based firm that specializes in identifying and fixing building-envelope problems, breaks it down further: "Normally we find that it's about 60% to 70% construction, 20% to 25% design, and 10% materials," she says. Her firm has experience to back up her claims. BDA has been involved in 1,500 remediation projects from Alaska to the Bahamas.

There are measures architects and builders can take in the design phase to help prevent roof failure. Here are some common reasons why pros flub roof designs and the ways they can improve their work.

Think in 3D

The conventional set of architectural drawings includes numerous sections. Eventually, though, those sections meet other sections and designers must figure out how the two will meet (i.e., how an edge condition should be flashed to prevent water intrusion). What happens all too often is that architects turn inadequate sectional drawings over to the contractors, who in turn leave it up to a roofing subcontractor to figure it out.