In a recent Building Science Corporation report, "Drain the Rain...On the Plane ... the drainage plane" Dr. Joe Lstiburek takes us on a deep dive into the mechanics of water managed walls, focusing on the ever-important drainage gaps behind sidings.

In many ways, this piece is a survey of not only of the various materials available to drain a range of siding materials, but of the physical principles that control the easy movement of water through the drainage spaces of various siding assemblies. Many of the principles are similar to what Dr. Joe covered in Water Managed Wall Systems, (Mar/03) and what Ted Cushman aptly summarized of Dr. Joe's work in Robust Walls (Nov/06).

Of course, there are some important changes, beginning with the fact that building codes have come a long way in catching up with building science. ASTM E2273 “Standard Test Method for Determining the Drainage Efficiency of Exterior Insulation and Finish Systems (EIFS) Clad Wall Assemblies” came for a very important reason: To address the rash of EIFS failures. .. And soon to come, Joe writes:

The model building codes (International Building Code, aka “IBC” and the International Residential Code, aka “IRC”) will both have the following requirement for stucco installed over wood based sheathings in the imminent future: “a minimum 3/16 inch space shall be provided between the stucco and water resistive barrier or a space having a drainage efficiency of not less than 90 percent, as measured in accordance with ASTM E2273 or Annex A2 of ASTM E2925, shall be added to the exterior side of the water-resistive barrier.”

Dr. Joe in the bad old days (when JLC was the tag line for New England Builder), around the time he coined the term "drainage plane." (For an explanation of how he came up with this term, read the notes of his recent BSC report).
Dr. Joe in the bad old days (when JLC was the tag line for New England Builder), around the time he coined the term "drainage plane." (For an explanation of how he came up with this term, read the notes of his recent BSC report).

This sea change for stucco aside, what is most fascinating to me is how this latest work of Lstiburek's is the culmination of a long evolution in building science, which JLC was able to document at the beginning by offering a rare platform in 1987 for Joe's article "How Insulation Can Peel Your Paint." As an industry we have come a long way with products, methods and an understanding of how to avoid the worst water problems in walls. And Dr. Joe has been shepherding that journey the whole way.

Read Dr. Joe's latest article here.