POV Photos – Benchmarking OSB/Foam Sheathing Moisture Performance

Originally published by the following source: SBC MagazineJuly 24, 2019
by SBCRI Staff with contributions by Professional Engineers working with SBCRI


The following nine photos provide an excellent side-by-side example of the same residential wall system, including the same windows, flashing, stud type, interior vapor barrier, and cladding system. The only difference between the various sections of the wall is the two different sheathing systems.

The photos represent a rare occurrence: a real-world moisture performance comparison.

For one section of the wall, OSB sheathing was attached directly to the studs. For the other section, foam sheathing was directly attached to the studs. Everything else was identical.

Readers have (correctly) responded with the following comments:

  1. The windows do not appear to be properly flashed.
  2. Caulking is likely poorly done.
  3. There does not appear to be a proper water resistive barrier present.
  4. These photos, based on a hunch given insufficient information, show that there seems to be a pattern: the portions of these walls with foam sheathing had comparatively little or no water damage. This is assuming that the house was constructed with intermittent bracing and foam sheathing between. This is also a tall window wall prescriptive bracing non-compliance.

These are all simple, yet accurate, observations and follow an evaluation founded in common sense.

As the exterior cladding is removed so that the walls of this home can be remediated, the deconstruction and reconstruction process will be used as a case study on cladding, window and moisture performance.

For anyone who has been involved in serious exterior wall assembly degradation litigation in Florida, it is very clear that the application of proper building science principles is a key to durable wall performance. And this particular wall assembly makes it possible to compare, firsthand, the difference in performance of OSB sheathing and foam sheathing.

Stay tuned for the next installment when the rehabilitation is underway.

For more information on thermal performance, moisture protection and vapor barriers, visit Continuousinsulation.org.