Tags: #buildingdesign #buildingmaterials #buildingproducts #buildingscience #facecolumn #materialsscience #osb #waterresistance

OSB versus Plywood. Here I use face columns to demonstrate what we already know to be true.

At 7.5 inches of water column, we see that water enters through the OSB panel in less than 15 seconds – essentially instantaneously. Though not everywhere, it still finds its path of least resistance. And there it flows. Other leaks emerge over the first hour. And by that time, our OSB sheet is already a hot mess. 

Our plywood panel easily resists this burden and no bulk water is released. The only water that escapes our column is that which flows within longitudinal sections of wood fibers as seen at the top of the column and intermittently at its base.

What’s the point of testing unprotected wood sheathing? To demonstrate their differences. One (OSB) represents porous wood – a matrix of small, cross-oriented wood strands held together by heat-cured adhesives where voids find each other and water flows. The other (plywood) represents veneers of semi-solid wood rolled from logs – its laminate interfaces protected by its fiber ‘guard’.