Can Oriented Strand Board (OSB) Get Wet?
Dan Webb
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7.31.23
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What is OSB?
Oriented Strand Board, abbreviated as OSB, is one of the most common building materials in the United States. The 4-foot by 8-foot sizing of OSB panels allows it to work well with the 16-inch on-center stud framing of single-family homes for applications like wall sheathing, roof decking, and subflooring.
You can think of OSB as a collection of wood shavings pressed into a panel using industrial adhesives and chemicals. These wood shavings are called strands, and these strands are oriented in a uniform direction to give the panel its strength.
Waterproofing vs. Water Resistance
Firstly, waterproofing and water resistance are terminology that building materials manufacturers use to delineate how well their building materials resist moisture damage. OSB is not waterproof or water resistant. Like most wood-based materials, OSB tends to expand and contract as moisture is wicked into and expelled out of wood fibers.
The wood fibers exposed to the elements swell as they interact with moisture in the air and water droplets. Then, swollen strands break apart from each other in a process called delamination. With the introduction of water between strands, the adhesive that bonds the materials together becomes weaker, causing the sheet of OSB to lose its strength and fail.
The addition of waxes or other additives creates a thin barrier from water damage. Waxes work by coating the board in a thin protective layer, which prevents moisture from interfering with the material in the first place.
Is OSB Waterproof? Our Test Results:
Can OSB get wet? Or is OSB Waterproof? Short answer: No.
We’ve tested conventional OSB alongside a piece of Plantd Structural Panel in a 24-hour soak test. But instead of water, we used one of the most common fluids on a job site: Mountain Dew. We considered other beverages thirsty homebuilding crews prefer, such as Monster Energy and Red Bull. However, Mountain Dew was the most popular in our research and represents a common job site spill.
The results were clear, in a 24-hour test, OSB swells much larger than Plantd materials. In internal laboratory testing, Plantd panels are shown to be 2x more moisture resistant than standard OSB.
At Plantd, we are creating a new type of building material to replace OSB. A carbon-negative building material made from a fast-growing perennial grass. This material is more moisture resistant, stronger, and is made with 71% less carbon emissions.
How to Protect Your Wall Sheathing and Roof Decking
Sealing new construction against the elements is one of the most important steps to take to avoid moisture damage issues on a construction site.
For roofing, it is important for roofers to install an underlayment barrier, commonly called felt paper. This material helps to seal moisture from entering the newly constructed roof.
House wraps provide a barrier for wall sheathing. Like roofing underlayment, house wraps are typically made from synthetic materials like plastics, which have significant embodied carbon emissions. These wraps create a moisture and air-resistant barrier on homes that prevents the newly installed wall sheathing from getting wet.
Sometimes these barriers are ineffective, particularly during thunderstorms with strong winds and heavy rain. In such situations, water may seep through the barriers and cause damage to the timber underneath. At this stage, the moisture resistance of the sheathing or roofing material underneath matters most.
This may not be an issue for homes built with moisture-resistant materials like Plantd Structural Panels. Plantd panels have been tested to retain significant levels of structural integrity, even when soaked in water. With conventional materials, contact with water may risk further damage to the structure or a collapse of the roof itself.
