Using particle board instead of wood in foundational work can result in major problems. Particle board, sometime used as a less-expensive alternative to plywood, takes the wood conservation inherent in plywood manufacture a step further. Because of particle board’s tendency to absorb water and swell, however, it’s not commonly used in home-building, and should never be used as a structural element. Just as the name implies, particle board is created by taking particles of wood (saw dust), gluing them together, and forming a uniform slab of material.
Plywood is made by pressing sheets of wood together so the grain in each sheet is perpendicular to the grain in the sheet above and below it. Before lumber makers began producing plywood and particleboard, planks of solid wood were used as sub-flooring and exterior wall sheathing (the later provides shear strength, which keeps the house from racking side to side). Particle board is cheaper to produce than laminated plywood, hence its popularity with some home-builders and mobile home manufacturers.
Unlike solid wood, however, which rots and becomes useless only after an extended exposure to water, particle board often is held together by water-soluble resin; so, once it gets wet, it swells and disintegrates.
Particle board is used when a smooth surface is more important than strength. For example, less-expensive kitchen cabinets are often made of particle board (underneath an oak or cherry veneer), as are many enclosures for electronic equipment, such as televisions. Countertops are often made of particle board beneath Formica or some other water-resistant material. Consequently, if the water-proof material gets a crack or a hole in it, water will find its way to the particle board and make it swell.
Assemble-it-yourself furniture is often made of particle board. Extended length surfaces of such furniture, such as shelves and desk tops, easily and quickly develop deflection, or sag, because particle board has no grain. It is particularly unwise to use particle board in construction of bathrooms and kitchens. If water spills from the tub or sink and finds its way to the edge of the vinyl or linoleum covering, it will get to the particle board and cause it to swell.
If particle board is used as a floor underlayment and gets wet, ripples or humps will appear in the floor. The damaging water doesn’t have to come from a catastrophic source, such as a water leak or a bathtub overflow. If the crawl space of a home is damp, water vapor can rise in the particle board and cause ripples.
Despite its drawbacks, some home-builders use particle board as a floor underlayment. Some of its advantages are that it provides a smooth, uniformly thick, solid base (free of knots, voids or grain) and adhesives spread easily and evenly over the smooth panel surfaces. Particle board panels are made to resist impact or denting. The panels are easy to cut with ordinary hand and power tools. Most building codes approve particle board as a floor underlayment.
The subfloor on which it is applied must be of wood construction, dry, level, securely nailed and free of all foreign matter and projections. Ground level in basementless spaces should be at least 18 inches below the bottom of the floor joists.
Never apply particle board underlayment over concrete or below grade.
A vapor barrier with a maximum rating of 1.0 perm should be used over board subfloors and as a ground cover in all basementless spaces.
Start laying the panels at a corner of the room. Leave a 3/8-inch gap between underlayment and walls. Arrange panels such that four panel corners do not meet at any one point. Butt panel edges and ends to a light contact.