While most people could identify the floor in their homes (I would hope…), many may feel unclear on what the subfloor is. Subflooring is part of the structure of the building itself that the floor is laid on top of. It is sandwiched in between the floor itself and the joists of the building. There are a multitude of common subfloor materials: concrete and plywood are two recognizable ones.
Floors are obviously important, for they give us something for our legs to stand on. Unless there has been a miraculous development in levitation technology that I missed, then floors need something to lean on too. Subfloor comes into play by providing stability for the structure as well as a sturdy base for the floor to attach to.
Alongside the variety of subfloor materials, there are a number of ways to install floors themselves. The quality and material of your subfloor can be critical in determining what type of floor to install and how. Whether you are nailing, gluing, or floating your floors doesn’t just boil down to personal choice. Certain subfloors are more or less compatible with different installation techniques. Just how much weight your floor will be able to carry is completely determinant of how well your floor structure has been designed.
Subfloors that are installed improperly – or using the wrong materials – can cause structural failures, excessive movement, sagging, and squeaking. It is important to be knowledgeable about subfloors before making any big decisions about a new floor.
Keep reading to learn about the 4 most common types of subfloors and the characteristics that determine the quality and long-term performance implications.
Common Subfloor Materials
There are four primary materials used as subfloor: plywood, oriented strand board (OSB), concrete, and high-performance panels.
There are other subfloors materials out there, but they are used in more niche situations. The construction industry is constantly evolving. For example, magnesium oxide (MgO) boards have become a common subfloor type in recent years – as an eco-friendly alternative to concrete, drywall, and other building materials.
We’re getting ahead of ourselves here. New flooring projects can be confusing enough on their own. There’s no need to go down the infinite rabbit hole of construction materials. This helpful guide has narrowed down the most common subfloor types. We’ll break them down one by one so that you’ll have an easier time recognizing your own subfloor material. That way, you can make an informed decision for the future of your flooring project.
Plywood is probably the most common subfloor material out there; in fact, until the 1980s, it was just about the only subfloor used in single-family homes. Plywood is made by layering fabricated sheets of wood veneer and bonding them together with special adhesives under heat and pressure.
Because these layers are cross-laminated and layered, plywood subfloor is solid and not susceptible to the expansion and contraction that hardwood is. Plywood typically comes in interlocking sheets that measure 4-foot by 8-foot and are either 5/8 or ¾ inches thick.
Because these sheets have a tongue and groove that interlock, plywood subfloor makes an incredibly secure base for just about any flooring, including hardwood, laminates, and bamboo. If you are installing new floors and subfloors and choose to go with plywood, remember to apply subfloor adhesive to the top of the floor joists. This will prevent the plywood subfloor itself from moving around and squeaking.
Oriented Strand Board (OSB)
Oriented strand board got its name because it is created by taking strands of 3- to 4-inch wood and layering them in a crossing pattern. They are then glued and pressed, creating a board that is denser and absorbs less water than plywood. Like plywood, installing OSB required the boards to be glued or nailed to the floor joists.
Generally speaking, ¾-inch thick bamboo (solid) floors would be installed right over the top of the ¾-inch thick OSB subfloor, and the planks at a 90-degree angle across the floor joists. This pattern will stabilize and strengthen the whole flooring system.
When installing engineered, solid, or floating that’s less than ½-inch thick, we recommend you add 3/8-inch or ½-inch thick plywood underpayment. This addition, when glued or screwed onto your OSB subfloor, will add stability.
You may think choosing concrete as a subfloor material will solve all your moisture problems, but concrete is susceptible as well. Concrete slabs, which are typically 4 to 6 inches thick and 3,500 – 5,500 –pounds per square inch (psi), are created using water, and they can take months to dry out fully.
Because of this, you will absolutely need to test your slabs before installing your finished floors. An easy way to do this is to tape a few plastic sheets down on several areas of your slabs and wait a few days. If moisture develops under the plastic, your slabs aren’t dry, and your bamboo floors should NOT be installed. To minimize water transfer from natural outdoor water levels, install plastic before pouring your slabs.
It is not always advised that traditional hardwood floors be installed over concrete slabs. In general, concrete subfloors are compatible with wood floors at- or above-grade. In layman’s terms, concrete is a viable subfloor material for hardwood installations on the ground floor or higher.
In contrast, engineered bamboo floors are warranted for installation below-grade. They are moisture resistant and can be easily replaced if they become damaged for any reason. Their rigid core makes them more dimensionally stable than other flooring materials. These are just a few of the traits that set bamboo floors apart for below-grade installations.
Concrete subfloors are primarily suitable for glue-down flooring installations. Floors can also be floated – if the subfloor is properly level. Glue-down methods are more likely to be rendered ineffective by subfloor moisture, so it is important to test properly before attempting to glue new floors.
High-performance panels are becoming more common in buildings. These panels are engineered and offer many of the same plywood and OSB benefits but with some distinct advantages. These boards are built specifically to be moisture-resistant and manufactured with special resins integrated right into the panels.
This significantly reduces water absorption and reduces swelling that is common to plywood and OSB subflooring. These engineered panels not only minimize swelling due to moisture but also cupping, warping, and delaminating. This eliminates any need for sanding or costly replacements.
In addition to standing up to moisture, high-performance panels are also more durable than traditional plywood or OSB underlayment. Thanks to added density and resin technology, the panels are stiffer and stronger and can hold nails better. Panels come in 19/32-inch, 23/32-inch, 7/8-inch, 1-inch, and 1 1/8-inch thickness, and install and remain flat.
Oftentimes when building a home, the subfloor gets installed before the roof does. This means the subfloor will be exposed to the elements and inevitably get wet from snow or rain. Both OSB and plywood will absorb water, leading to the subfloors swelling and requiring either sanding or total replacement before the finish floor can be installed on top.
There are differing opinions on which material stands up better to moisture. Many builders consider OSB to be more structurally sound than plywood. Many others say that OSB edges, particularly edges that have been cut, will swell when exposed to significant amounts of water amounts say that when plywood takes on moisture, it expands evenly throughout the panel, dries quicker, and shrinks its original size quicker than OSB.
Subfloor Installation Management Tips
Assuming you will be installing your bamboo floors over either plywood or OSB, the two most common and affordable subflooring materials, you’ll want to set your moisture meter accordingly and measure by taking at least 20 readings per 1,000 square feet. Compare that level to your new bamboo planks and follow the manufacturer’s guidelines for an acceptable percentage difference between the two.
Should you find areas of your subfloor where moisture may be a concern, consider installing a vapor retarder over your subfloor to minimize moisture transfer and the impact of seasonal humidity fluctuations.
Once you know your moisture levels will not be an issue, you’ll want to check to make sure the subfloor is stable. Check to make sure fasteners are not over or under driven, and fill or sand any uneven joints.
Once your subfloors are properly installed, dry, and stable, you’ll be ready to start laying your new beautiful bamboo planks.
If you have to questions, please contact us!
Last Updated: 1/6/2022