Yes, you can use pine subfloors as primary flooring. In many older houses, the pine subfloor was the only floor and it held up well. Uncovered pine subflooring appeals to recycling enthusiasts as well as fans of distressed wood. Drawbacks include a thinner, less-insulated floor and a less-durable surface than other flooring types.
Subflooring is installed when the house is built. It is attached to joists across the foundation or basement and usually extends under the interior walls. Builders who intend to install linoleum, carpet or thinner hardwood over the subflooring usually try to make the subflooring as tight and smooth as possible. Less attention is paid to the look of the surface, since it will be covered over. Plywood replaced pine as the subfloor of American builders' choice sometime in mid-20th century.
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Subflooring as Primary Floor
Leaving the subfloor as the primary floor is cheaper because you do not have to pay for the finished layer of linoleum or sheet vinyl, tile, carpet or hardwood. But as Rick Fitzsimmons, a renovation contractor who has worked in Missouri, Illinois, Ohio and New York, points out, you lose some insulating value if you do not add a finished layer of flooring. Regardless of the material, finished floors do more to block heat and moisture from the basement, Fitzsimmons says. Further, carpet deadens sound and vinyl and tile resist spills.
Hardwood vs. softwood
Conifers like pine and fir are softwoods; deciduous trees like oak and maple are hardwoods. In general, hardwood does not dent as easily, but it also is more difficult to work with. Sawing, nailing and attaching screws are all more difficult. Some hardwoods are so hard you have to use glue, rather than nails. Some deciduous hardwoods, like balsa, for example, are very soft. Some soft woods, like heart pine, are relatively hard.
Wood Hardness Scale
The lumber and flooring industries use various hardness scales to compare types of wood, measuring the amount of pressure needed to dent a piece of wood. As Fitzsimmons and many other professionals working with wood point out, such a scale works best as a comparison between species. For example, it works best when you are comparing the hardness of red oak (a benchmark species for flooring) and heart pine or bamboo. The Wood's the Best website notes that hardness within a species varies, according to the growing conditions of the tree (temperature, moisture, sunlight). Therefore, hardness scale numbers can vary considerably, depending on what boards are used for the testing.
The pine used for subflooring was often Southern longleaf yellow pine, which has a hardness scale of about 870, according to the Janka hardness scale used by the American construction and woodworking industries. In comparison, this same scale rates California redwood at a hardness of 420, African mahogany at 830 and red oak at 1290. Older floors intended to be primary floors were often built with heart pine, which the scale rates at 1250.
Comparing Wood Floors
Sifting through the ad claims of the hardwood flooring industry, heart pine is nearly as hard as red oak, depending on the growing conditions of either species. A better consideration than the species of the wood is looking at how the flooring was installed and how it has held up over time. A yellow pine subfloor that has been covered by linoleum for decades could be in better condition than a bare heart pine floor that's been walked on for decades. Once it is uncovered, the yellow pine will dent more. And both subfloors will be softer than new red oak.
Your Subfloor Could Be an Antique
The website for Grizzly Forest, a flooring manufacturer in South Carolina that also sells reclaimed antique heart pine flooring, describes heart pine flooring in glowing terms: "Originally used to rebuild the South during the last century, ... each plank contains a living history of that time when it was used to build America." Considered in that light, comparing a subfloor of heart pine to new flooring is like comparing an antique to new furniture. You do not choose an antique because it resists water better.