Hardwood Construction

Hardwood Construction

Comparison chart showing the types of hardwood flooring construction.

Hardwood floors can be installed on any level of your home and are available in multiple constructions to allow for installation flexibility over different subfloors and to mitigate moisture. Identify your subfloor and level of your home to determine what construction of hardwood to install (see chart).

It’s important to take moisture into consideration when you’re installing hardwood floors since changes in moisture can create issues such as warping and gapping. To mitigate the effects of moisture, keep moisture levels within manufacturer recommendations and choose the right construction of hardwood flooring and installation materials. For an added layer of protection against moisture damage, install a moisture barrier.

There are three primary subfloors over which you can install:

  • Basement or concrete below ground level
  • Concrete at ground level
  • Plywood subfloor at or above ground level

There are four constructions of hardwood floors to address each primary type of subfloor.

  • 3/4-inch Solid
  • 5/16-inch Solid
  • Engineered
  • Locking


3/4-inch Solid

This is a 3/4-inch-thick solid piece of hardwood floor and is what you might typically think of for hardwood floors. Because solid floors expand more when exposed to moisture than engineered floors, you can only install them over a plywood subfloor at or above ground level. If you have a crawl space, it’s a good idea to put a moisture barrier underneath the crawl space to help control moisture coming through the ground into your home.

*Most solid floors can be sanded and refinished. Check manufacturer’s warranty.

5/16-inch Solid

This is a thinner version of the 3/4-inch hardwood floor. Since it’s solid, you can’t install it in the basement or on concrete below ground level, but it’s thin enough to glue down to concrete at ground level or install over plywood at or above ground level. Urethane adhesives are required and moisture barriers are recommended for gluing down 5/16-inch solids.

*Most solid floors can be sanded and refinished. Check manufacturer’s warranty.

Engineered Hardwood

Engineered floors are designed for installation over concrete and to help mitigate potential moisture issues. The cross-layer construction prevents the floor from expanding as much as a 3/4-inch or 5/16-inch solid floor when exposed to moisture. Therefore, you can install engineered anywhere in the home, including the basement. Engineered floors are also more environmentally friendly and less expensive than solid floors because the veneer is only a few millimeters thick instead of 3/4-inch thick. The real hardwood veneer of engineered floors differs from laminate, which has a printed paper veneer.

*Some engineered floors can be sanded and refinished. Check manufacturer’s warranty.

Waterproof Hardwood

Waterproof hardwood flooring employs hardwood and bamboo veneers as well as a waterproof core and a proprietary protective coating. This flooring option resists moisture, but still presents the same texture and grain patterns of traditional hardwood, making it a perfect choice for those who are concerned about spills but still want genuine hardwood.

Locking Hardwood

A locking, or floating, floor is an engineered floor, but with the added advantage of a locking tongue-and-groove system. It’s the perfect do-it-yourself flooring solution because nails, staples, and glue are not required. All you have to do is roll out the moisture barrier underlayment and lock the planks into place.

*Some locking floors can be sanded and refinished.


It’s not recommended that you install hardwood flooring in full baths due to fluctuating moisture conditions.

Style Considerations

Room with hardwood flooring.


Finding the right species of wood is really a matter of personal taste and project budget. There are domestic species like oak, maple, and cherry as well as exotic species like bamboo, Brazilian cherry, and cork. Each species has a distinct grain pattern. For example, oak has a very distinguished grain whereas maple is very subtle. Exotics are very popular because of their distinct grain patterns and color.


Most domestic species of wood come in a variety of colors. Most exotic species, on the other hand, are not stained because their natural color is distinctive. Many exotic species are photosensitive and need exposure to sunlight to achieve their desired rich color.


Widths can easily change the look of a floor since the wider the plank, the fewer the seams that can be seen in the floor. Wider widths also showcase the natural beauty of the wood, especially hickory and tigerwood.


There are many types of texture, including smooth, hand-scraped, distressed, and wirebrushed.


Good to Know

You can buy prefinished hardwood floors that are already stained and finished with a coating that is stronger than most site-applied finishes.

Hardness Ratings

Janka hardness chart.

Janka Hardness Rating

The relative hardness of wood species is measured using the Janka Hardness Rating. This test measures the force needed to embed a steel ball (.444 inch in diameter) to half its diameter into the piece of wood being tested. The higher the number, the harder the wood. This means the wood is more resistant to indentations.

Different species also have varying degrees of hardness. Hardwood floors are a natural product and are susceptible to dents (not covered under manufacturer warranties unless specifically stated). If you expect your floors will take a lot of abuse, consider a species at least as hard as red oak based on the hardness chart to the right.

Hardwood Installations

Installation comparison chart.

There are four different ways to install hardwood flooring:

Locking or Floating

This is an excellent do-it-yourself product because nails, staples, and glue are not required. All you have to do is roll out the moisture barrier underlayment for moisture protection and then float the floor over the subfloor by locking the planks together. This type of installation offers the added advantage of allowing the flooring to better expand and contract with humidity.


Gluing involves troweling glue on the floor and setting the planks into the glue. Adhesive systems that incorporate a moisture barrier to help mitigate moisture-related issues are available.


Nailing involves driving a nail at an angle through the tongue of the hardwood floor into the wood subfloor. The nail is then hidden by the groove of the next row of boards.


This is similar to the nailing process, but with staples.

Hardwood Defects

Make sure you know the defect rate of the wood you’re buying. If the rate is over 50%, you’ll need to buy almost twice as much than a wood that’s rated 95% defect-free. Wood with high defect rates can also create issues with installation.

Hardwood Grade

The wood’s appearance determines its grade. All grades can be equally defect free, but each grade offers a distinct look. Clear and select grades are the cleanest looks with minimal knots and color variations. Millwood and cabin grades will allow all the characteristics of the species to show, such as knots, streaks, and color variations.

For more one this.

Fire Engineering

Construction Concerns: Sprayed-on Fireproofing


It has been known for nearly a hundred years that structural steel fails quickly when heated by fire. A short time later, building codes began to require protection of the structural steel in fire-resistive buildings, and rated the levels of protection as it did fire division walls (one-hour, two-hour, and so on).

The earliest forms of protection were to encase the steel columns and beams in terra-cotta (baked clay tile), concrete, or masonry. Later, gypsum plaster applied to wire lath was used, to reduce the weight of the fire protection. Multiple layers of gypsum drywall board were also used to reduce the labor required for installation. This method is still in use today.

Sprayed-on insulations were developed that could meet the Underwriters Laboratories (UL)/American Society for Testing and Materials (ASTM) fire rating tests, and became common after World War II. These materials were lightweight, provided the required heat resistance when tested in the laboratory, required less skilled labor to apply than masonry or plaster, and used asbestos fiber as the insulator and Portland cement or glue as binders.

In the 1970s, asbestos became a health concern, and was replaced in fireproofing by mineral wool and fiberglass. There is still a lot of asbestos out there in our buildings, so gross decontamination by low-pressure hoseline before removing SCBA or other personal protective equipment after interior firefighting is essential.

All sprayed-on fireproofing is not created equal. Those containing Portland cement or other inorganic binders seem more resistant to removal by fire hose streams than other types. The quality of the finished insulation depends on the cleanliness of the surface to which it is applied; the use of the right amount of water in the mixture; and the use of the correct air pressure while spraying.

Photo 1

Photo 1 shows insulation that has been sprayed onto bar joists and the underside of a fire-rated composite steel-and-concrete floor deck. A thicker layer of insulation yields more heat resistance. For higher fire ratings, additional layers can be added. For technical information on the use and application of these products, and UL Directory listings, visit www.cafco.com, the manufacturer of Isolatek and Blaze-Shield products

Photo 2

Photo 2 shows insulation that has been sprayed onto steel columns. The columns are partly exposed either because the surface of the steel (primer paint) was not clean enough, or because the batch was not evenly mixed (wet or dry spots in the spray mixer). These areas, and others like them, will have to be cleaned and resprayed before the building inspector’s next visit.

Any brands or brand names noted above are used only as examples, and the Web sites only as sources of additional information. Reference to them is not an endorsement of either product or manufacturer.

Gregory Havel is a member of the Town of Burlington (WI) Fire Department; retired deputy chief and training officer; and a 30-year veteran of the fire service. He is a Wisconsin-certified fire instructor II and fire officer II, an adjunct instructor in fire service programs at Gateway Technical College, and safety director for Scherrer Construction Co., Inc. Havel has a bachelor’s degree from St. Norbert College and has more than 30 years of experience in facilities management and building construction.

Article and photos by Gregory Havel


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