Wood Floor Finishes
The Lowdown on Low VOC Finishes

An increasing amount of information is available to the public on air quality issues, including the possible negative effects of off-gassing of volatile chemicals. Indoor air quality has become important to many designers and specifiers, including those that specify wood flooring.

In construction, the maximum concentration of VOCs (volatile organic compounds) is often specified by LEED, the U.S. Green Building Council, and many other federal and state/provincial authorities. The maximum allowable limits for VOC emissions include all the materials that can give off VOCs including paints, carpets, millwork, etc., and may limit the type of finish that can be used on the floors so that it fits within the specified limits.

VOCs are emitted as gases from certain solids or liquids such as paints, varnishes, cleaning agents, cosmetics, degreasers, and hobby products. If the end-user has chosen safe indoor air quality as a priority, it is important to educate them about other potentially harmful products that they may be using already, and perhaps suggest more favorable options.

Traditionally, the most popular finishes used in floor finishing contained VOC content as high as 750g/L. Government regulations have required manufacturers of finishes to change formulations to become more VOC-compliant over the last few years. These regulations vary from state-to-state and can be as high as 550g/L and as low as 275g/L. In order to achieve compliance, many manufacturers have had to substitute different components than what was traditionally used. The effect has been that finishes have become more expensive to produce and, in some cases, the ease of application has been compromised.

Choosing a finish becomes a real balancing act with many factors to consider. Typically, the end-user’s main concerns are appearance, longevity, maintenance, and air quality. There are many types of finishes that may be beneficial in some respect and a hindrance in others.

Conversion varnish, a film-forming finish that is durable and easily maintained, offers incredible clarity and enhances the color of the floor. Conversion varnish and varnish finishes fall within their own category for VOC regulations in most states. VOC levels may fall within the limit of 725g/L. VOC restrictions have limited the use of these finishes in some parts of the U.S.

Moisture-cured urethanes are usually applied in commercial settings such as roller rinks and gymnasiums. They offer excellent clarity and depth, are extremely durable, and easily maintained. The solvents used in this type of finish are dangerous and require adequate ventilation, the use of a respirator, and other safety precautions. This finish falls
within the wood coating category and may have levels around 550-700g/L.

Although conversion varnishes and moisture-cured urethanes are higher in VOCs at the time of application, an argument can be made that, due to their durability, this type of floor finish will not require refinishing as often as other types of finish.

Oil-modified polyurethane (OMU) is one of the most widely used finishes. This type of finish is amber in color and forms a thick film build that enhances the depth and color of the flooring. It will continue to amber out from the effects of oxidation and UV rays, so the floor will take on a yellowish cast as the floor ages. OMUs historically have been the most popular finishes that flooring contractors have used due to ease of application, flow, and leveling properties. For these reasons, contractors that have been using OMUs for a long time may be reluctant to use other types of finishes. Floor finish manufacturers recognize that many contractors prefer to use this type of finish, so have had to constantly tweak their formulations to comply with the VOC laws that vary from state to state. VOC regulations have limited use of some of these finishes in some parts of the U.S. VOC levels vary from
>275 up to 550 g/L within this product category.

Waterborne urethanes are very common finishes used in our trade. The reason for their popularity is largely due to using water as a carrier instead of solvents, so their VOC levels are inherently lower. Their appearance is similar to the finishes already discussed, and
they don’t amber out to the same degree. Some of the waterborne finishes have been limited to use in some parts of the U.S. due to VOC regulations. VOC levels vary from 0 to 450 g/L within this product category.

Natural oils and hardwax oils have seen a real increase in popularity. Many of these products state that they contain 0 g/L VOCs. Natural oils and hardwax oils use oils such as linseed or vegetable oils. These finishes have a distinct appearance that suits wide plank rustic flooring, which has become a very popular look. These finishes have a very low luster look that brings out the natural character of the wood but offers little to no sheen. This type of finish does not have a visible film and protects the surface of the flooring by bonding itself to the wood fiber. VOC levels can vary depending on the product and manufacturer.

There are a number of factors that contractors and end-users must consider before choosing any finish. The trick is to educate everyone involved as to what options are available in order to achieve the best balance between the look the end-user wants, the suitability of the finish to their lifestyle, and the impact on indoor air quality.

Kjell Nymark is Technical Advisor at the National Wood Flooring Association in St. Louis. He can be reached at kjell.nymark@nwfa.org.

CHAPTER 1

JOBSITE CONDITIONS Part I – Minimum Jobsite Requirements

Chapter 1 – Jobsite Conditions

A. Wood flooring should be one of the last jobs completed on the construction project. Limit foot traffic on finished wood flooring.

B. Evaluate the jobsite for potential problems before installation begins, and before wood flooring is delivered to the jobsite.

C. Unless a waiver or letter of protest listing exceptions exists, installation constitutes acceptance of subfloor/substrate, the jobsite itself – including the ambient temperature and relative humidity at the time of installation, and all impacting variables that may affect a wood floor.

1. Surface drainage should direct water away from the building.

2. Do not deliver wood flooring to the jobsite or install wood flooring until the building is enclosed.

3. If heating and/or air-conditioning is in operating condition, it needs to be operating. If it is not possible for the permanent heating and/or air-conditioning system to be operating before, during and after installation, a temporary heating and/or dehumidification system that mimics normal temperature and humidity conditions can enable the installation to proceed until the permanent heating and/or air-conditioning system is operating.

4. Do not deliver wood flooring to the jobsite or install wood flooring until appropriate temperature and humidity conditions have been achieved. Appropriate temperature and humidity conditions are defined as those conditions to be experienced in the building after occupancy.

5. Do not deliver wood flooring to the jobsite or install wood flooring until all concrete, masonry, plastering, drywall, texturing and painting primer coats are completed.

6. Basements and crawl spaces must be dry. If power washing is required in the basement, do so before wood flooring is installed and allow subfloor and basement to dry before installing wood flooring.

7. Crawl space should be a minimum of 18” (457mm) from ground to underside of joists.

8. Crawl space earth (or thin concrete slab) should be covered 100 percent by a vapor retarder of black polyethylene (minimum 6 mil) or any recommended puncture-resistant membrane, such as Class C, meeting ASTM D-1745. See Figure 1-1.

Chapter 1 – Jobsite Conditions

9. Crawl Space Conditions

a. Where a proper ground

covering is in place and

when venting is

required by local

building codes, the

crawl space should

have perimeter venting

equal to a minimum of

1.5 square feet per 100

square feet of crawl

space square footage,

unless local building

codes differ from this

specification. Note:

Local-building codes may differ. Follow local building codes.

b. For crawl spaces without ventilation openings, vapor retarder joints must k a minimum of 6 inches and be sealed or taped. The vapor retarder should also extend at least 6 inches up the stem wall and be attached and sealed to the stem wall. Continuously operated mechanical exhaust and perimeter wall insulation or conditioned air supply and insulation must be provided.

10. Note the grade level so that the correct type of flooring and system can be specified for the job. Engineered and floating floors can be appropriate for above-grade, on-grade and below-grade installations. Solid wood flooring can be appropriate for above-grade and on- grade installations, but not for below- grade installations. If the soil surrounding a structure is 3 inches or more above the floor of any level, consider that level below grade. This includes walk-out basements. In addition, the surrounding soil should be sloped away from the structure. See Figure 1-2.

11. Subfloors (wood or concrete) should be

checked by an appropriate method for

establishing moisture content. Average

subfloor moisture content should be

within the range as specified for the product by the product manufacturer. See Chapter 3, Moisture Testing.

12. Where the minimum jobsite conditions are present, the flooring can be delivered and stored in the rooms in which it will be installed. See Chapter 2, Acclimation.

Part III – Jobsite Checklist

See Appendix M

CHAPTER 2 ACCLIMATION

ALWAYS FOLLOW THE MANUFACTURERS’ RECOMMENDATIONS REGARDING HOW AND WHETHER TO ACCLIMATE WOOD FLOORING.

Part I – General Acclimation Guidelines

(For a more detailed discussion of acclimation issues, See Appendix B.)

A. Storage and Conditions

1. Do not store wood flooring at the jobsite under uncontrolled climate conditions. Garages and exterior patios, for example, are not acceptable areas to store wood flooring.

2. Ideal interior climate conditions vary from region to region and jobsite to jobsite. It is your responsibility to know what your “ideal” climate conditions are and build your floor around those conditions. For a general view of moisture-content averages by region, refer to Appendix D and Appendix E.

B. Acclimation

Note: Some manufacturers do not require acclimation for certain products prior to installation. If the manufacturer recommends that the wood flooring be acclimated before installation, proceed as follows:

1. Ensure that the building is enclosed.

2. Verify that the building is maintained at normal living conditions for temperature and humidity.

3. Where building codes allow, permanent heating and/or air-conditioning systems should be operating at least five days preceding installation to promote proper acclimation. For radiant heat see Appendix H.

4. If it is not possible for the permanent heating and/or air-conditioning system to be operating before, during and after installation, a temporary heating and/or dehumidification system that mimics normal temperature and humidity conditions can enable the installation to proceed until the permanent heating and/or air-conditioning system is operating.

5. Upon delivery, check wood flooring moisture content with a moisture meter to establish a baseline for required acclimation. Check the moisture content of multiple boards. A good representative sample is typically 40 boards for every 1,000 square feet of flooring. Acclimate to manufacturer’s recommendations or as necessary according to geographical location and your jobsite location.

6. Prior to installation, ensure that wood flooring is within acceptable range of moisture content with the wood subfloor. For solid strip flooring (less than 3” wide), there should be no more than 4 percent moisture content difference between properly acclimated wood flooring and subflooring materials. For wide-width solid flooring (3” or wider), there should be no more than 2 percent difference in moisture content between properly acclimated wood flooring and subflooring materials.

CHAPTER 3 MOISTURE TESTING

Part I – Moisture Testing for Wood Subfloors

A. Testing Requirements

Chapter 3 – Moisture Testing

1. Test for moisture at several locations in the room — a minimum of 20 per 1,000 square feet — and average the results. A high reading in one area indicates a problem that must be corrected. Pay special attention to exterior and plumbing walls

Part II – Acceptable Vapor Retarders Over Wood Subfloors

A. ALWAYS FOLLOW LOCAL CODES AND MANUFACTURERS INSTRUCTIONS FOR ACCEPTABLE VAPOR RETARDERS.

B. An acceptable vapor retarder is a vapor resistant material, membrane or covering with a vapor permeance (perm rating) of greater than or equal to .7 and less than or equal to 50 when tested in accordance with ASTM E-96 Method A. Installation of a vapor retarder reduces the potential for moisture or vapor related problems, but does not guarantee elimination of moisture or vapor related problems. Install a vapor retarder over wood panel or board sub-floors prior to installing nail down solid strip or plank flooring. Over-lap seams a minimum of 4 inches or more as required by manufacturer or specifier and local building codes.

C. Some examples of acceptable vapor retarders over wood subfloors include:

1. An asphalt laminated paper meeting UU-B-790a, Grade B, Type I, Style 1a.

2. Asphalt-saturated kraft paper or #15 or #30 felt paper meeting ASTM Standard D-4869 or UU-B-790, Grade D.

D. NOTE:

1. A vapor retarder has some extra benefits in that it eliminates wood-on-wood contact, wood strips slide more easily when positioned, minimizes the impact of seasonal humidity change and may reduce dust and noise levels.

2. However, by today’s standards, asphalt saturated kraft or felt paper may not be an effective vapor retarder in all applications. The 2006 International Residential Code requires a vapor retarder on the warm-in-winter side of exterior floors (a floor over a vented crawl space, for example), with a vapor permeance of 1 perm or less in Zones 5 and higher.

3. Over a wood subfloor, do not use an impermeable vapor retarder material with a perm rating of .7 or less, such as 6 mil polyethylene film or other polymer materials, as it may trap moisture on or in the wood subfloor.

4. Do not use common red rosin or building paper which is not asphalt saturated. They are not vapor retarders as their perm rating is far greater than 50.

Part III – Moisture Testing for Concrete Slabs

NOTE: All tests give a result – at the time the test is done. And in general give you the ability to start or not start a job – these tests do not give a permanent condition of your substrate merely a “at the time the test was performed” indication.

A. Testing Requirements

1. Before moisture testing begins, the concrete slab must be a MINIMUM of 30 days old.

B. Qualitative Moisture Tests

1. Electrical Impedance Test and Electrical Resistance Test (Moisture Meter)

Follow meter manufacturer’s instructions.

a. Use moisture meters designed specifically for concrete moisture testing.

b. Test within the body of the slab (electrical resistance), as well as at the surface (electrical impedance).

c. These testing methods are not recognized by any standard and should not be used for the purpose of accepting or rejecting a floor. These electronic tests are useful survey tools to broadly evaluate the relative moisture conditions of a slab and to select locations for quantitative moisture tests.

d. If the moisture meters indicate the presence of excessive moisture, as per wood flooring or meter manufacturer’s recommendations, further testing is required using relative-humidity testing (ASTM F-2170), calcium chloride testing (ASTM F-1869) or calcium carbide (CM) testing (ASTM D-4944-04 and MilSpec CRD-C154-77).

2. Phenolphthalein Test

a. Perform one test per 200 square feet of surface area, with a minimum of two tests per jobsite.

b. Chip a small section of concrete off the floor and apply 3 percent phenolphthalein in alcohol solution (available at most druggists) in the area. A red color indicates that moisture is present. Always chip the concrete as this protects against the possibility that a concrete sealer was applied.

IMPORTANT: Keep phenolphthalein out of direct sunlight. The average shelf life of phenolphthalein is six months.

c. If the phenolphthalein test indicates the presence of excessive moisture, further testing is required using relative-humidity testing (ASTM F-2170), calcium chloride testing (ASTM F-1869) or calcium carbide (CM) testing (ASTM D-4944-04 and MilSpec CRD-C154-77).

C. Quantitative Moisture Tests

1. Relative Humidity Testing – ASTM F-2170 (Standard Test Method for Determining Relative Humidity in Concrete Floor Slabs Using In Situ Probes)

a. Select test locations to provide information about moisture distribution across the entire concrete floor slab. For slabs on grade and below grade, include a test location within three feet of each exterior wall.

b. Perform three tests for the first 1,000 sq ft and one test for every additional 1,000 sq ft thereafter.

c. At least 48 hours before test is placed, concrete floor slabs should be at the same temperature and humidity that is expected during service conditions.

d. Use a rotary hammer-drill to drill holes in the concrete slab; 40% depth of slab is required for the holes when concrete is drying from one side and 20% when drying from both sides. Follow manufacturer’s instructions provided with test kits.

e. Allow 72 hours to achieve moisture equilibrium within the hole before making relative humidity measurements.

f. ASTM F-710 provides installation guidelines for acceptance of hardwood flooring using relative-humidity testing. Typical limits for wood and wood-based products are 75% relative humidity. When getting readings over 75%, you must use a proper vapor retarder, based on the flooring manufacturer’s recommendations, or wait for further concrete curing.

2. Calcium Chloride Test – ASTM F-1869 (Test Method for Measuring Moisture Vapor Emission Rate of Concrete Subfloor Using Anhydrous Calcium Chloride)

a. Select test locations to provide information about moisture distribution across the entire concrete floor slab.

b. Perform three tests per 1,000 square feet of surface area. Add one additional test for each 1000 square feet thereafter.

c. At least 48 hours before test is placed, concrete floor slabs should be at the same temperature and humidity expected during service conditions

d. The actual test area shall be clean and free of all foreign substances. Use approved OSHA work practices for removal of all existing flooring materials and debris.

e. Blast or grind a minimum area of 20 inches by 20 inches and let stand for a minimum period of 24 hours prior to setting test.

f. Follow manufacturer’s instructions for properly placing tests onto concrete.

g. Tests are to be covered and left in place for 60 to 72 hours. Follow manufacturer’s instructions for labeling and recording time and date of test.

h. Send the test to a certified laboratory for results and documentation, or perform the measurements as per ASTM F-1869.

i. Always following the flooring manufacturer’s guidelines and specifications to determine when the concrete slab is ready for installation.

j. ASTM F-710 provides installation guidelines for acceptance of hardwood flooring using calcium-chloride testing. Typical limits for direct glue-down wood flooring is 3lbs/1000sf/24hr. When getting readings over 3 lbs and up to 7 lbs, you must use a vapor retarder. A reading over 7 lbs may not be acceptable for wood flooring installation. Follow the wood flooring manufacturer’s recommendations. In the case

of a glue-down installation, the adhesive manufacturer may also have recommendations.

NOTE: For information on the tests listed above, contact your distributor or call NWFA at 800-422-4556 U.S. or 800-848-8824 Canada for the source nearest you.

3. Calcium Carbide (CM) Test – ASTM (modified) D-4944-04, MilSpec CRD-C154-77

a. The calcium carbide test, also known as the CM test or calcium carbide bomb, is more widely used in Europe than in the United States. It is a gas-pressure test in which moisture in the concrete reacts with calcium carbide crystals to create acetylene gas, and the gas pressure produced is measured to provide a moisture content reading, expressed as a percentage of moisture. Follow the directions provided by the test-kit manufacturer. A reading of over 2.5% requires use of a vapor retarder. A reading over 4% may not be acceptable for wood flooring installation. Follow the wood flooring manufacturer’s recommendations. In the case of a glue-down installation, the adhesive manufacturer may also have recommendations.

Part IV – Acceptable Vapor Retarders Over Concrete

A. ALWAYS FOLLOW LOCAL CODES AND MANUFACTURERS INSTRUCTIONS FOR ACCEPTABLE VAPOR RETARDERS.

B. Test concrete for moisture. For concrete slabs with a calcium chloride reading of greater than 3 lbs, a relative humidity reading of greater than 75%, or a calcium carbide (CM) rating of greater than 2.5%, install an impermeable vapor retarder with a perm rating of less than .15 perm. Adding a vapor retarder is not required on installations over slabs with a calcium chloride reading of 3 lbs or less, a humidity reading of 75% or less, or a calcium carbide (CM) rating of 2.5% or less. However, in on-grade and below grade applications, adding a vapor retarder is always recommended.

C. The 2006 International Residential Code defines a vapor retarder as a vapor-resistant material, membrane or covering such as foil, plastic sheeting or other material recommended by the manufacturer having a permeance rating of 1 perm or less, when tested in accordance with ASTM E-96 Method A.

D. The NWFA recommends an “impermeable” vapor retarder with a perm rating of less than or equal to .15, thereby limiting the passage of moisture to near zero.

E. Some acceptable vapor retarders over concrete include:

1. A minimum 6 mil construction grade polyethylene film, with perm of .13, or other impermeable material with a perm of .15 or less is recommended. An premium polymer material meeting ASTM D-1745 for concrete with higher tensile, tear and puncture resistance is highly desirable.

2. Double felt: Two layers of #15 asphalt saturated felt paper that meets ASTM Standard D-4869, with the first layer adhered to the slab in a skim coat of appropriate adhesive, and a second layer adhered to the first layer with appropriate adhesive.

Chapter 2

Acclimation and Conditioning of Wood Flooring

Always follow the manufacturer’s recommendations regarding how and whether to acclimate wood flooring.

Part I

General Acclimation/Conditioning Guidelines

Definitions:

Acclimation: The process of adjusting (conditioning) the moisture content of wood flooring to the environment in which it is expected to perform.

Equilibrium Moisture Content: The moisture content of wood when in equilibrium with its environment. When wood is neither gaining nor losing moisture, equilibrium moisture content (EMC) has been reached.

A. Storage and Conditions

1. Do not store wood flooring at the jobsite under uncontrolled environmental conditions. Garages, and

exterior patios, for example, are not acceptable areas to store wood flooring.

2. Ideal interior environmental conditions vary from region to region and jobsite to jobsite. It is the flooring

professional’s responsibility to know what the “ideal” climate conditions are and customize the floor around those conditions.

a. Determine what the expected seasonal change of wood moisture content is for your geographical

location. For a general view of moisture‐content averages by region, See Appendix D and Appendix E.

b. Upon delivery, check wood flooring moisture content with a moisture meter to establish a baseline

for acclimation. Check the moisture content of multiple boards. A good representative sample is typically 40 boards for every 1,000 square feet of flooring. Calculate what the optimal wood moisture content is (baseline) by dividing the high season and low season. Example: If your region has an expected EMC from a low of 6% to a high of 9%, the baseline MC of the wood would be 7.5%. If wood flooring is delivered and recorded to its baseline MC for the geographical location and proper relative humidity conditions are maintained, no acclimation may be required. If the moisture content of the product received is well outside of the range of optimal moisture content, it will be very difficult to acclimate the product properly without substantial dimensional change, distortion, and structural damage. Example: If the moisture content of the delivered wood is 12% and the optimal range is 6%, excessive shrinkage, bowing, cupping and other physical anomalies would be expected during the acclimation process. The wood flooring should not be accepted.

c. Optimal wood moisture content represents only a base line to begin from and does not represent the final EMC required for the interior environment. Acclimation is often required to customize the moisture content of the wood flooring to the interior environment in which it is expected to perform.

B. General

Note: Some manufacturers do not require acclimation for certain products prior to installation. If the manufacturer recommends that the wood flooring be acclimated before installation, proceed as follows:

1. Ensure that the building is enclosed.

2. Verify that the building is maintained at normal living conditions for temperature and humidity.

3. Where building codes allow, permanent heating and/or air conditioning systems should be operating at

least five days preceding installation to promote proper acclimation and should be maintained during and

after installation. For radiant heat, see Appendix H.

4. If it is not possible for the permanent heating and/or air conditioning system to be operating before,

during and after installation, a temporary heating and/or dehumidification system that mimics normal living (occupied) conditions can enable the installation to proceed until the permanent heating and/or air conditioning system is fully operational.

5. Acclimate the wood flooring as necessary (see Chapter 2, Part II, Acclimation).

Note: Not properly acclimating wood flooring may cause excessive expansion, shrinkage, dimensional distortion or structural damage. The worst‐case scenario is one in which wood flooring is stored at the jobsite in an uncontrolled environment, then immediately installed. This is especially true when the materials are stored in an area that is subject to excessive moisture and humidity conditions. Acclimation outside of the area in which the wood is to be installed does no good at all; in fact, it is likely harmful to store wood flooring at the jobsite under conditions that don’t reflect expected normal environmental conditions.

6. Prior to installation, ensure that wood flooring is within acceptable range of moisture content with the wood subfloor. For solid strip flooring (less than 3” wide), there should be no more than 4 percent moisture content difference between properly acclimated wood flooring and subflooring materials. For wide‐width solid flooring (3” or wider), there should be no more than 2 percent difference in moisture content between properly acclimated wood flooring and subflooring materials.

Part II

Acclimation

Wood flooring is a hygroscopic material subject to dimensional change as a result of variations in moisture, temperature and humidity within the surrounding environment. Wood flooring simply needs to reach moisture content level in equilibrium with the surrounding environment (EMC) in which it will be installed, at or near normal living conditions. The process of reaching this equilibrium is defined as acclimation, which allows the wood to properly adjust itself to the normal living conditions within the structure; that is, the temperature, humidity conditions and moisture content that will typically be experienced once the structure is occupied.

A. The Process of Acclimation

If the manufacturer recommends that the wood flooring be acclimated before installation, proceed as follows:

1. Acclimation can be facilitated by breaking the floor units into small lots and/or opening the packaging. A

common practice is to cross‐stack the materials with spacers (3⁄4” to 1” sticks) between each layer of

flooring to allow air circulation on all sides of all boards.

2. Most recommendations state that the materials need to acclimate from a minimum of 3 days up to no

given maximum. While it takes time to acclimate a product, the most important aspect is that the materials reach a moisture content that is in equilibrium with its expected use. Acclimate the materials as long as necessary to accomplish this task, taking the necessary moisture readings to indicate when the materials have reached the proper moisture content and when no further changes occur.

a. For site‐finished wood flooring, after installation and before sanding and finishing takes place, allow

the flooring to acclimate (settle‐in) to the controlled environment, and to stabilize for a period of time. Some flooring professionals suggest 5 to 7 days. Engineered flooring installed using an adhesive application system may require a longer post‐installation acclimation period to allow all residual off‐gassing to occur prior to application of a finish. Follow adhesive manufacturer’s recommendations.

b. Tropical imported species generally require more time in order to properly acclimate the wood flooring. Some tropical species lose moisture or gain moisture at faster or slower rates than domestic species due to higher overall density, oil and resin content and interlocking cell structure. In addition, the resins and oils make accurate MC readings more difficult. Resistance (pin type) meters require multiple readings of multiple boards in order to arrive at a more accurate average MC reading. Pinless meters that include multiple depth level adjustments may offer faster and more-accurate internal readings.

c. Engineered and solid factory finished flooring follows specific manufacturer’s recommendations and some may not require acclimation. Follow manufacturer’s guidelines to retain all warranty coverage. Warranty coverage generally requires that jobsite conditions be maintained between 30% to 50% relative humidity and that those conditions must be maintained before, during and after installation for the life of the floor. Failure to comply with these manufacturer’s requirements may result in irreversible structural damage and void related warranties.

1. As a general rule, with geographic exceptions, wood flooring will perform best when the interior environment is controlled to stay within a relative humidity range of 30 to 50 percent and a temperature range of 60° to 80° Fahrenheit. (In some climates, the ideal humidity range might be higher or lower, 25 to 45 percent or 45 to 65 percent, for example.)

2. The chart below indicates the moisture content wood will likely have at any given combination of temperature and humidity. Note the equilibrium moisture content in the recommended temperature/humidity range (shaded area) coincides with the 6‐to‐9 percent range used by most flooring manufacturers during the manufacturing/shipping process. Although some movement can be expected between 6 and 9 percent, wood flooring can shrink or swell more dramatically outside this range. When wood is neither gaining nor losing moisture, equilibrium moisture content (EMC) has been reached.

Equilibrium Moisture Content of Solid Wood Species at Various Temperatures and Relative Humidity Readings

Wood flooring has a comfort level too. Wood flooring will perform best when the interior environment is controlled to stay within a relative humidity range of 30% to 50% and a temperature range of 60° to 80° Fahrenheit. Fortunately, that’s about the same comfort range most humans enjoy. The chart below indicates the equilibrium moisture content of wood flooring at various temperatures and humidity conditions. The left column indicates temperature in degrees Fahrenheit and Celsius. The bottom row indicates percent relative humidity. The values in the chart indicate the equilibrium moisture content (EMC) for any given combination of temperature and humidity. For example, at 70° Fahrenheit and 40% relative humidity, the equilibrium moisture content is 7.7%. The shaded area indicates the generally recommended range for wood flooring – 6% – 9% EMC, which occurs when temperature is 60° – 80° Fahrenheit or 15° – 26° Celsius, and 30% – 50% relative humidity.

Coefficients of Change: How Moisture Affects Wood Flooring

See Chapter 9, Solid Strip and Plank Flooring Installation.

Strip, plank, or parquet?

Wood floors come in three styles: strip, plank, and parquet. Each is available in a variety of species, colors and widths, so choosing the right style simply is a matter of preference

Strip flooring is less than 3” wide, and creates a linear effect in a room. It generally is considered “traditional” wood flooring.

Plank flooring is greater than 3” wide. It is linear, like strip flooring, and evokes a casual look.

Parquet flooring can vary in size and generates a geometric, non-linear look. It can be simple or complex in design.