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.

9. Crawl Space Conditions

  b. For crawl spaces without ventilation openings, vapor retarder joints must  overlap 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.

A. All finished wall coverings and painting should be completed. Note: Base and shoe mold may be installed and finished after the flooring installation.

B. After installation, if you choose to protectively cover the floor, cover the floor completely, since some species are light-sensitive and uncovered areas may change color. However, covering a glue-down application may not allow some adhesives to properly cure. Follow the flooring and adhesive manufacturer’s recommendations. Use a covering material with a vapor permeance (perm rating) of 1 perm or more (tested I accordance with ASTM E-96) to avoid trapping moisture/vapor on or within the floor. A common reinforced builder’s paper is a good choice. Any covering should be taped, using a low-adhesion tape, to base or shoe moldings. Avoid taping to finished flooring. When taping paper or sheets together, tape them to each other, not to the floor.

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

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.

A. Testing Requirements

  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

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 that meets 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.

A. Testing Requirements

B. Qualitative Moisture Tests

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

  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.

  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.

    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.

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.

B. In on-grade and below grade applications, always add a vapor retarder. 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.

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.

  3. A chemical retarder or urethane membrane, as recommended by the adhesive or wood flooring manufacturer. These are usually in the form of a liquid-applied or trowel-applied membrane dispensed from a bucket following manufacturer recommendations.

A. Always follow the manufacturers recommended installation procedure.

B. Unfinished and factory-finished solid plank should be installed perpendicular to the joists or on a diagonal for any single layer subfloor. (Exception: Over diagonal, solid subfloor boards, install perpendicular to joists or subfloor direction.)

C. When ¾" solid plank flooring is laid parallel with the floor joists, follow one of these two steps:

  1. Add a layer of minimum nominal ½" (15/32”) CD Exposure 1 (CDX) plywood underlayment to the existing subfloor (as previously recommended)

  2. Or brace between truss/joists in accordance with the truss/joist manufacturer’s recommendations and with local building codes. Some truss/joist systems cannot be cross-braced and still maintain stability.

D. Before installing wood flooring, place an approved vapor retarder. 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 that meets ASTM Standard D-4869 or UU-B-790, Grade D.

E. Wall Line Layout

  1. Choose a starting wall according to the most aesthetically or  architecturally important elements in the room, taking into consideration fireplaces, doors, cabinets and transitions, as well as the squareness of the room. The starting wall will often be the longest unbroken wall in the room.

  2. Snap a working line parallel to the starting wall, allowing ¾” expansion space between the starting wall and the edge of the first strip or plank run.

  3. As a general rule, a ¾” expansion space must be left around the perimeter and at all vertical obstructions.

  4. Random-width plank is laid out with alternating courses varying by widths. Start with the widest board, then the next width, etc., and repeat the pattern.

  5. Lay one row of strip or plank along the entire length of the working line.

  6. Top-nail and blind-nail the first row (hand-nail if necessary), using appropriate fasteners. Denser species may require pre-drilling. Each succeeding row should be blind-nailed with the nailing machine wherever possible. At the finishing wall and other obstructions, it may be necessary to blind-nail by hand until top nailing is required.

  7. Racking rule of thumb: Stagger end-joints in adjacent rows at least three times the width of the boards, as product allows. Avoid H-joints. (See Figures 1 and 2.)

Figure 1 Stagger End Joints		Figure 2 Avoid “H” Joints

9. Where spacing is required: Use a washer or removable spacer to leave additional space

every few rows and/or start in center of room and work out to both sides. Do not use

spacers that may cause damage on factory-finished products.

10. Nailing: Blind-nail through the tongue using 1½"-2” fasteners. Use 1½" fasteners with

nominal ¾" plywood subfloor direct to concrete slab. Face-nail boards where needed

using 6d-8d casing or finish nails. Fasteners should be spaced every 6”-8” on blindnailing,

or every 10”-12” on face-nailing.

11. For additional fastening, any of the following options may be used in addition to the

nailing schedule. (See Appendix F, Fastener Schedule.)

12. Follow manufacturer’s instructions for installing plank flooring.

13. For wide-width plank flooring (5” or wider), to assist the nailing schedule of 6”-8” and

increase holding power, there are three options.

a. Screw and plug at end joints, alternating at staggered locations and intervals along

each board.

b. Apply an approved wood flooring adhesive.

c. Use kerfing or relief cuts every 8” to 12” parallel to the grain – using more relief cuts

for wider boards. Typically, the relief cut should be 3/8” on a ¾” board.

14. Blind-nail and face-nail, as necessary, to complete the final rows.

F. Center Line Layout

1. Find the center of your room, measuring off the two longest walls, and snap a line down

the center of that room.

Copyright 2007 National Wood Flooring Association 13 Revised March 2007

Chapter 9 Solid Strip & Plank Flooring Installation

2. Install a starter board on the line. Fasten the starter board to the floor using wood

screws.

3. Nail the first row of wood flooring against the starter board, being careful not to move the

starter board when nailing. The groove of the flooring should be against the starter

board.

4. Drill and hand-nail the first three rows through the tongue. DO NOT USE TOP NAILS.

5. Use a blind nailer to install the remaining rows of wood flooring. Use the nailing practices

described earlier in the chapter.

6. After installing in one direction, remove the starter board and start rows going in the

opposite direction.

7. Install a spline or a slip tongue in the groove of the board that was against the straightedge.

Put wood glue down the entire length of the groove before installing the spline.

8. Install the spline using a blind nailer. To keep the spline in alignment for the next flooring

board, use a scrap piece of wood flooring to run along the length of the spline as you

nail.

9. Install the remaining rows in the opposite direction. Use the nailing practices described

earlier in the chapter.

A. Engineered wood flooring can be installed directly to screeds, provided the engineered flooring is a minimum of ¾” thick. For engineered flooring less than ¾” thick, the screed system must be overlaid with proper subflooring. See Appendix I, Installation Over Screeds.

B. Note on random-width plank

  1. Random-width plank is laid out with alternating courses varying by widths. Start with the widest board, then the next width, etc., and repeat the pattern.

  1. Choose a starting wall according to the most aesthetically or architecturally important elements in the room, taking into consideration fireplaces, doors, cabinets and transitions, as well as the squareness of the room. The starting wall will often be the longest unbroken wall in the room.

D. Glue-Down Engineered Strip and Plank

  1. There are several different ways to start the installation of glue-down engineered wood flooring. The following has proven successful. However, where instructions differ from manufacturer recommendations, manufacturer recommendations prevail.

  2. Test the substrate for moisture according to appropriate moisture testing procedures in the General Guidelines. Excessive/elevated moisture should not be present. The subfloor should be within acceptable moisture content as per adhesive and wood manufacturer’s recommendation before installing.

  3. Expansion space should be left around the perimeter in accordance with the manufacturer’s recommendation.

  4. Snap a working line parallel to the starting wall, the width of the board, plus the tongue and recommended expansion space.

  5. Install a starter board along the edge of the working line and begin installation. Alternatively, lay one row of plank in the adhesive along the length of the working line.

  6. Follow manufacturer instruction for tongue and groove direction and placement.

  7. Use an adhesive approved by the flooring manufacturer. Follow the installation procedure recommended by the adhesive manufacturer, which includes subfloor moisture content, spread rate, trowel size, open time, working time and flash time as necessary. Spread the adhesive as instructed up to and along the working line

  8. Distribute lengths, avoiding “H” patterns and other discernible patterns in adjacent runs. Stagger end joints at least three times the width of the boards, as product allows. (See Figures 1 and 2.)

Figure 1 Stagger End Joints		Figure 2 Avoid “H” Joints

  9. If recommended by the manufacturer, use tape or tensioners to maintain a tight floor.

  10. If recommended by the adhesive manufacturer, roll the floor with the proper roller.

E. Mechanically Fastened Strip and Plank

  1. If necessary, add a vapor retarder.

  2. Snap a working line parallel to the starting wall, allowing expansion space as specified by the manufacturer.

  3. Lay one row of plank along the entire length of the working line.

  4. Top-nail and blind-nail the first row (hand-nail if necessary), using appropriate fasteners. Denser species may require pre-drilling. Each succeeding row should be blind-nailed wherever possible.

    b. Typical: every 3-4” with staples, every 4-6” with cleats, and within 1-2” of end joints. Use appropriate size fastener for top nailing first row, last row and any area where blind nailer will not fit.

  5. Add each additional row of flooring. Distribute lengths, avoiding “H” patterns and other discernible patterns in adjacent runs. Stagger end joints at least three times the width of the boards, as product allows.

  6. During installation of flooring pieces, push or gently tap boards flush to the previous row. Tap against the tongue; tapping the groove may damage the edge. To prevent damage to the finish, avoid tapping the face of the board with a rubber mallet.

F. Floating Engineered Flooring

  1. Subfloor flatness is critical to the success of a floating floor installation. (See Chapter 4, Wood Subfloor Guidelines, and Chapter 5, Concrete Subfloor Guidelines.)

  2. Test the substrate for moisture according to appropriate moisture testing procedures in Chapter 3. Excessive/elevated moisture should not be present. The subfloor should be within acceptable moisture content as per manufacturer recommendation before installing.

  4. If necessary, add vapor retarder. (See Acceptable Vapor Retarders in Chapter 3, Moisture Requirements and Moisture Testing.)

  5. Expansion space should be left around the perimeter or in accordance with manufacturer’s recommendation.

  6. Typical: Subfloors are covered with a resilient material, foam underlayment or cork. Follow manufacturer's instructions for correct materials and thickness.

  7. Typical: floating engineered flooring is edge-glued or edge-attached with a self-locking mechanism.

    a. For edge-glued products, use an adhesive approved by the manufacturer.

    b. Apply adhesive at the spread rate to the side grooves and/or ends as recommended by the manufacturer.

  8. Starter boards should be aligned with the groove side and end against the starting wall. Tapping block should be used against tongue only.

  9. Stagger end joints per manufacturer’s recommendation. Typical: 18”-20”.