A19 - WOOD PANEL UNDERLAYMENT

A19-1 Preparing wood substates
A19-2 Installation of wood panel underlayment
Preface:
This guide covers general criteria for the selection and installation of wood panel underlayment where resilient (vinyl, rubber, linoleum) floor coverings are scheduled for installation. Individuals using this guide should verify all such criteria with the manufacturers of any proposed wood panel underlayment for suitability and warranty issues with any floor coverings that are under consideration for the particular project.
1 • PREPARING WOOD SUBSTRATES 

.01 Refer to General Requirements. Verify acceptable substrate requirements and conditions with material manufacturers of floor coverings to be installed before proceeding.

.02 New and existing wood framing systems supporting wood substrates: The following general requirements for both shall apply.

  • All wood framing systems shall be designed to span between supports in accordance with Building Code load and deflection requirements to provide a structurally sound system free of vertical movement and horizontal expansion that would be detrimental to flooring materials installed as well as to provide acoustical and fire separation in accordance with Building Code requirements.
  • All wood flooring systems over crawl spaces shall be designed in accordance with the above noted requirements with the clearance to the underside of the wood framing system to be a minimum of 300 mm (12") above the interior grade surface (except 450 mm (18") where required by Code). This "crawl" space (unless insulated and used as a warm air plenum) shall be either naturally cross or mechanically ventilated and must have an approved moisture impervious barrier in accordance with Building Code requirements to prevent rising ground vapour moisture from causing damage detrimental to the flooring assembly from dry rot, mould, mildew, swelling, and buckling, etc. (The relative humidity within the space shall not exceed more than 70%).
  • The moisture impervious barrier may be 50 mm (2") of asphalt or concrete, Type S roofing or 0.15 mm (6 mil) polyethylene sheet. Alternately, if the joist spaces are insulated and where approved by authorities having jurisdiction, the framing system may be sealed on the underside using a moisture retarder installed on the warm side (i.e., fixed to underside of floor sheathing with floor joists wrapped prior to installing insulation).
  • Moisture: All wood substrates (i.e. floor sheathing) that were installed wet or that have been exposed to the elements before closing in the area must be tested for moisture content and confirmed dry in accordance with the floor covering, adhesive and/or panel underlayment manufacturers requirements before application. An electronic pin moisture meter set to the correct wood species type and reading no more than 12% moisture content is a general guide. In all cases ensure the substrate meets the manufacturers requirements for subfloor moisture content before proceeding with installation. 
  • Flatness: All wood substrates, subfloors and underlayments shall be provided smooth, flat (not undulating) to within 3/16" over 10' with no abrupt changes and/or in accordance with the floor covering material manufacturer's recommendations and in accordance with requirements noted below. Substrates should be meet flatness tolerances prior to any panel underlayment being installed.

​.03 Subfloor Sheathing: Plywood, hardwood, particle board, or oriented strand board used as subfloor sheathing must conform to and be installed in strict accordance with building code requirments in regard to acceptable materials, thickness, support, span, and fastening. Where flooring materials (such as carpet) are installed directly over these materials (i.e., an underlayment is not used) particular attention must be paid in regard to panel edge fastening and gaps. Such subfloor materials and their installation must also be acceptable for use by the flooring material manufacturer and be installed in strict accordance with the floor covering material manufacturer's requirements as well
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.04 Panel Underlayments: Plywood, hardwood, particle board or any other panel products used as a floor underlayment must be of a type that is specifically manufactured by the materials manufacturer for that purpose and must also be of a type that is pre-approved for this use by flooring material manufacturer. Such material must be installed in strict accordance with Building Code and the floor covering material manufacturer's requirements.
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Note: Floor Covering Manufacturers do not recommend the installation of resilient flooring over wood panels attached directly to on grade or below gradeconcrete subfloors or over sleeper constructed subfloors on or below grade concrete slabs.  Refer to Part A10 - Acceptable Conditions for wood substrate requirements.

Note:  The installation of an approved wood panel underlayment over strip or plank flooring will minimise the potential telegraphing effect and compensate for the seasonal expansion and contraction characteristics of the boards and is therefore strongly recommended.  Refer to Part A10 - Acceptable Conditions and Part D06 (Hardwood) Installation Guide for further explanation and requirements.

.02 Basic Preparation Requirements: 

.1    Strip and Plank Floors:  Any loose and squeaky boards must be securely nailed and all broken or unsound boards or board sections replaced.  The entire flooring should be sanded until even and sealed to prevent moisture absorption.  Cracks in excess of 1.6 mm between boards should be filled level.
 
.2     Underlayment Panels:  The following types of panel materials are acceptable depending on floor covering material to be applied, floor covering manufacturers recommendations and pre-approval of panel manufacturer’s. Panel underlayment must be stamped as approved for use directly beneath the scheduled floor covering product.
  • Plywood.
  • Particle Board.
  • Oriented Strand Board (OSB).
  • Cementitious Board.
 
Refer to Part A10 - Acceptable Conditions for wood substrate requirements.
.03   Basic Underlayment Panel Preparation Requirements:
  1. Ensure that underlayment panels and the fastening procedure employed are in compliance with the floor covering manufacturers recommendations.
  2. Panel thickness differences at joints shall be corrected by sanding until even.
  3. Contaminates which potentially could stain or discolour the new flooring must be removed.
  4. Ensure that the entire area has been thoroughly cleaned and all detachable objects have been removed.
  5. Open knotholes and other imperfections must be patched flush.
  6. Generally only gaps between panels in excess of 1.6 mm should be filled unless otherwise specified.
  7. Refer to Part A13 - Patching and Filling for recommended patching / levelling compounds.
2 • INSTALLATION OF WOOD PANEL UNDERLAYMENT
Spec Note: Panel underlayment will be installed in strict accordance with manufacturers installation guidelines. Panel underlayment products not stamped as approved for installation beneath the scheduled flooring are not acceptable. Panel underlayment products that do not come with full installation guidelines and requirements are not acceptable.
Manufacturers installation guidelines supersede the guidelines written in the section below.
  1. Structural Subfloor requirements.
    1. Wood subfloors should be standard double-layer construction with a finished thickness of at least 1". 
    2. Install wood panel underlayment over a clean, dry, level, original sound structural sub-floor, or existing floor. •
    3. Thoroughly scrape, sweep and vacuum the entire surface and strip any wax if installing over existing vinyl.
    4. Do not use any adhesive beneath wood plywood underlayment unless approved by the manufacturer of the panel underlayment.Materials
  2. Materials
    1. Condition all materials to be used to service (eventual living) conditions, approximately 20c (70°F), for 24 to 48 hours prior to use.
    2. Store all panels on their 8' edge (separately if possible) to allow equal air flow over the face and back of the material.
    3. Examine each piece of wood panel underlayment by flexing and visually inspecting.
    4. Follow these steps:
      1. Stand a piece of plywood underlayment vertically with its 4' edge on the floor and the panel face towards you (the panel face will have the nailing pattern on it).
      2. Grip the top panel edge with your right hand and firmly place your left palm against the center of the panel face.
      3. Pull down with your right hand approximately 3" while simultaneously pressing forward with your left palm approximately 3". Hold this position during inspection.
      4. With the panel in this flex position, thoroughly inspect the entire panel surface for irregularities, which will look like “bubbles” or “creases.”
      5. Do not install panels that exhibit irregularities such as bubbles, delimitation, fraying, compromised edges.​​
  3. Panel Placement​​
    1. Run underlayment panels perpendicular to the floor joists.
    2. Begin by laying out the floor in a corner of the room where you can get the greatest amount of coverage without having to cut the underlayment panels. 
    3. The face with the nailing pattern is designed to go up.
    4. Position underlayment panels 1/8" to 1/4" from the walls to allow for expansion.
    5. The panels should be cut so that the factory edges go together at the seams in the field of the floor.
    6. Hand cut exterior edges for installation next to the walls.
    7. Stagger underlayment panels to create a 2" minimum offset between the underlayment panel and sub-floor seams.​
    8. Install the panels without an expansion joint and without a seam filler for installation under vinyl, vinyl composite tile, luxury vinyl tile, carpet, engineered flooring and wood floors. For a panel underlayment installation without an expansion joint, lightly butt the panels together without applying any pressure so they barely touch at the joints.
    9. Cut and place plywood underlayment on the sub-floor without any fasteners or “dry fit” all panels first before beginning any fastening.
    10. Plywood underlayment panels should be laid in an offset at the mid point between sheets (brick style pattern) so that four corners of the panel underlayment never directly intersect.
  4. Fastening of Panel Underlayment
    1. Do not use any adhesive beneath wood plywood underlayment unless approved by the manufacturer of the panel underlayment.Materials
    2. Use a pneumatic fastener tool that incorporates an adjustable depth-drive control to prevent over driving or setting of the fastener. If this feature is not available, adjust the air pressure on the compressor to an appropriate level to ensure correct setting of fasteners.
    3. Use galvanized coated chisel point staples with a 1⁄4” maximum crown or galvanized coated ring shank underlayment nails with a 3/16” diameter head, or flathead wood screws treated with a moisture resistant coating (such as galvanized or zinc).
    4. Do not use drywall screws. Do not select a fastener that is uncoated, cement or resin coated, as they may rust and discolour your finished floor.
    5. The length of the selected fastener should be a minimum of 5/8”, and must not protrude through the bottom side of the subfloor.
    6. Stand on each panel during fastening to ensure full contact with the sub-floor. Any “crackling” or “popping” noises indicate debris is underneath the panel. Should this occur, stop the installation, remove and discard the panel, then scrape, sweep and vacuum the sub-floor again until all debris is removed.
    7. All fasteners should be slightly countersunk below the surface of the new underlayment.
    8. Fasten the 8' edge first at 2" on center - 1/2" from edge – starting from the corner of the room.
    9. Leave an expansion joint of 1/8" to 1/4" between the panel and the edge of the walls.
    10. Stand on the panel to insure full and flush contact with the structural sub-floor and do not overdrive the fasteners.
    11. Return to the starting corner and fasten the 4' edge at 2" on center – 1/2" from the edge of the panel.
    12. Return to the starting corner and fasten the diagonal at 4" on center to the opposing corner.
    13. Return to starting corner and fasten the “field” of the panel every 4" on center working in a diagonal direction across the face of the underlayment panel.
    14. Make sure to put a fastener in each of the manufacturers fastener placement marks (typically an “x”) as you work diagonally across the panel.
    15. ​Fasten the remaining 4' edge 2" on center – 1⁄2" from the edge of the panel.
    16. Finish the sheet by fastening the remaining 8' edge 2" on center – 1⁄2" from the edge of the panel. Note that the same procedure is used as well for the offset sheet​which would start the next row of underlayment.
  5. Telegraphing seams after floor covering installation.
    1. ​Setting the fasteners at the correct depth and eliminating 'blow through' wear the staple is set too deep is key to avoiding Telegraphing seams.There are many factors that can cause telegraphing seams. The most common are:
    2. The use of too much seam filler
    3. Not allowing the seam filler to dry sufficiently
    4. Not sanding the seam filler smooth and even with the plywood underlayment
    5. Panels being butted too tightly together
    6. Panels not properly acclimated
    7. Too high moisture content in flooring environment
    8. Uneven sub-floors
    9. Placing the fasteners more than 1⁄2” from the edges of the panels
    10. Inconsistent fastener depth and blow-through along​ the edges of the panels
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Typical telegraphing issue. Installation related.
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Factory applied markings for fasteners
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Visual inspection
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Strictly follow the fastener schedule
End of section