Restoration Guide: Sheathing, Subfloor and Underlayments

Shannon Lee

Editor's Note: This is article 3 of 6 in Chapter 5: The Partitions, Ceilings, Walls, Stairs Guide of Old House Web Restoration Guide. This guide was developed and edited for old homes from original materials in the U.S. Housing and Urban Development Rehab Guide.


Section 1--Overview

An old house built before the late 1930s and early 1940s often had straight-edged or tongue-and-groove boards as sheathing, laid perpendicular or diagonally to the floor joists. In some homes this sheathing actually became the finished floor. Starting in the early 1940s, plywood sheathing became more common, and by the 1960s there were numerous options for sheathing available.

Advances in sheathing materials--notably oriented-strand board (OSB)--have led to sheathing that is more water-resistant and durable.

3.1: Repairing Damaged Floor Sheathing

The most common floor sheathing damage is moisture-related, though there could be other factors at play, including settlement, insect damage, earthquakes, and other natural disasters that affect the structure of the house. You should understand and eliminate the cause of any damage before proceeding with home restoration efforts.

Basic repairs entail cutting out the damaged area and replacing it with a piece of similar material. For extensive damage, the new sheathing should have a span rating that is appropriate for the framing space.

Section 2--Floor Squeaks

Though floor squeaks can originate in many places in an old house, a common culprit is the shank of a nail rubbing against the sheathing. Refastening the sheathing to the joist might help. Here are some common techniques to consider:

  1. Apply more fasteners. Additional screws or nails can be concealed with wood plugs in the finished floor, or you can opt for nails that are designed to break off below the level of the finished floor.
  2. Refasten sheathing from below. If you can access the floor from underneath, wood blocking and a construction adhesive can help fill the gap between the sheathing and the joist.
  3. Use specialty fasteners. Readily available at home centers, specialty products that are designed to put a stop to squeaks work by mechanically drawing the sheathing to the joist.
  4. Add more nails to bridging. If the bridging has not been nailed properly, or if the nails have shifted out of the bridging, it can rub against the joists, causing squeaks. Re-nailing can eliminate the problem.
  5. New bridging. If the sheathing is too thin or the existing bridging is inadequate, add new bridging--and nail it down securely--to help stop the squeaks.
  6. Look at joist hangers. If the beams or joists were not attached properly to the hanger, or if the hanger is the wrong width or height, the resulting gaps can lead to squeaking by allowing the sheathing to move. Shimming the beam or joist is an easy fix.
  7. Examine ductwork. If the hole cut in the floor for ductwork or registers is too tight, squeaks can result. Ductwork with inadequate support can also be a problem.

Section 3--Underlayments

Typical underlayment materials in an old house include plywood, cement board, particleboard, or hardboard. These underlayments are used on top of the sheathing to create a firm, even base for sheet vinyl, linoleum, and other surface materials. Underlayments can be damaged by plumbing leaks, abuse, excessive wear, and high humidity.

  1. Repairing underlayment. Unfortunately, it is usually not possible to salvage damaged or deteriorating underlayment. Localized patching is practical, but only if the repairs are very small.
  2. Replacing underlayment. Plywood is a common underlayment, but cement board is often recommended for use with ceramic tile. Your new underlayment should be appropriate to the material you are using for your finished flooring. Keep in mind that reducing strips between the old and new material might be required.

Whether you chose to repair or replace damaged underlayment, make sure you follow manufacturer recommendations to ensure your warranty remains valid.

About the Author

Shannon Dauphin is a freelance writer based near Nashville, Tennessee. Her house was built in 1901, so home repair and renovation have become her hobbies.

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