Cedar Shingle Roof: Proper Roof Sheathing and Underlayment

Cedar shingle roof styles were common in early America because timber was in abundance and the shingles could be made and installed relatively easily. Despite advancing roofing technology and materials over the decades, wood shingles are still used on a small percentage of buildings, especially for custom houses and restoration projects. Having proper roof sheathing and underlayment on a cedar shingle roof will prevent updrafts that can cause fire to penetrate through the roof. Sheathing and underlayment also provide insulation and will deter wind-driven snow and other foreign material from entering the attic. Sheathing and underlayment will make the cedar roof shingles last longer as well as the wood underneath the shingles and sheathing. This will extend the life of the roof by protecting it from the elements, which in turn will delay or prevent the underlying wood from rotting.

Open Sheathing

Cedar wood shingles that have a smooth finish require open sheathing of 1 by 6 boards, spaced apart. The spacing allows air to circulate around the shingles, preventing moisture buildup. Whenever doing a project like this, be sure to check local building codes, as each town and city may have different regulations that must be followed. Most of the codes are dependant on the weather conditions of the area because regions that get more severe weather will need a higher level of protection that buildings in mild weather.

Solid Sheathing

If the wood shingles being installed on the roof have deeply grooved textures, more commonly found on cedar shakes, not shingles, solid sheathing can be used because the deep grooves on the shingles allow for air ventilation. But, it is a good idea to use 30-pound felt underlayment, or opt of open sheathing.

Felt Underlayment/Tar Paper

First, check the local building codes as different regions have different requirements. Typically, felt underlayment, or tar paper, that is 15lb or heaver is required by most areas. Even if an underlayment is not required, it is cheap insurance against future roof problems. Felt Underlayment has many benefits, such as:

  • Providing extra weather barrier in case of water penetration or blow offs.
  • Roof deck protection from rain prior to roof installation.
  • Helps prevent unevenness in the roof sheathing.
  • It is typically required for the UL fire rating because shingles are often tested with underlayment.
  • Protection against any resins that bleed from the sheathing.
  • Provides insulation.

Synthetic Underlayment

New products are always being made to protect roof decks and extend the life of a ceader shingle roof. These new synthetic underlayment products are made from various materials, including polyester, fiberglass, and polypropylene. These products are lighter than felt underlayment and will last up to 6 months when exposed directly to the weather. Synthetic Underlayment has many benefits, such as:

  • It is moisture resistant and hardy.
  • It resists degradation from exposure to UV rays.
  • Great for use in disaster response because it is durable and long-lasting.
  • It resists moisture.
  • It is tear resistant.
  • Just as easy, if not easier to install as felt underlayment.
  • Provides insulation.