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All About White Cedar Shingles

Ask This Old House general contractor Tom Silva explains the architecture, installation, and maintenance of white cedar shingles.

Tom starts with some general information about the architectural history of white cedar shingles:

  • Eastern white cedar is a prevalent species in the Northeast, which is why it is common to see it in the Northeast.
  • It is naturally insect and rot resistant, so Native American tribes were using it to build canoes for hundreds of years.
  • When the early colonists arrived and saw how well the cedar performed for canoes, they started using it as a building material to make shingles as well.
  • The shingles were usually left exposed, and they would eventually weather over time. The exposed, cedar shingles have been a classic look in coastal homes since.

Tom points out some common failure points for white cedar shingles:

  • Rot – Because the shingles are left untreated, they are exposed to water and can rot overtime. To slow that process down, Tom recommends that installers leave 5” between the roof and the final course of shingles. What happens is the roof shingles will get wet when it rains, and if the shingles touch the cedar, the cedar will absorb the water, which will eventually lead to rot. Leaving more of a gap will allow the shingles to dry.
  • Mold and mildew – Naturally, the white cedar shingles will form a mold or a mildew that discolors the shingles and turns them into a grayish color. That’s a natural part of the process that Tom thinks shouldn’t cause too much concern, though eventually the mold and mildew will overtake the shingles and they’ll fail. This shouldn’t happen for at least 20 years.
  • Moss – Especially on North-facing sides of the house, moss can grow over the shingles and leave a slight green color on them. The moss holds too much water and saturates the shingle, which will cause it to rot.
  • Cupping – Especially on the South-facing sides of the house, the hot sun can dry out the shingles too quickly, which will cause them to cup and break.

Tom then gives some advice for installing white cedar shingles:

  • White cedar shingles should be replaced roughly every 20 years.
  • There are natural and dipped shingles. Natural shingles are the traditional raw wood, left out to weather shingles. Tom also points out that there are dipped white cedar shingles that are more protected, which means it lasts longer. These lose that natural, “weathered” look, but then you can have any stain or color you want and don’t have to worry about painting it after the fact.

When it comes to installing the new shingles, first remove the old ones.

  1. Check the house wrap on the sheathing, if it has any. Apply new house wrap if it needs it. Usually it’s just an adhesive backing that you can stick directly on the wood.
  2. Then, apply a breathing membrane on top of the house wrap. This step is important. The cedar shingles will absorb water naturally, so the membrane allows them to dry out on all sides.
  3. Nail the shingles through everything.
  4. Use 7d galvanized box, stainless steel, or shingle nails.
  5. Double up on the first course of shingles to ensure there are no gaps for water to get in.
  6. Snap a chalk line where the shingles should go. There should be a maximum 5” reveal, to help prevent the shingles from curling. The first course does not have a chalk line because the chalk line goes on top of each course of shingles.
  7. Apply a straight edge (which is usually just a piece of dimensional lumber) along the chalk line to make it easier to line up the next course of shingles.

Resources:

Tom explained the maintenance of exposed white cedar shingles, which are a common building material in coastal New England.

For the demonstration in the barn after the house call, Tom demonstrated SBC white cedar shingles in a variety of stains. The combination house wrap/air gap Tom used on top of the sheathing was Slicker HP Rainscreen 6mm, which is manufactured by Benjamin Obdyke. For nails, Tom recommended a 6p box nail with a galvanized finish. In the demonstration, he used Grip-Rite 6p galvanized box nails, which can be found at most home centers.

Expert assistance with this segment was provided by SV Design.