Should You Seal a Cedar Shake Roof?

Why cedar needs to breathe

Cedar shake is a hygroscopic material — it absorbs and releases moisture as conditions change. This movement is normal and expected. The problem with film-forming sealants is that they interrupt this cycle. Moisture that enters the wood through the underside, through cut ends, or through micro-cracks cannot escape. It stays trapped, creating the conditions for rot, mold, and fungal growth from the inside out.

This damage is not visible from the surface until it is advanced. A shake can look intact from the ground while the interior wood is significantly compromised.

What about penetrating preservatives?

Penetrating preservatives — products that absorb into the wood rather than forming a surface film — are generally considered more appropriate than film-forming sealants. They can help slow weathering and inhibit organic growth without blocking the wood's ability to dry.

Whether any treatment is appropriate for a specific roof depends on the current condition of the shakes. Applying a preservative to shakes that are already splitting, cupping, or showing organic growth may not extend their life meaningfully — and in some cases may mask conditions that warrant repair or replacement.

What is known

• —Cedar shake is a natural material that requires ventilation to perform correctly.
• —Film-forming sealants can trap moisture and accelerate decay.
• —Penetrating preservatives are generally considered more appropriate than surface sealants.
• —The condition of the shakes at the time of any treatment matters significantly.
• —Organic growth — moss, algae, lichen — can hold moisture against the wood surface and should be addressed before any treatment.

What remains property-specific

Whether any treatment is appropriate for your roof — and which product, if any — depends on the current condition of the shakes, the degree of weathering, the presence and type of organic growth, the ventilation of the roof assembly, and the specific climate exposure of your property. These are not questions that can be answered from the ground or from a photograph.

What happens if you seal a cedar shake roof?

A film-forming sealant can prevent the wood from drying out after rain or condensation. Trapped moisture promotes rot, mold, and fungal growth from the inside out — damage that is not visible from the surface until it is advanced.

Are there any treatments that are appropriate for cedar shake?

Penetrating preservatives — products that absorb into the wood rather than forming a surface film — are generally considered more appropriate than film-forming sealants. Whether any treatment is appropriate for a specific roof depends on the current condition of the shakes, the degree of weathering, and the presence of organic growth.

How do I know if my cedar shake roof needs treatment?

A condition assessment is the starting point. Crown Eagle evaluates the current state of the shakes — splitting, checking, cupping, organic growth, and drainage integrity — before any treatment conversation begins.

Can moss or algae damage a cedar shake roof?

Yes. Organic growth holds moisture against the wood surface and can accelerate weathering and decay. The presence and extent of organic growth is one of the factors Crown Eagle documents during a cedar shake assessment.

How long does a cedar shake roof last in Colorado?

Cedar shake roofs in Colorado can last 20 to 40 years or more depending on the quality of the original installation, the maintenance history, the exposure of the property, and the specific climate conditions. Hail is a significant factor in South Denver — large hailstones can split shakes and accelerate deterioration. A condition assessment is the only way to know where a specific roof stands.