Professional Guide: How To Install Cedar Shakes For Maximum Roof Longevity

Installing cedar shakes requires a systematic approach to moisture management, focusing on proper spacing, staggered joints, and the installation of a breathable underlayment system. Adhering to manufacturer guidelines regarding weather exposure, nail placement, and ventilation is critical to preventing premature rot and achieving a design life exceeding 30 years.

Essential Preparation, Tooling, and Safety Protocols

Cedar shake installation is a high-precision trade that balances aesthetic appeal with strict structural integrity. Before beginning, ensure the roof deck is clean, dry, and structurally sound. Cedar shakes perform best when they are allowed to breathe; therefore, the choice of underlayment and the installation of a proper ventilation gap are as vital as the shakes themselves.

• Essential Tools: High-quality pneumatic roofing nailer (adjusted to avoid over-driving), utility knife with hook blades, chalk line, tape measure, hammer, tin snips for flashing, and a ladder stabilization system.
• Safety Equipment: OSHA-compliant fall protection harness, roof anchor points, slip-resistant footwear, and eye protection.
• Material Requirements: #1 grade taper-sawn or handsplit cedar shakes, 30-lb asphalt-saturated felt or high-temperature synthetic underlayment, stainless steel or hot-dipped galvanized ring-shank nails (minimum 6d size), and corrosion-resistant flashing (copper or lead-coated copper are preferred for longevity).
• Benchmarks: An average professional installation for a standard 2,000-square-foot roof typically requires 3 to 5 days, depending on slope complexity. Budget for an additional 10% material waste factor for hip and valley cuts.

Procedural Workflow for Cedar Shake Application

Step 1: Substrate Preparation and Underlayment

Ensure the roof deck is sheathed with 1/2-inch or 5/8-inch CDX plywood. Before installing shakes, apply a layer of high-quality underlayment. In colder climates, install an ice and water shield along the eaves and in all valleys. Over the remainder of the deck, install a breathable synthetic underlayment or 30-lb felt.

Pro-Tip: Install cedar breather mats or UV-resistant rainscreen mesh between the underlayment and the shakes. This creates a critical air space that allows the underside of the cedar to dry, drastically reducing the risk of fungal decay and curling.

Step 2: Starter Course and First Row

The starter course must consist of a double layer of shakes to ensure water shed at the eaves. Install the first layer flush with the drip edge, and then install the second layer directly over it, ensuring that the joints of the second layer do not align with the joints of the first. Maintain a 1/4-inch to 3/8-inch gap between every shake to allow for the natural expansion of the wood when it absorbs moisture.

Step 3: Determining Exposure and Chalk Lines

Determine the weather exposure based on the slope of the roof and the length of the shakes. For a standard 18-inch shake, a 7.5-inch exposure is common. Snap chalk lines horizontally across the roof deck to ensure that every course remains perfectly level. If the lines are not level, the entire roof will appear visually skewed, and water shedding efficiency will be compromised.

Step 4: Installing Subsequent Courses

Lay the shakes along your chalk lines. Each shake should be secured with two nails, positioned approximately 1 to 2 inches from the edges and 2 inches above the exposure line. Never drive nails through the exposure area of the course below. Ensure that the space between shakes (the side lap) is at least 1.5 inches apart from the joints in the course below to ensure a watertight bond.

Warning: Do not overdrive your pneumatic nails. The head of the nail should be flush with the surface of the shake. If it is driven too deep, it will fracture the wood fibers and create a pathway for moisture to seep into the roof deck.

Step 5: Flashing and Finish Work

Valleys, chimneys, and roof-to-wall transitions require specialized metal flashing. Use shingles or sheet metal to weave the flashing into each course of shakes as you progress up the roof. At the ridge, install cedar ridge caps, overlapping them in the direction of the prevailing wind to prevent driving rain from infiltrating the attic space.

Technical Specifications and Material Comparisons

Addressing Installation Failures and Field Corrections

• Root Cause: Water infiltration due to "keyway" alignment.
  
  
  • Actionable Fix: Ensure a minimum of 1.5 inches of offset between the joints of overlapping courses. If misalignment is discovered, use a strip of corrosion-resistant flashing under the gap to divert water over the lower shake.
• Root Cause: Cupping or warping of shakes.
  
  
  • Actionable Fix: If cupping occurs due to lack of ventilation, retrofit the area by installing a cedar breather mat. If the damage is severe and structural, the affected area must be stripped and replaced with proper air-gap spacers.
• Root Cause: Corrosion of fasteners leading to loose shakes.
  
  
  • Actionable Fix: If standard nails were used instead of stainless steel, they will eventually oxidize and fail. Replace failed fasteners with 316-grade stainless steel ring-shank nails to prevent "black streaks" and future roof failure.

Frequently Asked Questions

Do cedar shakes require chemical treatment?

While natural, untreated cedar has inherent oils that resist decay, modern environmental factors often necessitate treatment. Applying a borate-based preservative or a UV-inhibiting wood sealer can significantly extend the lifespan of the roof by preventing rot and excessive silvering.

Can I install cedar shakes over existing shingles?

It is not recommended to install cedar shakes over existing asphalt shingles. Cedar requires a clean, solid, and ventilated substrate to prevent moisture entrapment; stacking shingles compromises the weight load capacity of the rafters and prevents the wood from drying out properly.

What is the ideal weather exposure for an 18-inch shake?

The standard exposure for an 18-inch shake is 7.5 inches. This allows for the necessary overlap to ensure water protection while maximizing the material's structural coverage on slopes greater than 4:12.

How do I prevent moss and lichen growth on cedar shakes?

Keep the roof free of overhanging branches to maximize sun exposure and airflow. If moss or lichen appears, use a gentle cleaning solution of oxygen bleach and water, scrubbing with a soft brush to avoid damaging the wood fibers.

Consult with a certified cedar roofing specialist to finalize your material grade and procurement schedule for your specific climate. Ensure your installation meets local building codes to maintain compliance and maximize your structural investment.