The Professional Guide To Cedar Shake Installation: Technical Standards For A Lifetime Roof

Successful cedar shake installation requires a precise "interlayment" system where 18-inch strips of number 30 roofing felt are woven between every course of wood to create a staggered, waterproof barrier. Installers must maintain a 1/4-inch to 3/8-inch expansion gap between individual shakes and ensure a minimum 1.5-inch side-lap offset between joints in successive courses to prevent vertical water migration. Adhering to these technical thresholds ensures the assembly meets CSSB (Cedar Shake and Shingle Bureau) standards and survives extreme weather cycles.

Essential Material Selection and Site Preparation Requirements

Before the first fastener is driven, the roof deck must be evaluated for structural integrity and ventilation capability. Unlike asphalt shingles, cedar shakes are organic "living" materials that expand and contract with hygroscopic fluctuations. Failure to provide adequate airflow or using the wrong grade of timber will result in premature rot, cupping, and structural failure within less than a decade.

Comprehensive Equipment and Material Checklist

• Primary Materials: Certi-split Grade 1 Blue Label Western Red Cedar shakes (hand-split and resawn), 18-inch wide Type 30 ASTM D226 felt (interlayment), and stainless steel fasteners (Type 304 for inland, Type 316 for coastal zones).
• Essential Hand Tools: Roofing hatchet (for trimming and gauging exposure), shingle ripper, pneumatic coil nailer with a flush-drive attachment, and a high-quality chalk line.
• Safety Gear: OSHA-compliant fall arrest system, magnetic sweep for stray fasteners, and heavy-duty gloves to protect against cedar splinters.
• Prerequisite Standards: Minimum roof slope of 4:12 (lower slopes require specialized waterproof membranes), solid or spaced sheathing (1x4 or 1x6 boards), and drip edge flashing.
• Project Benchmarks: An experienced two-man crew can typically install 1 to 2 squares (100-200 square feet) per day, depending on the complexity of the roof geometry and the number of valleys or dormers.

Systematic Execution of the Cedar Shake Assembly

Step 1: Substrate Preparation and Eave Protection

The longevity of a cedar roof is dictated by the quality of the substrate. While solid sheathing is common in modern construction, "spaced sheathing" (also known as skip sheathing) remains the gold standard for cedar because it allows the wood to breathe from both sides. If using solid sheathing, a nylon matrix breathable underlayment must be installed first to provide a drainage plane.

Begin by installing a 36-inch wide ice and water shield membrane along the eaves. This membrane must extend at least 24 inches past the interior wall line to protect against ice damming. Over this, install a heavy-gauge "W-profile" valley flashing in areas where roof planes intersect. Use only copper, stainless steel, or high-grade aluminum; avoid galvanized steel, as the natural tannins in cedar will chemically react and corrode the zinc coating, leading to holes in the metal within years.

Step 2: Establishing the Double Starter Course

The first course at the eave must be doubled to ensure the joints are protected and the roof has a finished aesthetic profile. Start by installing a layer of 18-inch or 24-inch cedar shingles or shakes directly over the drip edge, allowing for a 1.5-inch overhang beyond the fascia. This overhang ensures that water sheds into the gutter rather than wicking back into the wooden rake boards.

Fasten this first layer using two nails per shake, positioned approximately 1 inch from each edge and 2 inches above the butt line. Immediately lay a second course of shakes directly over the first, staggering the joints by at least 1.5 inches. This "double-butt" provides the necessary thickness at the edge of the roof to support the angle of subsequent courses.

Step 3: The Interlayment Process (The Shake Shield)

Shakes are more porous than shingles and require an interlayment of felt paper to act as a secondary water barrier. This is the most critical step in the installation. After the starter course is secured, measure up from the butt of the shakes to your desired exposure (usually 10 inches for a 24-inch shake) and snap a chalk line.

Place an 18-inch wide strip of #30 felt paper so that its bottom edge is positioned at a distance above the butt of the first course equal to twice the exposure. For example, if you are using a 10-inch exposure, the bottom of the felt should be 20 inches up from the butt of the shakes. This ensures the felt covers the top portion of the shakes and extends up onto the sheathing, effectively creating a "shingle" of felt between every wooden layer.

Step 4: Laying and Spacing Successive Courses

Place the next course of shakes onto the felt interlayment. Maintain a strict 1/4-inch to 3/8-inch gap between each shake. This gap is non-negotiable; as cedar absorbs moisture, it expands. If shakes are installed tight against one another, they will "buckle" or "tent," pulling the fasteners out of the wood.

When choosing the placement of each shake, ensure that the joints (the gaps) are offset by at least 1.5 inches from the joints in the course below. Never allow a joint to align vertically over three courses (this is known as "tracking"). Use your roofing hatchet to trim the width of shakes as needed to maintain this offset. Drive two fasteners into each shake approximately 1 inch from the edges and 1 to 2 inches above the exposure line of the next course. The goal is for the next layer of shakes to completely cover the fasteners of the layer below, protecting them from the elements.

Step 5: Hip and Ridge Application

Once the field of the roof is complete, the ridges and hips must be capped. Use pre-fabricated "factory-assembled" hip and ridge units for the most professional finish. These units are made of two pieces of cedar pre-fastened at an angle.

Start at the bottom of a hip or the end of a ridge away from the prevailing wind. Install these units with a double-starter course, similar to the eaves. Use longer fasteners (usually 2.5-inch or 3-inch nails) to ensure penetration through the multiple layers of wood and into the structural ridge beam. Maintain the same exposure used on the main roof. At the very peak where two ridges meet, or where a hip meets a ridge, install a "lead-plug" or a specialized flashing piece to prevent water from driving into the apex.

Critical Material Specifications and Fastener Requirements

The following table outlines the industry-standard exposure and fastener requirements for Western Red Cedar Shakes based on Certi-split Grade 1 standards.

Common Installation Failures and Technical Remediation

Professional roofing inspections often reveal specific patterns of failure related to cedar shakes. Identifying these early can save tens of thousands of dollars in structural repairs.

• Scenario: Split or Cracked Shakes along the Fastener Line

  
  
  
  • Root Cause: Over-driving nails or using a pneumatic nailer with the pressure set too high. This crushes the wood fibers, creating a stress point that splits as the wood dries.
  • Actionable Fix: Adjust the nailer's depth-of-drive so the nail head sits flush with the surface of the shake without indenting it. If manual hammering, use a "light touch" for the final blow. Split shakes must be removed and replaced using a shingle ripper.

• Scenario: Premature Rot at the Eaves

  
  
  
  • Root Cause: Lack of a "starter course" or insufficient overhang, causing water to wick into the fascia and the underside of the first layer of shakes.
  • Actionable Fix: Ensure the 1.5-inch overhang is maintained. If rot is present, the first three courses must be removed, the fascia replaced, and a proper drip edge installed before re-shingling with a double starter course.

• Scenario: Fastener "Bleeding" or Rust Streaks

  
  
  
  • Root Cause: Use of electro-galvanized or zinc-coated nails. Cedar’s natural acetic acid reacts with these metals, causing them to dissolve and leave black or orange streaks.
  • Actionable Fix: There is no "wash" for this. The only permanent fix is to replace the affected shakes with new ones using stainless steel fasteners. In severe cases, the entire roof may be compromised if the nails have thinned to the point of losing withdrawal resistance.

Frequently Asked Questions

What is the difference between a cedar shake and a cedar shingle?

Cedar shingles are sawn on both sides, resulting in a thinner, more uniform appearance with a smooth surface. Cedar shakes are typically hand-split on one side and resawn on the back, providing a thicker, highly textured, and more rustic aesthetic that offers superior durability in heavy snow or high-wind environments.

Can I install cedar shakes over an existing asphalt roof?

No. Cedar shakes require a clean, level substrate and proper ventilation to prevent rot. Installing them over old asphalt shingles traps moisture between the layers, which will cause the wood to decay rapidly and may violate local building codes or manufacturer warranties.

How often do cedar shakes require maintenance?

To achieve a 30-to-50-year lifespan, cedar roofs should be inspected every 3 to 5 years. Maintenance involves removing debris from the gaps (which can trap moisture), treating the wood with a topical fungicide or UV-stabilizer to prevent moss growth, and replacing any individual shakes that have curled or split.

Is it necessary to use pressure-treated cedar shakes?

In high-humidity climates or heavily forested areas with low sun exposure, pressure-treated (CCA) shakes are highly recommended. These shakes are factory-impregnated with preservatives that prevent fungal decay and wood-boring insects, significantly extending the life of the roof compared to untreated wood in damp conditions.

Elevate Your Property with Professional Grade Cedar

Precision in cedar shake installation is the difference between a roof that fails in a decade and one that protects for generations. By adhering to these technical standards and using premium stainless steel components, you ensure a high-performance envelope that enhances both the value and the resilience of your home.