Cedar Shake Calculator
Calculate the number of cedar shakes or shingles needed for walls or roofing. Enter values for instant results with step-by-step formulas.
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Formula
Net area is calculated by subtracting window and door openings from gross wall/roof area. A waste factor of 10-15% is added. Coverage is measured in squares (100 sq ft), with bundle count varying by application (4 bundles/square for roofing, 5 for walls at standard exposure).
Last reviewed: December 2025
Worked Examples
Example 1: Sidewall Cedar Shake Installation
Example 2: Cedar Shake Roof
Background & Theory
The Cedar Shake Calculator applies the following established principles and formulas. Structural and construction engineering is governed by fundamental load analysis, material science, and regulatory standards that ensure the safety and durability of built structures. The primary distinction in load analysis is between dead loads โ the permanent self-weight of structural elements, finishes, and fixed equipment โ and live loads, which represent variable occupancy, furniture, and environmental forces such as wind and snow. These are combined using factored load equations, such as the ASCE 7 formula U = 1.2D + 1.6L, where D is dead load and L is live load. Concrete mix design is governed by the water-cement (w/c) ratio, which is the primary determinant of compressive strength and durability. A w/c ratio of 0.40โ0.45 typically yields concrete with 28-day compressive strengths of 30โ40 MPa. Common mix ratios by weight for structural concrete are approximately 1 part cement : 1.5โ2 parts sand : 3 parts coarse aggregate. Structural steel is characterized by its yield strength (the stress at which permanent deformation begins, typically 250โ350 MPa for mild steel) and ultimate tensile strength (typically 400โ500 MPa). Mid-span deflection of a simply supported beam under a central point load is given by ฮด = FLยณ / (48EI), where F is force, L is span length, E is Young's modulus, and I is the second moment of area. Building insulation is rated by R-value, a measure of thermal resistance in units of mยฒยทK/W (SI) or ftยฒยทยฐFยทh/BTU (imperial). Higher R-values indicate greater resistance to heat flow. Foundation design depends on the allowable bearing capacity of the underlying soil, which ranges from approximately 75 kPa for soft clay to over 10,000 kPa for bedrock. Drainage gradients for surface water are typically specified as a minimum of 1โ2% slope away from building foundations to prevent hydrostatic pressure and water infiltration.
History
The history behind the Cedar Shake Calculator traces back through the following developments. The history of construction engineering spans thousands of years of accumulated empirical knowledge and, more recently, rigorous scientific analysis. The ancient Egyptians built the Great Pyramid of Giza around 2560 BCE using an estimated 2.3 million stone blocks, demonstrating sophisticated logistics, geometry, and workforce organization. Roman engineers advanced the field dramatically through the use of pozzolanic concrete โ a mixture of volcanic ash, lime, and seawater โ enabling the construction of the Pantheon dome (43.3 m diameter, completed around 125 CE) and a vast network of aqueducts and roads across the empire. Cast iron emerged as a structural material during the Industrial Revolution, first used prominently in the Iron Bridge at Coalbrookdale, England, completed in 1779. Wrought iron and later steel allowed far greater spans and heights. The Eiffel Tower, completed in 1889, demonstrated the structural possibilities of wrought iron at scale and influenced the development of steel-frame skyscraper construction in Chicago and New York. Reinforced concrete was systematically developed by Joseph Monier, a French gardener, who patented iron-reinforced concrete pots and panels in the 1860s, and later by engineers including Franรงois Hennebique who created the first comprehensive reinforced concrete framing system in the 1890s. The 1906 San Francisco earthquake caused widespread devastation and galvanized the engineering profession to develop seismic design provisions. Subsequent earthquakes โ including the 1971 San Fernando and 1994 Northridge events โ drove successive improvements in seismic codes, base isolation technology, and ductile detailing of reinforced concrete and steel frames. Building codes became increasingly standardized in the twentieth century, with the International Building Code (IBC) first published in 2000 providing a unified model code adopted across much of the United States. Building Information Modeling (BIM) emerged in the 2000s as a digital workflow integrating architectural, structural, and MEP design into a unified three-dimensional model, fundamentally changing coordination practices across the industry.
Frequently Asked Questions
Formula
Squares = Net Area x (1 + Waste%) / 100; Bundles = Squares x Bundles per Square
Net area is calculated by subtracting window and door openings from gross wall/roof area. A waste factor of 10-15% is added. Coverage is measured in squares (100 sq ft), with bundle count varying by application (4 bundles/square for roofing, 5 for walls at standard exposure).
Worked Examples
Example 1: Sidewall Cedar Shake Installation
Problem: Calculate cedar shakes for 40 ft of wall by 10 ft high with 60 sq ft of window deductions, using 18-inch shakes at 7.5-inch exposure. Shakes cost $350/square.
Solution: Gross area = 40 x 10 = 400 sq ft\nNet area = 400 - 60 = 340 sq ft\nWith 10% waste = 374 sq ft\nSquares = 374 / 100 = 3.74\nBundles (5/square for walls) = ceil(3.74 x 5) = 19\nCourses = ceil(120 / 7.5) = 16\nShake cost: 3.74 x $350 = $1,309\nNails: ~9 lbs = $72\nHousewrap: 3 rolls = $135\nTotal materials: $1,516\nLabor: 3.74 x $200 = $748\nTotal: $2,264
Result: 3.74 squares | 19 bundles | Material: $1,516 | Total: $2,264
Example 2: Cedar Shake Roof
Problem: Calculate for a 50 ft x 20 ft roof area (1,000 sq ft) with no deductions, 24-inch shakes at 10-inch exposure, $400/square.
Solution: Net area = 1,000 sq ft\nWith 15% waste = 1,150 sq ft\nSquares = 11.50\nBundles (4/square for roofing) = ceil(11.50 x 4) = 46\nShake cost: 11.50 x $400 = $4,600\nNails: ~18 lbs = $144\nFelt interlayment: 3 rolls = $75\nFlashing: 5 pieces = $75\nTotal materials: $4,894\nLabor: 11.50 x $250 = $2,875\nTotal: $7,769
Result: 11.50 squares | 46 bundles | Material: $4,894 | Total: $7,769
Frequently Asked Questions
What is the difference between cedar shakes and cedar shingles?
Cedar shakes are split from bolts of wood, creating a rough, textured surface with irregular thickness that gives a rustic, handcrafted appearance. Cedar shingles are sawn on both sides, producing a smooth, uniform surface with consistent thickness that creates a more refined, even look when installed. Shakes are thicker (typically 3/4 to 1-1/4 inches at the butt) compared to shingles (approximately 3/8 to 1/2 inch), which means shakes provide greater weather protection and tend to last longer in severe climates. The rough surface of shakes creates more shadow lines and visual depth on the wall or roof, while the smooth surface of shingles delivers a cleaner, more formal aesthetic. Shakes generally cost 20 to 40 percent more than shingles due to the manual splitting process and higher material waste during manufacturing.
How many bundles of cedar shakes cover one square?
A roofing square equals 100 square feet of coverage, and the number of bundles per square depends on the shake length, exposure, and whether the application is roofing or sidewall. For roofing applications, 18-inch hand-split shakes at 7.5-inch exposure require 4 bundles per square, while 24-inch shakes at 10-inch exposure also require 4 bundles per square. For sidewall applications, the same shakes at tighter exposure settings may require 5 bundles per square because the reduced exposure means more courses and more material per square foot. Bundle sizes are standardized by the Cedar Shake and Shingle Bureau (CSSB), with each bundle containing enough shakes to cover approximately 25 square feet at the specified exposure. Always verify the bundle coverage listed on the packaging, as some premium or specialty shakes may have different coverage rates than standard products.
What exposure should I use for cedar shakes?
Exposure is the portion of each shake visible after the course above is installed, and it varies based on the shake length and whether the application is roofing or sidewall. For roofing, the maximum recommended exposure is approximately one-third of the shake length minus one-half inch, so 18-inch shakes have a maximum roof exposure of 7.5 inches and 24-inch shakes have a maximum of 10 inches. For sidewall applications, the exposure can be increased because walls are not subject to the same water runoff as roofs, allowing up to half the shake length or about 8.5 inches for 18-inch shakes. Reducing the exposure below the maximum creates a thicker, more layered look with better weather protection but uses significantly more material and increases cost. In areas with heavy rain, high wind, or severe weather, reducing the exposure by 0.5 to 1 inch below maximum provides an extra margin of protection.
Do cedar shakes need a special underlayment?
Cedar shake roofing requires an interlayment of 18-inch wide, 30-pound asphalt-saturated felt (roofing paper) installed between each course of shakes, which is unique to shake roofing and not required for composition shingles. The interlayment is placed so that its bottom edge is positioned above the butt of the shake by a distance equal to twice the exposure, creating a double layer of weather protection at every point on the roof. A full layer of 30-pound felt is also installed over the entire roof deck before the first course of shakes as an additional moisture barrier. For wall applications, a weather-resistive barrier (housewrap) is installed over the wall sheathing, similar to any other siding material, and no interlayment between courses is required. In high-wind or coastal areas, some building codes require ice and water shield membrane at the eaves and valleys in addition to the standard felt interlayment.
Can I install cedar shakes over existing roofing?
Installing cedar shakes directly over existing asphalt shingles or other roofing is generally not recommended and is prohibited by most building codes because shakes require proper air circulation beneath them to prevent moisture buildup and premature decay. Cedar shakes should be installed over spaced sheathing (skip sheathing) or over a ventilated nailing strip system that allows air to flow under the shakes, which is impossible to achieve over an existing solid roof surface. Tear-off of the existing roofing to the deck is the standard practice, followed by installation of the appropriate underlayment and new sheathing if needed. Some retrofit systems use vertical furring strips over the existing roof to create an air gap, but these add significant cost and complexity and must be engineered to handle wind uplift and structural loads. Additionally, the weight of cedar shakes (350 to 450 pounds per square) added to existing roofing may exceed the structural capacity of the roof framing, creating a safety hazard.
What maintenance do cedar shakes require?
Cedar shake maintenance involves annual inspection for damaged, split, or missing shakes, moss or algae growth, and debris accumulation in valleys and behind chimneys. Cleaning the shakes every 2 to 3 years with a low-pressure wash and appropriate cleaning solution removes moss, algae, and dirt that trap moisture and accelerate decay. Applying a wood preservative or water-repellent treatment every 3 to 5 years extends the life of the shakes by replacing the natural oils that leach out over time from sun exposure and weathering. Individual damaged shakes can be replaced without disturbing the surrounding courses by splitting out the damaged shake and sliding a new one into position, securing it with a single nail driven under the course above. Keeping overhanging tree branches trimmed back at least 10 feet from the roof reduces shade that encourages moss growth and eliminates the needle and leaf debris that traps moisture on the shake surface.
References
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