How to Bend Cedar Shingles for Curved Surfaces
Installing cedar shingles on a curved wall or rounded surface presents a unique challenge for even experienced siding installers. When you try to bend a dry cedar shingle around a tight radius, the wood fibers resist the compression on the inside of the curve and the tension on the outside, often resulting in splits and cracks. Fortunately, with the right techniques and a bit of preparation, you can achieve smooth, beautiful curved cedar siding installations that will last for decades.
Cedar shingles and shakes have been used for centuries as siding material, prized for their natural beauty, durability, and resistance to rot and insect damage. Western red cedar, in particular, is lightweight, stable, and contains natural oils that make it weather-resistant. These same properties make it workable for curved installations when handled properly.
Understanding the Challenge: Why Cedar Shingles Split
To understand why cedar shingles split when bent, it helps to know a bit about the material. Cedar shingles are sawn from logs, with the grain running parallel to the long dimension. When you bend a shingle, the fibers on the outside of the curve are stretched (tension), while those on the inside are compressed. Cedar can handle a certain amount of tension, but when the radius is too tight, the fibers on the tension side separate, creating a split.
The tightness of the curve is measured by the radius — the distance from the center of the curve to the surface. A gentle curve with a large radius (24 inches or more) is relatively easy to achieve with standard shingles. A tight curve with a small radius (12 inches or less) requires more preparation and care. For extremely tight curves (6 inches or less), you may need to use narrower shingles or consider alternative materials.
Several factors affect how easily a shingle can be bent: the thickness of the shingle (thinner shingles bend more easily), the moisture content (drier shingles are more brittle), the grain pattern (straight, vertical grain bends better than irregular grain), and the width of the shingle (narrower shingles bend more easily than wide ones).
Soaking: The Traditional Method
The most common technique for bending cedar shingles is to soak them in water before installation. Soaking softens the wood fibers and makes them more pliable, allowing the shingle to conform to the curve without splitting. The traditional approach is to submerge the shingles in water for 24 to 48 hours before installation. Some contractors use hot water to speed up the process, as warm water penetrates the wood more quickly than cold water.
To set up a soaking station, fill a large trough, wheelbarrow, or kiddie pool with water and stack the shingles in it, weighing them down with a brick or heavy board to keep them submerged. After soaking, remove the shingles and allow the surface water to drip off before installation. Work with a batch at a time — don’t soak more shingles than you can install in a single day, as they can begin to mold if left wet too long.
One variation of this method is to spray the shingles with water and stack them overnight under a plastic tarp. The moisture penetrates the wood more slowly this way, but it’s effective for gentle curves and requires less water. This method works best when the shingles are stacked with the butt ends aligned and the tarp is sealed tightly to retain moisture.
Once installed, the shingles will dry in place and conform permanently to the curve. As the cedar dries, it may shrink slightly, which is normal. For more on cedar siding installation techniques, see our complete guide.
Scoring the Back: Alternative Approach for Tight Curves
For tighter curves where soaking alone isn’t enough, you can use a technique called “scoring” or “kerfing.” This involves cutting shallow grooves across the back of the shingle perpendicular to the grain. The grooves relieve the compression stress on the inside of the curve, allowing the shingle to bend without the tension side splitting.
To score a shingle, lay it flat with the back side (the side that will face the wall) up. Using a utility knife or a circular saw set to a very shallow depth (about 1/8 inch or less), cut grooves spaced about 1/2 to 3/4 inch apart across the width of the shingle. The grooves should extend from one edge to the other, covering the area that will be bent. The closer the spacing, the tighter the curve you can achieve.
The depth of the grooves is critical — too deep and the shingle will be weakened, too shallow and the relief won’t be sufficient. A good rule of thumb is to cut no deeper than one-third of the shingle thickness. For standard #1 grade cedar shingles that are about 3/8 inch thick at the butt, the grooves should be about 1/8 inch deep.
After scoring, soak the shingles briefly (30 minutes to an hour) to further soften the fibers, then install them immediately. The combination of scoring and soaking allows you to achieve surprisingly tight curves — even radii as small as 6 to 8 inches in some cases. This technique is commonly used for eyebrow dormers, rounded gable ends, and curved architectural features.
Choosing the Right Shingle Grade and Width
Not all cedar shingles are equally suitable for curved installations. For best results, choose #1 grade (also called “Blue Label”) shingles, which are clear heartwood with no knots or defects. The straight, tight grain of #1 grade shingles provides the best bending characteristics. Avoid #2 grade (“Red Label”) or #3 grade (“Black Label”) shingles, which have more knots and imperfections that can create weak points where splits will start.
Shingle width also matters. Standard shingles come in random widths from about 3 to 14 inches. For curved installations, select narrower shingles — 4 to 6 inches wide — which bend more easily than wide shingles. The narrower profile conforms to curves with less stress on the individual shingle. If your design calls for wider shingles on a curve, you can rip standard shingles to narrower widths using a table saw or circular saw with a fence.
Consider using shingles that are shorter than standard for tight curves. Standard shingles are 18 inches long, but “junior” shingles at 16 inches or even 12 inches can be easier to bend. The shorter length means less material has to conform to the curve, reducing the stress on the wood fibers. For very tight radii, consider using cedar shakes (which are split rather than sawn) — their irregular texture and thicker butt can hide minor bends better, though they’re harder to bend overall.
Installation Techniques for Curved Surfaces
Before installing the shingles, prepare the curved substrate. The surface should be smooth and free of bumps that would telegraph through the shingles. For tight curves, consider installing a layer of 15-pound roofing felt as a slip sheet between the substrate and the shingles — this allows the shingles to move slightly as they dry and season, reducing the risk of splitting.
When nailing shingles on a curve, use corrosion-resistant nails (hot-dipped galvanized or stainless steel). The nails should be long enough to penetrate through the sheathing — typically 1-1/2 to 1-3/4 inches for standard installations. Place the nails about 1 inch above the overlap line and about 3/4 inch from the edge. On curves, nail placement is even more critical — the nails should follow the curve, not force the shingle into a straight line.
For tight curves, predrill the nail holes to prevent splitting. Use a drill bit slightly smaller than the nail diameter and drill through the shingle at the desired nail location. This step takes extra time but virtually eliminates splitting from nailing on curves. Space the nails about 1 inch apart along the overlap line for maximum holding power.
Work from the bottom up, just like a standard shingle installation, but pay extra attention to the reveal (the exposed portion of each course). On a convex curve (bulging outward), the reveals will naturally be slightly wider at the bottom of the curve. On a concave curve (curving inward), the reveals may need to be adjusted to maintain a consistent appearance. See our exterior trim and siding tips for more installation guidance.
Tool Recommendations for Curved Shingle Work
Having the right tools makes curved shingle installation much easier. A good quality utility knife with plenty of spare blades is essential for scoring. For cutting shingles to fit curves, use a fine-toothed handsaw or a jigsaw with a wood-cutting blade. Avoid power miter saws for curved work — they can shatter the shingle if it’s not perfectly supported.
A shingle hatchet or shingle hammer with a weighted head and a cutting edge on the poll (the back of the head) is traditional for shingle work. These tools allow you to cut and nail with a single tool. For curved work, a standard framing hammer or siding nailer (pneumatic or cordless) can also work — just be careful to control the angle of the nail to follow the curve.
For tighter curves, consider using a bending form: a jig made from a piece of plywood cut to the desired radius. You can clamp the shingle to the form while the adhesive or fasteners are applied. This is especially useful for factory pre-assembly of curved sections that are then installed as a unit. This technique is more labor-intensive but produces consistent, professional results on complex curves.
Common Mistakes and How to Avoid Them
The most common mistake in curved cedar shingle installation is trying to bend the shingle too far without preparation. If the shingle resists, don’t force it — it will split. Instead, increase the soaking time, add scoring, or use a narrower shingle. Remember that you’re working with a natural material that has limits.
Another mistake is installing shingles that are too dry. Cedar shingles should have a moisture content of 15-20% for normal installation. For curved work, higher moisture content (20-30%) is beneficial. If your shingles have been stored in a dry environment, they may need longer soaking times to reach the desired pliability.
Finally, don’t rush the installation. Curved shingle work takes more time than flat wall installation — plan for it. Each shingle needs individual attention to ensure it conforms properly to the curve, is nailed securely, and aligns with the adjacent shingles. The time investment pays off in a beautiful, long-lasting installation. For more on siding maintenance and weatherproofing, see our maintenance guide.
When working on curved roof features like rounded dormers or turrets, selecting the right roofing materials for curved surfaces is just as important as proper shingle installation.
Conclusion
Bending cedar shingles for curved surfaces is a skill that improves with practice. The key techniques — soaking, scoring, selecting the right shingles, and using proper fastening methods — are all straightforward and achievable for most skilled DIYers and professional contractors. Start with gentle curves and work your way up to tighter radii as you gain confidence.
Remember that cedar is a forgiving material when treated properly. The natural flexibility of the wood, combined with proper preparation, allows you to create sweeping architectural curves that add distinctive character to any home. Whether you’re working on a rounded bay window, an arched entryway, or a decorative turret, the techniques described here will help you achieve professional results without the frustration of split and wasted shingles.