What Causes Cedar Siding to Warp?

Cedar is one of the most beautiful siding materials you can use to clad your home’s exterior. It is naturally resilient, aesthetically pleasing to look at, and very compatible with our Pacific Northwest climate. Cedar siding, either cedar shingles or cedar shakes, are ideal for homeowners who want to pair wood with stone or brick. But there’s no denying that it can be high maintenance if not routinely maintained. What does cause cedar siding to warp?

Different Types of Warping

First let’s discuss the four main types of warping that affect cedar siding.


Curling is the result of a combination of natural stresses in the wood that occur when it is cut into shakes or shingles and extended exposure to the elements. When the edges of cedar siding start to curl up, the integrity of the siding has been compromised.


Cupping occurs when the edges of individual shingles appear to be higher that at the centre. It can look like the bottom of the inside of a cup or a dent.


Bowing tends to happen where shingles or shakes are wider, allowing more exposure to moisture. Over time, moisture absorption causes the shingles to bow and crack at the centre of individual shakes.


In general, warping is any type of distortion including the ones mentioned above. It can also refer to the effects of the elements on cedar siding and environmental impacts such as pollutants and moss/mold growth.

Improper Installation Techniques

Since warping is typically the result of too much moisture, cedar siding requires installation by skilled siding technicians in order to ensure watertight results. When nails are improperly spaced – too few or not correctly aligned – water can seep in behind the shingle.

If the nails are hammered into place too tightly during the installation, the natural process of contraction (response to cold conditions) and expansion (response to warm conditions) won’t be able to occur.

Iron nails can’t be used when installing cedar siding. Iron reacts badly with cedar, causing wood rot and the shingles or shakes to fall off the house. 

Inferior Materials

When inferior materials and manufacturing techniques are used to produce cedar siding, it might not be as durable as it could be. It will also be more prone to weathering, aging, and warping.

Cedar shingles usually have a protective finish. If the chemical coating isn’t of high quality, it begins to wear away in three to five years. This can make the cedar siding susceptible to UV ray damage, resulting in some type of warping.

Properly cured shingles are shrink-resistant, durable, and reliable. Ask questions – ensure that the manufacturer of the brand of shingles you are purchasing is employing industry-standard techniques

To avoid premature aging, select thick shingles or shakes for your cedar siding – some manufactures will appear to give you a good deal on cedar siding but the shingles are thinner.

Inadequate Maintenance

Warping, in its infant stages, is not always perceptible to the eye and by the time it is, the damage has been done. To prevent warping and expensive repairs or even replacement, cedar siding should be routinely maintained.

  • Painted or stained every 3 to 5 years
  • Inspected regularly for damage
  • When damaged, repaired as soon as possible
  • Cleaned regularly – accumulation of dust and dirt can compromise its protective finish

Moss and Mold

Too much moisture, especially in places behind the cedar panels not in contact with fresh air and sunlight, can make your siding susceptible to moss and mold. Since they are living organisms, as they grow, over time they eventually cause the cedar to warp.


Microclimate is created by factors unique to your home’s exterior and yard. It can impact your siding and cause warping in the following ways:

  • One side of the house or a particular section of siding receives too much sun
  • Portable fire pit or grill is too close to an exterior wall
  • Sprinkler system hits the cedar siding
  • Shrubs grow against the siding
  • Climbing vines, particularly in damp climates, cover exterior walls