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Why do my Wood Shingles Curl?

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Curling wood shingles

The most economical and feasible solution to correcting a curled wood shingle is to remove and replace the shingle with a new wood shingle.

Photo © Jurin Roofing Services, Inc. www.jurinroofing.com

You may consider some wood shingle roof systems to be friendly to passer-byes. As you pass by and look up it almost appears that the shingle roof is beginning to wave at you. Even though wood shingles are one of the most impressive roof systems to install on your home or business, they are no friendlier than the average asphalt or slate roof. What you are seeing as you pass by is the curling of the wood shingles and not the wave of a friendly shingle.

What Causes Wood Shingles To Curl?

Wood shingles are a natural wood product. As with any wood product, they do soak up moisture through the surfaces of the wood shingles. Through blow back and other factors where snow and rain are forced under the shingle, moisture accumulates on the underside of the shingles as well as on the exposed surface of the shingle. After the precipitation ends and the roof begins to dry out, the exposed surface of the shingles dries but the underside of the shingles remains moist.

This moisture remains on the underside of the wood shingles in certain situations where the underside of the shingles is not properly ventilated. It is recommended that wood shingle roof systems have ventilation built into the roof system between the top of the roof deck and the underside of the wood shingles to allow the wood shingles to properly ventilate. In situations where this ventilation is not properly installed, the wood shingles are not able to dry out.

As the wood shingles dry out on the exposed surfaces on top of the shingles, the underside of the shingle remains moist. This creates a dynamic where the surface of the wood shingles that is exposed to the external environment dries out and contracts while the surfaces of the wood shingles that are concealed do not dry out. This creates an effect where the exposed wood contracts while the concealed wood remains swollen with moisture. As this takes place the top of the wood shingle contracts while the bottom remains wet and swollen creating the curling effect.

How do I Repair My Curled Wood Shingles?

The most economical and feasible solution to correcting a curled wood shingle is to remove and replace the shingle with a new wood shingle. Repairing or uncurling the wood shingle that is curled is not practical. However, it is recommended that a source of ventilation be introduced into the roof system as part of remediation of this condition. If a source of ventilation is not provided, the same conditions will reoccur over time.

How Do I Ventilate My Wood Shingle Roof?

There are multiple products, solutions and methods for providing ventilation to a wood shingle roof system. These solutions involve the complete removal and replacement of the roof system. Most solutions that are available require the system or solution to be incorporated into the original design of the roof system when the building is constructed. Applying a solution without removal and replacement of the roof system is difficult and in most cases impractical.

An example of a solution to incorporate into a wood shingle roof for ventilation is to incorporate a system of lathe into the roofing process. The lathe is installed horizontally across the roof surface after the underlayment (e.g. felt paper) is installed. The lathe is spaced on intervals equal to the exposure of the wood shingles being installed. This allows for cross ventilation under the wood shingles. The cross ventilation allows the moisture to be removed from the underside of the wood shingles.

Another example of another solution is a product manufactured by the Benjamin Obdyke Corporation. The product is called Cedar Breather. It is a product that is applied across the roof surface prior to the application of the wood shingles. It provides a continuous and uniform path for air flow beneath the wood shingles when the wood shingles are installed over solid deck. It allows the moisture to be ventilated out from the underside of the wood shingles.

Ventilation Is Important

As with all steep sloped roof assemblies, it is important to provide ventilation for wood shingle roof systems. In the case of wood shingle roofs, it may be necessary to provide and install two sources of ventilation. These roof systems may require ventilation for both the wood shingles themselves as well as the attic space in the home. By providing adequate ventilation, wood shingle roofs will provide a long life and add to the aesthetic appearance of the home or building.

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