Decking or Sheathing

Welcome back to another exciting Toronto roofing blog from Professional Roofers! In our last two blogs, we discussed what roof rafters, joists, and trusses are: a series of evenly spaced parallel beams that support the structure of your roof and walls, as well as providing a space for ventilation and insulation in your home.

For this post we are now going to be discussing what goes on top of those beams to allow easy movement on a roof, and to block the elements from your home: the “sheathing”, which is also sometimes referred to as “decking” of a roof. A roof’s sheathing is simply a board that is nailed to rafters, trusses, or roofing joists, covering them from the elements. If you know what wall decking is, roof decking is similar, but generally made from thicker and stronger materials than your wall.

Essentially, this sheathing provides a flat surface that adds a certain amount of stability to a roof, while also creating the first layer of defense from the elements. Since roof decking tends to be made from wood and wood can rot when mixed with moisture and heat, after being laid, this layer of defense should be protected quite quickly with waterproofing membranes.

That said, it is nonetheless still one more layer of protection and stability for a roof, and an incredibly important part of the roofing process, as roof decking provides the foundation for all other protective membranes and materials like shingles, flashing, or membranes to be applied. It must therefore be strong enough to support the materials that are attached to it, and durable enough to cope with the stresses of the elements and its constant use. Your sheathing, if applied correctly, will significantly increase the rigidity and strength of your roof.

In residential roofing, a roof’s sheathing is generally made from a layered wooden board (usually plywood or oriented strand board); however, it can be made from metal, concrete, or even cement depending on the home or how much weight the decking is needed to hold. Sometimes homeowners opt to install radiant barrier sheathing, which is a wooden board that has aluminum on one side. When installed, the aluminum side of radiant barrier sheathing will face down into an attic space and reflect the heat coming off the roof, preventing additional summer heat from entering your home. This type of sheathing is particularly useful in hotter climates and can reduce the need for air conditioning.


Sometimes at Professional Roofers we run into a home that is having roofing problems caused by improper sheathing installation. If your roof is made with wooden decking (as it likely is), it should be applied with approximately 1/8 of an inch distance between each board, to allow for the expansion and contraction of the boards as the seasons change. Moisture and heat can cause wood to expand, and if your contractor didn’t space out your decking properly then the boards might push up against each other as they expand, causing ripples along your roof or shingles that might break off or lay incorrectly. It is absolutely a recipe for disaster, and is something that is easily avoidable with proper installation.

Hopefully you have found this blog as informative and helpful as our last blogs, and we look forward to sharing more of our roofing insight with you next time!

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