Sheathing Fun Facts

Sheathing was introduced to improvise the roofing system only after 1970.  Prior to that, roofing was constructed using a layer of board (plywood was not available till 1940’s) beneath the shingles only.  The space in between is the culprit of causing leaks and water damage. 

Sheathing which is also known as decking creates a protective layer beneath the shingles.  It supports the roofing structure working efficiently by distributing additional weight from the accumulation of snow dam, etc.

As we learn from the earlier blog, we build the roof by layering of all the essentials material that provide respective functions to keep the integrity of a good roofing system.  Today, we are referring to just sheathing and why it is a vital component.

Sheathing distribute the pressure of the layering beneath the shingles which is generally about 25 pounds each.  Its main role is to barricade your home from the potential damages.  Losing shingles during extreme bad weather like hurricane is very common resulting in structural failure.  In fact, failing trees, high gusts of wind and hail are all the threats to the sheathing.

Modern plywood under the sheathing has been sprayed with fire or flame retardation nowadays and sheathing can help to stop the spreading against fire as well.  In addition, it provides prevention from water leaking from the moisture collected from your rooftop.

Now let us proceed to discuss about the type of sheathing to choose from.

Radiant barrier sheathing – this is by far the best option to help cutting down your electrical bill.  It is made from aluminum material which can blocks up to 97 percent of radiant heat.  It creates a barrier between the rooftop and your home, thus keeping your attic and home cooler in a hot summer day.

Plywood sheathing – consist of multiple layers of thin wood in 4 x 8 ft sheets and form a thickness ranges in between ¼ inch to 1 inch.  3/8 inch is the minimum thickness required.  The most common grade used widely is called CDX.  Plywood sheathing is sturdy and does a great job in holding nails in place.

Determining the size of the plywood sheathing depends on your roof slope, space in rafters and other layering components.  A tar paper should be added after installing the sheathing.

Zip System sheathing – comprises of multiple control layers built in to a single panel.  It is water resistant in a strong wood panel. This feature provides additional protection against water leak and also cost of installation by eliminating step of adding felt to your roofing.

OSB sheathing – Oriented Strand Board comprises of layers of wood strand and water resistance adhesive.  Cheaper in cost but less durable even though it is recommended by the National Roofing Contractors Association and Asphalt Roofing Manufacturers.  This material is unlikely to swell during the changes of moisture aspect therefore, the possibility of rotting wood is high when expose to too much moisture.  Luckily there are rot-resistant material available to give you an option.

My final thought

Both OSB and plywood release formaldehyde gas however, OSB produces carcinogenic gas that is hazardous to health. Plywood sheathing is harder leading 10 percent more integrity to keep the roof intact. In contrary, OSB panel is built larger than plywood, more uniform in structure and provide a better stability.

Despite the two differences between the two, they are both built to serve the same function.  At the end of the day, it is all up to your preference.