How often does roof decking need to be replaced?

home with a roof decking in good condition

Roof decking under your materials

What’s up on the rooftop is one question, what is under the shingles, roof decking vs sheathing is another question. There are a many components to a roof, most of it we don’t see from the ground, like the roof decking. To understand your roof better, explaining what roof decking and other components are, we have a break down what is under the shingles: 

  • Trusses: The foundation of the roof, this creates the peak of your roof and provides support for the rest of the roofing components, especially the roof decking.
  • Chimney: If your home has a fireplace, it needs a chimney to carry the ash and soot from the fireplace out, so it doesn’t fill your home. 
  • Flashing: This metal strip is installed where different roof angles meet, around the chimney , and other areas that are prone to leak.  
  • Vent pipe: This small pipe extends up, allowing fresh air into the plumbing so that sinks, toilets, and tubs can drain. 
  • Sheathing: This is the subject of today’s article, sometimes referred to as the roof decking, and the first layer of the roof, and maybe called roof decking or sheathing. This will be either roof decking osb vs plywood and is attached to the trusses, creating the foundation for the shingles. 
  • Underlayment: This thin layer of material is attached to the sheathing, aka roof decking, is typically an asphalt coated felt, is the barrier from element and helps water to shed when a shingle is loose or missing, minimizing the chance of roof decking exposed. 
  • Shingles: This is the part you see and comes in several colors, styles,  and textures. 
  • Ridge Vent: This is at the peak of the roof, runs the entire length and keeps moisture from collecting in your attic and maintains a consistent temperature in the attic. 
  • Ridge cap: These are some shingles that cover the ridge vents and keep moisture out so the ridge vents can do their job. 
  • Fascia: This is the board you see running along the bottom of the roof trusses to keep things out of the attic and the elements blowing up under the roof decking.

What is better for a roof OSB or plywood?

When comes to choose between OSB or plywood for roof decking, both having structural characteristics, both rated Exposure 1 for temporary element exposure, and resistant to nail withdrawal, is one better than the other? It really becomes the builder’s or roofing contractor’s choice, with the following facts helping them make their decision. 

OSB, an engineered wood with particleboard like feel and look, is manufactured with strands of wood compressed together in specific orientation, unevenly, creating the rough surface you feel. It is available in different rigidity, sizes, strengths, and thickness.  It is a water-resistant material but does need the addition of an additional membrane to create complete water impermeability. 

OSB offers consistent density and doesn’t have knot holes other natural flaws that can create weak areas. A structural uniform product that is less expensive than plywood and has a stronger load-bearing capacity. 

Plywood has an advantage in stiffness, making the ideal material for subflooring, and is often used as roof decking with 24-inch truss spacing in 7/8-inch thickness. A higher quality material than OSB, and still dominates the market for many builders, contractors, and homeowners. 

What is the best option for roof decking?

When your builder or roofing contractor is choosing the roof decking for your home, they are choosing a material that they feel  will last for years, protecting your investment. In most cases, OSB has become the first choice. 

In 2006, almost 60% of all new houses had OSB for their roof decking. The intertwined and bonded wood strands provide optimal resistance to moisture, however, if water does work its way to the roof decking, OSB will rot faster than plywood. 

This reiterates why roof decking must be covered in quality roof felt and why regular inspections of the roof are important. Making sure there aren’t any missing shingles or flashing where water can penetrate to the roof decking. 

How thick should roof decking be?

Roof sheathing should always be nailed to the trusses, never stapled, using 8d ring-shank nails.  The roof sheathing itself should be no less than 19/32-inch thick and up to ¾ inch thick, the most common thickness. 

When a house is being built, the builder may choose to use roof decking with insulation, using a foam board insulation product. A homeowner can have a contactor install insulation  to the underside after the home is built as well, usually with a spray foam insulation material for ease. Other types of insulation like bat rolls and foam board aren’t as easily attached to the roof decking after construction is completed. 

How do I know if my roof decking is bad?

The roof of your complement the exterior and is also a layer of defense against the elements. Under the shingles that does all this is the roof decking. If the roof decking is compromised, your entire home is compromised Indications that your roof decking may be compromised are: 

  • Shingles buckling and curling.
  • Asphalt granules thin on the shingles.
  • Holes in the roofing.
  • Mildew or mold in the attic.
  • Loose or missing shingles.
  • Roof has spongy feel when contractor or inspector walk on the roof.
  • Damage found around the chimney, pipes, or other penetration.
roof with quality decking

Should I replace the plywood on my roof?

If you, a roofing contractor, or inspector find any of the things we just listed with your home’s roof, then yes, a roof decking replacement may be needed. An experienced roofing contractor can advise you if the entire roof decking needs replacing, or just certain areas. Either way, follow the advice after getting two to three estimates. The roof decking is what is protecting your home under the asphalt shingles. Need help with your roof and its decking in Chesterfield and St. Louis, MO? Call (314) 786-3732 today!