During roof replacements, most homeowners focus on visible aspects like tiles, shingles, and flashings. However, beneath them all lies the true strength of your roof—the roof decking.
Most people aren’t aware of roof decking, its components, or its uses. If you’re also curious about it, let’s dive right in.
What is Roof Decking?
Roof decking (also known as roof sheathing) is a flat layer of material that forms the base of your home’s roof. It is like the foundation for what goes on top, i.e., the roofing materials. It’s installed on top of the rafters or trusses (framing) of the roof.
In simpler terms, it’s like a “table” that supports and stabilizes everything else. The roof decking part is completely hidden from plain sight. Still, it plays a huge role in your roof’s durability and the safety of the individuals residing within it.
What is Roof Decking Made Of?
With a global market size projected to be $13.09 billion in 2025 and expected to reach $20.01 billion by 2033, you’ll find a variety of materials for roof decking, depending on the house’s design, local climate, building codes and regulations, and even the homeowner’s budget. Here are the most common materials for roof decking.
Plywood
In plywood roof decking, the material is 3/8 to 3/4 inches thick. It is made of multiple layers of wood veneer glued together. This option is most popular because of its durability, cost efficiency, and moisture resistance. It is most commonly used in residential homes in localities with moderate climates.
Oriented Strand Boards (OSB)
Oriented strand board is made from compressed wood strands piled with adhesive resins. It’s a popular choice due to its lower cost compared to plywood. It also weighs much less and has a consistent quality.
Plank
This one uses a solid wood board made of fir or pine, measuring 1” x 6” in dimensions. These are commonly found in vintage structures or older homes that haven’t been renovated for decades.
Concrete
More commonly installed in commercial buildings, concrete decking uses strengthened concrete slabs. They’re a popular commercial choice owing to their high durability and fire resistance.
Steel
Crafted from corrugated steel panels, steel decking is a go-to in commercial and industrial buildings due to its impressive strength-to-weight ratio. The only issue is that it requires additional insulation and waterproofing to prevent corrosion.
What is Roof Decking Used For?
A roof deck isn’t just built to create a platform for the things placed above it. It serves numerous significant functions. Let’s explore these functions.
Structural Support
The roof decking connects the rafters and trusses. This distributes the weight of the roofing material and any additional loads (such as snow or wind) across the roof structure evenly.
Fire and Wind Resistance
When installed properly, high-quality roof decking supports your roof, enabling it to withstand major issues. Certain options are treated with fire-resistant or retardant materials, while others have specific wind uplift ratings.
Weather Barrier
The roof decking material or structure itself is not waterproof. However, when combined with the underlayment, it creates an additional layer of protection that prevents moisture intrusion into your home.
Fastening Surface
Owing to the decking, it creates a secure and flat surface. This is ideal for attaching underlayment, shingles, flashing, tiles, and anything else.
Types of Roof Decking
Based on installation methods, different types of roof decking are available in the market. However, not all are suited for all structures. You need to understand the specific types and their features as follows.
Open, Skipped, or Spaced Decking
In this, roofers place spaced wood planks across rafters. There are gaps in between, leading to the name “spaced” decking. This is most common in old homes or houses with wood shingles and shakes or tile roofing, as it offers optimal ventilation.
Benefits: It requires less material, and the spacing allows airflow.
Challenges: This isn’t suited for modern shingle installations. In those cases, solid sheathing must be added.
Closed or Solid Decking
Closed or solid decking utilizes a continuous array of plywood or OSB panels to create a “space-free” surface. This is the most common in modern homes and suits almost all roofing materials.
Benefits: This offers more support than open options and is moisture-resistant.
Challenges: It uses much more material, making it heavier and more expensive than skipped decking.
Tongue and Groove Decking
In this decking type, wooden boards are designed to interlock with one another. Every board has a side with a “tongue” edge and another with a “groove” edge, creating a slightly overlapping sequence of boards.
Tongue-and-groove decking is more common in exposed beams, where it can be seen indoors.
Benefits: It is strong and creates a seamless appearance.
Challenges: This installation method is labor-intensive and expensive.
Sheet Decking or Sheathing
Sheet decking uses flat rectangular materials with thicknesses of 3/8, 1/2, 5/8, or 3/4 inches, depending on the rafters’ span. These are more common in houses built in the 1970s, which typically use plywood or OSB planks. Currently, OSB is more commonly used.
Benefits: The plywood option is strong and has a long lifespan, whereas the OSB version is durable and more affordable than plywood.
Challenges: Plywood ones risk warping, while OSB variants may split due to the damage to wood fibers by moisture.
How to Know If Your Roof Decking Needs Replacement
While most homeowners can identify a damaged roof, not many are aware of the signs of faulty roof decking. So, here are all the symptoms that urge a quick replacement.
- Your roof continues to leak despite repeated patching.
- Ice dams frequently form during the winter.
- There’s a pungent smell of mildew, but you can’t locate the source.
- Moisture stains appear on the rafters, ceilings, and walls of the attic.
- Mold stains or discoloration are visible.
- The wood under the roof feels soft or spongy to touch.
- Roof lines are sagging.
Should You Replace Roof Decking During a Roof Replacement?
There is no rule stating that you have to replace roof decking during roof replacements. However, it’s a wiser choice for these instances.
- Your current roof decking is over 20 years old.
- You’re opting for a heavier roofing material.
- You’re dealing with stubborn leaks and mold in the attic and other rooms.
- The existing roofing decking doesn’t adhere to the latest building codes.
When replacing your roof decking, don’t compromise on expertise to save money. Rely only on certified professionals to avoid the following issues.
- Nails and shingles are coming loose
- More mold and rot
- The roof warranty is being voided
- Reduced durability of the new roof
Final Words
While roof decking isn’t visible in most structures, it’s like the backbone of your roof. Now that you understand its importance and the various options for materials and installations, it’s time to make a well-informed decision for your home.
If you’re seeking quality materials or the right roofers for roofing deck work, we at LA Roofing Materials are here to help.