The foundation of a strong roof starts with the roof substrate. Also known as the roof deck, it plays an essential role as the surface on which materials like shingles and underlayment are directly installed.
Your roof substrate is responsible for providing structural support for the entire roof and helps shield your home's interior against the elements. Because it plays such an integral part in your roof's longevity and durability, understanding exactly what a roof deck is and how it functions can help you make informed choices about your roofing system.
What Is a Roof Deck?
The word "substrate" refers to an underlying substance or layer, and that's exactly what this roof component is. Your roof deck is the roofing layer that sits above the rafters and trusses in your attic, acting as the surface material for installing shingles and underlayment. In other words, this layer provides a steady, straight surface to give these materials stability.
The roof substrate helps prevent your roof from sagging and distribute the weight of roofing materials, snow, rain, and other objects. It also serves as a final barrier against water infiltration that can reach your rafters and trusses if your roof underlayment—the layer between your roof substrate and shingles—is compromised. Since you'll need to tear off your roof's upper layers to reach a damaged roof deck, the health of your roof substrate directly impacts the lifespan of your roof.
Common Roof Substrate Materials
Plywood
Plywood decks are one of the most common materials for roof substrate. Made up of thin panels of wood veneer connected to one another with glue, these panels are installed perpendicular to adjacent layers for additional strength. While still considered cost-effective, plywood is typically more expensive than oriented strand board (OSB). Plywood weighs less than OSB, so it puts less stress on your roofing frame and generally has better moisture resistance.
OSB
A more budget-friendly option, OSB is made of wood strands arranged in layers and connected with heat-cured adhesives. OSB swells more when it's reached by moisture and remains swollen permanently, unlike plywood panels, which go back to the same thickness after they dry. OSB is generally considered more environmentally friendly than plywood since the trees the wood comes from grow quickly. It also has fewer soft spots than plywood panels.
Wood Planks
Wood planks are less common than plywood or OSB in new construction, so you'll typically find them in older homes. These rectangular boards are quite strong individually but require a much longer installation time than their modern counterparts. In addition to their lower installation costs, plywood and OSB are generally cheaper materials than solid wood planks. In terms of looks, however, wood planks provide a timeless aesthetic that's difficult to match.
Concrete and Metal
Your roof deck can also be made out of concrete or metal. Metal roof decking is a popular option for commercial roofs since it's strong yet lightweight, allowing it to support the weight of larger roofs, foot traffic, and heavy equipment. Metal roof decks are also highly fire-resistant. Concrete roof decks are frequently used in commercial buildings, as well, as they offer an excellent fire rating and wind uplift resistance.
Key Considerations for a Healthy Roof Deck
Thickness and Span
When choosing materials, one consideration is the proper panel thickness based on the rafter spacing and your local building codes. Panel or board thicknesses generally range from three-eighths of an inch to three-quarters of an inch. However, the lower end of this spectrum is no longer widespread due to building regulations, with seven-sixteenths of an inch being the more common minimum thickness. Your roofing contractor will be familiar with your local building code requirements and can help you choose the best option for your home.
Local Weather Conditions
Your location is also important. For example, if you live in an area that commonly experiences storms, plywood is likely your best bet due to its superior moisture resistance. If you live in an area prone to wildfires or need to meet certain safety codes, you may need to use a more specialized material, like fire-retardant plywood sheathing. In addition, OSB and plywood are built to resist pests, while some wood planks may require treatment.
Fortunately, a range of roof deck protection materials can enhance your roof substrate's performance. Products like GAF Deck-Armor™ Premium Breathable Roof Deck Protection, FeltBuster® Synthetic Roofing Felt, and Tiger Paw™ Premium Roof Deck Protection add another layer of protection against wind-driven rain, while VersaShield Fire-Resistant Roof Deck Protection can increase your roof deck's UL fire rating.
Proper Installation
Even the most well-built materials can be vulnerable when not installed correctly. Hire an experienced roofer who follows the correct nailing patterns and knows when a roof has adequate ventilation. If a roof doesn't have enough ventilation, heat and moisture can build up, leading to wood rot and sagging decks. Your contractor should also install flashing around roof penetrations to help prevent leaks that can reach the decking.
If you notice problems like sagging, buckling, discoloration, or spongy areas, it might mean it's time for a deck repair or replacement. Call a roofer when you see any of these issues to avoid bigger problems, like a total roof collapse. You can also take a more proactive approach with products like Shingle-Mate® Roof Deck Protection to reduce the chance of wrinkling and buckling.
How Roof Substrate Affects Other Roofing Components
The roof deck is just one part of your entire roofing system. It works hand in hand with the roofing underlayment and shingles to keep your home protected. Your shingles and underlayment need a stable surface to which they can remain securely attached. Since they're attached with fasteners, a solid, thick roof substrate can increase your shingles' wind uplift resistance. In return, the shingles and underlayment protect the roof sheathing from outside moisture. When all these materials are in good shape and properly installed, you can expect a durable, weather-resistant roof.
A well-maintained roof deck can ensure the longevity of your roof and its materials. A damaged roof substrate can require an expensive roof replacement, so make sure to use roof underlayment and other roof deck protection materials that can help keep the roof deck better protected. Remember to get your roof deck inspected regularly, and consult with professional roofers for repairs or replacements.
