Are you doing research for your upcoming roof replacement? Do you keep seeing or hearing decking and sheathing being used interchangeably?
The roofing industry is full of terminology that has different variations of the same thing depending on how the contractor learned about roofing. This isn’t a bad thing.
It just gets a little confusing sometimes when talking to different roofing contractors. So, when homeowners hear decking and sheathing, they ask, “Are they the same thing?” “Do they each do something different?” “Does your roof need one or the other?”
For over 30 years, Bill Ragan Roofing has educated and provided information to homeowners so they have the information they need before making such a large investment. So, let’s break down roof decking and roof sheathing.
By the end of this article, you’ll have the answers to:
Yes, roof decking and roof sheathing are the same. Roofing contractors may use different terminology, but they’re talking about the same exact thing.
I use roof decking, but you’ll still hear sheathing thrown around depending on the roofer you’re talking to. But no matter what it’s called, it's a crucial piece of your roof system.
Roof decking (or roof sheathing) is the wooden foundation of your entire roof system. I say foundation because the roofing material and components are installed directly onto the wood boards.
That’s why the roof decking’s integrity cannot be compromised before installing a new roof (more on this in a minute).
While knowing roof decking and sheathing are the same thing is great, there’s more to learn. The first thing is understanding the types.
The two types of decking are plank decking and sheet decking. Both are still used on roofs today, but they are very different.
Plank decking is made up of elongated and rectangular wooden boards that come in two different sizes, 1x6 or 1x8. It was the main type used in the roofing industry before the invention of plywood.
While not as common as today, we still see plank decking on older homes. But if your plank decking has gaps wider than what’s allowed per code, it’ll have to be replaced (more on this later).
Sheet decking (or sheathing) are flat sheets of wood that take up much more surface area than planks. There are two types of sheet decking: plywood and OSB.
OSB (oriented strand board) is the most common type of decking used on roofs today. It’s made up of wood chips/strips compressed together to form a flat 7/16” sheet.
Plywood comes in several different thicknesses (⅜”, ½”, ⅝”, and ¾”), depending on the span of the rafters. While OSB is more common, plywood is still a popular choice.
However, both are great options. So, it really depends on your budget and the availability of the wood.
As I said in the beginning, your decking must be able to handle a new roof. So, any decking boards that are compromised or rotting must be replaced before installation begins.
Usually, there are a few boards that have to be changed out. However, it’s always possible that a section or the full roof deck needs replacing.
Unfortunately, a roofing contractor can’t tell exactly how much is needed until after tearing off your old roof. They may get an idea during their inspection, but you never know the full extent until it’s clear.
So, most roofing contractors add a few boards automatically to an estimate or have a clause stating how much it’ll cost if any decking needs replacing.
I just mentioned the main reason why roof decking needs replacing. While this is to ensure your roof won’t fail, there are actually building codes that state when decking must be replaced.
According to code R905.2.1 of the 2018 International Residential Code: asphalt shingles shall be fastened to solidly sheathed decks. This code means that your roof decking (roof sheathing) must be able to withstand and hold your new roof when it’s installed.
However, a code also affects decking replacement based on proper installation. Per IRC code R905.1: roof coverings (roofing materials) shall be applied in accordance with applicable provisions of this section and the manufacturer’s installation instructions.
Since 2021, shingle manufacturer’s installation instructions state any plank decking with more than a 1/8” gap between the planks must be replaced. This ensures that nails can hit solid wood instead of slipping through a gap that guarantees roof leaks.
The price of wood is heavily area-driven and fluctuates frequently, so it’s hard to give an exact price on roof decking. However, I can provide a rough price range for what replacement decking costs.
Plank decking is priced per linear foot and can range anywhere from $2.00 to $5.00 for labor and materials. Unlike planks, sheet decking is priced out per sheet instead of by linear foot.
Depending on the type, replacing sheet decking can be anywhere between $70.00 to $120.00+ per sheet for labor and materials. While the linear foot price may seem better, it's actually cheaper to go over the top of the existing plant decking with OSB 7/16” or 3/8” CDX plywood if a lot of plank decking needs replacing.
However, you won’t know the exact cost until your roofing contractor determines the type and how much roof decking needs to be replaced.
After reading this, you better understand roof decking, the types, the cost, and more. Remember, roof decking is a crucial piece of your roof system.
So, it’s crucial that it’s structurally sound before installing the rest of your roof. But what are the different materials and components that get installed over a roof deck?
Knowing this helps you understand what you’re paying for and ensures your roof gets everything you need. That’s why it’s crucial to learn about all the pieces of your roof system and why they’re important.
Check out 9 Materials Included With Your Roof Replacement to learn all the parts of a roof system you’ll pay for when getting a new roof.