The Homeowner's Guide to Roof Decking

Does your roof’s decking need replacing? Read our guide to learn the warning signs of damaged roof sheathing and find out how much replacement will cost.

Joe Roberts
Updated Jan 24, 2023
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8 min read

Roof decking consists of wooden panels—typically OSBs—installed on the roof’s trusses and rafters as a base for the rest of the roofing system. Image source: The Home Depot

Your roof’s decking is one of your home's most important structural elements, but you don’t usually see it unless you’re building a new roof or your shingles are rotting away. Without seeing it every day, it’s easy to forget that your decking is even there – but it’s still providing critical protection and support for the rest of your roofing system. 

If your decking needs to be replaced or you’re constructing a new home from the ground up, getting the best decking materials and properly installing them is essential to your home’s lifespan, beauty, and energy efficiency since decking helps insulate a building. 

Keep reading, and we’ll break down roof decking options and costs. Then, once you’re ready to have your decking installed, we’ll help you find the right contractor for the job. 

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What is roof decking?

Decking, or roof sheathing, is the foundation of your roofing structure. It consists of multiple panels installed on top of your roof’s rafters, trusses, or joists, connecting them and covering the spaces between them. It also provides the base for your home’s other roofing materials like underlayment, ridge caps, and shingles. 

Whatever type of roof covering you get—whether it’s made from asphalt shingles, clay tiles, or metal sheets—you need strong, moisture-resistant decking to support it. Otherwise, it may sag, leak, or buckle over time. 

Different types of roof decking

There are two main types of residential roof decking: plank decking and sheet decking. Plank decking is made with long, rectangular wooden boards, while sheet decking is made with wide boards or sheets. The boards in most sheet decks are made of either CDX plywood or oriented strand board (OSB). 

Plank decking isn’t used much these days since it tends to be very expensive to install, and it leaks more often than sheet decking, but you still sometimes find plank decks on older roofs. Sheet decking is more commonly used nowadays because it’s cheaper and more resistant to leaks.

For nonresidential purposes, concrete and metal decking are also popular options. However, they generally cost too much for the average homeowner to pay for them, and they provide more strength than necessary for most homes. 

CDX plywood decking

This cross-section of a plywood sheet shows the different layers of hardwood veneer that make up its construction. Image source: Lowe’s Home Improvement

CDX plywood is made by gluing and pressing multiple thin wood veneers together. This construction makes plywood stronger and more water-resistant than OSB, so it’s the best roof decking material for residential purposes. Unfortunately, it also tends to be more expensive than OSB. 

The strength of plywood is especially beneficial in climates where roofs have to support immense loads of snow and ice in winter. Similarly, if you plan to install a heavy stone or metal roof covering, the strength of plywood is necessary. If you plan to use typical asphalt roofing shingles, though, you may not need plywood decking. 

OSB decking

Oriented strand board is constructed by pressing chips of wood fiber together in a mold to form a board. Image source: Lowe’s Home Improvement

OSB is similar to particle board in that it’s made by compressing small strands of wooden fiber together in a rectangular mold. This construction makes OSB sheets a little weaker and less moisture-resistant than plywood sheets, but they tend to be much cheaper. The affordability of OSB makes it one of the most popular materials for roof decking. 

If you live in a dry, warm climate and plan to use light roofing shingles, then you can probably get away with decking your roof with OSBs. This will be more cost-effective than getting expensive plywood panels that provide more strength than your roof will actually need. 

How much does roof decking cost?

Roof decking panels typically cost between $0.43 and $1.80 per square foot. The costs for OSB panels usually fall on the lower end of this range, and the price for premium plyboards is generally on the higher end. This is just the price range for the decking panels, though, and it doesn’t include the labor costs for installing them. 

The average cost for labor is usually between $1 and $3 per square foot. The labor costs for this project vary widely depending on which roofing company you hire, where you live, and how difficult your roof is to service.

How to calculate the cost of your roof deck installation

To get a price range for installing your roof deck, you need to multiply these two ranges by the size of your roof and add them together. For example, if your roof measured 1,000 square feet, you could expect to pay $430–$1,800 for your decking panels plus $1,000–$3,000 for the labor. This would bring your total range to $1,430–$4,800. 

However, if you’re replacing old decking instead of putting a new deck on an entirely new frame, your costs will likely be much higher for a few reasons. Firstly, the roofing contractors will need to remove your old roofing and decking, adding additional labor costs. 

Secondly, you’ll probably need to replace more than just the decking since it’s the foundation of everything else. It’s likely that the contractors will also have to replace your old roof’s underlayment and covering, unless some of it can be reused. A roof replacement like this costs about $14,000 on average, though costs can be as high as $44,000.

Check out our roofing repair and replacement cost guide to learn more about roofing prices.  

Should you install your decking yourself or hire a contractor?

Since the labor costs of decking installation are higher than the costs of the actual materials, you may be tempted to install or replace your decking yourself to save a significant amount of money on this project. We would advise against this. Even seasoned home improvement DIYers shouldn’t undertake decking installation, let alone beginners.

The primary reason for this is safety. Installing decking requires you to scale tall ladders, walk between rafters, and handle heavy materials at every step. So, in addition to being fairly difficult, it can be very dangerous if you don’t have proper training and safety equipment.

For another thing, your roof decking has to meet local building codes to guarantee that it's safe and reliable. Installing decking yourself without first getting up to speed on what is required in your area can result in expensive revisions and rebuilds after your new roof’s inspection. Local professionals will already know how to meet these standards.

Lastly, improperly installing your decking can have disastrous results, such as leaks, water damage, and even collapses. Since improper installation can void the warranties on your materials, any disastrous results won’t be covered under your warranties, and you’ll have to pay for the repairs yourself.

So, while the costs of hiring professionals may seem steep up-front, the peace of mind that comes from knowing qualified professionals crafted your roof is more than worth it. Considering the financial risks of DIY installation, it can save you money to just get your decking installed by pros. 

When to replace your roof decking

You should install decking if you’re building a new roof, but what if you aren’t? Sometimes the decking in an existing roof requires repairs or replacement, but since you don’t often see your decking, it can be hard to know when it needs a little love. 

Watch for these tell-tale signs to know when your decking requires maintenance:

  • Leaks in your roof: A water leak is the most apparent sign of damaged or rotten decking. If your ceiling drips during rainstorms or when the snow melts, the decking over that spot needs to be patched up or replaced. 
  • Stains in your walls or ceiling: If your top floor’s interior walls or ceilings have dark stains, your ceiling is probably leaking, and you may need to replace some of your decking to fix the problem. 
  • Mold, mildew, and water damage on your rafters: If you can access your attic to inspect your roof’s rafters, you should do so once or twice a year to check for signs of water damage. Mold, mildew, wet wood, and dried stains should all be treated as serious problems that require urgent decking maintenance.
  • Sagging in your roof: This is a sign you can usually see from the street in front of your home. If a portion of your roof sags noticeably, it means that the decking—and possibly the rafters—have lost their structural integrity and need to be replaced ASAP to prevent collapse. 
  • Rotten boards: During shingle replacement, the roofing crew may notice a few rotten decking panels that need replacing. This can result in unexpected costs, but you should always replace rotting boards to prevent rot from spreading to the rest of your roof.

If you notice any of these warning signs of damaged roof decking, don’t wait. Call a roofing contractor as soon as possible to prevent the damage from worsening and costing you even more money. 

Roof decking 101

Now that you know when decking needs to be replaced, and you’ve learned all about the different decking materials, it’s time to inspect your old decking. If you notice anything concerning, there’s no better time than the present to take care of it. Waiting can only result in additional damage and hurt you in the long run. Contact a local company to handle your roofing needs as soon as possible.

If you’re building a new home and need to get sheathing for your roof’s rafters, a local roofing company can also handle that for you. Getting any part of your roofing system professionally installed or replaced will never be cheap, but it can save you a lot of cash over time by preventing costly disasters.

Get a quote from a local roofing contractor today