Did you know that outdated roof decking could cause your insurance company to deny coverage? Or that a failing roof deck might lead to leaks and expensive structural damage?
If you own an older home in Seattle, you might be wondering if your roof deck meets modern code requirements—and what happens if it doesn’t. Having outdated roof decking can mean a higher risk of leaks, as well as potentially losing warranty and insurance coverage.
In other words, it’s pretty likely that you’ll have to pay for expensive water damage repairs or mold remediation all on your own.
At RoofSmart, we repair and replace hundreds of roofs every year. We work with all kinds of materials: asphalt and synthetic shingles, metal, shake, tile, and flat roof materials. Before installing new shingles on your roof, we make sure that your roof deck is in good condition and meets code requirements.
In this article, we’ll break down everything you need to know about roof decking, the materials that meet code, and how to make the right choice for your home. By the end of this article, you’ll be able to decide which type of roof deck you need for your roof.
Can I lose insurance coverage if my roof deck isn’t up to code?
Roof decks support your roof material and are the next line of defense for your home in case your roof fails. They protect your home from further damage.
If your home has improper roof decking, you could be at risk of premature roof failure or damage like leaks. This is an especially big concern in a rainy, wet place like the Greater Seattle area.
If your roof is damaged because your roof decking is outdated, you can lose coverage from your manufacturer’s warranty. This means that you won’t be able to get coverage for repairs in case there is a manufacturing defect on your shingles.
You are also at risk of losing or significantly reducing the amount of insurance coverage you might get if your roof is damaged. Insurance companies only provide coverage for sudden damage due to a specific event (like a fire or a fallen branch), so they will not pay for water damage caused by improper roof decking.
This can impact how much coverage you get or even void it altogether. And, if your insurance company finds out that your roof decking is not up to code, they might not allow you to renew, leaving you to find new insurance coverage.
It’s important to make sure that your roof deck meets code requirements to avoid costly damage or potential coverage issues.
Code requirements have changed a lot over the years, leaving a lot of older homes outdated and in violation of roof building codes. The updated code requirements are covered in the IRC code chapter on roof assemblies.
The rest of this article will go over roof deck requirements based on this code.
What are the different roof deck materials I can use with asphalt shingles?
When it comes to residential roofs, you have two roof deck options: OSB or plywood. These are the most common roof deck materials contractors use because they’re the only two that meet code requirements for most roofs.
To help you consider which is right for you, here are the pros and cons of each one:
Pros and Cons of OSB
OSB stands for oriented strand board. It is made of leftover wood chips and shavings that get compressed together with glue. The standard size is 7/16ths of an inch.
- Pros
- Cheaper than plywood: OSB typically costs about 10% less than plywood.
- More eco-friendly: OSB is better for the environment because it is made of wood scraps and uses the entire tree rather than discarding extra pieces. It prevents waste.
- Cons
- Crumbles when wet: When it gets wet it swells up and falls apart easily because it loses its structural integrity. OSB is made by compressing all of the wood scraps and glue down, so when it swells up that means the OSB is falling apart.
- Susceptible to mold: In addition to easily absorbing and spreading moisture, the glue used in OSB grows mold easily. OSB sheets sitting in your attic retaining moisture create the perfect dark, damp environment for mold growth.
Pros and Cons of Plywood
Plywood is made from a bunch of different layers of wood. The layers are stacked up with the direction of the wood grain (vertical vs. horizontal) alternating each time. They are measured in eights of an inch because that’s how big each ply is, but a standard board thickness is ½ an inch in total.
- Pros
- Stronger than OSB: The way that the board is layered fortifies it and makes it stronger than OSB. While OSB is a bunch of loose wood scraps pressed together, plywood is made of several sheets strategically layered on top of each other.
- Better water resistance: Plywood is more resistant to water so it takes longer to deteriorate and spread water to the boards around it.
- Lasts longer: Because of its strength and water resistance, it has better longevity and durability than OSB
- Cons
- Higher cost: Because plywood is made with better materials and built to be stronger, it is more expensive than OSB
What roof deck materials are no longer up to code for asphalt shingles?
You might encounter a variety of different roof deck materials underneath your asphalt shingle roof. But codes and regulations have changed a lot over the years, so not all roof decks meet modern requirements.
Using the wrong roof decking places you at risk of losing your insurance coverage and paying for costly repairs on your own.
One example of this is dimensional lumber. This is just a bunch of planks laid horizontally along the rafters. We see this a lot in houses that were built 60 to 80 years ago. Back then, it was an approved method for installing roof decking, but this is no longer the case.
This is what it looks like:
Image from Great Central Lumber and Millwork
Another example is shiplap, which is a similar concept to dimensional lumber. Shiplap is thinner and usually used for aesthetic purposes, so it does not make the best roof deck. This is another roof deck material that was common in older homes but is no longer allowed.
This is what it looks like:
Both dimensional lumber and shiplap do not meet code requirements for an asphalt roof and cannot be used with it.
Are there special roof deck materials for flat or shake roofs?
In certain specialty applications, you might need something other than wood on your roof. The alternative materials include concrete, gypsum (a type of fireproof material), and metal.
These are typically only used on flat roofs or rooftop decks. If you have a standard home with a sloped roof, you probably won’t encounter these materials.
Some homes have skip sheathing, which means that the boards are spaced out with gaps between them. Skip sheathing is ONLY supposed to be used with shake or tile.
This is what it looks like:
How do I choose the right roof deck for my home?
When deciding which roof deck material you want, it is important to keep in mind the key factors that will impact your decision:
- Code requirements for certain roof types: For most people, this will narrow down your options a lot because certain roof types require certain roof deck materials. For example, if you want shake or tile, then you’ll need skip sheathing. But if you want asphalt shingles, then you’ll need either OSB or plywood.
- The environment you live in: Technically, all of these roof deck materials can be used anywhere as long as they meet code requirements. But as a resident of the Greater Seattle area, your home is more susceptible to leaks and water damage. On top of that, the rain and humidity also make your attic a prime place for mold to grow if you have poor ventilation. So, if that’s a concern for you and you have asphalt shingles, it might be worth it to get plywood because it has better water and mold resistance. At the very least, the best way to protect your home from leaks is to make sure that your roof decking is up to code.
- Cost: Where do you fall in terms of cost? Some people want to save money and choose more affordable options. Others decide to spend more for added protection and durability. It’s important to know what your budget is and how much you want to spend on each item.
In Seattle’s rainy climate, leaks are a serious concern. Plywood is often the better choice for this environment because it resists water damage more effectively than OSB.
Making the Right Choice for Your Roof Deck
Now that you understand the role of your roof deck and the materials available, you can make an informed decision based on your needs and budget. Given Seattle’s wet climate, choosing the right material is essential for preventing costly water damage.
Having your roof damage insurance claim can be stressful. If you’re worried that you won’t get coverage because your roof deck isn’t up to code, check out our article “What Do I Do if My Insurance Claim for Roof Damage Is Denied?”.
This will guide you through the steps you can take to negotiate for better coverage.
Worried that your insurance coverage might’ve been denied for other reasons too? Read our article “4 Reasons Your Roof Damage Insurance Claim Was Denied” to learn about the common reasons that claims get denied and what to do when that happens.
Topics:
