Did you know that outdated roof decking could cause your insurance company to deny coverage?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Seattle, you might be wondering if your roof deck meets modern code requirements—and what happens if it doesn’t. Having outdated roof decking can mean a higher risk of leaks, as well as potentially losing warranty and insurance coverage.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.
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If your roof is damaged because your roof decking is outdated, you can lose coverage from your manufacturer’s warranty.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Code requirements have changed a lot over the years, leaving a lot of older homes outdated and in violation of roof building codes.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.
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:
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.
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.
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.
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:
When deciding which roof deck material you want, it is important to keep in mind the key factors that will impact your decision:
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.
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.