What is the Roof Code for Gaps Between Plank Roof Decking Boards?

Does your roof have plank decking? Did a roofer mention that it may or does need to be replaced because of gaps?

Your roof is an essential part of your home. And like your home, it’s required to follow specific codes set forth by the International Residential Code. 

Well, a newer code residential roofers have to follow has to do with gaps between plank roof decking. Unfortunately, plenty of bad roofers ignore it to save money and/or time. 

This creates huge problems that go beyond building codes. So, whether you have plank decking or just want make sure things are done right, you need to understand what having wide gaps in between planks means to your new roof investment. 

For over 35 years, Bill Ragan Roofing has educated homeowners on all the ins and outs of the roofing industry. Now, I’ll help you understand the roofing code for gaps in plank decking and much more. 

By the end of this article, you'll learn the answers to:

• What is plank roof decking?
• What is the roof code for gaps between plank roof decking boards?
• What happens if the plank decking roof code isn’t followed?
• How does a roof contractor replace plank decking with gaps?
• How much will it cost to replace plank decking?

What is plank roof decking?

Plank decking is one kind of roof decking, with sheet decking being the other type. Sheet decking (or sheathing) is large flat sheets of wood, either OSB and plywood. 

Sheet decking is the most common type of decking installed on roofs today. However, plank decking was the standard choice for roof decking before the invention of plywood. 

Plank decking is made up of elongated and rectangular wooden boards that come in two different sizes, 1x6 or 1x8. Even though it's not as common as it used to be, you’ll still find plank decking on older homes.

What is the roof code for gaps between plank roof decking boards?

When it comes to the gaps between planks, roofers must follow the 2018 International Residential Code to determine if the decking must be replaced. The first one is R905.1: Roof Covering Application. 

This code means your roofing contractor must follow all installation instructions provided by manufacturers. As of 2021, manufactures require plank decking with more than a 1/8” gap between the planks must be replaced per the manufacturer’s installation instructions before the roofing material can be installed.

(Plank decking with gap larger than 1/8")

Simply put, plank decking must be replaced before installing the new roof if your roofer finds a gap larger than 1/8” in between planks. If it isn't, you'll be looking at bigger problems that extend far beyond your roof not being up to code. 

What happens if the plank decking roof code isn’t followed?

I understand it may seem tedious for shingle manufacturers to require plank decking to be replaced if the gaps are too wide. However, they do it to protect you and themselves. 

Nails need to be driven into firm and solid wood when installing shingles, both for the installation instruction code and also per code IRC Code R905.2.1. If the gap is too wide, the nail goes through the shingle with no solid wooden foundation underneath it.

So, failing to replace plank decking with gaps will lead to leaks when water runs down the nail (or nails) into your home. While a leak is bad enough, there's also the fallout of ignoring shingle manufacturer’s installation instructions.

Not following the installation instructions to replace plank decking with gaps voids your roofing material warranty. This means if there’s ever a problem with the shingles themselves, the manufacturer won’t honor the warranty because their product wasn’t installed properly.

How does a roof contractor replace plank decking with gaps?

If a roofer has to replace plank decking, what they use and how they do it depends on the situation. If there's just planks in a small area or a few spread out of the roof, they'll just remove the old boards and install new ones to ensure there aren't gaps. 

(Sections of planks after being replaced)

On the other hand, widespread gaps is a bigger problem. If there's a large section(s), they'll remove the planks and install sheet decking to the rafters. 

(OSB sheet decking replacing plank decking sections)

However, if the gaps are widespread enough, it could lead to a full redeck. In this case, they'll nail over the entirety of the planks with sheet decking instead of ripping up boards and replacing them.

Now, this will add a large expense to your roof replacement. However, this is the only to ensure everything is done in compliance with codes and your roof is installed on a solid deck. 

How much will it cost to replace plank decking?

The cost to replace plank decking is constantly changing due to the fluctuation of wood prices. Wood prices are pretty high right now in 2025, which means it could add a large amount to your roof investment if a lot has to be replaced.

However, I can at least give you an idea of how much it would cost to replace roof decking per piece (for labor and materials). It will cost around $3.50 per linear foot to replace plank decking with new planks, while nailing sheet decking over planks will cost around $90 per sheet. 

Just know that plywood is more expensive than OSB, so sheet decking's cost depends on the type. I know using sheet decking is more expensive on the surface, but replacing large areas with planks actually ends up being more expensive. 

This is simply because sheet decking covers more area, and which means needing less boards and spending less time working on the roof deck. 

What else gets replaced when getting a new roof?

After reading this article, you know the code for plank decking, what happens if it's isn't followed, and much more. Just know that some roofers completely ignore this code because it makes prices more expensive. 

Even worse, this is just one thing bad roofers leave off roof replacements to make estimates cheaper. The last thing you want to happen is to pay for a new roof just to have it ruined because something was left off the estimate. 

That's why I wrote another article breaking down all the materials and components that must be included in a roof replacement estimate. 

Check out 9 Materials Included With Your Roof Replacement to learn everything your roof needs and what you'll paying be for when getting a replacement.