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

March 28th, 2022 | 6 min. read

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

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

One of the most recent codes we’re running into has to do with gaps between plank roof decking. The truth is, this code won’t apply to everyone’s roof. 

However, it’s still important enough information to know because of the impact it has on a roof replacement. 

For over 30 years, the team at Bill Ragan Roofing has educated homeowners on the ins and outs of the roofing industry. Now I’ll help you understand the roofing code for gaps in plank decking. 

To start this article, I’ll briefly review what plank decking is. After that, I’ll get into the gap code, what happens if the code isn’t followed, and why a roofing contractor would ignore it.  

The difference between plank roof decking and sheet roof decking

Before we get to the roofing code, I need to make sure we’re talking about the same thing. Let’s do a quick overview of the two types of roof decking. 

Sheet decking (or sheathing) is literally flat sheets of wood and comes in two different types, OSB and plywood. 

osb and plywood sheet roof decking(Left: Plywood; Right: OSB)

OSB (oriented strand board) sheet decking is 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. 

plank roof decking

Plank decking is made up of elongated and rectangular wooden boards that come in two different sizes, 1x6 or 1x8. This was the most common type of roof decking before the invention of plywood.

Now that we’re 100% on the same page let’s get to the roofing code for gaps between plank decking. 

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

There are a couple of different roofing codes for roof decking. But the roofing code, per the 2018 International Residential Code for the gap between plank roof decking boards, isn’t specifically about roof decking. 

The code actually has to do with following the shingle manufacturer’s specific installation instructions. According to code R905.1: roof coverings (roofing materials) shall be applied in accordance with applicable provisions of this section and the manufacturer’s installation instructions. 

This means your local roofing contractor must follow all installation instructions provided by the manufacturer of your shingles or other roofing material. But what does this have to do with roof decking?

big gap between plank roof decking boards

As of 2021, if plank decking has more than a 1/8” gap between the planks, your roof decking must be replaced per the manufacturer’s installation instructions before the roofing material can be installed. If your roofing contractor finds a gap larger than 1/8”, the boards will need to be replaced after your old roof is torn off. 

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

Now you know the code for gaps in between plank decking boards. Even though it may seem tedious for shingle manufacturers to make this part of their installation instructions, it’s for good reasons. 

The first reason is that you’ll have a roof leak where the nail goes through the gap. Nails need to be driven into firm and solid wood when installing shingles. 

nails through gap between plank roof decking boards

If there’s no wood because of the gap between planks, the nail goes through the shingle with no solid foundation underneath it. Eventually, water will run down the nail (or nails) and leak into your home. 

The second reason has to do with the fallout of not following the shingle manufacturer’s installation instructions. Not following the installation instructions 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. But voiding your roofing material warranty isn’t the only problem it causes.

Ignoring this code could also lead to a failed home inspection because your roof isn’t technically up to code. It might not be as noticeable as leaving off drip edge, but it’s a possibility. 

Why would a roofing contractor ignore the plank decking roof code?

You shouldn’t run into the problems I mentioned in the last section as long as you hire a great roofing contractor. Unfortunately, some roofing contractors will completely ignore the plank decking roofing code. 

But why would they do this? This comes down to simply keeping their prices lower to win your business. 

Wood prices continuously fluctuate and tend to be on the higher end these days. Well, the more wood that needs to be replaced, the more it adds to the cost of your roof replacement

Leaving off a line item to replace rotten roof decking or plank decking with gaps keeps a roofing contractor’s bid lower than others. Now, they could have a hidden fee for replacing decking in their fine print to keep that initial number down. 

But some roofing contractors leave it off completely to keep their material and labor prices down enough for you to buy a roof from them. If this happens, you’ll have more than just decking problems on your hands. 

Get the checklist you need to hire a great roofing contractor

After reading this article you not only know what the code for gaps between roof decking is, but you also know what happens if it isn’t followed and why a roofing contractor would ignore it. Remember, you shouldn’t run into problems mentioned here as long as you hire a great roofing contractor. 

Unfortunately, this is easier said than done, especially with how saturated the roofing industry is all over the country. The best way to find a great one is by asking the right questions when meeting with or talking to potential roofing contractors. 

That’s why we created a checklist of 16 questions every homeowner needs to ask a roofing contractor. But that’s not all it includes. 

The checklist also has the right answers a reputable roofing contractor will give back. Avoid making the wrong hiring decision by getting the free checklist now. 

Since 1990, the team at Bill Ragan Roofing has provided high-quality roofing services to thousands of homeowners in Nashville and surrounding Middle Tennessee areas. You can count on us to do things the right way, and we offer a lifetime warranty to back it up. 

If you’re local to Nashville, Franklin, Brentwood, Belle Meade, or another surrounding Middle Tennessee area, don’t hesitate to contact us for any of your roofing needs. 

Here’s your Checklist of Questions to Ask a Roofing Contractor so you can make the right hiring decision for your upcoming roofing project.

roofing contractor questions checklist

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