Should Decking Boards Be Installed Crown Up or Down?

Henry A
Decking Installation

Anyone who has the experience and knowledge can build a decking. However, it can be quite difficult for beginners. You will need to decide on a lot of things. You’ll need to decide what materials to use, where to build it, and what type of fasteners to use, among other things. As someone who’s building a composite decking, you might have asked; should decking boards be installed crown up or down? And why does it matter?

What Is a Crown Decking Board?

To understand better, let’s briefly talk about decking board crowns first. What are the crowns of a decking board? When lumber is harvested, the boards’ quality depends on how close it is to the centre of the log. For decking boards, the ones farthest to the centre are often used. These types of boards are what we call flat grain cuts.

The grain of these run parallel to the width of the board. The more expensive ones are edge grain boards. They are closer to the centre, and their grains are parallel to the height of the boards. The most expensive boards are the one from the centre of the logs.

When the lumber is cut, the boards are flat and uniform. However, the change in moisture will slightly bend towards the side opposite of the bark side. It will form an arch, also called crowning. Likewise, if you flip the board, the bend is facing downwards, it’s called cupping. You can expect this change in shape when using flat grain boards. As for edge grain boards, there is very little chance for it to warp and bend.

So when getting decking boards, you’re the best bet is to get materials closest to the centre of the log. If not, you’ll want to get edge grain boards. However, you can still work with flat grain boards as long as you know which side you should install up.

Should You Install Crown Up or Crown Down?

should decking boards be installed crown up or down

When working with boards, you must install the boards properly. So the question is, should you install boards with crowning at the top? Or should decking boards be installed crown up or down? And why is it important?

When installing the boards, you will want to install the crown up. However, the bend or the crowing is not always noticeable. To install it properly, you can look at the edge of the boards. See the grains. The crowning is up if the grains form smile-shaped lines. Why do you want to install it this way? Because of the natural shape of the boards, water and snow will slide off the boards.

On the other hand, do not install the boards with the crowns down (cupped). It’s a recipe for disaster. Instead of sliding the water or snow away from the boards, they will more likely accumulate when the boards are installed.

Remember to install all the boards crown up. Failure to do so may result in having rotting and warping boards. You also wouldn’t like having a decking which some of them have warped boards.

Other Alternatives

Since crowning or cupping is guaranteed in flat grain boards, you may want to use other materials instead. As previously mentioned, you can use heart cut or edge grain boards. But aside from those, you can also consider getting capped or treated decking boards. These are boards that have a film of protection against moisture, minimizing crowning, cupping, and warping. You can also use sealants on your boards after you install them. This helps the board prevent the moisture from entering. However, you will need to reapply it every few years.

Another method is using a different material other than wood. One of your options is using composite decking. Composite decking boards do shrink and expand, but not as much as wood. But the good thing about them is that they are usually resistant to warping. If it’s a major concern for you, you should consider using composites instead.


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