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Douglas Fir Porch Decking: Clear vertical grain or mixed grain?

March 8, 2012 by | Jennifer | There have been 0 comments

Sipping a glass of tea on a big front porch is the essence of Americana: classic, neighborly, and relaxing. If you’re building a porch, you can probably picture it right now. What you may not have pictured in your front-porch daydream is what kind of lumber you need to turn that dream into reality.

Prefinished CVG Douglas Fir | AltruFir Doug Fir Flooring

CVG Douglas Fir

Traditionally, porches on historic homes were built with clear, vertical-grain Douglas fir decking. Though grown in the Pacific Northwest, it was shipped all over the country to serve as porch floorboards as far away as Chicago and New Jersey.

Why? Because 100-125 years ago, old-growth Douglas fir with beautiful vertical grain was not only recognized as a superior choice for quality and durability, it was also plentiful and affordable.

These days, vertical grain Douglas fir is still the recommended choice for a porch that will last for your home’s next several decades—but it’s more expensive than a shipment of mixed-grain Douglas fir decking. Some homeowners think, if you’re just going to paint your porch floor anyway (another historic home tradition) who's going to know what type of porch decking is under that paint?

Unfortunately, you will be able to tell in just a few years whether you’ve opted for a wood product that will stand the test of time, or one that will begin to wear out and buckle.

To understand why clear vertical grain Douglas fir (you might see it abbreviated at lumber suppliers as CVG) works so well for an outdoor use like a porch floor, first you need to understand what woodworkers mean when they talk about CVG vs. mixed-grain.

Vertical Grain means that the grain of the wood runs parallel along the face of the board. When you look at it, you’ll see straight lines running up and down the length of the board. These straight vertical lines give CVG Douglas fir some important benefits.

For one, those parallel lines mean that as CVG Douglas fir naturally expands and contracts in response to moisture—as any wood product does—it expands and contracts evenly. It is less prone to warping, buckling, or bending. This is especially important when you’re talking about a porch, where the wood will be exposed to constantly-changing weather conditions.

CVG Douglas fir is also generally regarded to be the most durable grade of Douglas fir, holding its shape well and holding its fasteners tightly.

Mixed grain is exactly what its name sounds like—a mixture. That means that when you order a batch of lumber from your supplier, some of the boards you get will be vertical grain. Others, however, will come from boards that were sawn the other way, parallel to the annual growth rings of the tree. These are called flat grain, sometimes FG, and you won’t see neat lines running along the face of the board. You’ll see a wavy pattern of wood grain, which is attractive in its own way, but not best suited for an outdoor application.

The historic home experts at “This Old House” magazine wrote about this very problem in a Q&A column: the homeowner wrote in that his porch had been replaced with fir graded “D & Btr mix-grain,” that was primed and then painted. “Now every winter the floor buckles, and in the spring it flattens out again,” he wrote.

This Old House’s master carpenter, Norm Abram, replied: “Flat-grain boards expand and contract more than vertical-grain wood, which has rings nearly perpendicular to the face. To make matters worse, all that swelling wood is pushing against your porch piers and your house without anywhere to go. Buckling is the inevitable result.”

A CVG Douglas fir porch, on the other hand, if treated properly and regularly painted and maintained, will last 40 years or more. Tim Carter, a building contractor who writes a nationally-syndicated “Ask the Builder “ column, writes that vertical grain Douglas fir is his number-one choice for porch decking. “Some of the wood is over 100 years old and still in good condition,” he said in his column.

So when you’re choosing your porch decking, take a lesson from what historic homeowners across the nation can tell you about the quality and durability of vertical grain Douglas fir.

Or what they would tell you, if you could get a hold of them. They’re all outside with their feet up, sipping tea on their big front porches.

- Jennifer Rouse

This post was posted in Douglas Fir Flooring and was tagged with douglas fir porch decking, cvg douglas fir

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