Ask the Builder

Get the most out of your wood porch decking by using century-old tricks

Douglas fir porch decking has tongue-and-groove joints.
Douglas fir porch decking has tongue-and-groove joints. (Tim Carter/tim Carter)
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By Tim Carter
Saturday, July 24, 2010

DEAR TIM: I'm restoring an older home that has a patio porch deck. It's covered, so perhaps it's just a deck porch. The wood was painted but is in bad shape due to neglect. What material would you install if you wanted to maintain the character of the house? I've seen composite porch decking, but I'm worried that I could have problems with it and that it just wouldn't look real. Are there any trade secrets you can share about decks and porches? -- Sara G., Mt. Orab, Ohio

DEAR SARA: I'm really familiar with porch decks, especially ones made from wood. Every house I've owned has had one, and some of the wood is more than 100 years old and still in good condition. There are several reasons why the wood has lasted that long, not the least of which is diligent care on the part of the homeowner.

Wood porch decking is a classic look. You'll find it on many a covered porch in older homes out in the country as well as houses in the city. I know for a fact that there are thousands of houses in Cincinnati, which is near you, that have original wood porch decks that are still in use. They may be painted, but they're still wood.

If you study your porch -- assuming it was installed correctly when your home was built -- you'll discover that it probably is not level front to back and that the wood strips were installed opposite of the way you might think they should be.

Carpenters well over 100 years ago discovered that even though porches like yours were covered, wind-driven rain would saturate the wood in fierce storms. The quicker that water got off the wood, the better. Installing the wood so that it has a fall of an eighth of an inch per foot allowed for excellent drainage.

To ensure that no water got trapped between the pieces of wood decking, the carpenters ran each individual strip of wood perpendicular to the front wall of the house. That way the seams between the pieces of wood acted as natural conduits for the water to drain to the end of the porch at the overhang. Installing the wood parallel with the front wall of the house creates a dam between pieces of wood that traps the water.

The wood that I prefer to use for these porch decks is vertical grain Douglas fir. It can still be found at many traditional lumberyards. The wood that was installed on many of the old porches, and on the ones I built, had a tongue-and-groove profile. This profile is the same used when milling oak for interior hardwood floors. It allows for blind nailing of the strips of wood and adds significantly to the strength of the wood as each strip interlocks with the one on either side of it. This minimizes or eliminates sag or bounce when you walk on the wood in between the floor joists that support the porch decking. It's time-tested technology that works.

I tested a composite porch decking that was made to mimic the wood material. It failed miserably. The instructions said to make sure the decking was protected from the sun. That's pretty much impossible to do, as the sun can often hit the edges of the decking early and late in the day and as the seasons change with the sun lower in the sky. In my case, even though the decking was installed per the manufacturer's specifications, it developed huge humps from the heat expansion of the plastic in the composite product.

If you want your new wood material to last for generations, you have to treat it with borate chemicals before it's installed. Cut the pieces to the exact length you want and then soak each piece of wood in hot water that contains borate powder. Let each piece soak under water in a trough for about two minutes. Stack the wood in a shaded area, making sure to put wood spacers between layers so the wood can dry.

Once it's dried for two weeks, then paint the wood on all edges and surfaces before it's installed. You can use semi-transparent wood preservatives instead of paint if you want the natural look. The key is to coat all the surfaces of the decking so that water will have a very difficult time entering the wood. If you don't pre-treat the wood before it's installed, you'll never be able to coat all the surfaces.

Tim Carter is a columnist for Tribune Media Services. He can be contacted through his Web site,

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