Q&A / 

Porch Decking

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 won’t look real. Are there any great trade secrets you can share about decks and porches? Sara G., Mt. Orab, OH

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 over 100-years old and still in very 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.

This is real Douglas Fir porch decking. It’s tongue and groove allowing the nails to be hidden. PHOTO CREDIT:  Tim Carter

This is real Douglas Fir porch decking. It’s tongue and groove allowing the nails to be hidden. PHOTO CREDIT: Tim Carter

 Wood porch decking is absolutely 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, OH, which is near you, that have original wood porch decks that are still in use. They may be painted, but it’s 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 are 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 1/8 inch per foot allowed for excellent drainage.

To ensure no water got trapped between the individual 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 the ones I built, had a tongue and groove profile.

This unique 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 covered from the sun. That’s pretty 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 pretreat the wood before it’s installed, you’ll never be able to coat all the surfaces.

Use double-dipped hot galvanized finish nails to install the wood. These will last for generations, especially if the wood is covered with a roof. If you have to cut a piece of wood that’s been treated or painted, be sure to coat the cut end with the borate solution and then the finish sealant or paint.

If you want to minimize any cupping or warping in the wood, consider installing a vapor barrier on the soil under the porch. This will slow water vapor from pouring into the underside of the wood, even though you’ve treated it.

The wood used on many of the old houses had another huge advantage over wood available today. It came from ancient trees whose growth rings were very small. As such there was often as much dense summer wood in the lumber as there was the lighter spring wood. Lumber today seems to have a much higher percentage of light spring wood than the dense dark summer wood. Spring wood, because of its open cellular structure, is much more susceptible to rot than the dense summer wood.

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7 Responses to Porch Decking

  1. Is there a way to seal the spaces between the tongue & groove boards before sanding and repainting if they have separtated slightly over time?

  2. Thank you for this article.
    So, you suggest hand-nailing the t&g Fir boards?
    What are your thoughts on using an air floor nailer?
    I am concerned about splitting the tongue, or the possible buckling of boards, with the wood slipping right over the head of a regular finish nail (though unlikely when the wood has been properly treated)...
    not to mention missing a nail, denting the wood, bending a nail, etc..
    I have a porch job coming up - I bought a box of 2.5" stainless steel ring shank finish nails. The job is about 270 square feet.
    There seems to be so many different opinions on this particular point that I cannot find two alike on the internet, and therefore am a little unsure as to the best method.
    .75 x 3.50" t&g Douglas Fir - hand nail the SS ring shanks or air nail galvanized 2" L cleats???
    I also heard about 'casing' nails with a better head profile for added strength. Since the job is only about 270sq ft I thought I'd take a crack at nailing it myself. I'll be nailing into the original joists (though I may have to put in a couple support 2x8 pieces here and there. But I keep worrying about splitting the tongue, and having to toss boards out.
    Any thoughts???
    I greatly appreciate any feedback ! ! !
    Thank you ! ! !

  3. I have a small partially covered front porch that needs reflooring and I had to tear out two partially rotted Doug-fir T&G floors. I am curious of your choice of Douglas fir which has relatively poor rot resistance relative to other species. I would think cedar or perhaps a tropical hardwood like T&G Ipe might be longer lasting. Any thoughts or comments?

    • Use Douglas Fir T&G again. Do not mix woods as they have different expansion and shrinkage characteristics. I am doing the same thing on my 150 year old cape in Maine. Use 1x4 T&G fir, prime wiht oil base primer and try to blind nail as much as possible. Lay the last piece in by cutting off the bottom of the groove side piece, drop it in tight and either epoxy it there or sink a few stainless steel rimshank nails and cover the holes with sawdust from the fir flooring mixed with yellow wood glue. Sand and seal or paint.

  4. What width of board do you recommend and what are my considerations. I have 1x3 tg douglas fir boards (2 1/4" on the face) on my deck currently and because the pitch was not sufficient water pooled and over time rot set in in several placed.

    I am not sure that I can successfully source matching lumber to replace individual boards and repair will not solve the pooling problem.

    So if I have to replace the whole thing can I/should I use wider boards like 1x4 or 1x6?

    Thanks for the great article.

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