Support For Tongue & Groove Porch Flooring

Question:

Dear Bruce,

I found your step-by-step article on the tongue & groove porch floor very informative. I'm thinking of replacing the T & G porch floor on my 125 year old house, and had a couple questions for you. 

My porch is 30' long by 6' wide. The joists underneath are huge 12" X 12" "logs" that run parallel to the house (not cantilevered.) The joists sit on brick columns that are about 30 in. high, and appear to be in excellent condition. There are a couple sagging spots, but I plan on shoring them up with cement footers and pressure-treated 6x6's. As the floor joists of my porch are on 20-23 inch centers, I plan on using "five quarter" thickness t & g for the floor.  

I was wondering how level the joists have to be before you can start laying the t & g. I know that t & g can be "made" to conform to slightly unlevel/irregular joists, but will it warp and crack when the first humid weather/rain come along? 

Basically, I feel pretty confident I can handle the job, my big worry is that I'll get all the t & g laid and the a month later it will have warped, cracked, and split itself to hell. 

Any advice you can give me would be greatly appreciated.

Thanks, Scotty

Reply:

I'm not sure that 5/4 flooring would be thick enough to span 20 to 23 inches and be rigid enough to feel good and solid. There's a chance that the floor will feel spongy between joists.

I would seriously consider adding some supplemental joists or beams running parallel to the originals, reducing the flooring span to around 12 inches. Then you can use 3/4" thick flooring (nominal 1x flooring, that is) which should give you a much greater choice of woods at lower cost. I've seen pressure-treated Southern Yellow Pine 1x4 tongue-and-groove flooring sold in stores in the Midwest.

Planing the high spots is a good idea. If you can be certain all the old nails have been removed, I would just use a basic hand-held block plane to shave down the joists. But being certain about the nails isn't so easy. I would do a quick sanding down of the surface to make it easier to see any partial nails embedded in the wood.

Sears sells a couple of really good inexpensive block planes. Stanley makes a good one too. If you never hit a nail, and store the plane away from metal objects, it'll remain sharp for years.

As for the issue of warping and splitting, well the answer is... YES. The wood will do all sorts of things over time. Splitting at the ends is hard to prevent, but warpage is easy to control by nailing the hell out of the flooring, which is another reason in favor of adding an extra row of joists/beams. The next time I do a floor I am going to use the 2-½" ring-shank stainless steel nails that I've been using for exterior siding and trim lately. Home Depot should sell these, about $28 for 5 pounds, and worth every cent. These little buggers are nearly IMPOSSIBLE to remove. They hold unbelievably well. I would also consider pre-drilling the holes for these nails, at least at the ends of the boards, to reduce the chances of splitting.

Whatever you can do to reduce the moisture that travels through the wood, the fewer problems you'll have with splitting and warping. In our article we explained a process of dipping the wood in home-made water repellent. This works well. Also, priming ALL sides of the wood really does make a difference in how long the paint lasts and how badly the wood reacts to wetness. I've taken to priming all sides of all exterior wood, siding, trim, decking, etc. Double prime the end grain.

Bruce W. Maki, Editor.