The old part of the house (c. 1922) was constructed with 3/8" solid oak strip lain perpendicular over 1x6 planks perpendicular to the 16" O.C. joists. The makes the flooring parallel to the joists.

Convention is to lay the flooring perpendicular to joists, but seems that with plank subfloor not diagonal, but perp, common sense says to lay across the planks, which is what they did.

The new addition has I-joists running the same direction as the old with plywood over, instead of plank. I would like the new flooring to match the orientation of the existing, but, again this goes "against the grain" of what I've read.

Q: Did the 1922 boys screw-up the original? Is this an OK exception? Can I do the same thing on the addition?

-Brad

If you addition floor joist are 16" gap you can lay hardwood directly overtop of the joist with tongue and groove only stopping the head joints on the joist. BUT, only if that will past code in your state. In 1922 that is usually how they done it. This is why wood flooring is tongue and grooved for that reason...let me know how it works out for you..i hope i answered your question if not ThreeGeclipse01@aol.com e-mail me

Solid boards subfloors, like the kind in the original home, are much stiffer and do not deflect to the same degree as engineered panel (OSB and plywood) subfloors. There are two reasons why NOFMA and the NWFA plus most manufacturers want the flooring to be run perpendicular to the joists/trusses. First, some floor joists maybe uneven. It is preferable to run the flooring across than parallel to uneven joists. It should be noted here that uneven subfloors of any type should be brought into spec before installing wood flooring over them. The second and most important reason to run perpendicular to the joists is deflection. NOFMA states 5/8" plywood subfloor is the minimum allowable for nailing 3/4" solid flooring, assuming joists are 16" OC. But that is for installing at right angles to the joists. If you were to install the wood parallel, there would be sag and deflection between the joists. This could result in noises and gaps between the finished floors. However, I rarely say NEVER. IF your new subfloors are high quality 3/4" plywood (GP Sturdi-Floors) installed 16" OC over floor trusses that have not been over spanned, you may be able to install your new flooring parallel to the new trusses/joists. It is a matter of the new subfloor being stiff enough. If you can access the area underneath the new addition, then adding blocking between the joists (every 16 to 24 inches) with 2x6's will stiffen the subfloor and support the flooring running parallel to the joists.