How do I compensate for wood expansion when laying 2 1/4 oak strip flooring parallel to a tile floor?
You should have at least a 1/2″ to 3/4″ expansion gap at all side edges, (depending on your climate and how many boards have spanned the room). Including the one that abuts the tile. If the tile is 1/4″ or more higher than the hardwood, you are in luck. Boarder the tile with wooden reducing strip, of the same wood species as the hardwood floor. They are usually sold along with both prefinished and unfinished hardwood floor, and come in several widths and thickness. If the wood floor is higher than the tile you simply finish off the floor with a thinner reducer strip to reduce down to the tile, again covering the gap.
But if both floors are about the same level, you will have to install a thin threshold. They do make T shaped thresholds that will bridge and cover the gap. These would be the best as they are very strong. But you can bevel the edges of 3/8″ by 2″ strip of hardwood, and nail this across the level gap.
The least elegant way is to use a metal strip, as used for vinyl tiles floors. Yeach!