Tile layout

I am going to be laying 18x18 travertine tile in our kitchen and dining room. Is there any "rule of thumb" on layout where the tile meets hardwood or in a doorway?

The same as around the perimeter of the room. DO NOT lay it out so you wind up with a "sliver" at those points.

You have to do some dry layouts to make sure you have no "slivers" as hj mentioned, and try for approximately even borders.

18 X 18 tiles require a level of care and expertize up a notch from basic work.
> It is very important to get straight seams lining up over the entire length. If you go cockeyed, it will be obvious.
> It is difficult, and critically important, to get each tile level in all directions , with a plumb joint from tile to tile. A very long true straightedge will be a useful tool.

There are a few things you need to verify before you embark on this. First, you need to verify that the joist structure is strong enough for a natural stone tile. The industry standards require it to be twice as stiff as for a ceramic installation, it should be L/720 verses L/360 for ceramic. Unless the room was designed to install stone, it probably doesn't meet those requirements. Second, you need TWO layers of plywood, installed properly. Then, you need a decoupling layer. this can be either something like CBU (cement board), or a membrane, like Ditra (www.schluter.com).

If I was going to do this, I'd use one of the leveling systems: either Tuscan Leveling System, or LASH tile leveling system. Both of these are clips that you install on each corner of a large tile, then insert a cap or wedge, depending on the system you choose, which forces each tile to align exactly in height. A pro would take time to get a big tile like that level, and a DIY'er probably doesn't have a chance of doing it with any speed. Either of those systems will speed you along and save you a huge amount of grief.

When grouting, you must leave a space around the edges of the room, and depending on how large of an area you are tiling, you MAY need to account for expansion joints, especially if the floor gets a lot of direct sunlight from large windows. If you don't do this, you could end up with the tile delaminating (called tenting), which will ruin your day.

I highly recommend you check out www.johnbridge.com for help on tiling this, and you can use their deflection calculation (Deflecto) to verify your floor structure is good enough to support this stone. Now, if this is over a slab, there are still conscerns if there are any cracks. An isolation membrane like Ditra would be good there as well.

Good luck, and let us know how it goes.