Tile & Hardwoods never lower the value of a home.. unless poorly maintained. Slate is different than ceramic or porcelain in that the thickness can be different from tile to tile. Slate is most beautiful if left in random color. It will typically be a dark floor, so considering you have a townhouse youâ€™ll need to look at the overall picture. A dark floor in a small kitchen with little sunlight will make the room seem smaller than it really is. Things to research would be quartzite or buff slate for a lighter color tone. If you do go with Slate, you might consider a pattern like brickwork. The tiles themselves are not all equal, and 12â€x12â€ is nominal. Also, like Dorene said Slate can shale if heavy items are dropped on it, and makes for a larger chip than say porcelain would.
FYIs on DIY: Slate will require a concrete backerboard over the wood substrate, You'll also need to seal the tiles before installation & after, and allow 24 hours to cure before walking on.