We are often asked if the countertop of the island needs to match the existing kitchen countertop in style, or what will be installed as the main kitchen countertop. In most homes I would say it does match, but it really does not have to at all, nor does the material need to be the same. In fact, if you are not going to match them up exactly it's better if it looks like you are not even trying to match them, so using a completely different color and surface is perfectly acceptable.
Space and Design are Important : You need around 3 feet of walking space around the island unit, and you must be sure that the drawers and doors in the cabinets have room to open. If you keep to the 36 inches then you should be OK. The only dimension that must be stated is that of the counter height. Ideally it should be the same as the rest of your kitchen units. If not, then it is not a disaster, but can be disconcerting when you are working on the various surfaces at varying heights.
Regarding colors and designs, kitchen islands can be made from a number of different materials. The framework is usually wood, but the main visible surfaces could be metal or even stone - granite is a popular substance used for counter tops. Stainless steel is also good, but try to avoid aluminum if possible, because that is very soft and easily cut and scratched, and the metal oxidizes to a dull finish.
Allow adequate countertop space on both sides (left and right) of the kitchen island if a sink or cooktop will be used. Include at least 15 inches of countertop space on each side, and if your kitchen is large enough, allow even more space. You can never have too much countertop space in a kitchen. Also, rounded countertop corners help protect everyone from bad bruises -- this is true about all kitchen countertop corners.
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