Looking to bump out a kitchen wall about 4 feet. The area to be built over is a concrete porch that sits one story off the ground. The porch is a concrete slab about 5 inches thick. It is rectangular, maybe 25 ft x 35 ft. The porch sits over a crawlspace (porch is supported on 2 sides by the house and on the other two sides by a concrete and block wall). Question: Will the concrete slab work as a radiator bringing cold air into the kitchen if it is built on? In other words, what kind of insulating is sufficient to provide a thermal break between the pad and the kitchen floor. The 4 foot space will probably be cabinets and countertop.

I’ve thought about enclosing the crawlspace below the porch with 6 mil plastic and spray-foam to about 6feet from the wall. Or, is some kind of insulation over the concrete pad and under the cabinets sufficient to insulate the space.

My concern is a big pocket of cold/hot air under approximately 50 square feet of the kitchen with a large heat/cold sink extending into the kitchen as well. The remainder of the kitchen sits over the basement – oh, and the house was built around 1920 – stucco exterior and built like a tank.

Hope this is clear and thanks for any suggestions.