What is a rat slab?

A "Rat Slab", is a placement of concrete in the crawl space of a house. A rat slab is sometimes required by local codes, but not always. It helps to resist burrowing rodents and can when placed over a vapor barier, help reduce groundwater invasion. As a bonus it makes for a clean underfloor and a better crawling space for sub contractors. The concrete is generally placed 2" in thickness without steel reinforcement. It is a good idea to add fiber to the mix to reduce cracking. The finish is not as fine as a floor slab. Usually only a bull float is used with sometimes minor trowelling.