Installing a French drain around the inside perimeter is most commonly done after the house has been built. Most commonly, this is done in response to a wet basement or right before performing a basement finishing. To install this kind of drain, the perimeter of the basement floor is jackhammered down to the footing and the concrete is removed. A layer of stone is laid down, and a perforated drain pipe is laid on top of it. Water is collected from the basement wall floor joint as it enters, and a pump is installed to remove water from the house and away from the foundation. Once completed, the area, save for a gap around the edge, is concreted over. This gap exists to allow water in from the basement walls. This can be installed very quickly—one to two days by an experienced crew. The system is easy to maintain once installed, and the sump pump will need annual maintenance to perform properly. An interior French drain is much less likely to clog than an exterior, partially due to the fact that it is not sitting underneath several feet of soil. Interior French drain installation is an effective way to waterproof a basement but requires the use of a sump pump. Many contractors will install plastic sump pumps that can quickly break down or neglect to install a battery backup sump pump, making the basement vulnerable to flooding during power outages. Sump pumps should be installed with a battery backup system in a proper sump liner of size or larger to prevent the sump from having too little water and turning on and off continuously. French drain has evolved significantly from its origins- starting off as a hand-dug ditch, moving on to ceramic tile, PVC pipe, and eventually to the new French drain innovations on the market. Each new system is able to address weaknesses of the old as the French drain continues to improve and evolve. For example, whereas Henry French used chippings of tree bark to provide anti-microbial properties, an anti-microbial additive can now be included in the material of the plastic channel. In the U.S., municipalities may require permits for building drainage systems as federal law requires water sent to storm drains to be free of certain contaminants and sediment. In the UK, local authorities may have specific requirements for the outfall of a French drain into a ditch or watercourse.