A green home is a type of house designed to be environmentally friendly and sustainable, and also focuses on the efficient use of energy, water, and building materials. Green certification can be a valuable marketing tool for builders as homebuyers start to focus more attention on energy efficiency, durability and healthy interiors. Green homes have become more prevalent as green affordable housing emerges. Green affordable housing shares the same aims as traditional green homes but emphasizes affordability, which is thought by some to inherently reduce the environmental friendliness of the home. Some residential green home certifications include LEED for Homes, the National Green Building Standard, and many local programs.