Ideally, heat islands would not appear had cities been built more sparsely. With the damage already done, the situation can be alleviated by adding more open spaces and green areas within cities. Planting trees along traffic islands on main roads and in parking areas in order to shade the asphalt and concrete for several hours a day would also prove extremely effective in lowering temperatures on the ground. The same applies to underused areas, such as open spaces around apartment buildings. Better building insulation could be provided by green roofs – or appropriate insulation of flat roofs so that, where possible, shrubs and grass can be planted. The United States, which continues to see rapid construction in urban areas, has had its own problems with heat islands. The country’s Environmental Protection Agency estimates that Americans would save some $4 billion annually on energy consumption for air conditioning if the country used more environmentally friendly construction materials.