The ultra-low energy trend has finally expanded from new building construction to envelop retrofits for commercial buildings. Ultra-low energy buildings are defined as ones that produce as much energy as they use, on average, through the adoption of a renewable energy system. Cost is still an issue for ultra-low energy building retrofits, although the costs for materials, equipment, and labor have been declining. High-efficiency appliances and equipment have grown more affordable over the past several years. For example, LED replacements for linear fluorescent lamps currently cost less than the DOE prediction for 2020. And, although labor costs vary widely, the workers involved in retrofits have been gaining greater understanding of the most effective measures and techniques.