Building installation businesses fit the systems and equipment that make buildings usable, comfortable and secure. Depending on their specialism, they may install electrical wiring and lighting, plumbing and drainage, heating and hot-water systems, air conditioning and ventilation, fire alarms, security equipment, lifts, or renewable energy systems. Some also fit insulation, doors, windows, ceilings and other fixtures as part of a wider building project. Customers may use these contractors for installations in new homes and commercial premises, or for upgrades and replacements during refurbishment. Work can include assessing requirements, supplying or connecting equipment, testing systems and completing associated repairs or adjustments. The scope varies between businesses: some undertake several types of installation, while others focus on a particular trade or system.