The share of the world's total energy consumption used by buildings is increasing every year. When existing structures are examined, it is clear that they have insufficient performance data, far from the standards expected from 2030 and 2050 buildings. The building sector is responsible for nearly 40% of total energy use, and clean, sustainable, cost-effective, and environmentally friendly retrofitting technologies are vital if existing buildings are to meet Zero Energy Building (ZEB) and nearly Zero Energy Building (nZEB) standards.

Heating, ventilation, and air conditioning (HVAC) systems constitute an important part of the energy consumed in buildings. The replacement of these systems with alternative reinforcement systems is important to effectively minimize the energy consumption of buildings. In addition, strong, light, and sustainable materials with high thermal resistance are needed in the facade and roof areas of buildings. Next generation insulation materials, coating and paint solutions, alternative insulation on facades and roofs, new energy storage technologies, and thermal regulation strategies are all important in the transition to buildings with low carbon emissions and energy consumption. Green walls, dynamic insulation, energy-generating facades, and glazed areas all have serious potential in this regard.

The aim of this Special Issue is to gather research into innovative materials and energy systems to develop solution strategies for the energy-efficient and cost-effective renovation of the world's existing building stock. We welcome both original research and review articles.

Potential topics include but are not limited to the following:

• Building-integrated photovoltaic and photovoltaic/thermal (BIPV and BIPVT) systems
• Solar-assisted facade and roof design
• Thermal superinsulation materials
• Adaptive façade and roof design
• Active and passive solar systems
• Cladding, coating, and paint solutions
• Novel glazing systems
• Solar and optical control in buildings
• Novel HVAC systems
• Waste heat recovery in buildings
• Dynamic insulation
• Solar chimney and Trombe wall solutions
• Phase change materials
• Facades with sensible and latent heat storage
• Solar thermal energy