Like any wall cladding material, stucco can provide additional insulation to a home, although only a little.
Materials
Stucco is composed of Portland cement along with other materials such as lime, sand, water or pieces of rock to create the chunky look some styles of stucco are known for. Cementitious materials such as these are generally not penetrable by water or air, keeping cool or hot air inside of the home.
Methods
Stucco is often applied in three or more layers on top of a metal lath that's laid over a home's exterior wall. The more layers of stucco, the thicker the rock-hard material will be and the higher insulating ability the stucco will have.
R-Value
The amount of insulation any material provides is measured in r-value, which means the amount of thermal resistance a material has. Thermal resistance is the ability of the material to keep warm air in and insulate any given area. Stucco has an r-value of 0.2, which is considerably low when compared to actual insulation materials such as polyurethane foam or polystyrene, which both have r-values of more than 5. However, stucco has a higher r-value when compared to other wall cladding materials, such as concrete, stone, some brick walls and tile, which have r-values ranging from 0.05 to 0.1.
Synthetic Stucco
Synthetic stucco is a type of wall cladding that resembles stucco from the outside, but is actually an insulator as well. Synthetic stucco begins with a piece of foam insulation such as polystyrene, which is then coated with a flexible stucco-like material on top. Synthetic stucco has a much higher insulation value than regular stucco, and is a good insulator.