What is a cavity wall primarily used for?

Cavity walls are specifically designed with two layers of masonry, creating a space or cavity between them. This design primarily enhances insulation and moisture control. The air gap in a cavity wall acts as an insulating layer, which helps to reduce heat transfer between the inside and outside of a building, thereby improving energy efficiency. Additionally, this cavity allows for the drainage of moisture that might enter the wall structure, preventing water from penetrating into the inner layer and damaging the interior spaces or the wall materials.

The other options do not accurately reflect the main purpose of cavity walls. While a single layer wall does not provide the same insulation and moisture control benefits, decorative features are not the primary function of cavity walls, nor are they specifically designed for soundproofing, although they may offer some sound reduction due to the air gap. Ultimately, the key function of a cavity wall is to significantly enhance a building's energy performance and protect against moisture ingress.