A cavity wall is a wall consisting of two masonry leaves with an air gap (cavity) between them. The inner leaf carries the structural load, the outer leaf protects against weather and wind. The cavity between them provides insulation and moisture control.
How is a cavity wall constructed?
A cavity wall consists of three layers:
1. Outer leaf — The external masonry layer (often brick). Protects against rain, wind and sun.
2. Cavity — The air gap between the two leaves. Nowadays this is almost always filled with insulation material.
3. Inner leaf — The internal load-bearing wall. Often made of calcium silicate blocks or concrete blocks.
The two leaves are connected by wall ties: metal connectors that keep the wall stable as a whole.
Why a cavity wall?
The cavity wall is the standard in residential construction in the Netherlands, and for good reason:
- Moisture control — Rain that penetrates the outer leaf runs down through the cavity and is drained away. The inner leaf stays dry.
- Insulation — The cavity provides space for insulation material (mineral wool, PIR or EPS). A filled cavity easily achieves an R-value of 3.5 or higher.
- Condensation prevention — The air gap prevents warm interior air from condensing directly on a cold exterior wall.
Cavity wall for a garage build
When building a garage, you encounter the cavity wall if you opt for masonry walls. The construction is the same as for a dwelling, but with a few notes:
- An unheated garage does not strictly need insulation, but it is advisable if you also use the garage as a workshop
- The cavity width is typically 70-100 mm
- With a flat-roofed garage, pay extra attention to the junction between roof and cavity wall to prevent moisture problems
Cavity wall vs. solid wall
| Cavity wall | Solid wall | |
|---|---|---|
| Construction | Two leaves + cavity | One thick wall |
| Insulation | Excellent (fill the cavity) | Poor to moderate |
| Moisture control | Good (cavity as buffer) | Risk of moisture penetration |
| Cost | Higher (more material) | Lower |
| Application | Dwellings, garages | Garden walls, simple sheds |
Common mistakes
- Bridging the cavity — If mortar falls into the cavity and forms a bridge between inner and outer leaf, moisture can travel inward. Use a cavity batten while laying.
- Missing drip sills — Without a drip sill at windows and doors, water runs into the cavity without proper drainage.
- Wrong insulation — Not every insulation material is suitable for the cavity. Use moisture-resistant material.
Related terms
- Bond pattern
- Half-brick wall
- Single-brick wall
- Insulation value (R-value)
- Drip sill
- Frame