Masonry Walls Explained

1. Insulation Retaining Clip: Fitted to a WALL TIE, it holds the INSULATING BOARDS in position. Badly fitting or missing clips can lead to the misalignment of boards, compromising thermal performance.

2. Blockwork: The structural, load-bearing part of the wall, typically made of cement and aggregates like sand and stone. Blocks come in many sizes but the industry standard is 440mm x 215mm (the equivalent of six standard bricks); they are usually 100mm thick. Aircrete blocks are more lightweight and allow you to build with less insulation in the CAVITY.

3. Cavity: A space between the BLOCKWORK and BRICKWORK designed to slow down the rate of heat loss and to provide a rain barrier. This partial-fill cavity wall has an INSULATING BOARD fixed to the BLOCKWORK, leaving a gap of a minimum of 50mm. It provides the most effective barrier to rain penetration, as water cannot cross the cavity. Full-fill cavities, which leave no gap, make it easier for water to soak through to the inside, so are not advised on exposed sites, although they do eliminate ‘thermal bypass’, which is the circulation of air around and in between poorly fitted boards. The cavity must be a minimum of 100mm in total width.

4. Insulating Board: Fixed to the BLOCKWORK, the thickness of board required is dependent on both the specification of the blocks and the board itself. But as a guide, to achieve a U-value of 0.35, you will require around 30-45mm, and to achieve 0.27, you will need closer to 50- 60mm, calling for a wider CAVITY. You can use a rigid board, as here, or wool/fibre batts— common for full-fill applications, where insulation can alternatively be sprayed in afterwards.

5. Brickwork: The external skin does not have to be indicative of the build method. Aside from bricks, rendered BLOCKWORK and timber cladding are also options. Bricks are, however, the most popular choice in the UK. You will need to use those rated either F (high) or M (medium) for frost resistance on external walls. They are usually ordered per 1,000.

6. Wall Tie: A (usually) steel anchor across the CAVITY, mortared into bed joints to secure the BRICKWORK to the BLOCKWORK. They must be level or sloping to the outside, to prevent water crossing the CAVITY to inside. They should be bedded at least 50mm into each leaf, and need to be positioned around 750mm apart horizontally and 450mm vertically. Improper installation can lead to water damage or fungal growth in the CAVITY 

NB: This diagram shows a partial-fill cavity, with insulating board. Full-fill cavities are capable of creating narrower wall sections but are not really suitable on exposed sites

Further reading: 

• Rainwater Goods Explained 
• Fire Safety Explained
• Roof Structures Explained