Blockwork vs Brickwork: Which Should You Use and Where?

Summary

Brickwork and blockwork are both masonry systems built with mortar-bedded units, but they serve different roles in almost every UK domestic build. Bricks are small, dense, and available in a huge range of colours and textures, making them the default choice for anything that will be seen — external elevations, garden walls, chimney stacks, feature walls. Blocks are larger, faster to lay, and come in a range of densities from lightweight aircrete (thermal blocks) to dense concrete (load-bearing and acoustic performance), making them the default for anything that will be covered — internal leaves of cavity walls, party walls, internal partitions and foundations up to DPC level.

The most common misconception among clients (and some less experienced tradespeople) is that blockwork is a "cheaper, lower-quality" substitute for brickwork. In reality they are specified for different structural and thermal purposes and are frequently combined in the same wall — a modern cavity wall is brick outer leaf, cavity insulation, block inner leaf, all tied together with wall ties per BS EN 845-1. Substituting one for the other outside its intended role (e.g. rendering blockwork externally without adequate weather protection detailing, or using facing brick internally where thermal blockwork was specified) causes real performance and compliance problems, not just cosmetic ones.

Cost, speed of build, thermal performance (U-values), sound insulation, and fire resistance all differ significantly between brick and block, and Building Control will expect the correct material used for the correct function — particularly around Part A (structure), Part B (fire), Part E (sound) and Part L (thermal).

Key Facts

• Standard brick size — 215mm × 102.5mm × 65mm (co-ordinating size 225 × 112.5 × 75mm with a 10mm mortar joint), giving roughly 60 bricks per m² of single-leaf (half-brick) wall
• Standard block size — 440mm × 215mm face size, in thicknesses of 100mm, 140mm, 150mm, or 215mm, giving roughly 10 blocks per m²
• Aircrete (thermal) blockwork — density 400–900 kg/m³, thermal conductivity as low as 0.11 W/mK, used for inner leaves to reduce U-values without extra insulation thickness
• Dense concrete blockwork — density 1,800–2,200 kg/m³, used where load-bearing capacity, acoustic mass (Part E separating walls) or fire resistance is the priority
• Compressive strength — dense blocks typically 7–10.5 N/mm², aircrete blocks typically 2.9–7.3 N/mm²; bricks range from 20 N/mm² (commons) to 100+ N/mm² (engineering brick)
• Mortar designation — cavity wall inner and outer leaves typically use mortar designation (iii), roughly 1:1:6 cement:lime:sand, per BS 5628 and manufacturer guidance
• Wall ties — stainless steel vertical twist or double-triangle ties per BS EN 845-1, spaced at 900mm horizontal x 450mm vertical (standard) or tighter around openings, per Approved Document A
• Cavity width — typically 100–150mm on new build to accommodate full-fill or partial-fill insulation and maintain a residual cavity where partial-fill is used
• Party wall blockwork — for a robust detail meeting Part E (Resistance to Sound), typically dense block leaves with a minimum 200mm clear cavity, no wall ties bridging the cavity (or resilient ties only), and no mortar droppings in the cavity
• Speed of build — a bricklayer typically lays 400–600 bricks per day vs 8–12 m² of blockwork per day (roughly equivalent output by wall area, but blockwork requires far fewer individual lifts and joints)
• Fire resistance — a single-leaf 100mm dense block wall typically achieves 60 minutes fire resistance; aircrete blockwork achieves higher fire resistance per mm than dense block due to its cellular structure, per manufacturer BS EN 1364 test data
• Rendering onto blockwork — external blockwork must be rendered (or clad) with a system compatible with the block's movement and breathability characteristics — never seal aircrete block with an impermeable render or paint system
• Cost differential — facing brick typically costs 2–4× more per m² than a standard aircrete block, driven largely by unit quantity (60 vs 10 per m²) and labour time per m²
• Frost resistance (bricks) — clay bricks are classified F2 (frost resistant, used with sulfate-resisting mortar), F1 (moderately frost resistant, not for exposed/saturated work) or F0 (not frost resistant, internal use only) per BS EN 771-1
• Movement joints — brickwork requires vertical movement joints roughly every 12m (clay) or 6m (concrete brick/block) per BDA/manufacturer guidance to accommodate thermal and moisture movement

Quick Reference Table

Detailed Guidance

When to specify brickwork

Brickwork is specified wherever the finished appearance matters and where the wall will be exposed to weather without a protective render or cladding. This covers external facing leaves on cavity walls, freestanding garden and boundary walls, chimney stacks above roofline, and feature elements like brick arches or soldier courses over openings. Engineering bricks (Class A or B, per BS EN 771-1) are specified below DPC level, in retaining walls, and anywhere high compressive strength or very low water absorption is needed — for example DPC courses, manholes, and copings exposed to saturation and freeze-thaw cycling.

Facing brick selection should match existing brickwork on extensions (see brick matching for sourcing and matching guidance) and must be specified with the correct frost resistance category (F0/F1/F2) and soluble salt content category (S0/S1/S2) for its exposure per BS EN 771-1.

When to specify blockwork

Blockwork is the default for anything that will be covered — plastered internally or rendered/clad externally. Aircrete thermal blockwork is used for inner leaves of cavity walls specifically to reduce the U-value of the wall without needing thicker cavity insulation, since it has roughly a third of the thermal conductivity of dense block. Dense concrete blockwork is used where the design needs load-bearing capacity beyond what aircrete can provide (e.g. supporting floor or roof loads over larger spans), or where acoustic mass is the priority — most Robust Detail party wall constructions for Part E compliance specify dense block leaves precisely because mass, not insulation, is what stops sound transmission.

Blockwork below ground (foundation walls up to DPC) is almost always dense concrete block or, on larger jobs, poured concrete, because of the compressive loads and ground moisture exposure — aircrete block is not suitable below DPC.

Mixing brick and block in the same wall

Standard UK cavity wall construction is inherently a brick/block hybrid: brick outer leaf for weather resistance and appearance, insulated cavity, aircrete block inner leaf for thermal performance and speed. The two leaves are tied together with stainless steel wall ties at the spacing and pattern set out in Approved Document A, staggered so ties don't align vertically and create thermal bridges or damp paths. Getting tie spacing, cavity width and insulation fit wrong is one of the most common Building Control queries on new cavity walls — see foundation inspection checklist and Approved Document A Table 12 for the current tie spacing rules.

Rendering and finishing blockwork externally

If blockwork is used as an external leaf (single-skin outbuildings, garden rooms, some render-finished new builds), it must be finished with a render system compatible with the block. Aircrete block needs a breathable, flexible render system (typically a polymer-modified or lime-based render with a mesh reinforcement coat) because it has high movement and moisture buffering characteristics — a rigid sand:cement render without reinforcement is prone to cracking and debonding. See render types for render system selection.

Frequently Asked Questions

Can I use blockwork instead of brickwork for a garden wall?

Yes, but it will need a weatherproof finish (render, cladding, or a proprietary reconstituted-stone block designed for exposure) unless you use a dense, frost-resistant block rated for external exposure. Standard internal-grade aircrete block left bare and exposed to UK weather will absorb moisture, suffer frost damage, and degrade quickly — it is not designed for that exposure class.

Is blockwork cheaper than brickwork overall?

Material cost per m² is significantly lower for blockwork (fewer, larger units, less mortar per m² by volume of wall, faster laying), but a true cost comparison depends on the finish required. Facework brickwork needs no further finish. Blockwork used externally needs render or cladding added on top, which can close or even reverse the apparent cost gap once labour and materials for the finish are included — see render application pricing guide for typical render costs per m².

What thickness of blockwork do I need for a load-bearing internal wall?

This depends on the wall height, loading, and whether it's laterally restrained, and must be calculated per Approved Document A or by a structural engineer for anything beyond the simplest prescriptive cases. As a rule of thumb, 100mm blockwork is used for non-load-bearing partitions, while 140mm or 215mm dense block is typical for load-bearing internal walls supporting floor and roof loads — but always confirm with a structural calculation rather than assuming.

Do I need planning permission to change from render to exposed brick, or vice versa?

Changing the external finish of a wall is usually permitted development for most houses, but can require planning permission in a Conservation Area, on a listed building, or where an Article 4 Direction removes permitted development rights. Always check with the local planning authority before altering an external finish, particularly on older or protected properties.

Why does my brickwork need movement joints but my client's neighbour's wall doesn't seem to have any?

Older brickwork (pre-1970s, generally) was often built without movement joints and relied on lime mortar's flexibility to accommodate thermal and moisture movement. Modern brickwork with cement-based mortar is stiffer and requires engineered movement joints (typically every 12m for clay brick, closer for concrete brick or block) to prevent cracking — omitting them is a common cause of later cracking claims.

Regulations & Standards

• Building Regulations Approved Document A (Structure) — prescriptive rules for wall thickness, wall tie spacing, and cavity width in masonry cavity wall construction

• Building Regulations Approved Document B (Fire Safety) — fire resistance periods for separating walls and compartment walls

• Building Regulations Approved Document E (Resistance to Sound) — Robust Details and mass requirements for party wall constructions

• Building Regulations Approved Document L (Conservation of Fuel and Power) — U-value targets driving inner-leaf blockwork specification

• BS EN 771-1:2011 — Specification for masonry units: clay masonry units, including frost resistance (F0/F1/F2) and soluble salt content (S0/S1/S2) categories

• BS EN 771-3:2011 — Specification for masonry units: aggregate concrete masonry units (dense and lightweight aggregate blocks)

• BS EN 771-4:2011 — Specification for masonry units: autoclaved aerated concrete (aircrete) masonry units

• BS EN 845-1:2013+A1:2016 — Specification for ancillary components for masonry: wall ties, tension straps, hangers and brackets

• BS 5628 (historic, largely superseded by Eurocode 6) — Code of practice for use of masonry, referenced for mortar designation guidance in many manufacturer literature

• Approved Document A: Structure — gov.uk Building Regulations guidance

• BS EN 771 series — Specification for masonry units — BSI product standards

• The Concrete Block Association — technical guidance — density, strength and application guidance for concrete masonry units

• Brick Development Association — technical guidance — clay brick specification, frost resistance and detailing guidance

• brick matching — sourcing and matching brick for extensions and repairs

• cavity wall ties — wall tie failure diagnosis and replacement

• brick quantities — brick and block quantity calculator with mortar coverage

• render types — render system selection for external blockwork finishes