Brickwork and blockwork design
Brick and block are the two workhorses of UK walling, usually paired as a cavity wall where the block inner leaf carries load and the brick outer leaf handles weather and appearance. We design brickwork and blockwork to the Eurocodes for clients across the UK.
Which leaf of a cavity wall carries the load?
Usually the inner leaf. In a typical house the floors and roof bear on the inner block leaf, which carries the vertical load down, while the outer brick leaf mainly handles weather, appearance and its own weight. Wall ties make the two leaves share the wind load.
Bricks, blocks and how they differ
Bricks and blocks are both masonry units, but they do different jobs. Clay bricks are small, dense and durable, good in the outer leaf where they shed weather and give the finished face, and they are graded for compressive strength and frost and sulfate resistance. Blocks are larger and come in several types, from dense aggregate blocks that carry heavy load, through lightweight aggregate blocks, to aerated blocks that trade strength for insulation and easy handling. The inner leaf of a house is often aerated or lightweight block, chosen as much for thermal performance and speed of laying as for strength.
Choosing the right unit is the first design decision, because a wall is only as strong as its weaker component allows once the mortar is taken into account. A heavily loaded pier or a wall carrying a steel beam usually needs dense concrete blocks or engineering bricks, while a lightly loaded partition can use an aerated block. We match the unit strength and the mortar class to the load, and for the outer leaf we also match the frost and exposure grading to the location, so a coastal or fully exposed wall gets a more durable brick than a sheltered inner-city one.
Designing cavity walls to BS EN 1996
Cavity wall design to BS EN 1996 treats the two leaves as connected but distinct. Vertical load from floors and roof usually comes down the inner leaf, so we check its compressive capacity for slenderness and load eccentricity, while the outer leaf mainly carries its own weight and wind. Wall ties across the cavity are the critical detail, because they make the two leaves share lateral wind load and stop the slender outer leaf buckling outward, so we set the tie type, spacing and embedment for the cavity width and the wind exposure. Openings are bridged by lintels sized for the masonry and any load gathering above.
The detailing decides whether the wall performs and lasts. We coordinate the damp-proof course, cavity trays and weep holes so water that crosses the cavity is thrown back out rather than reaching the inner leaf, place movement joints for the differing movement of clay brick and concrete block, and set bed-joint reinforcement where a wall panel is long or lightly restrained. Where a beam or joist bears on the blockwork we design the padstone and check the bearing stress, since a concentrated load on a lightweight block will crush it without a spreader.
Movement, durability and buildability
Brick and block move in opposite directions over time, and ignoring it is the commonest cause of cracked masonry. Clay bricks take up moisture and expand slowly over years, while concrete and aerated blocks shrink as they dry out, so movement joints are spaced more closely in blockwork than in brickwork and positioned at changes of height, long runs and openings. Getting the joint spacing and the bed-joint reinforcement right is what keeps a wall crack-free once it is finished and loaded.
Durability comes down to keeping the right unit in the right place. Below the damp-proof course and anywhere near the ground we specify engineering bricks or dense blocks that tolerate saturation and frost, and we match the mortar class and sulfate grade to the exposure. Buildability matters too, because a design that assumes a block strength or a special that is hard to source will stall on site. We specify units and details that are readily available and that the bricklayer can build accurately, and we advise where a change of unit or bond simplifies the work without losing capacity.
What we check.
The points our calculations resolve for a project like this.
- Unit selection between clay brick, dense, lightweight and aerated block
- Inner leaf compressive capacity for slenderness and eccentricity
- Wall tie type, spacing and embedment for cavity width and wind
- Lintel sizing and load gathering over openings
- Movement joint spacing for brick expansion and block shrinkage
- Padstone and bearing design where beams land on blockwork
From enquiry to sign-off.
Enquiry
Send drawings or describe the problem. We confirm the scope, the deliverables and a target timescale.
Information
We agree the survey, drawings or data we need and any site access required.
Engineering
Design, calculation or assessment to the relevant Eurocodes and UK National Annex.
Issue
A clear, defensible report or set of calculations, with assumptions and limitations stated.
Common questions
Which leaf of a cavity wall carries the load?
Usually the inner leaf. In a typical house the floors and roof bear on the inner block leaf, which carries the vertical load down, while the outer brick leaf mainly handles weather, appearance and its own weight. Wall ties make the two leaves share the wind load.
Can I use aerated blocks for a load-bearing wall?
For light loads, yes, and their thermal performance and easy handling make them popular for inner leaves. For heavy loads, a pier, or where a steel beam bears on the wall, we usually specify dense concrete blocks or engineering bricks, because aerated blocks can crush under a concentrated load without a padstone.
Why does blockwork crack more than brickwork?
Because the movements differ. Concrete and aerated blocks shrink as they dry, while clay bricks slowly expand, so blockwork needs movement joints at closer spacings. Placing those joints and any bed-joint reinforcement correctly is what keeps the finished wall free of cracks.
What bricks should I use below ground?
Engineering bricks or dense units that tolerate saturation and frost, with a mortar and sulfate class to match. Ordinary facing bricks below the damp-proof course can spall and erode over time. We specify the unit and mortar to suit the exposure for projects across the UK.
Tell us what you are building.
Send the drawings or describe the project. We confirm scope, deliverables and a realistic timescale.
Start a project