Brickwork on medium and high-rise buildings: how it keeps water out and lasts for decades

Brick has a strong record on medium and high-rise buildings. It does not burn, it weathers slowly, it needs no painting, and a well-built brick facade can last as long as the building. But when a brick facade on an apartment building goes wrong, it is expensive: cracked and bulging brickwork at the floor lines, white salt staining, rusted steel, and water inside units that no amount of sealant seems to stop.

Those failures almost never come from the bricks. They come from how the wall was designed and built to manage two things: water and movement. This article explains how brickwork works on a multi-storey building, what the NCC and standards require, and what to look for in design, construction and inspection.

A note on what we have and have not verified. The NCC clauses below were checked against the published NCC 2022 text. AS 3700 is a paid standard; where we refer to its content we do so at the level of what it covers, not specific numbers, unless a source is listed. Spacings, gaps and tie details for any building are the engineer's call.

How brick works on a multi-storey building

On a house, brick is often part of the structure. On a medium or high-rise building it almost never is. The concrete or steel frame carries the building. The brick is a facade: an outer leaf of brickwork, usually 110 mm thick, tied back to a backing wall (concrete, blockwork or a framed wall) with a cavity between them.

That arrangement does three jobs:

1. The outer leaf is the first line of defence against rain. Brick and mortar absorb water and, in driving rain, some always passes through. That is expected.
2. The cavity is the drainage path. Water that passes through the outer leaf runs down the inside face of the brick, is caught by flashings and is let out through weepholes. The backing wall stays dry because the cavity is never bridged.
3. The ties and supports hold the brick to the frame against wind and its own weight, while letting the brick and the frame move separately.

The key idea is that a brick facade is a drained wall, not a sealed one. It works because water is expected to get behind the brick and is given a way out. Most serious leaks happen where that path is blocked, bridged or missing.

Why medium and high-rise is different

A two-storey brick house and a twelve-storey brick-faced apartment building use the same bricks, but the high-rise has problems the house does not:

• Height and exposure. Upper floors face higher wind pressure and more driving rain, so more water is pushed through and across the wall.
• Differential movement. This is the big one. Clay bricks expand slightly and permanently after they are fired, as they take up moisture over years. A concrete frame does the opposite: it shrinks as it dries and shortens under load over time (creep). Over one storey the difference is small. Over many storeys it adds up, and if the brickwork is built tight against the frame, the growing brick and the shrinking frame load each other.
• Support. A tall brick leaf cannot just sit on the ground and rise unbroken to the roof. On most multi-storey buildings the brickwork is carried storey by storey (or every few storeys) on steel shelf angles fixed to the slab edges, with a soft joint under each angle.
• Access. Repairing a brick facade on a high-rise means scaffolding or swing stages, so a defect costs many times what it would on a house.

What the NCC and standards say

For Class 2 to 9 buildings (apartments, offices, hotels, commercial), NCC Volume One applies:

• Weatherproofing. Performance Requirement F3P1 requires that a roof and external wall, including openings around windows and doors, prevent the penetration of water that could cause unhealthy or dangerous conditions or loss of amenity for occupants, or undue dampness or deterioration of building elements. Under the Deemed-to-Satisfy Provisions, F3D5(1) accepts masonry, including masonry veneer, unreinforced and reinforced masonry, that complies with AS 3700. In other words, the NCC's weatherproofing pathway for brick is built on AS 3700 being followed in full. A wall that departs from it needs a Performance Solution.
• Structure. B1D4 names AS 3700 for the structural design of masonry, including masonry veneer, alongside AS 3600 for concrete and AS 4100 for steel. Performance Requirement B1P1 lists the actions a building must be designed for, and these include time-dependent effects such as creep and shrinkage, differential movement and thermal effects. Movement between brick and frame is a structural design matter, not a site detail.
• Rising damp. F1P4 requires that moisture from the ground be prevented from causing undue dampness, deterioration or unhealthy conditions. F1D6 sets out damp-proofing, and where a damp-proof course is used it must comply with AS/NZS 2904 or AS 3660.1. The guidance gives a damp-proof course in masonry walls above finished ground level as an example of an acceptable measure.
• Fire. In buildings required to be of Type A or Type B construction (which includes most medium and high-rise buildings), C2D10 requires external walls and all their components, including the facade covering, framing and insulation, to be non-combustible. Concrete and masonry are listed among materials that can be used wherever a non-combustible material is required. That is one reason brick has become more attractive since the cladding reforms. The other components in the wall, such as insulation in the cavity or backing wall, still need to meet the requirement or a listed exemption.

AS 3700, Masonry structures, is the standard the NCC relies on. It covers structural design, and the detailing that matters for durability and water: cavities, damp-proof courses and flashings, control joints (contraction and expansion joints, and their spacing), wall ties and other built-in components, and durability requirements by exposure environment. Wall ties are made to AS/NZS 2699.1 and given a durability class. Under AS 3700:2018 the class required depends mainly on distance from the coast and whether the coast has breaking surf, with Grade 316 stainless steel used in the most severe coastal band.

In NSW, the external walls and the waterproofing of a Class 2 building are "building elements" under section 6 of the Design and Building Practitioners Act 2020. Their designs have to be prepared and declared by registered practitioners, and the builder has to declare the work was built to them. See our article on NSW building reforms and the duty of care.

The six details that decide whether it lasts

These come from the mechanics of the wall and from what we see in inspections and defects reports. They are not a measured failure rate.

1. A clear, drained cavity

The cavity only works if water can run down it and out.

• Mortar droppings that fall into the cavity during laying build up on ties and flashings. They bridge the cavity, carry water across to the backing wall, and block the weepholes. This is the most common construction fault behind brick facade leaks. It is avoided with care while laying, cavity battens or boards, and a clean-out before the wall is closed.
• Nothing should cross the cavity except ties and properly flashed openings. Services, packers and mortar bridges are all water paths.
• Cavity width is a design item under AS 3700 and the drawings. Building it narrower than designed, to make up for frame tolerances, increases the risk of bridging.

2. Flashings that collect water and send it out

A flashing is a waterproof sheet built into the wall to catch water in the cavity and direct it outward.

• They are needed wherever the cavity is interrupted: at every shelf angle and floor line, over window and door heads, under sills, at the base of the wall and at roof and balcony junctions.
• They must step up from the outer leaf to the inner, so water falls outward, and turn up at the ends (stop ends) so it does not run off the side and into the wall.
• Laps and joints in the flashing must be sealed and lapped the right way. A flashing that stops short or leaks at a lap simply moves the leak.
• The material has to suit the location and last as long as the wall. Flashings are effectively impossible to replace without taking the brickwork down.

Our article on where buildings leak covers flashing sequence at junctions.

3. Weepholes that stay open

Weepholes are open perpendicular joints in the brick course just above each flashing. They let water out and air into the cavity.

• They need to be directly above the flashing, at the spacing on the drawings, and clear of mortar.
• They must not be sealed, rendered over or blocked by landscaping, paving or a raised balcony floor. Covering weepholes to stop insects or draughts is a common cause of leaks a few years later.

4. Shelf angles and the soft joint underneath

On a multi-storey building, a steel angle bolted to the slab edge usually carries the brickwork above it, often at every floor.

• Directly under each shelf angle there should be a horizontal gap filled with a compressible material and sealed, not mortar. This is where the frame's shrinkage and the brick's growth are taken up. If it is filled with mortar or the brick is built tight to the angle, the load from the floor above goes into the brick below, and the result is cracking, spalling and bulging along the floor lines.
• The angle and its fixings carry the full weight of the brickwork above, outdoors, in a damp cavity, for the life of the building. They need a corrosion protection or stainless grade that suits the exposure, and fixings designed by the engineer. A rusting shelf angle expands, cracks the brick around it, and in the worst case loses its fixing capacity.
• A flashing goes over each shelf angle, with weepholes above it, so the angle sits on the dry side of the drainage path.

5. Vertical and horizontal movement joints

Brickwork needs vertical joints along its length as well as horizontal joints under the shelf angles.

• Vertical expansion joints in clay brickwork allow the brick to grow along the wall. They are typically placed near corners, at changes in wall height or thickness, at openings and at regular spacing set by the design under AS 3700.
• Joints must be clear through the full brick thickness, free of mortar, with a compressible filler and a sealant over a backing rod.
• Ties next to a joint must still restrain the brickwork on both sides. A joint is a deliberate break, not an unsupported edge.
• Joints must not be grouted, rendered or bridged during later repairs. See our article on rigid joints, pinned joints and movement joints.

6. Ties that match the exposure

Wall ties are small, hidden and carry all the wind load from the brick back to the structure.

• Grade and durability class must suit the site. A building near the coast needs a higher class (Grade 316 stainless in the most severe band) than one inland. Using standard galvanised ties on an exposed coastal site leads to corrosion that cannot be seen until the brick starts to move.
• Spacing and embedment follow the design: ties at the specified centres, extra ties around openings and next to movement joints, and enough embedment in the mortar bed at both ends.
• Ties must slope down toward the outer leaf, or have a drip, so water does not run along them to the backing wall.
• On a concrete or steel frame, ties are usually fixed to the frame by channels or brackets that allow vertical movement while resisting wind. A rigid tie defeats the movement joint.

Other things that make a difference

• Brick and mortar selection. Bricks are rated for salt attack resistance, and the right rating depends on exposure (coastal, near the ground, parapets, retaining). Mortar must suit the brick and the exposure. Too strong a mortar makes the wall less tolerant of movement; too weak a mortar erodes.
• Copings and parapets. The top of the wall is one of the most exposed parts. Parapets need a coping that overhangs and drips clear of the face, and a flashing underneath.
• Sills, heads and window junctions. Sill and head flashings, with the window frame isolated from the brickwork (see our article on glazing and frame connections).
• Cleaning. Acid-cleaning new brickwork too strongly, or without pre-wetting, damages mortar joints, stains brick and attacks aluminium frames and steel. See cleaning chemicals and building materials.
• Sealers. Clear water-repellent sealers are not a substitute for a working cavity, and some trap moisture and salts in the face of the brick.

Warning signs in an existing building

For strata committees and building managers, these are worth reporting and investigating:

• Horizontal cracking or bulging brickwork at floor lines, often with the brick pushed out at the corners. This usually points to a blocked or missing joint under the shelf angle.
• Rust staining or cracking around steel at floor lines, lintels or balconies.
• White powdery deposits (efflorescence) that keep coming back, or brick faces breaking down. Repeated efflorescence means water is moving through the wall more than it should.
• Damp, staining or mould inside units at window heads, at the floor line or below balconies (see damp patches and mould).
• Vertical cracks near corners or a steady pattern along a wall, which can mean missing or too few expansion joints.
• Weepholes that have been sealed, rendered over or buried by paving, planter boxes or a raised balcony floor.
• Sealant in movement joints that has split, hardened or been replaced with mortar.

Treat a repeat leak or a repeating crack as a design or construction problem, not a maintenance one. Patching it with sealant or mortar usually moves it, and can make it worse. An investigation with selective opening up (removing a few bricks to look at the cavity, ties, flashing and shelf angle) usually finds the cause. Our article on strata defects reports covers what to do next.

What to check, by role

Developers and designers:

• Brief the structural engineer to analyse differential movement between the frame and the brickwork, and to design the shelf angles, ties and joint gaps accordingly.
• Show the flashing, weephole, shelf angle and movement joint details on the drawings at every condition: floor lines, openings, parapets, balconies, corners and the base.
• Specify brick salt attack rating, mortar class, tie durability class and shelf angle corrosion protection for the site's exposure.
• Confirm the fire compliance of every component in the wall, not just the brick.

Builders and trades:

• Keep the cavity clean while laying, and inspect and clean it out before each lift is closed.
• Check flashings, stop ends, laps and weepholes at every floor line before they are covered.
• Keep the joint under each shelf angle and every vertical joint free of mortar.
• Check tie type, spacing, slope and embedment against the drawings. Do not substitute tie grades.
• Photograph each of these before it is covered. We treat them as hold points.

Strata committees and building managers:

• Ask for the facade drawings, the engineer's movement joint and shelf angle details, the tie specification and the construction photos as part of the building records.
• Include brick facades, movement joint sealants and weepholes in the maintenance schedule, with an inspection cycle and a sealant replacement allowance in the capital works fund.
• Make sure balcony, landscaping and paving works never cover weepholes or bridge the cavity.
• Commission an envelope inspection if warning signs appear, and check defects within the statutory warranty periods.

A pre-construction checklist

1. Has the engineer assessed differential movement between the frame and the brickwork for this building's height and frame type?
2. Where are the shelf angles, what gap is under each, and what fills and seals it?
3. Where are the vertical expansion joints, and how are ties arranged on each side?
4. What is the cavity width, and how will it be kept clean during laying?
5. Where are the flashings, how do they step and lap, and where are the stop ends and weepholes?
6. What durability class are the ties, and what corrosion protection do the shelf angles and fixings have, for this site's exposure?
7. What salt attack rating are the bricks, and what mortar class is specified?
8. Are all wall components compliant with C2D10 or a listed exemption?
9. What are the hold points, and who signs off the cavity, flashings, ties and joints before each lift is closed?

How we approach it

At Precision Projects Group we work across new construction, renovation and strata building maintenance, so we see brick facades both as they are built and as they age. On new work we treat the cavity, flashings, ties, shelf angles and movement joints as hold points, check them before they are covered and record them in the handover record. On existing buildings we inspect the facade, open up where needed to find the cause, and recommend a repair that fixes the mechanism rather than the symptom.

If you are planning a brick-faced building, or you manage one showing cracks, staining or leaks, get in touch or see our services. For the low-rise side of the topic, see double brick vs brick veneer.

Sources

• NCC 2022 Volume One, Part F3 Roof and wall cladding, Australian Building Codes Board (F3P1, F3D1, F3D5)
• NCC 2022 Volume One, Part F1 Surface water management, rising damp and external waterproofing, Australian Building Codes Board (F1P4, F1D6)
• NCC 2022 Volume One, Part B1 Structural provisions, Australian Building Codes Board (B1P1, B1D4)
• NCC 2022 Volume One, Part C2 Fire resistance and stability, Australian Building Codes Board (C2D10)
• AS 3700:2018 Masonry structures, Standards Australia; AS/NZS 2699.1 Built-in components for masonry construction, Part 1: Wall ties; AS/NZS 2904 Damp-proof courses and flashings
• Durability class of masonry wall ties under AS 3700:2018, Australasian Corrosion Association conference paper
• Wall tie durability rating, Leviat Ancon
• Shelf angles, BRANZ Build magazine (New Zealand practice, background only)
• Detailing shelf angles, Masonry Advisory Council (United States practice, background only)
• Design and Building Practitioners Act 2020, section 6 (Building elements), NSW Legislation via AustLII

This article is general information, not engineering or legal advice for your building. Cavity widths, movement joint spacings and gaps, shelf angle and tie design, and material selection depend on the building's height, frame, exposure and class, and must be designed by a qualified engineer under AS 3700 and confirmed with your certifier. Full website disclaimer