Cavity Walls In New Buildings In South Africa

SANS 10400-XA (Energy Usage in Buildings)

The 2021 SANS 10400-XA revision requires the construction of cavity walls in place of 230 mm solid brick external walls. This energy-saving change is applicable in all the energy zones in South Africa except in zones 3, 5 and 5H.

How wise this course of action is considering the lack of skills in the building trade will have to be seen!

What is a cavity wall?

A cavity wall consists of two skins separated by a hollow space (cavity). The advantage is that a cavity wall gives better thermal insulation than a solid wall. The space between the two leaves of cavity walls reduces heat transmission into the building from outside.

The following are the advantages of cavity walls when compared to solid walls.

  • This type of wall gives better thermal insulation than solid walls.
  • The hollow space between leaves prevents moisture penetration through the wall from the outside. This prevents dampness internally.
  • They also act as good sound insulators.
  • These walls also prevent efflorescence from occurring.

Construction of cavity walls

how to build a cavity wall using DPC and brickforce
window built in on a cavity wall with vertical DPC

The construction of these walls is technically more difficult than for solid 230 mm walls.

  • The cavity between the two masonry leaves should be a minimum of 50 mm. The gap must be consistent from the bottom of the wall to the top.
  • Below the DPC level, the bricklayer must fill up the wall cavity with concrete or mortar before installing the DPC.
  • The bricklayer then installs the DPC at slab level to step down from the slab-level interior wall across the cavity to the outer wall and weep holes. Its purpose is to drain away any water in the cavity towards the weep holes to discharge it outside.
  • Weep holes must be provided in the external leaf above the Damp Proof Course (DPC) at every 4th brick horizontally.
  • The bricklayer must build in wall ties at every 5th course of brickwork vertically and space them horizontally at every second brick to tie the two leaves of brickwork together.
  • Mortar dropping down in the cavity can stop water from draining away. The bricklayer should leave some bricks out temporarily at the DPC level to clear mortar droppings at the end of each day’s work.
  • The normal method of preventing mortar droppings from falling to the base of the cavity is to use a cloth-rapped batten (38 x 38 mm) or specially sized 50 x 38 mm planed to 45 mm. The bricklayer places the batten on the wall ties while building the wall. The bricklayer raises the batten, using wire tied to its ends and then positions it on the next row of ties.
  • Furthermore, the bricklayer should install a vertical DPC on the sides of doors and windows when closing off the cavity wall. This is to prevent water from driving to the inner face.
  • In addition, the bricklayer should install a layer of DPC and weep holes in the cavity above exposed doors and windows similar to the DPC at floor level. This is to prevent moisture from penetrating the inner leaf.
  • At the roof line, the bricklayer should fill or brick up the cavity for two or three courses below the roofline to stiffen and distribute the load over both leaves. He should also build in roof ties at this level to tie down the roof trusses or beams.
  • No wide brick force can be used to span both leaves and cavities of brickwork. A 90 mm width of brickforce will need to be used on every 5th layer of brickwork on both leaves up to window or door height and every course above that until the cavity is closed at roof height.

My Concerns with the new requirements

The Western Cape Province has already been following this practice for many years. Cavity walls are also better for damp prevention than solid walls. The introduction of cavity walls nationally is to satisfy regulatory requirements for building energy efficiency.

However, such sweeping changes to the construction of brick buildings in other areas of the country may have serious consequences because of skills shortages. They may lead or may have led to substandard work because of the lack of sufficient skills and training of bricklayers and their supervisors!

The newer generation of bricklayers and builders never adhered fully to the requirements of the building regulations before with the construction of solid 230 mm walls! Most of them have had no experience with building cavity walls either!

I have listed some of the issues I have seen on building sites below:

  • In my experience, the bricklayers in the building trade never used collar jointing of the solid brick walls leading to weakened wall structures.
  • The bricklayers seldom place the DPC on a half layer of mortar on the brickwork. Instead, they place the DPC directly on the brickwork. This often led to moisture intrusion in the structure at the DPC level.
  • Generally, no bricklayer has installed DPC on the sides or above the door and window openings to prevent moisture intrusion through the wall at the windows and doors inland from the coastal areas.
  • Few bricklayers build in the correct number of layers of brickforce reinforcing above windows and doors.
  • Often, the bricklayers tooth the brickwork of the internal walls to external walls and corners instead of stepping back the brickwork as required.
  • The mixing of large amounts of mortar resulting in the retempering (adding additional water) of mortar is a common practice. This causes weakened mortar and brickwork.

Most of the issues result from a lack of knowledge and training. This includes not only the bricklayers but also the supervisors!

So how do we get the bricklayers to build the more technical cavity walls correctly?

  • One way is to train the supervisors who in turn can train the bricklayers!
  • Various brick associations and training schools offer bricklaying training. The various training associations and schools may be open to do on-site training.
  • Both the supervisors and the bricklayers can learn from videos that show how to build cavity walls. They all have cellphones on which they can view the videos.
  • Articles by the Clay Brick Association can update supervisors and bricklayers with the technicalities of building a cavity wall.

Let us hope the above happens so that new homeowners will have properly constructed homes!

Conclusion

With the correct training, newly built cavity walls will provide the thermal benefit required by the new revision of SANS 10400-XA. In addition, the construction of cavity walls will minimise moisture intrusion into new buildings if constructed properly. They also provide sound insulation benefits.

CONTACT ME

Inspected Once, Inspected Right!®

SEE WHERE I INSPECT IN GAUTENG!

THE HOME DETECTIVE » maintenance inspection

How to monitor cracks

Worried About Cracks In Your House? Having Sleepless Nights?

crack
Here the foundation on the corner of the domestic bathroom had subsidised! Disguising cracks with paint and Polyfilla won’t work! You need to find the cause first and fix that before you patch walls!
crack
The problem here was with the pooling of water on the paving and the level of the paving being close to or at the floor level of the bathroom. In addition, it appeared the bath waste or water supply may be leaking.

How to monitor cracks in your walls and floors!

Often, home buyers and homeowners are worried by cracks in the house and boundary walls, especially plastered walls!

The good news is that, generally, concrete, stone, brick and masonry walls and concrete or screeded floors that have cracks less than 1 mm wide (the thickness of a credit card) are common and usually do not warrant any corrective action. Most of these small tight cracks are caused by normal shrinkage as the moisture in the walls and floors evaporates over time or settlement of the structure which usually occurs within the first few years after construction.

Be warned, however, that changes in condition around the structure may also cause settlement many years later! Examples are planting a new garden or tree or removing a garden or tree that is against or close to the house.

Crack Fillers

Note that all cracks should be sealed with paint, caulk (sealer) or mortar to prevent water from getting into the structure.

Moreover, if a horizontal, vertical, or diagonal masonry crack is filled with hard masonry patching compound, any substantial future movement is likely to show up as a new crack in the patched area or nearby.  Therefore, always use a non-shrinking grout to prevent stressing yourself!

Continued movement

Cracks that continue to move are a reason for concern! Continued movement in cracks should be evaluated as there may be a need for corrective action. Therefore, if you notice a crack has re-cracked or the crack has opened or gotten larger it should be monitored! However, first, make sure there is no shrinkage of the filler product.  All cracks that are 5 mm and greater should be carefully monitored to ensure there is no continued movement.

Continue reading “How to monitor cracks”

Damp Walls

Damp Walls In Your Home

gutters

I posted on my blog, in November last year, about damp walls that arise as a result not having gutters on your home to control the flow of rainwater off your roof.

On Saturday I inspected a four-year-old property that had a one tile overhang on the roof, no gutters but had paving surrounding the house.

However, the external walls of the house were in a desperate state because of the three most destructive mistakes architects, developers, builders and homeowners make!

As a result, I’m going to repeat part of the issues mentioned in my blog again!

Damp walls caused by no gutters

Gutters collect the rainwater runoff from the roof, discharging it into downpipes which conveys the rainwater away from the house in a controlled manner. In addition, they also protect the timber roof structure at the eaves of the house. Furthermore, gutters protect the exterior walls, windows and doors of the house and its foundation from damp and potential damage.

damp walls

The splashing up against the walls was the most serious cause of the penetrating damp on the walls of the house. Moreover, the crazing cracking (spiderweb-like fine cracking) in the plasterwork was the main indicator of the penetrating damp caused splashing up of rainwater. No cracking was observed higher up on the walls.

Even if your house has a reduced overhang at the eaves, gutters will still provide the required protection against heavy rain and wind storms your house may be subjected to.

Insufficient roof overhang at the eaves

Roofs with no gutters which have a two-tile overhang (600mm in the case of a metal roof) or less will allow water to pour from the roof close to the walls, windows and doors and the foundation.

Continue reading “Damp Walls”

Section Title Schemes

Responsibilities of Owners and Body Corporates

Body corporates

I do a fair amount of inspections in sectional title schemes. Often, owners ask me if body corporates will pay for repairs inside their units. Obviously, their concern is about damage caused by external factors such as rainstorms, burst geysers, and so on.

Each case is usually based on its merits. Usually, the body corporate’s trustees use their discretion when deciding to whom they allocate the cost of repairs and replacement. However, there are many grey areas and differences between the owner’s and body corporate’s liability and responsibility.

The Body Corporate’s obligations

Body corporates are responsible for the repairs and maintenance and upkeep of the common properties.

Furthermore, the body corporate maintains all pipes, ducts, wiring, etc., for the common property and services to more than one unit.

Your obligations as an owner of a section

You must maintain and keep your section in a good state. Moreover, you must also keep any part of the common property to which you have the right neat and tidy. These are exclusive use areas such as gardens, patios, balconies, parking areas, garages, etc.

Continue reading “Section Title Schemes”

Boundary Walls

Preventing and Repairing Cracks in Boundary Walls

Damaged boundary walls around your property can spoil the whole look and feel of your property. Furthermore, cracked and leaning walls can also pose a danger to passers-by should the wall fall over.

boundary wall
This was a wall that was butt jointed against the neighbour’s wall. The danger here is that when the wall falls over portions of the wall will be spread over the pavement and possibly into the road. If a pedestrian is close by serious injury could result!

This article explains the correct way to repair boundary walls and install expansion joints!

Firstly, if your walls have ugly cracks and broken plasterwork and brickwork at the expansion joints do not plaster them up as shown in the photos below!

boundary wall
This expansion joint was chopped open and plastered up. The joint will crack at the joint again. This is a waste of time and money and will cause more problems than before!

Furthermore, the work done on these boundary walls will result in more cracking in the walls!

Many boundary walls and retaining walls may fail prematurely due to the lack of provision for movement. However, this is usually not a fault in the materials used, but usually a lack of proper design. Even when the design is correct, the construction of the boundary wall and expansion joints are often faulty.

What is an expansion joint?

It is a separation between two portions of the same structure. A butt joint in a boundary wall is not an expansion joint!

Expansion joints in boundary walls

When building a boundary wall, an expansion joint is a separation designed to relieve stress on building materials caused by movement induced by thermal expansion and contraction. They are therefore specifically provided in boundary walls to avoid cracks occurring in the wall.

Temperature changes and seasonal changes mostly cause the movement in the boundary walls. However, expansion joints also permit movement due to ground settlement, seismic events and expansive soils.

Continue reading “Boundary Walls”