Fit to be tied
Garage brick-veneer boundary walls must be secured to a Standard. Ken Turnbull reports.
A worrying practice has been uncovered by state building inspectors and it’s likely occurring nationally.
Victorian Building Authority (VBA) staff has detected a major problem in some brick-veneer garage boundary walls that are being built before the timber frame (stud wall).
Site inspections revealed that brick ties had been screwed into the mortar afterwards, next to the timber studs, which goes against Australian Standard AS3700 Masonry structures.
The authority says that if garage boundary brickwork has to be built first due to difficult access and adjacent structures, the brick ties must be embedded 50mm into the mortar and spaced in accordance with Australian Standard AS3700.
The timber frame should then be constructed appropriately so that studs line up with the embedded wall ties.
In addition, it is crucial that builders adequately brace single-skin brickwork during construction until it is tied and supported by the framework (you don’t need much imagination to picture what could happen to an unsupported brick wall).
Geoff Anderson is chief executive of Abey Australia, Australia’s major provider of compliant brick ties for various aspects of wall construction.
“This discovery by the VBA is very serious. This is an accident waiting to happen,” Geoff says.
“Attaching ties retrospectively in this way is completely illegal. The ties have to be laid into the mortar as the brick veneer wall is being built, hence the corrugations at the wall end. This means precisely working out the position of frame studs beforehand.
“Screwing ties into relatively soft mortar to match stud spacing after the brick wall has been built is obviously an easy way out. The worry is, it directly contravenes the Standard, which was developed for the very good reasons of stability and durability.”
Emeritus Professor Adrian Page of the University of Newcastle’s School of Engineering is an expert in structural masonry and he offers this advice.
“Tying the brick to the timber frame is fundamental to ensuring that when the external veneer is subjected to lateral wind suction forces (or earthquake-induced lateral forces), the tie does not detach from the brickwork and the wall, thus losing support of its back-up frame (the back-up frame is the only means of support for the wall).
If a tie is to be retrofitted to the wall after its construction, to comply with AS3700 the adequacy of the attachment method would have to be established using the standard tie calibration test, which applies a tensile and then compressive force on a representative wall-frame assemblage with the tie installed in the intended manner.
This inherently assesses not only the tie properties but the effectiveness of its anchorage to both the brickwork and the stud. It is very likely that the support of the tie by a screw into the mortar joint would not survive a test of this nature,” says Adrian.
The VBA stipulates that if a builder is planning to construct a brick-veneer boundary wall in this way, the work needs approval from the relevant building surveyor before the job starts. Also, the building surveyor may require a procedure or design prepared by a structural engineer.
The VBA recommends that builders speak to the relevant building surveyor and structural engineer before carrying out any work that falls outside the Building Code of Australia (‘deemed to satisfy’ provisions) and Australian Standards.
Building inspectors are advised to report to the relevant building surveyor any alternative solutions employed in construction that don’t form part of the approved documentation or don’t comply with the above code and Standards.
During the inspection process it is not the building inspector’s role to approve alternative solutions that haven’t been considered and passed by the relevant building surveyor.