GOLD COAST HOME OWNER WAS TOLD URGENT UNDERPINNING WAS REQUIRED COSTING THOUSANDS OF DOLLARS. THANK GOODNESS HE CONTACTED FORENSIC ENGINEERS FOR AN INDEPENDENT REPORT, BECAUSE WE FOUND IT SIMPLY WAS NOT TRUE. HERE ARE SOME REPORT HIGHLIGHTS.

PROPERTY DESCRIPTION

The house comprises;

• Multi-level
• Masonry, stud & blueboard walls
• Slab on ground, suspended slab & timber floors
• Tile roof

FINDINGS

Exterior

 

• Garage left entry, erosion void under edge of firewall footing
• Similar slight erosion noted under edge of firewall of units 7&8
• Front storm water downpipe not vertical (as installed)
• Front wall some blueboard sheet joint edge gaps, some blueboard crack repairs
• Front driveway (old) cracks
• North wall some crack repairs
• West outdoor living roof beam joint seal split

Interior

• Garage slab cracks
• Garage & store wall cracks, ceiling (slab) fine cracks
• Family/dining (added) stud wall edge gaps
• Kitchen bulkhead some edge cracks
• Some door architrave /wall gaps
• 3rd level window reveal trim wear & some ceiling sheet edge gaps
• 2nd level laundry wall crack
• 2nd level hallway & bed 3 wall cracks

FLOOR LEVELS

*Relative zero was reset for each floor. Test locations are approximate and may be restricted by household items. Carpet wear affects readings, bathroom slabs fall to the floor waste and garage floor slabs are often finished with a fall to the door. Unit 9 (adjacent) recorded a level of -11 at the front left entry
We took levels on the floors (illustrated in mm in red highlights). There are some variations that would be “as finished” levels and also floor level variations which are likely to be associated with some slight ground movements. It is our interpretation that any floor level variations caused by ground movements are minimal, and are well within the allowed tolerances of AS 2870 appendix C and table 4.1.

CRACK CATEGORIES

Wall cracks are up to category 2 in accordance with AS2870-2011 Appendix C. Garage slab cracks are category 1 in accordance with AS2870-2011 Appendix C

CAUSES

Foundation soil movements

Our local experience indicates that the founding soils of the housing estate consist of clean landfill which was pre-consolidated prior to commencement of construction.

Although the quality density of the founding material would be certified by civil engineers as a suitable standard for high level footing construction, there can be some slight initial / normal footing settlements under applied loads which are within design tolerances.

Some landfill can also have the capacity to shrink and swell with variations in moisture content – again which is generally not significant and within design tolerances.

In this case it is likely that there has been some slight initial footing/slab settlements which caused some cracks & gaps. In addition, some current, slight footing & slab movements is likely to be a contributing factor.

Settlements, drains & erosion.

We could not identify any evidence or likelihood that the slight erosion under the garage firewall edge has caused any settlements or footing/slab instability.

Other causes of cracks & gaps

The building elements; blueboard, concrete, plasterboard & framing can undergo differential expansion and contraction with variations in temperature and humidity.

This can be exacerbated by the quality of finishing and fitments at the construction stage.

Garage floor slab cracks

The cracks in the garage floor are “plastic shrinkage cracks” which would have originated shortly after the slab was poured. The cracks occur due to concrete shrinkage as it cures and the cracks generally grow as the surface edges wear and they become more visible as they collect dirt. They are not a structural defect.

RECOMMENDATIONS

Brief

There is no evidence or likelihood of any significant movements of the footings or slabs and in particular there is no evidence that the unit 10/unit 9 garage common firewall and slab have sustained any settlements as a consequence of the erosion from the storm drain.
And there is certainly no requirement to stabilize / support the garage firewall footing and/or slab with any type of underpinning.
Repairs

• The storm drains should have sealed connections and seepage should not be allowed under the footing ot slab edges. The void can be plugged with non-shrink cementitious grout.
• The exterior blueboard sheet edge gaps can be repaired by raking out and sealing with polyurethane compound such as Sikaflex 11FC.
• Any exterior door & window frame gaps can also be sealed with SIKAFLEX 11FC or similar.
• Interior ceiling & wall cracks can be filled and painted. Use of fibreglass joint tape is recommended.
• Garage floor cracks do not require repair
• Masonry and concrete cracks can be raked out and repaired with high bond strength non-shrink cementitious grout.

PEACE OF MIND

If your house develops cracks and gaps, Do yourself a favour.
Before jumping into any kind of expensive underpinning, it is essential to get an independent engineer report to find out is it is actually necessary and if it is, then which type is the most appropriate.

HOW MUCH DOES AN ENGINEER REPORT COST?

An expert RPEQ Engineer subsidence Report from Forensic Engineers generally costs between $650 – $900 ex GST. (local service area only).

UNDERPINNER ARRANGING ENGINEER REPORTS FOR YOU

Some underpinners offer to arrange a report from their own engineer. The cost is considerably more than Forensic Engineers. And there is a huge conflict of interest. Forensic Engineers reports are 100% independent. We are not working for, or paid by an underpinner and we are certainly not trying to sell you any type of underpinning.

TALK TO US

Before committing to any type of underpinning, for peace-of-mind, contact us at Forensic Engineers for a chat and an independent opinion.