Underpinning in The Gap
In The Gap, Queensland's geological survey puts granite under three of our five sample points and flood-plain alluvium under the other two. Digging beside a footing for underpinning is building work in Brisbane City Council's guideline, and a licensed building certifier decides what approval a given job needs.
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Underpinning around The Gap
We sampled the survey at five points across the suburb. Three came back as the Enoggera Granite, a biotite granite and granodiorite of Late Triassic age. The centre and the north came back as Quaternary flood-plain alluvium, mapped as clay, silt, sand and gravel. The unit takes its name from Enoggera, yet in our samples it lies mostly under The Gap.
QBCC says sandy sites and rocky terrain are usually not prone to the swelling and shrinking of clay soils. The survey maps rock in one part of The Gap and clay-bearing alluvium in another, so it offers two different starting points for a diagnosis rather than one. It cannot say which lies under your footing: CSIRO notes that soil classification usually comes from a geotechnical report.
Permits and Brisbane City Council rules
Small parts of The Gap sit in Brisbane City Council's landslide overlay. Council says overlays can change how much filling or excavation is allowed without planning approval, and that digging directly related to underpinning is classed as building work. Look your lot up on City Plan online, then ask a licensed building certifier what the job needs.
Source: Brisbane City Council, Filling and excavation guideline (May 2026) and Filling and excavation page; City Plan 2014 landslide overlay mapping, read 21 September 2026. — confirm current requirements with Brisbane City Council.
Our The Gap service area
An enquiry from The Gap is referred on to an independent provider, who gets in touch to look at the house.
See all Underpinning in Brisbane. We also work in Enoggera, where the same survey maps a different rock.
Call (07) 3523 1792Last reviewed · Updated · First published