Building in the Hills usually means building on a slope, and a slope changes the footing, the retaining and often the frame. This page covers what is worth knowing before you start, whether it is a new home on a Mount Barker estate or an extension on a steep block in Stirling, Hahndorf or Woodside.
Why Hills Blocks Need More Engineering Than Flat Ones
A sloping block needs more engineering because the house has to be stepped, propped up or cut into the ground, and each of those choices changes the footing. On flat land a single slab level often works. On a slope the designer has to decide how much to cut, how much to fill and how much to bridge with a suspended floor or a split-level slab, and the structure follows that decision.
Hills ground can also change over short distances. One end of a block can be on clay and the other on weathered rock, or on fill placed when the lot was formed. That is why the soil test bores are placed to catch the variation, and why the site classification under AS 2870 (the Australian Standard for residential slabs and footings) is read alongside the levels, not on its own.
Cut and Fill: What Happens to the Footing
Where a block has been cut and filled, the footing must either reach natural ground through the fill or be designed for the fill itself. Fill that was placed and compacted under control, with records, can sometimes be built on. Fill with no records usually can't be relied on, so the footing goes deeper, often with piers down to natural ground. The soil test report states what it found, and the design responds to that report.
Cutting into a slope also leaves a face that has to be held up. That is a retaining wall, and its footing and drainage are designed together. Our retaining wall guide covers the approval thresholds in South Australia and why drainage behind the wall matters as much as the wall.
Split-Level Footings and Stepped Slabs
A split-level footing lets the house follow the slope in steps instead of forcing one flat platform onto it. It often means less excavation and lower retaining walls, but the step between levels carries load and soil pressure, so it has to be detailed as part of the structure. Where the drop is large, a suspended timber or steel floor on piers can be simpler than a slab. The engineer who designs your job will set out the options that suit the plans and the levels from the survey.
Trees, Wind and Exposed Sites
Large trees are common on Hills blocks, and they matter because their roots dry the ground around them. On reactive clay (clay that swells when wet and shrinks as it dries), a tree close to the house can change how much the ground moves, and removing one can change it again. The soil test records the trees, and the footing design allows for them. Our reactive clay guide explains the mechanism.
Ridgeline and open hillside sites can also see higher wind than a sheltered suburban street. The wind classification is set for each site from its height, terrain and shielding, and it drives roof tie-down, bracing and the design of any carport, pergola or shed.
Many Hills properties sit in bushfire-prone areas. A bushfire attack level (BAL) assessment is a separate requirement handled by others; if one applies to your job, your designer or certifier will tell you.
New Estates Around Mount Barker
New estates in the Mount Barker growth area often come with a soil report for the subdivision, but each house still needs a classification for its own lot. Estate lots can be benched and filled during civil works, and the result can vary from lot to lot even on the same street. A lot-specific test, read with the estate earthworks records where they exist, is what the footing design relies on.
A site and drainage (S&D) plan shows the levels, the building position and where stormwater goes, which on a slope is a structural question as much as a plumbing one. Site visits and inspections in the Hills are quoted with travel. Terms and conditions apply to the package offer below.
Full Package
Take the whole sequence and 10% comes off.
Where we carry out the site and drainage plan, footing design and structural design for the same address, 10% comes off the total of that work. You do not have to book it all at once: bring us the third at any stage of the project and the discount is applied then, across everything at that address.
One address, one client. The discount holds while all of the work stays with us; if part of it is cancelled or moved to another consultant, the discount no longer applies. At least one of the three has to be booked through your client portal. Surveys, soil tests and timber truss design do not count toward it. Full terms are set out in the fee offer we send you.
How a Hills Job Runs
A Hills job runs the same way as any other: survey and soil test first, then the design. Soil tests and surveys are carried out by specialist contractors that the practice briefs and coordinates. The office is in the Adelaide CBD, and documents are issued through your client portal (see how the client portal works and what it gives you). If you come back later for a deck, a pool or a retaining wall, the survey and classification are already on file for that address and are not re-tested or re-charged. Builders can read how we work with builders, and the full list of work is on our services page.
Working elsewhere? See our pages for Gawler, the Barossa and northern Adelaide and the Fleurieu, Murray Bridge and regional SA, or all service areas.
This page is general information about structural engineering in South Australia, not advice for a specific site. Every job is priced for its own site and scope, and you get a fixed fee in writing before any work starts.