Why footings need engineering
Much of Melbourne sits on reactive clay that swells when wet and shrinks when dry. Add sloping blocks, old fill, trees, neighbouring footings and existing buildings, and the footing is often where a project's risk is concentrated.
A well-engineered footing is sized for the actual site rather than a generic assumption. It avoids both under-design, which can lead to cracking and movement, and over-design, which costs you concrete and steel you didn't need.
Site conditions that shape the design
- Soil reactivity and site classification: how much the ground is expected to move, and therefore how stiff the footing system must be.
- Trees and drainage: both change soil moisture, and with it the movement of reactive clays.
- Fill: uncontrolled or deep fill usually means founding deeper, on piers or piles.
- Slope: stepped footings, deeper edge beams or piers, and sometimes a retaining wall.
- Existing and neighbouring footings: extensions have to work with the footings already there, and new footings must not undermine a neighbour's.
Geotechnical input
Foundation design depends on knowing the ground. For most projects that means a geotechnical report — often called a soil test — with a site classification and borehole logs.
MEG doesn't carry out soil investigations. We'll tell you what investigation the design needs, then either work from a report you commission or coordinate with a geotechnical consultant for you. The geotechnical consultant is responsible for the investigation and report; we're responsible for the footing design that uses it.
Footing systems we design
- Stiffened raft and waffle slabs
- Strip and pad footings
- Bored and board-formed piers
- Screw piles, including designs to suit a nominated supplier's product
- Pile caps, ground beams and suspended slabs
- Plinths and footings for plant and equipment
- Substation and switchyard footings
- Footings for extensions, designed to work with the existing footings
- Retaining wall footings (see retaining wall design)
What you receive
- Footing drawingsLayout, sections, reinforcement and details, ready for the building permit.
- CalculationsDesign calculations that support the drawings, for your building surveyor.
- Construction notesFounding criteria, hold points and the inspections the design requires.
- Permit supportResponses to the building surveyor's engineering questions, and a certificate of compliance for design where required.
What we need from you
- Architectural plans: floor plans, elevations and sections
- Site plan or feature survey showing levels, trees, easements and boundaries
- Geotechnical report and site classification, or the go-ahead to arrange one
- Structural loads, if another engineer is designing the building above the footings
- Details of existing footings, for extensions (photos of test holes are helpful)
- Any preferred system or supplier, such as a particular screw pile product
Don't have everything yet? Send what you have. We'll tell you what's missing and whether it affects the proposal.
How it works
- Plans and site informationWe review your plans and tell you if a soil report or survey is still needed.
- ProposalA written proposal confirms the scope, fee and programme.
- Design and documentationWe design the footings and prepare drawings and calculations.
- Permit and constructionWe answer the building surveyor's questions, and we can inspect footings before the pour if you engage us to.
Who does what
MEG provides
- Footing and foundation engineering design
- Drawings, calculations and construction notes
- Construction-stage advice and inspections, if engaged
Not included, or by others
- Geotechnical investigation and soil testing (by a geotechnical consultant)
- Land surveying
- Civil stormwater and drainage design, unless specifically agreed
- Issuing building permits (the building surveyor's role)
Questions
Do I need a soil test?
For almost all new footings, yes. The site classification in a geotechnical report sets the basis for the design. For some small structures, an engineer may be able to work from reasonable assumptions. We'll tell you which applies to your project.
What is a site classification?
It's a category, based on the soil investigation, that describes how much the ground is expected to move. Classes range from stable sand and rock to highly and extremely reactive clays, with separate categories for problem sites such as deep fill. The footing design follows from it.
Can you design screw piles using a specific product?
Yes. We design based on your product and the project's requirements, and set installation criteria the installer can verify on site.
Can you design footings for an extension next to my existing house?
Yes. This is one of the most common situations we see. The key is making sure the new and old footings behave compatibly. We may ask for a test hole to expose the existing footing.
Do you also design the structure above the footings?
For homes and small buildings, yes — beams, lintels, framing and connections. See residential structural engineering.