The footing choice for a replacement deck begins with the ground and the access, not with a claim that one system is always faster. Screw piles and concrete footings can both be appropriate, but their practical advantages depend on the engineered deck, soil conditions, installation method and what already occupies the site.
A renovation adds constraints that a vacant site does not have. Old footings may be in the way, a narrow passage may limit equipment, and mature landscaping may make reinstatement expensive. Compare complete foundation proposals for the same replacement deck, including the connection to the frame and the evidence needed to confirm that the work meets the design.
Establish what the new deck must support
Give the structural designer the intended footprint, height, surface and uses of the replacement deck. Include stairs, barriers and any planned roof supports or substantial built-in features. Foundation selection follows that defined brief; it should not begin with a standard number of supports chosen from the deck’s area alone.
Tell the designer which existing parts you hope to retain. Reusing old posts or footings requires assessment for the new structure. Their age, appearance or previous service does not establish capacity for changed loads or support positions.
Where a roof or other addition is only a future possibility, ask how it should be treated. Either include a clearly defined future requirement in the design or record that the later project will need reassessment. An unspecified promise that the deck is future-proof is not useful foundation documentation.
Resolve the deck layout before pricing individual supports
Changing the beam arrangement or moving a stair can change where supports are needed. Ask the designer to coordinate the foundation plan with the frame and finished deck layout. A cheap price per pile is not decisive if the actual proposal requires a different number of supports or substantial changes above them.
Map what is already in the ground
Provide available information about drains, utilities, old footings, retaining walls and nearby foundations. The contractor must arrange appropriate service-location and site checks before ground work. A drawing is useful evidence, but it should not be treated as proof that no unrecorded service or obstruction exists.
Use ground information to narrow the options
The engineer needs suitable information about the soil and site to design the foundations. Ask what investigation or geotechnical advice is required for this deck. Nearby building records may help, but the designer must decide whether they adequately describe the proposed support locations.
Discuss sloping ground, fill, rock, groundwater and any history of movement. These conditions can influence both the foundation design and how it is constructed. Do not select screw piles merely because excavation sounds inconvenient, or concrete merely because that is what the old deck used.
Screw Piling Experts’ published service information states that its shaft and helix are designed for the project’s loads and geotechnical conditions. The important principle for a homeowner is the dependence on actual design information, not the supplier’s broader promotional claims about speed or cost.
Ask how uncertainty will be handled
If an obstruction or unexpected ground condition is encountered, the contractor needs a defined process for obtaining the required design response. Ask who makes that decision and how any variation will be documented and priced. The installer should not improvise a reduced depth or moved support without appropriate acceptance.
Identify the assumptions that matter to the quote. An allowance based on straightforward ground conditions may be reasonable if it is clearly explained. It is less useful when the limitation appears only after installation equipment has arrived.
Understand what screw piles change on site
A screw-pile system uses a steel shaft with a helical element or elements installed into the ground using suitable equipment. Its geometry, protection, installation criteria and connection to the deck are design matters. It is not a generic metal substitute that can be selected solely by diameter.
For a replacement deck, a screw-pile proposal may offer a different access and construction sequence from excavated concrete footings. Ask the contractor to describe that sequence for the actual property. Avoid translating a general supplier claim into a guaranteed installation time for your site.
Determine what equipment is required and how it will reach each support position. A machine that fits through the side gate may still lack room to operate beneath eaves or beside an existing wall. The operating envelope matters as well as the transport width.
Specify the evidence of installation
Ask the designer and pile installer what installation records, testing or certification are required for the selected system. The required evidence should be identified before work begins and supplied at the relevant completion stage.
A pile disappearing into the ground is not, by itself, evidence of an accepted foundation. Keep records that identify the installed locations and any approved changes. These details allow the deck builder and engineer to confirm the relationship between the completed foundations and frame.
Consider durability and the head connection
Ask how the pile system is specified for the ground and exposure conditions, including the portion near the surface. The connection to the post or frame needs coordination with the deck material and any relevant corrosion-protection requirements.
Do not assume all adjustment heads or brackets are interchangeable. The complete connection should form part of the accepted design. If the supplied head changes the frame height, review the doorway and stair geometry before construction continues above it.
Understand what concrete footings require
Concrete footings can take different forms depending on the engineered design and ground conditions. Their excavation, reinforcement where specified, concrete and connection details must match the project. A familiar construction method still needs the correct site-specific arrangement.
Your Home’s concrete-slab guidance describes how concrete construction varies with the structural and site context. Although a deck footing is a different element from a house slab, the same planning caution applies: a concrete surface or volume alone does not establish the required foundation design. The engineer must specify the deck’s actual footing system.
For more detail on this part of the project, see What Is the Best Flooring for a Concrete Slab?.
Ask how excavated material will be handled and how concrete will be delivered or placed with the available access. The contractor should include any relevant equipment, protection and reinstatement in the proposal. A small quantity of concrete can still involve considerable access work.
Coordinate inspection and readiness for the frame
Identify which inspections are required before concrete is placed and what documentation will be provided. Agree who arranges those checks so the foundation stage does not depend on somebody assuming another contractor has done it.
The responsible professionals should determine when the completed concrete work is ready for subsequent loading and construction. Do not use a generic waiting period from another project. Concrete specification, conditions and the proposed work need to be considered in the actual programme.
Plan for weather and open work areas
Ask how excavations and disturbed ground will be managed if work is interrupted. The contractor must plan safety, water and access around the foundation works. Homeowners should not enter excavations or alter temporary protection to inspect them.
Consider how long garden routes and doorways will be affected. If the deck is the normal way out of the house, the builder needs a suitable temporary access or restriction plan. That practical constraint belongs in the programme whichever footing system is used.
Compare the effect on retained structures and landscaping
New supports may be close to house foundations, retaining walls, trees or old deck footings. Have the designer assess relevant interactions before installation. A support that fits neatly on plan may be difficult or unsuitable once concealed elements are considered.
Ask whether old footings are removed, bypassed or retained as part of an assessed arrangement. Include removal and disposal where necessary. The fact that a screw pile uses a different installation method does not make an old concrete obstruction disappear.
Discuss tree roots with an appropriate specialist where they may be affected. Neither excavation nor pile installation should be assumed harmless to a tree simply because the surface disturbance appears small. Coordinate the foundation design with any required protection.
Include the last part of reinstatement
Lawns, paths, irrigation and garden edging may need repair after equipment and materials have passed through. Ask for the boundary of reinstatement to be defined. “Leave site tidy” does not necessarily mean restoring a damaged paved route or replacing disturbed plants.
Take agreed photographs of access areas before work, where useful. They can help clarify the original condition and intended reinstatement without relying on memory. Keep these practical records separate from the technical evidence for the foundations.
Compare full foundation prices in AUD
Request Australian dollar quotations with GST treatment identified. Compare the designed number and location of supports, connections, mobilisation, access, inspections, testing, disposal and reinstatement. A unit price is helpful only within a complete and comparable scope.
- What design and ground information does the price assume?
- Which installation equipment and access works are included?
- How are existing obstructions and unexpected conditions handled?
- Does the price include the connection ready for the deck frame?
- What records and professional confirmations are provided?
- Which surfaces and services are reinstated afterwards?
For an invented budget exercise, assume one proposal totals A$5,400 for its defined foundation scope. A second is A$4,700 but excludes A$900 of access and reinstatement that the first includes. Assuming GST is included in all amounts, the comparable second total becomes A$5,600.
These amounts are not current Australian footing prices and do not favour either system. They simply show why an apparently cheaper initial quote can change once inclusions are aligned. Add any other genuinely different scope items before making a decision.
Value programme differences carefully
A shorter foundation stage can be valuable if it shortens the actual deck programme. It offers less benefit if the frame will not arrive for several weeks or a separate approval remains unresolved. Ask the builder to show the critical dependencies rather than attaching a cash value to theoretical time savings.
Likewise, a familiar concrete sequence may fit an existing contractor’s programme well. Compare confirmed availability and coordination, not just material characteristics. The best sequence is the one the project team can deliver for the assessed site.
Check where each contractor’s responsibility ends
A foundation contractor may supply an installed pile or footing while the deck builder supplies the post connection. Ask both parties to confirm the same interface detail before accepting separate quotes. Otherwise, an apparently complete foundation package may stop below the component needed to connect the frame.
Nominate who checks the installed positions and levels against the frame requirements. This is especially useful with a prefabricated deck frame whose dimensions are fixed before delivery. Resolving a discrepancy before fabrication or assembly is preferable to asking the builder to accommodate it through an unreviewed bracket or shifted post.
Use the final design to make the choice
Screw piles deserve consideration where the engineered system suits the ground, equipment access is workable and the installation evidence and frame connection are clearly defined. Concrete footings deserve consideration where their designed arrangement, excavation and placement suit the property and programme.
In a hypothetical renovation, narrow access might initially suggest compact piling equipment. A site assessment could then identify an obstruction requiring a different approach. In another project, concrete may remain practical because access and excavation are straightforward. The initial preference should remain open to the evidence.
Before starting, confirm the applicable approvals and inspection requirements with the project’s professionals. Keep the foundation plan consistent with the frame drawings. Any accepted change in location or level should be reflected in the records used for the rest of the deck.
At handover, retain the relevant design, installation and inspection documents. Ask what ongoing observations are appropriate around exposed supports and drainage. A replacement deck should sit on foundations selected for its actual site, with a clear record of how the chosen system was installed and accepted.
Reference basis
Screw Piling Experts, screw-piling service information; Australian Government, Your Home: Concrete slab floors. Supplier performance claims are not treated as independent comparisons. This article provides selection questions, not foundation dimensions or installation procedures.
A related guide to consider while planning this work is Removing a Concrete Slab for Renovation: Cutting, Demolition and Disposal Costs.