A low deck over concrete can look like an easy replacement: remove the old boards, keep the slab and fit a new surface. The difficulty is usually the space between the concrete and the door. That shallow zone must accommodate support, decking, drainage and the requirements of the chosen materials.
Begin by finding out why the original deck needs replacing. If it stayed wet underneath, blocked a drain or concealed problems at the house, a new board colour will not fix the cause. The replacement should be designed around the existing concrete and building junction, with a clear decision about what can remain and what needs alteration.
Measure the whole available construction zone
Arrange a survey of the concrete levels, door thresholds, adjacent paving and the proposed deck perimeter. A slab that appears flat may fall in one direction, contain local high points or sit at different distances below the doorway. The tightest location can control the feasible assembly.
Ask the designer to show the complete build-up in section. Include decking thickness, support members, any levelling system and the clearances required by the selected products. A statement that a board is suitable for low decks does not establish that the whole frame will fit.
Record openings and features on the house wall that must remain functional or accessible. These may include ventilation openings, drainage features, service access and termite-inspection provisions. Have the relevant professionals determine the required relationship rather than using the old deck height as the only reference.
Do not sacrifice the doorway detail
A flush-looking transition can be appealing, particularly for easier movement between inside and outside. Explain that goal to the designer early. It must be coordinated with the door system, weather exposure and drainage; simply raising the deck surface can create a different problem.
Draw the critical corner
The junction beside the door often combines the highest concrete point, the narrowest clearance and the most important water detail. Request a specific section there rather than relying on a typical detail taken through the middle of the deck. Include how the edge will be inspected and cleaned after completion.
Assess whether the concrete is suitable to retain
Have the contractor assess the slab’s condition and its intended role in the replacement. A concrete surface may be adequate as a retained ground surface without being verified as a structural foundation for new concentrated supports. Those are different uses and require different assumptions.
Tell the assessor about cracking, movement, previous repairs and any history of ponding. Significant or unexplained changes may need engineering advice. Covering the concrete can make future observation harder, so resolve relevant questions before it disappears beneath the deck.
Ask whether the proposal relies on fixings into the slab, supports bearing on it or foundations that pass through or beside it. The designer should determine suitability and necessary investigation. Homeowners should not drill or cut concrete based on an assumption that it contains no reinforcement or services.
Use the old deck removal as an inspection opportunity
Once the contractor has safely removed the relevant old construction, arrange the agreed inspection before new materials cover the area. This is the moment to confirm concrete levels, drainage routes and concealed conditions at the house.
Include a decision point in the programme if those findings could alter the design. Ordering the entire frame before the concealed zone is assessed may leave little flexibility. The builder should explain which measurements are reliable beforehand and which need confirmation after removal.
Understand the product-specific clearance requirements
Different decking products set different conditions for low-level installation. Read the instructions for the exact range, not a general claim about composite or timber decking. The support system and the environment beneath it must meet the relevant requirements together.
Ekodeck’s Designer Series installation information distinguishes clearance conditions according to whether drainage is adequate. The important point for planning is that clearance and drainage are linked in the product requirements. Do not copy a dimension from one product into another system or treat it as a universal Australian deck rule.
Ask the installer to identify what the manufacturer means by the relevant clearance and where it is measured in the proposed assembly. A measurement to the underside of a board is not necessarily the same as a measurement to the lowest framing member. The drawing should remove that ambiguity.
Coordinate board support and ventilation
A shallow deck still needs the specified support and fastening arrangement. Choosing thinner supports merely to fit the available height is not acceptable without appropriate design. The board manufacturer’s support requirements must be coordinated with the structural frame.
Discuss how air and water move through the finished space, including at the perimeter. Closely fitted edge boards, garden beds and adjacent paving can alter conditions under the deck. The designer should assess the completed enclosure, not only an open frame before finishing.
A related guide to consider while planning this work is Raised Garden Beds Beside a House: Moisture and Inspection Clearances.
Trace water across the concrete to its destination
Before choosing support positions, identify the intended drainage path across the retained concrete. The deck should not interrupt that path or make an existing drain impossible to maintain. Show drains, outlets and relevant falls on the plan.
A support arrangement can create barriers or pockets where leaves and water accumulate. Ask how the proposed layout avoids that problem and how unavoidable obstructions are addressed. Do not assume board gaps alone will make the concrete beneath drain properly.
Your Home’s stormwater guidance emphasises that water management is affected by site conditions and local drainage requirements. In this retrofit, confirm where water from the covered slab will go and whether the existing discharge remains appropriate. The solution should not rely on pushing water towards a neighbouring property or the house.
Distinguish ordinary runoff from a leak
If the old deck concealed persistent wetness, investigate relevant plumbing, roof-water connections and building junctions. A damp area may have a source other than rain falling through the boards. Share the timing and location of symptoms with the appropriate trade.
Have necessary repairs completed and checked before enclosing the area again. A new drainage allowance should identify the actual work; a vague promise to improve ventilation does not resolve an identified leak.
Compare the feasible replacement approaches
Retain the slab with an appropriately designed low frame
This can be a candidate where the slab condition, levels, drainage and available clearance suit the selected assembly. Ask the designer to show how it is supported, secured where required and kept compatible with the building junction.
A related guide to consider while planning this work is Joining an Existing Deck to a Paved Alfresco Area: Levels and Drainage.
The advantage is retaining a large part of the existing site work. The limitation is that the old concrete’s geometry still governs the design. A low frame cannot be assumed to overcome a slab that falls towards the house or occupies the space needed for a suitable threshold detail.
Alter selected concrete or drainage areas
Local alterations may be considered where a defined obstruction or drainage defect prevents an otherwise suitable design. The relevant professionals should assess the effect on the slab, nearby structures and services before cutting or removing concrete.
Ask whether the alteration genuinely resolves the constraint or simply moves it. A new drain that cannot be accessed after decking is installed may replace one maintenance problem with another. Include access and reinstatement in the proposed detail.
Remove the slab or choose a different surface
If a reliable deck assembly cannot fit, broader concrete removal or a different finished surface may deserve comparison. Paving, tiles or a repaired concrete finish require their own suitable substrate and drainage assessment; they are alternatives to investigate, not automatic solutions.
Keep the household’s aim in view. If the primary goal is a pleasant, easy-to-use outdoor area, a deck is one way of achieving it. Avoid forcing a timber or composite appearance into a space where the necessary construction conditions cannot be met.
Design maintenance access before the boards are laid
Identify drains, service points and other features that will need access. Ask for removable sections or another appropriate arrangement where required, with their positions shown on the board layout. A promise that boards can always be lifted later should be checked against the actual fastening system.
Consider how debris will be removed from beneath a low deck. A narrow gap may be difficult to reach, especially beside a wall or behind a built-in bench. Discuss an achievable maintenance method that does not require the homeowner to dismantle structural framing.
Keep access sections usable after furniture and landscaping are installed. A planter, barbecue enclosure or fixed seating can obstruct a carefully placed inspection opening. Coordinate these items before the final layout is approved.
Make edge finishing serve the assembly
Decide how the perimeter looks from the garden while preserving the required drainage and ventilation conditions. The edge detail should also avoid creating an awkward trip or snag point. Ask for the specified solution, including transitions to adjacent paths.
At the house, do not fill the junction with an improvised sealant bead simply to hide a gap. The designed gap or opening may serve a function. Any change should be reviewed by the responsible designer and relevant product supplier.
Prepare a quote that includes the concealed work
Request AUD pricing with GST treatment stated. Separate removal of the old deck, assessment and preparation of the concrete, new supports, boards, drainage work and finishing. Identify which items are fixed and which depend on findings after removal.
- Exact decking range and compatible support and fastening system.
- Verified finished levels and product clearance requirements.
- Concrete repairs or alterations included in the scope.
- Drainage routes, discharge and maintenance-access provisions.
- House-junction and threshold work.
- Reinstatement of adjacent paving, garden edges and services.
For a hypothetical comparison, assume a retained-slab deck scope is A$8,200, with A$1,400 of separately identified drainage alterations and A$600 for access sections. If all assumed amounts include GST, the combined total is A$10,200. These figures demonstrate addition of scope items, not current Australian installation prices.
Compare that complete amount with other fully defined proposals. Do not compare it with a board-only allowance or a price that excludes concrete preparation. If further investigation is needed, agree how the findings will be priced before the contractor proceeds with changed work.
A hypothetical layout that changes after inspection
Imagine a homeowner replacing a small deck outside a laundry. The original proposal keeps the same footprint and adds a neat perimeter fascia. After removal, the contractor finds that the highest concrete point is beside the doorway and that the existing drain sits beneath the proposed fixed bench.
The revised design is assessed around those findings. The selected assembly must fit at the doorway, the drain receives an accessible section, and the bench moves so maintenance does not require dismantling joinery. The fascia detail is also checked against the required conditions beneath the deck. None of these decisions changes the preferred board colour, but each affects whether the replacement will work better than the original.
Check the hidden details at the right time
Ask the builder which checks occur after the slab is exposed and which occur before the boards are installed. The relevant professionals should confirm the support, drainage and building-junction details at stages when they can still be seen.
Keep photographs of the completed arrangement beneath the deck and a simple plan of access points. Record the exact products used. These details are particularly valuable for a low deck because future visual inspection may be limited.
At completion, check the door operation, transitions and agreed removable sections. Follow the contractor’s guidance for observing drainage after ordinary rain from a safe location. Continuing ponding, unexplained wetness or movement deserves attention before it becomes another concealed long-term problem.
A low deck over concrete succeeds when its depth, drainage and maintenance access are treated as one design. Confirm those conditions before selecting the surface, then retain the slab only where it supports a dependable result. The space beneath the boards may be small, but it deserves a clear and complete plan.
Background sources
Ekodeck, Designer Series installation information; Australian Government, Your Home: Stormwater. Product requirements apply to the specified product and configuration. No universal clearance, support spacing or drainage dimension is prescribed here.