Alfresco, patio and shed slabs

Under the CCAA guidance a patio carrying only people should be no thinner than 75 mm, laid over a compacted base with a small fall to shed water, while a shed slab follows the shed maker’s base drawing or the engineering in its building permit. A Melbourne guide lists patio and entertaining slabs at $84 to $190 per square metre, and a typical 20 square metre shed slab at $1,575 to $3,675. Your enquiry goes to an independent concreter in the area; the quote, the contract and the workmanship are between you and that business.

Alfresco slab or patio: what is the difference?

On many new homes the alfresco is the covered area under the main roof at the back, finished by the builder. An alfresco extension or patio slab is the concrete added beyond it, often to sit under a later pergola or verandah. A shed slab is a separate pad, usually in a back corner, sized to the shed kit plus a small apron.

Slab	Typical use	Price guide (Melbourne)	Main thing to get right
Patio or alfresco extension	Outdoor dining, barbecue area	$84 to $190 per square metre	Height and fall against the house
Shed slab	Garden shed, storage	$1,575 to $3,675 for about 20 square metres	Permit, easement and hold down bolts
Coloured or exposed finish	Patio matched to the house	$100 to $210 per square metre or $125 to $210 per square metre	Finish texture for bare feet

Ranges come from a Melbourne concreting guide verified in October 2026. Excavation and old concrete removal are extra, as explained in the Kalkallo driveway and slab cost guide.

Getting the height right against the house

A patio poured against the back wall has the same risks as a side path. Under the NCC requirements quoted in the CCAA driveways and paths data sheet, the patio must slope away from the wall, leave a gap of 75 mm or more below the damp-proof course, and keep the termite inspection strip in view. If the existing alfresco floor is the builder’s slab, the new pour has to meet it at a step or with an isolation joint; it should not be bonded straight onto the house slab.

For a smooth, easy to clean surface near a barbecue or outdoor kitchen, the CCAA guide notes that smoother finishes clean better and a sealer stops spills soaking in. Around a pool or where people walk barefoot, it warns against a texture that is too coarse.

When does a shed slab need a permit?

The slab is not the issue on its own; the shed is. The BPC practice note BP 01, When is a building permit required says a freestanding garage, carport or shed is exempt from a building permit only if it meets every condition, including:

• a floor area of no more than 10 square metres
• a height of no more than 3 m, or 2.4 m within 1 m of a boundary
• not built of masonry
• set no further forward than the front wall of the house it serves.

A larger shed needs a building permit under the Building Regulations 2018, and the slab then has to match the engineering in that permit. The same practice note says a planning permit may also be needed, and that a shed over an easement or an authority asset may need that authority’s consent first. Your land title and plan of subdivision show any easements; some lots carry drainage or sewer easements along a boundary, so check before choosing the corner.

What a shed or garage slab involves

1. Confirm the shed kit’s base size, the bolt layout and the door openings with the supplier’s drawings.
2. Set out the slab square and level, allowing for the apron in front of the door.
3. Excavate topsoil, compact a crushed rock base and set forms.
4. Place mesh on chairs, add any edge thickening the drawings call for, and pour.
5. Finish to a flat steel trowel or light broom, and cure for at least 3 days as the CCAA guide recommends.

Hold down bolts are either cast in or drilled in after curing; agree which before the pour. A rolled edge or a small set down at the door stops water running under the shed wall.

Hot days and patio slabs

Backyard slabs are often poured in summer so they are ready for outdoor entertaining. The CCAA guide says concrete should not be placed above 30 degrees ambient without precautions, because the surface can dry and crack before it is finished. A careful concreter may start at first light, use shade or wind breaks, or move the pour to a cooler day.

What a provider will check before quoting

• Access to the backyard: side gate width, whether a pump or barrows will be needed.
• Height of the existing alfresco slab, door sills and weep holes.
• Location of downpipes, stormwater pits and the sewer line.
• Easements on your title and the shed’s permit status.
• Whether a pergola or verandah will be added later, so footings can be planned.

The Melbourne cost guide notes that a site the concrete truck cannot reach needs a pump or barrows, priced on top. On a new Kalkallo block with a narrow side setback, expect to discuss it for backyard work.

What a careful concreter will not do

• Pour a slab for a shed over 10 square metres without asking about the permit.
• Build over an easement without the authority’s consent.
• Tie the new slab rigidly to the house slab.
• Raise the patio to the door sill if that buries the damp-proof course.

Linking the backyard to the rest of the job

A patio or shed slab is usually joined by a side path; see coloured and plain concrete paths. If the driveway is also being done, ask for the jobs to be quoted separately and together so you can compare. Homes in Mickleham and Donnybrook raise the same questions about easements and side access.

What to do next

Note the slab size, the shed model if there is one, and take photos of the backyard, side access and back wall. Then send your slab details for a quote.

Send a job enquiry