Home Extensions near you

The type you choose is usually decided by the block rather than by preference. A wide block with a deep rear yard favours going out; a narrow inner-suburban lot with a small yard usually forces you up; a house already raised on stumps may have its cheapest new floor area directly beneath it.

An addition is assessed against your council's development controls before it is assessed against the Code. Front, side and rear setbacks fix where the walls may sit; site coverage and floor space controls cap how much of the lot may be built on; height and storey limits and overshadowing tests constrain a second storey; and private open space, deep soil and tree protection provisions decide how much of the yard has to survive. Two neighbouring councils can reach different answers for the same design, which is why an early pre-lodgement conversation is worth more than a second opinion from a builder.

New South Wales offers a faster route where the design meets every standard. The Department of Planning states that complying development covers alterations and additions to a house, that a council or an accredited certifier can determine it, and that it can be decided in as little as twenty days against an average determination time for a development application of seventy days. Meeting every standard is the condition, though, and a single variation pushes the proposal back to a full application. Victoria keeps the two questions separate: the council decides whether a planning permit is required, and a registered building surveyor whom you appoint issues the building permit. Queensland requires a building development approval from a building certifier.

In New South Wales the energy certificate applies to additions as well. The NSW Planning Portal states that renovations of fifty thousand dollars or more require a BASIX certificate, which most additions of any size will reach, and the resulting commitments for insulation, glazing and hot water become conditions of the approval rather than optional upgrades.

Unlike a whole-home renovation, an addition is often built while the household stays put, which makes the sequence and the site protection a bigger part of the job. The point of maximum disruption is when the existing external wall is opened up and the two structures become one; everything before that can usually be built alongside the house rather than through it.

If you are still choosing a builder, LokalMatch lets you set out the addition once — the type, the rough size, the postcode and the timing — and builders working in your area reply to you directly. They pay for the leads they receive, which is how the platform makes its money. LokalMatch does not build, price or supervise anything, and does not vet, rate or recommend businesses, so verifying registration and insurance is a step you keep.

The junction between an addition and the original house is where most long-term problems show up, and the reason is movement. The NCC's Housing Provisions require the foundations where footings and slabs are located to be classified in accordance with the Australian standard for residential slabs and footings, and much of suburban Australia sits on reactive clay that swells and shrinks with soil moisture. An old house on shallow footings and a new addition on modern ones respond to that ground differently, and the crack that opens at the join is the visible result.

Designers deal with it in one of two ways: either the new footings are designed to behave like the old ones so the structures move together, or the two are deliberately articulated so they can move independently without tearing. Both are engineering decisions, and both need to be made before the slab is poured rather than after the first summer. The same logic applies where an addition meets an existing roof: the flashing at that junction has to accommodate movement as well as shed water.

Before a design is worth drawing, somebody has to find out what is already in the ground. Water authorities own assets that often run through backyards, and building over or beside them is controlled. Sydney Water requires its written approval to build over or adjacent to its assets before work starts, will refer building or excavation work that is over or close to its pipes and structures to a water servicing coordinator, and issues a building over sewer advice letter recording the outcome. Other states' utilities run equivalent processes; the principle everywhere is that the authority must retain access to maintain the pipe.

Every addition has a window where the existing house is exposed: when the external wall is opened, or when the roof comes off for a second storey. Australian conditions make the timing of that window matter. In the tropical north the wet season brings sustained heavy rain and cyclone risk; along the eastern seaboard summer storms can arrive with very little warning; in the south-east a wet winter can keep a site soft for weeks. None of this stops work, but it should be discussed before the programme is set.

Ask the builder specifically how the opened part of the house will be protected, what the plan is if a storm arrives overnight, and who carries the risk for damage to the existing building during that period. Contract works insurance and the builder's public liability cover are the right place for that answer, and it is a reasonable question to ask before signing rather than afterwards.