Up, Out or Under? Choosing the Right Way to Extend Your Home

When you need more space, one of the first design questions is where should it go?

For many Brisbane homes there are three broad options: extend up by adding another level, extend out into the site, or build under an existing raised house.

Each can work well. Each also has different implications for cost, structure, planning, outdoor space and how the existing home functions.

The best solution isn't necessarily the one that creates the most floor area. It's the one that makes the best use of the house, site and available budget.

Option 1 — Extend Out

A ground-level extension is often the most straightforward way to add space.

For traditional Brisbane houses, this commonly means extending towards the rear to create a new kitchen, living and dining area with a stronger connection to the garden, deck or pool.

When does extending out make sense?

It can be a good option where:

• there is sufficient usable land around the existing house

• retaining a generous backyard isn't a major constraint

• the existing floor level suits the proposed addition

• you want living areas connected directly to outdoor spaces

• the existing house can be reconfigured without major structural intervention.

One of the advantages is that new spaces can often be designed relatively independently of the existing structure.

What should you consider?

Every square metre added to the building footprint is a square metre no longer available as outdoor space.

Setbacks, site cover, existing trees, pools, services, slope and planning controls can also limit where an extension can be located.

There can also be a temptation to simply attach more rooms to the back of the house. A better question is whether some of the existing floor area can be used more effectively before adding more.

Option 2 — Extend Up

Adding another storey can provide substantial additional accommodation without increasing the building footprint.

It can be particularly useful on smaller sites or where retaining gardens, pools and outdoor living areas is important.

When does going up make sense?

Consider it where:

• the site has limited room for a ground-floor extension

• maintaining outdoor space is a priority

• additional bedrooms or a separate parents' or children's zone is required

• views, breezes or improved outlook are available at the upper level

• the existing house and foundations can accommodate the proposed work, or can reasonably be strengthened.

Going up can also create an opportunity to reorganise the house vertically—for example, bedrooms upstairs with living areas remaining connected to the ground and garden.

What should you consider?

A second storey isn't simply the cost of the additional rooms.

You'll also need to accommodate a staircase, which consumes space on both levels, and structural work may be required to the existing building and foundations.

Roof removal and reconstruction, temporary weather protection and working over an existing house can also make construction more complex.

The additional floor area therefore needs to provide enough benefit to justify that complexity.

Option 3 — Build Under

Many Queenslanders and other raised timber houses offer a third possibility: making better use of the space underneath.

This can be particularly attractive because the building already occupies that part of the site.

But “there's space underneath” doesn't necessarily mean it's ready to become habitable floor area.

When does building under make sense?

It may be worth considering where:

• the existing house is already sufficiently elevated

• the house can reasonably be raised to achieve suitable floor levels

• additional accommodation can work successfully on the lower level

• the existing upper floor is worth retaining

• maintaining the existing building footprint is desirable.

Building underneath can potentially accommodate bedrooms, living areas, garages, laundries and other supporting spaces depending on the property.

What should you consider?

Floor levels are critical.

Achieving appropriate head height may require the existing house to be raised, excavation below it, or a combination of both. Excavation can introduce retaining, drainage, waterproofing and structural issues that significantly affect cost.

The relationship between the two levels also needs careful thought. Simply enclosing the area underneath an existing house doesn't automatically produce a well-functioning two-storey home.

Natural light, ventilation, privacy, internal circulation and connection to outdoor areas all matter.

Could the best solution be a combination?

Absolutely.

Some of the most effective renovations don't rely exclusively on one approach.

A project might:

• build under part of a Queenslander

• extend the main living areas towards the rear

• add a smaller upper-level component only where required.

This can sometimes produce a better outcome than trying to accommodate everything within one large extension.

The starting point should therefore be the accommodation and relationships you need, rather than deciding in advance that you need to go up, out or under.

Which option costs less?

There isn't a universal answer.

A simple ground-floor extension will often involve fewer structural complications than building over or underneath an existing house. But that doesn't automatically make extending out the most economical solution for a particular property.

Cost can be affected by:

• the amount of existing building being altered

• foundations and structural strengthening

• excavation and retaining

• roof alterations

• site access

• existing and new floor levels

• services and drainage

• planning requirements

• level of finish

• how efficiently the additional floor area can be incorporated.

  
  

This is also why comparing options purely on a $/m² construction rate can be misleading.

→ How much does a renovation really cost?

What about planning and building requirements?

Before choosing an extension strategy, it's important to understand what the property will allow.

Setbacks, building height, site cover, flood constraints and other planning considerations can affect the options available. For older Brisbane homes, character controls may also influence how and where additions can occur.

Structural feasibility is another consideration, particularly when adding another level or raising an existing house.

These issues don't necessarily determine the design, but understanding them early helps avoid developing an option that later proves impractical.

→What’s the difference between a DA and BA?

So, should you go up, out or under?

Start by asking four questions:

1. What additional spaces do we actually need?

2. What parts of the existing house are worth retaining or reworking?

3. What opportunities and constraints does the site present?

4. Which option gives us the best overall outcome within the available budget?

Sometimes the answer will be obvious. Often it's worth testing two or more approaches before deciding.

That's one of the purposes of early concept design: compare the options while they're still inexpensive to change rather than committing to a solution too early.

Not sure which option suits your home?

Our Needs & Options Review looks at your existing home, site and objectives and explores the practical ways your project could be approached.

→How do we get our project started?