What Size Granny Flat Should I Be Building Build?

One of the most common questions homeowners ask is “what size granny flat should I build?” The right answer depends on your land, budget, and how you plan to use the space — whether for rental income, family accommodation, or long-term value.

This guide breaks down the standard granny flat sizes in NSW and helps you determine what size granny flat you should build for the best outcome.

1. Granny Flat Size Rules in NSW

In NSW, granny flats are classified as secondary dwellings and are subject to size limits under planning controls.

Key regulations include:

• Maximum internal floor area of 60 square metres
• Minimum private open space requirements
• Setback and site coverage rules
• Compliance with BASIX and the NCC

Understanding these rules is essential when deciding what size granny flat you should build on your property.

2. Common Granny Flat Sizes and Layouts

While 60m² is the maximum, many homeowners choose smaller footprints based on site constraints and budget:

• Studio or 1-bedroom: ~35–45m²
• Compact 2-bedroom: ~50–55m²
• Full 2-bedroom: ~60m²

Each size offers different benefits depending on your intended use and tenant profile.

3. Choosing the Right Size for Rental Income

If your primary goal is rental return, a 60m² two-bedroom granny flat typically delivers the strongest weekly income.

However, in some suburbs, a well-designed one-bedroom granny flat can still achieve excellent returns due to lower construction costs and strong demand for smaller dwellings.

Balancing build cost with rental yield is key when deciding what size granny flat you should build.

4. Choosing the Right Size for Family Use

For parents, adult children, or extended family, comfort and accessibility often matter more than maximum size.

Important considerations include:

• Storage and circulation space
• Accessibility and step-free entry
• Bedroom separation and privacy
• Natural light and ventilation

A slightly smaller granny flat with better layout efficiency can often feel more liveable than a poorly planned 60m² design.

5. How Block Size and Layout Affect Granny Flat Size

Your block plays a major role in determining what size granny flat you should build. Factors include:

• Available backyard area
• Setbacks to boundaries and the main dwelling
• Slope, drainage, and easements
• Site access for construction

A professional site assessment helps identify the maximum practical size without unnecessary cost or compromise.

6. Budget Considerations When Choosing Size

Larger granny flats generally cost more to build, but size is not the only cost driver.

Costs are influenced by:

• Design complexity
• Site conditions
• Inclusions and finishes
• Service connection distances

In some cases, a slightly smaller granny flat with higher-quality inclusions can offer better long-term value.

Expert Tip

Don’t design purely to the maximum size. A well-planned 55m² granny flat can outperform a poorly laid-out 60m² design in both liveability and rental appeal.

Why Choose Granny Flat Solutions

At Granny Flat Solutions, we help homeowners determine what size granny flat they should build based on real site constraints, rental demand, and long-term goals.

With in-house approvals, true turnkey pricing, and thousands of completed builds across NSW, we design granny flats that maximise space, value, and performance.

Still Wondering What Size Granny Flat You Should Build?

Every property is different, and the right size depends on more than just square metres.

Book your free site consultation with Granny Flat Solutions today and receive expert advice tailored to your block, budget, and objectives.