Last reviewed: August 2026
A granny flat usually adds value, but not automatically and not always by the amount it cost. The value comes from two separate things: the income it can produce, and what a future buyer thinks it is worth to them. Those two can point in different directions, and which one dominates depends on your suburb and your buyer.
This article covers how to work it out for your property rather than quoting a number that was true for someone else’s.
The two ways a granny flat creates value
1. Income
A granny flat that can be rented produces income, and income is what valuers and investors respond to. For an investor buyer, a property producing two rents is straightforwardly worth more than the same property producing one.
This is the more reliable of the two, because it is measurable. You can look up what comparable granny flats rent for in your suburb today.
2. Buyer appeal
This one is less predictable, because it depends who is buying.
| Buyer type | How they see a granny flat |
| Investor | Positive. Second income stream. |
| Multi-generational family | Positive, often strongly. It may be the reason they buy. |
| Family wanting a big backyard | Negative. It took the yard. |
| Downsizer | Neutral to negative. Extra maintenance they do not want. |
| First home buyer | Positive if they can rent it to help the mortgage. |
In a suburb full of young families who want lawn, a granny flat covering half the backyard can narrow your buyer pool. In a suburb with lots of multi-generational households or investors, it can widen it considerably.
What decides whether it adds or subtracts
| Factor | Adds value | Subtracts value |
| Yard remaining | Enough usable yard left | Backyard almost entirely consumed |
| Privacy | Separate access, screened from the house | Windows facing each other, shared entry |
| Parking | Parking retained for both dwellings | Parking lost or awkward |
| Build quality | Properly built, approved, certified | Visibly cheap, or unapproved |
| Approval status | Fully approved with an occupation certificate | No approval, which is a serious problem |
| Design | Looks like it belongs with the house | Obviously bolted on |
| Suburb | Investor or multi-generational demand | Family-and-backyard suburb |
The one that matters most is approval status, and it is not close.
The unapproved granny flat problem
An unapproved secondary dwelling is a liability, not an asset.
When you sell, it has to be disclosed. A buyer’s solicitor will find it. It can affect finance, because a lender may not value an unapproved structure or may refuse the loan. Insurance can be affected. Council can require it to be brought into compliance or removed.
This is why the approval pathway is worth doing properly even when it is slower. A fully approved granny flat with an occupation certificate is an asset on the title. An unapproved one is a problem you have to solve before you can sell.
How to work out the answer for your property
Nobody can tell you the number from a blog post. Here is how to find it.
Step 1: Find the rental comparison. Search current listings for granny flats and one or two bedroom units in your suburb. Not last year, now. That gives you a realistic weekly rent.
Step 2: Find the sales comparison. Ask a local agent what properties with an approved granny flat have sold for in your suburb compared to similar properties without one. Agents know this and will usually tell you.
Step 3: Get your actual build cost. Not a market range, a quote for your block including site costs and approvals.
Step 4: Compare. You now have three real numbers instead of three assumptions.
Step 5: Ask the people whose job it is. A valuer can tell you the valuation effect. An accountant can tell you the tax position. Both are worth the fee before you spend six figures.
A realistic expectation
The honest position is this. A well designed, fully approved granny flat on a block that still has usable yard, in a suburb where people want rental income or room for family, generally adds value and generally produces income that pays back over time.
A poorly positioned one that swallows the backyard, on a block in a suburb where buyers want lawn, may add less than it cost.
Anyone promising you a specific percentage return without seeing your block and your suburb is guessing.
Frequently asked questions
Will a granny flat add as much value as it cost to build?
Sometimes, but it should not be assumed. The value effect depends on your suburb, your buyer pool and how much yard is left. The income it produces is usually the more dependable benefit. A local agent and a valuer can give you a grounded answer for your property.
Does a granny flat affect my ability to sell?
It changes who your buyers are rather than simply helping or hurting. It appeals strongly to investors and multi-generational families and less to buyers who want a big backyard. In most Sydney suburbs the first two groups are substantial.
Do I have to declare a granny flat when I sell?
Yes. It forms part of the property and its approval status has to be disclosed. This is why an unapproved structure causes problems at sale.
Does a granny flat affect capital gains tax?
It can, particularly if part of your property is used to produce income. The rules depend on your circumstances, so this is a question for a qualified accountant before you build, not after.
Is it better to renovate the main house instead?
It depends what you want. A renovation improves the house you live in. A granny flat adds a second dwelling that can produce income or house family. They solve different problems, and the right answer comes from what you are trying to achieve.
Get real numbers for your property
The value question has a real answer for your address. It just needs your suburb’s rental data, your suburb’s sales data, and a proper quote for your block.
Book a site assessment, or call BlueGum on 1300 060 651.
BlueGum Granny Flats is a licensed NSW builder, licence number 247388C. This article is general information and is not financial, taxation, valuation or investment advice. Speak to a qualified accountant, valuer or financial adviser about your own circumstances before making a decision.
