Most people who ring us have already made up their mind about building. What they really want to know is when they’ll get the keys. It’s a fair question, and the honest first answer is “it depends”, which is exactly the reply nobody finds useful. So here is a straighter one, based on the granny flats we design and build across the Illawarra.
How long it takes to build a granny flat comes down to three stages, and only one of them is the actual building. Get the order right and the whole thing is a lot more predictable than people expect.
The short answer, before the fine print
From your first conversation with us through to handover, a typical granny flat runs about four to six months. On a straightforward block using a fixed design and the fast approval path, it can be quicker. On a tricky site, or if you keep changing your mind, it stretches out.
That four-to-six-month figure splits roughly like this: a few weeks of design and paperwork, a few weeks for approval, and then the build itself. The build is the part most people picture, but it’s usually not the part that decides your finish date.
Approval is where the clock swings most
The single biggest thing that moves your timeline is which approval path your project takes. There are two.
The first is a CDC, short for Complying Development Certificate. It’s the fast track. If your block and your design tick every box in the state planning rules, a certifier can sign it off without going to council. In NSW the assessment period for complying development is capped at 20 days, so you’re often looking at a few weeks rather than a few months.
The second is a DA, a Development Application through your local council. You need this when the block or the plan can’t meet every CDC standard, for example an odd-shaped lot, a heritage overlay, or a flood or bushfire constraint. A DA is assessed by the council rather than a private certifier, and that typically takes somewhere between six and twelve weeks depending on the site and how complete your submission is.
This is the whole reason we build fixed-design, CDC-approved granny flats. When the design is already shaped to comply, we can usually keep you on the fast path and skip the council queue. If you want the detail on both routes, we’ve written up how granny flat approval works in the Illawarra separately.
The build itself: around 12 to 16 weeks
Once the approval is in hand and the slab is down, most granny flats in NSW go up in roughly 12 to 16 weeks. That’s the range we see, and it lines up with what other builders quote across the state.
Here’s what those weeks are actually doing:
- Site prep and slab: clearing, levelling, plumbing rough-in and pouring the concrete slab. Wet weather hits this stage hardest because you can’t pour into mud.
- Frame and roof: the wall frames go up and the roof goes on. This is the fast, satisfying part where the shape appears in a week or two.
- Lock-up: windows, external doors and cladding go on so the building is weathertight and secure.
- Fit-out: electrical, plumbing, plaster, kitchen, bathroom, flooring and paint. This is the longest stretch because a lot of separate trades have to come through in the right order.
- Handover: final checks, the occupation certificate, and keys.
You can see the full breakdown on our granny flat construction service page, and our complete guide to granny flat construction walks through each stage in more depth.
What actually slows a build down
When a granny flat runs late, it’s rarely the trades sitting idle. It’s almost always one of these.
Design changes after approval. Moving a wall or swapping the kitchen layout once the plans are locked means re-drawing, sometimes re-approving, and re-ordering. A change that takes you five minutes to decide can add two or three weeks. Fixed designs exist precisely to stop this.
The site itself. A steep slope, poor soil, rock, big trees or tight access all add time at the start. We pick this up early, which is the point of walking the block before anything is promised.
Weather. The Illawarra gets its share of wet stretches, and rain mostly affects the early groundwork and slab. Once the roof is on, the weather matters a lot less.
Materials and connections. A back-ordered product or a slow power or water connection from the utility can hold up an otherwise finished build. Ordering early is how you dodge most of it.
Why a fixed design finishes sooner
A custom, one-off granny flat has to be drawn from scratch, engineered, and usually pushed through a full DA. Every one of those steps adds weeks. A fixed, CDC-ready design has already cleared the drawing and compliance work, so the front half of your timeline is largely done before you start.
That’s the model we run, backed by Jaya Builds, our local construction partner. Predictable designs plus an established local team is how you turn “it depends” into a date you can plan around, which matters a lot if you’re lining up a tenant or a family member moving in.
Common questions about granny flat build times
How long does it take to build a granny flat from start to finish?
Allow roughly four to six months from your first conversation to handover. That covers design, approval and construction combined. A straightforward block on the CDC fast path can come in under that, while a DA or a difficult site pushes it longer.
How long does granny flat approval take in NSW?
A CDC (the complying development fast track) has a 20-day assessment cap, so it’s often a matter of weeks. A DA through council usually takes six to twelve weeks. Which path you’re on depends on your block and design meeting the state planning standards.
Is it faster to build a granny flat or extend the house?
A detached granny flat on the CDC path is often quicker to approve than a home extension, because extensions frequently need a full DA and tie into your existing structure. Build time is broadly similar, but the approval stage is usually where the granny flat wins on speed.
Can you speed up a granny flat build?
Yes. The three biggest levers are choosing a fixed CDC-ready design, locking your plans and not changing them after approval, and getting the site assessed early so surprises don’t surface mid-build. Ordering long-lead items ahead of time helps too.
Does bad weather delay a granny flat build?
It can, but mostly at the start. Rain affects site prep and the slab pour more than anything else. Once the roof is on and the building is at lock-up, most work moves inside and weather stops being a major factor.
Do granny flats increase your property value?
They usually add value and, more to the point, income. A well-built second dwelling on the right block can lift both what the property is worth and what it earns in rent. The gain varies by suburb and block, so it’s worth looking at your specific situation.
If you’d like a realistic timeline for your own block rather than a general range, that’s exactly what we work out with you. See how we build granny flats across the Illawarra or get in touch, and we’ll map out the likely dates from approval to keys before you commit to anything.
