Additions and second storeys
Engineering for extensions, renovations and second storeys in Canberra
A house extension in the ACT needs building approval, and your certifier needs the structural details to give it. We design the footings, beams, framing and tie-downs, priced from your plans.
- Fixed quote for your extension, priced from your plans
- Fixed quote in under 20 minutes on average, during business hours
- No exemptions from building approval for detached houses in the ACT
Prefer to talk? Call 02 6189 9876
Or email info@canberrastructuralengineers.com.au
Monday to Friday, 8:00am to 5:00pm
- Engineering onlyWe never sell the repair or the build.
- Fixed quote per jobPriced from your photos or plans before we start.
- Fixed quote in under 20 minutes on averageDuring business hours, Monday to Friday.
- Canberra and the Queanbeyan sideEvery district, plus Queanbeyan, Jerrabomberra and Googong.
In short
Engineering for a house extension in Canberra is a fixed quote, priced from your plans before we start. There are no building approval exemptions for detached houses in the ACT, so your certifier needs footing, slab, framing and tie-down details for the new work. We design them, and check whether existing footings can carry a second storey. Same prices across Canberra, Queanbeyan, Jerrabomberra and Googong.
- Fee
- Fixed quote, set from your plans before we start
- Quote
- Fixed, in under 20 minutes on average, during business hours
- You receive
- Calculations and drawings for your certifier and builder
- Wall removal
- From $890 + GST ($979 inc GST) when your plans open up a load-bearing wall
- Footings and site class
- From $1,290 + GST ($1,419 inc GST), soil test at cost
- Area
- Every Canberra district, plus Queanbeyan, Jerrabomberra and Googong
Do I need a structural engineer for an extension in the ACT?
Yes, for the structure. An extension needs building approval, and your certifier needs footing, slab, framing and tie-down details before giving it. We design those details.
There are no building approval exemptions for detached houses in the ACT. ACT Planning says so plainly on its building approval page. So a rear addition, a second storey, or a renovation that changes the structure needs building approval (BA) from a licensed certifier you appoint.
Development approval (DA) is a separate question. Whether your extension also needs a DA depends on whether it meets the exempt development controls for your block. Your designer or certifier checks that against the plans. Work can't be DA-exempt if it:
- sits in an easement or utility protection space without the utility's written permission;
- breaches the Urban Forest Act 2023, the Heritage Act 2004 or your Crown lease;
- takes the block to two or more dwellings (a granny flat or dual occupancy is a different path).
The whole approval process, step by step, is in our guide to building approval in the ACT.
What's included in extension engineering?
Engineering calculations and drawings your certifier and builder can use. Your fixed quote lists the parts your plans need, and says if a site visit is needed.
| Part of the job | What we provide |
|---|---|
| New footings and slab | Footing and slab design, with the founding depth and founding material, reinforcement and concrete strength |
| Existing footings | A check that they can carry the new load, which can mean a small inspection pit beside one |
| Openings and removed walls | Beams, posts and the footings under them (see wall removal and beam design) |
| Frame | Framing and bracing, tie-downs and fixings, and any steel or concrete members |
| Sloping blocks | Retaining walls where the addition cuts into the ground |
| Soil | A site classification where new footings need one, with the soil test arranged at cost |
These match what the Registrar's form AF2025-18 says a certifier must lodge for a house: footing and slab details with the "nominated founding depth and description of founding material", plus framing, bracing, tie-downs and fixings. An incomplete lodgement fails the completeness check.
What we don't do: draw the house design, approve the work or build it. Your designer draws the plans, your certifier approves them and your builder builds.
Can my house take a second storey?
That depends on the footings and walls you already have, so we check them before designing anything above. A second storey puts a new floor, walls and roof onto footings sized for one storey.
- The footings: how wide and deep they are, often seen in a small inspection pit beside one.
- What they sit on: clay, weathered rock or fill, and how firm it is.
- The walls: brick veneer or masonry, and which walls carry the roof now.
- The roof and ceiling framing that the new floor will replace or sit on.
- Signs of past movement, such as cracks or sticking doors, before we add any load.
Canberra's rock is often deeply and unevenly weathered. Rock can be near the surface on one part of a block and metres down on another, so one corner of a house can sit on firmer ground than the next. Our guide to Canberra soils and footings explains why.
Where existing footings can't take the extra weight, the design can add new footings, or carry the upper floor on its own posts and beams. Either way, the certifier sees the details before work starts.
1960s NCDC houses were almost all brick veneer, which shapes how new work joins them; see renovating an ex-govvie. If your home is in a registered heritage precinct, such as those in Forrest, Griffith or Kingston in the Inner South, its ACT Heritage Register entry adds rules of its own; see older and heritage homes.
Which other ACT rules apply to an extension?
Several rules travel with every extension. Most are for your designer, but each one can change what we design, so tell us about them early.
| Rule | When it applies | What it means for you |
|---|---|---|
| Building code edition | Building approvals from 1 May 2026 to 30 Apr 2027 | Use NCC 2022 with the ACT 2022 Appendix, or NCC 2025 with the ACT 2025 Appendix. Your project nominates one and can't mix them. NCC 2025 is mandatory from 1 May 2027, unless a DA was lodged before 1 Nov 2026. |
| Energy efficiency | Alterations and additions | ACT Part H6 sets the energy rules for additions. Your designer meets them; tell us if they change the wall or roof build-up. |
| Rainwater tank | DA-exempt homes, where the extension adds more than 50% of the existing gross floor area | The rainwater tank controls apply. The tank sizes are on our building near sewer and stormwater page. |
| Gas | All new and existing developments | No new gas network connections. If you're adding a heat pump or solar panels, we check the roof framing where needed. |
| Asbestos | Houses built, or started, before 1985 | The building approval application needs an asbestos removal control plan. |
| Protected trees | Work inside a protected tree's protection zone, including a neighbour's tree | Digging deeper than 100 mm over 4 m² or more is prohibited groundwork without approval. See protected trees and building. |
What sets the price of extension engineering?
It's a fixed quote, set from your plans before we start. We don't publish one number, because a small rear addition and a second storey are different jobs.
These are the things that move the quote:
- The size of the addition and the number of storeys
- The slope of the block, and whether the work cuts into it
- The soil, and whether new footings need a site classification
- The existing structure: walls coming out, new openings, footings taking new load
- How many drawings and details your certifier asks for
Parts of an extension that we also do as separate jobs have published prices, and every price is on our prices page.
What should I send for an extension quote?
We're engineers only. We don't build extensions or recommend builders, so nothing in the design depends on who gets the job.
- Your plans, or a sketch with rough sizes if the design isn't drawn yet
- A few photos of the house, inside and out, where the new work joins it
- The suburb, and the year the house was built if you know it
- Any earlier engineering, soil report or certifier's notes you already have
What happens next?
Three steps, and you know the price before anything is booked. We work across every Canberra district, plus Queanbeyan, Jerrabomberra and Googong.
Send your plans
Use the form above, or our full quote form. Add up to 5 photos or plans.
Get a fixed quote
In under 20 minutes on average, during business hours. It lists the parts we'll design and says if a site visit is needed.
Design and drawings
We check the existing structure where needed, then send calculations and drawings for your certifier and builder.
Often part of an extension
Every service is quoted at a fixed price before we start. Send photos or plans and we reply in under 20 minutes on average, during business hours.
Wall removal & beam design
Beam, post and footing design for opening up a load-bearing wall, with the documents your certifier needs.
$890 + GST($979 inc GST) See the service
Footings, slabs & site classification
Site classification and footing or slab design for new homes, rebuilds, granny flats and extensions, with the soil test at cost.
$1,290 + GST($1,419 inc GST) See the service
Renovating a 1960s ex-govvie
Where Canberra's 1960s government houses came from, how a brick-veneer govvie is put together, and the approvals and engineering behind removing walls, extending or going up.
Read the guideExtension engineering questions
Something else on your mind? Call 02 6189 9876, email info@canberrastructuralengineers.com.au or send photos for a fixed quote.
How much does a structural engineer cost for an extension in Canberra?
It's a fixed quote, set from your plans. A small rear addition and a second storey are different jobs, so we price yours before we start. Related design jobs have published prices, such as wall removal and beam design from $890 + GST ($979 inc GST).
Will my extension need development approval as well?
Sometimes. It depends on whether the work meets the exempt development controls for your block, which your designer or certifier checks. Work in an easement without the utility's written permission, or work that breaches the Heritage Act or the Urban Forest Act, can't be exempt.
Does a second storey need a soil test?
Not always. We start with the existing footings: their size, depth and what they sit on. If the design needs new footings, we may arrange a soil test at cost so they suit your site's soil, and your fixed quote says so up front.
Do you draw the plans for the extension?
No, we do the structural engineering. You, your designer or your builder provide the plans. We add the footing, beam, framing and tie-down design your certifier needs to approve them.
Can you check a builder's plans or quote before I sign?
Yes. A desktop review of plans or a quote is from $390 + GST ($429 inc GST). We read what you send and give written advice, with no site visit.
Who approves the finished extension?
Your certifier, not us. The certifier approves the plans and inspects the footings before the pour, the frame before it's lined, and the finished work. Certificates of occupancy and use come from the Construction Occupations Registrar.