Homeowners · Architects · Building designers
House extensions, renovations and second storeys in Hobart
Your architect or building designer draws the extension. We make sure it stands up: footings, framing, beams, bracing and tie-down, with structural drawings, calculations and a Form 35 your building surveyor can rely on.
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We design the structure. Your designer draws the house and any licensed builder can build it.
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Upload the architectural plans or concept sketches, with photos of the house and the address.
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In short
A house extension in Hobart needs structural drawings from an engineer: footings to suit the site class, beams, framing, bracing and tie-down, with a Form 35 for the building surveyor. For a second storey, we also check that the existing footings and walls can carry the new load. We work alongside your architect or building designer, priced by fixed quote.
- Fee
- Fixed quote per job, from your plans
- Works with
- Your architect or building designer, builder and building surveyor
- You receive
- Structural drawings, calculations and a Form 35
Structural drawings
What structural drawings does a house extension need?
A house extension needs structural drawings that show how every new load reaches the ground: footing and slab plans, framing and beam layouts, bracing and tie-down, and the connections to the existing house, with calculations behind them. Your building surveyor reads them alongside the architectural plans.
| Drawing | What it shows |
|---|---|
| Footing or slab plan | Footing sizes, depths and reinforcement, matched to the site class |
| Floor framing | Bearers, joists and stumps, or the slab and its beams |
| Walls, beams and lintels | Openings, any walls removed, and the posts under each beam |
| Bracing and tie-down | How the building resists wind, for the wind class of your site |
| Roof framing | Rafters, trusses or beams and how they are held down |
| Connections to the house | Where old meets new: matching floor levels and movement joints |
Timber framing within the limits of the residential framing standard can come from its tables. Anything outside them, such as long spans, steel beams, large openings or a second storey, is engineered.
Key takeaways
- Bring the engineer in while the layout can still change: spans and openings drive cost.
- A second storey starts with the existing footings, not the new frame.
- Every structural design comes with a Form 35 for your building surveyor.
- Wind class is site-specific, so bracing and tie-down are designed for your site.
The team
Who does what on a house extension?
An extension has four professional roles, and the structural engineer sits between the designer's plans and the building surveyor's approval.
Architect or building designer
Designs the layout and look, prepares the architectural drawings and handles any planning permit with council.
Structural engineer
Classifies the site, designs footings, framing, beams and bracing, and signs a Form 35 for the structure.
Building surveyor
Checks the design against the building rules, confirms the approval category and issues a Certificate of Likely Compliance.
Licensed builder
Prices and builds from the drawings. We can inspect critical stages, such as footings or a new steel frame.
When to bring the engineer in
Early. A long open span, a removed wall or a steep block can change the cost of the structure a lot, and it's easier to adjust a concept than finished plans. Send concept sketches and we'll quote from those.
Going up
Can my house take a second storey?
A house can take a second storey if its existing footings, walls and floor framing can carry the extra load, or can be strengthened to. That check comes first, before the design goes far.
- Existing footings: we expose a footing to see its size, depth and the ground it sits on, and check the site class.
- Existing walls: cracks or movement in the walls below show how the footings have behaved so far.
- Load paths: where new posts or walls upstairs will land, and how their loads get down through the ground floor.
- Floor and bracing: the old ceiling becomes a floor, and the taller house needs more bracing against wind.
If the footings fall short, the options include strengthening them by underpinning or carrying the new storey on its own posts and footings. Older homes, especially sandstone or brick ones, need extra care: see heritage and older homes.
Approvals
Does a house extension need approval in Tasmania?
Most extensions do, and your building surveyor confirms which kind. Building work in Tasmania is sorted into low risk, notifiable and permit work by the Director's Determination. For notifiable and permit work, the surveyor issues a Certificate of Likely Compliance, which needs a Form 35 from each responsible designer, including the engineer for the structure.
Council may also need to give a planning permit, for example in a heritage precinct. Hazard areas raise the category too: low-risk work in a landslip, bushfire, flood or coastal hazard area becomes notifiable, and Class 1 work in a High landslip band becomes permit work. If your block is in a landslip band, see landslip reports.
Designs lodged now are to NCC 2022, which applies in Tasmania until 30 April 2027; NCC 2025 applies from 1 May 2027. Our guide to building approvals in Tasmania covers the categories in more detail.
Bushfire-prone blocks
We don't offer BAL assessments or bushfire hazard management plans. If your site is bushfire-prone, a bushfire hazard practitioner prepares that, and we design the structure to suit.
Extension and renovation engineering
Priced from your plans or concept sketches, and fixed before we start.
- Footing, framing, beam and bracing design
- Second-storey check of existing footings
- Structural drawings and calculations
- A Form 35 for your building surveyor
Renovations and granny flats
What renovations need a structural engineer?
Renovations need an engineer whenever they change what the structure carries or how it carries it. These are common examples in older and newer Hobart homes alike.
Open-plan living
Removing or shortening a load-bearing wall needs a beam, posts and footings. See wall removal.
New openings
Wider doors, bifolds and big windows need lintels or beams, especially in brick and sandstone walls.
Heavier finishes
A tiled bathroom, stone benchtops or a bath on an old timber floor may need the joists and bearers checked.
Roof changes
Skylights that cut rafters, a heavier roof covering or solar panels on an old roof framing.
Granny flats and studios
The same engineering as a small house: a soil test, footings or slab, framing and tie-down. Read the granny flat guide.
Outdoor additions
A deck, pergola or carport off the extension. See decks, pergolas and carports.
Not sure your project needs an engineer at all? Our guide Do I need a structural engineer? walks through it.
Related services
Often needed alongside an extension
Site classification & footings
Soil tests and AS 2870 site classification, then slab and footing designs that suit the ground, with a Form 35 for your building surveyor.
Learn more
Wall removal & beam design
Load-bearing wall removal designed properly: the steel or LVL beam, the posts and the footings, with drawings your builder can build from.
Learn more
Heritage & older homes
Condition reports and repair designs for sandstone, brick and timber homes, with the structural drawings heritage approvals ask for.
Learn more