Structural · 7 min read
Double storey house structural design in Brisbane
A second storey doubles the load reaching the ground and adds a floor that has to span, deflect within limits and carry wind back to the footings. This guide explains what changes when you go from one storey to two in Brisbane, and what the design costs.
Load paths are the whole job
Every load on the upper floor and roof has to reach a footing through a continuous path. On paper it is simple; on a modern open plan house with a garage under living space it is where most of the engineering time goes.
- Suspended floor design — timber joists, LVL, steel beams or a suspended concrete slab
- Transfer beams and posts where upper walls do not sit over lower walls
- Column and pad footing design for concentrated loads
- Stiffened raft, piered footings or bored piers depending on the site classification
- Wind bracing and tie-down over two levels, including the upper storey racking
- Stair, void, cantilever and balcony framing
Adding a second storey to an existing house
Building up on an existing home is a different exercise from a new build. We inspect the existing structure, check whether the current footings and walls can take the new load, and design underpinning, new piers or steel framing where they cannot.
Older Brisbane homes on stumps often need new piers and a strengthened floor frame before the second storey can be supported. Finding that out early prevents an expensive redesign mid-build.
Deflection, vibration and finishes
Two storey homes generate complaints about bouncy floors and cracked cornices far more often than they generate structural failures. Both come from deflection and vibration, not strength.
We design floors to serviceability limits appropriate to the finishes, which matters most under tiled areas, stone benchtops and long open spans.
Cost and timing
Double storey structural design starts at $2,200 including calculations, drawings and RPEQ certification. A second storey addition to an existing home usually includes an inspection of the existing structure, quoted with the design.
Send architectural plans and, for an addition, photos of the existing subfloor and framing.
Frequently asked questions
- How much does double storey structural design cost in Brisbane?
- From $2,200 for a two storey home, including footings, framing, transfer structure, bracing, drawings and RPEQ certification.
- Can my existing house take a second storey?
- Sometimes, and sometimes only after strengthening. A site inspection of the footings, stumps and floor frame tells you which, and it starts at $400.
- Do I need a suspended concrete slab upstairs?
- No. Timber or steel framed floors are common and cheaper. Concrete is chosen for acoustics, wet areas or long term feel, and it needs stronger footings below.
Get a fixed fee for your two storey design from $2,200.
Request a quote