Building upwards lets you gain space on a small block without giving up the backyard. It is also among the harder renovations to get right, because few single level homes were designed to carry another floor.
Begin with the existing structure
Before any drawings are finalised, a structural engineer should look at what is already there. A single storey home has footings, walls and lintels sized for a roof, not for a floor full of people, furniture and another roof on top. The engineer will usually check:
- Footings and slab. Whether the existing footings can take the extra weight, or whether new piers, pads or strip footings are needed under the new load paths.
- Walls and beams. Where the upper floor will sit, and whether steel beams or new posts are needed to carry it down to the ground.
- Bracing and tie down. A taller house catches more wind, so the frame needs enough bracing and hold down to resist it.
- Soil. If the site classification is unknown or the ground is reactive, the engineer may ask for a geotechnical investigation.
The engineer's design becomes part of the approval documents, and the certifier will want to see that the work on site matches it.
Which approval fits
The Housing Code in the Codes SEPP allows first floor additions to be approved as complying development with a CDC, provided the whole design meets the code. The maximum height is 8.5 m, measured from natural ground level, and the side setbacks increase as the walls get higher. Landscaped area and floor space limits also apply.
Where the design falls outside the code, or the property is within a heritage conservation area or on other excluded land, council assesses a DA instead. Once council approves it, a construction certificate is also required before work begins.
Whichever route applies, a BASIX certificate is needed once the value of the work reaches $50,000. On bushfire prone land, the addition needs a bushfire attack level assessment and construction to suit under AS 3959.
Design details the certifier checks
A new upper level brings parts of the Building Code of Australia into play that a single storey house never needed:
- Stairs and balustrades. Riser and going sizes, handrails, and barriers on stairs, landings and any balcony.
- Smoke alarms. Each level needs an alarm, including the hallway outside bedrooms. Once a home has more than one alarm, they must all be interconnected.
- Fire separation. An upper wall less than 900 mm from a side boundary must be built to resist fire, and openings in it are restricted.
- Wet areas. An upstairs bathroom needs waterproofing that protects the rooms below.
- Privacy and overlooking. The Housing Code includes privacy controls for upper floor windows, decks and balconies.
Getting these right on the plans is far cheaper than fixing them on site. Our plan assessment service can review drawings before they are lodged.
Living through the build
Most second storey additions involve taking off part or all of the roof. Talk to your builder about weather protection, staging and whether the family can keep living there while work is under way. Wiring, plumbing and drainage often need rerouting, and every downpipe from the new roof has to discharge into the approved stormwater system.
The principal certifier carries out the mandatory critical stage inspections, such as new footings, framing before linings go on, wet area waterproofing and stormwater connections. Our guide to Critical stage inspections: what we check and when explains each stage. Once everything is complete, an occupation certificate is required before anyone uses the new level.
Next steps
Bring your concept plans, a survey and the engineer's preliminary advice together early. That shows early on which approval route suits the design. Find out more about how we certify home alterations and additions, or request a quote for certifying your second storey.
Local help across NSW
CertifiBuild certifies Class 1 and Class 10 work in 39 council areas. Local rules on these council pages are a good place to start: Wollongong City Council, Kiama Municipal Council, City of Newcastle, Hawkesbury City Council, Blacktown City Council, Cumberland City Council.
Suburb pages with local planning notes: Keiraville, Kiama, Kotara, Kurrajong Heights, Lalor Park, Lambton, Lidcombe, Lilyfield, Lithgow, Liverpool. You can also browse every service area.
Sources
- Housing Code overview, NSW Planning Portal
- BASIX for alterations and additions, NSW Planning Portal
- Smoke alarm requirements for houses, ABCB Housing Provisions
- External wall fire separation (Housing Provisions Part 9.2), ABCB