Your plans are the most important documents in your build. They're what you sign off on, what the certifier approves and what every trade builds from. Knowing a little about sheet sizes and scales helps you read them properly, and stops you making one very common, very expensive mistake: measuring off a print that's been shrunk.

What sizes are Australian house plans?

Australia uses the international ISO A-series paper sizes. Each size is half the one above it, and they all have the same proportions, so a drawing can be scaled up or down without distorting.

  • A0: 841 x 1189 mm. Large site plans and big projects.
  • A1: 594 x 841 mm. The usual "full size" sheet for house plans and engineering drawings.
  • A2: 420 x 594 mm. Sometimes used for smaller jobs.
  • A3: 297 x 420 mm. Very common for homeowner copies, contract sets and site prints.
  • A4: 210 x 297 mm. Specifications, schedules and paperwork.

So when someone talks about "full-size drawings" for a house in Australia, they usually mean A1. Many residential sets are now drawn to be printed on A3 as well.

You may come across US drawings that use inch-based sizes such as ARCH D or ANSI D. They're not used for Australian house plans, so you can ignore them.

What do the scales mean?

Drawings are drawn to a scale written as a ratio. At 1:100, 1 mm on the drawing equals 100 mm (10 cm) in real life. Typical scales on a house set are:

  • Site plan: 1:200 or 1:500
  • Floor plans and elevations: 1:100, sometimes 1:50
  • Sections: 1:50 or 1:100
  • Details: 1:20, 1:10 or 1:5

Bigger paper doesn't mean more detail

A common misunderstanding is that a bigger sheet shows more detail. It doesn't. The drawing scale decides the detail. A floor plan at 1:100 shows the same information whether it's printed on A1 or A3. Details like a wet area set-down or a window head flashing are drawn at bigger scales such as 1:10 or 1:5 so the small parts are visible.

The classic mistake: measuring off a reduced print

This is the one that catches people out. A plan drawn at 1:100 on A1 and printed on A3 is now roughly 1:200, because A3 is half the size of A1 twice over. If you measure it with a scale ruler set to 1:100, everything will be out by half.

To avoid it:

  • Check the title block. It should state the scale and the sheet size the scale applies to, for example "1:100 @ A1".
  • Use the scale bar if there is one. A scale bar shrinks with the drawing, so it stays accurate.
  • Better still, use the written dimensions. Never scale off a reduced print to set out anything. If a dimension you need isn't shown, ask the designer for it.

What's in a set of house plans?

A typical residential set includes:

  • Site plan: where the house sits on the block, setbacks, levels, services and drainage.
  • Floor plans: the layout from above, with dimensions, doors, windows and fixtures.
  • Elevations: each side of the house, showing heights, finishes and window positions.
  • Sections: a slice through the house showing how the slab, walls and roof fit together.
  • Details: enlarged drawings of particular items.
  • Schedules: windows, doors and finishes.
  • Engineering drawings: slab or footings, and often frame and bracing, from the structural engineer.
  • Energy assessment: the NatHERS report and stamped plans showing the insulation, glazing and other requirements.

In Australia, technical drawings generally follow the AS 1100 series.

Plans and approvals in Queensland

Before work starts, a private building certifier must issue a building approval based on your plans and engineering. Some work also needs council plumbing or planning approval. The approved set is the one your builder must build to, so make sure the plans in your contract match the approved plans.

What to check on your plans before you sign

  • Sheet size and scale in each title block, and whether your copy has been reduced.
  • Revision letter and date on every sheet. All sheets should be the current revision, and the contract should list them.
  • Consistent dimensions. Overall sizes on the floor plan should match the elevations and site plan.
  • Ceiling heights, window sizes and floor levels match what you've agreed.
  • Engineering drawings are included and match the architectural plans.
  • Energy assessment requirements (insulation, glazing, roof colour) are shown or referenced.

If anything doesn't add up, ask your designer or builder before you sign. A question now is free. A change later is a variation.

Who to ask

Your designer or architect for the drawings, the engineer for structural details, and your builder or site supervisor once construction starts. Every change should come through as a new revision, labelled and dated in the title block.

Further reading

Decode Residential Floor Plans Like a ProConfused by the floor plan symbols? This article deciphers reading residential floor plans, from layout to labels, helping you make informed decisions for your dream home.Understanding Surveys & Contour Plans: A guide 4 homeownersA contour survey maps land elevation,important for new homeowners in planning and construction. Understand RP and SP roles, contour lines, and reduced levels. This guide helps interpret survey plans for accurate design, drainage, and compliance.Who Owns the Copyright to Your Plans? Know Before You Build!Curious about the copyright for your dream home’s plans? Discover the importance of knowing the copyright owner before signing a builder’s contract. Learn how to secure design rights for your home, ensuring the freedom to build it again.