How to Read Construction Plans

Most Australian plan sets follow a broadly consistent structure, even though the exact sheet numbering varies between architects and drafting practices. Recognising each drawing type by what it’s trying to show you is the fastest way to navigate an unfamiliar set.

• Site plan — shows the whole allotment: boundaries, setbacks, easements, existing structures, contours and the building’s position and orientation on the block.
• Floor plans — the layout of each level, showing room names, wall positions, door and window openings, and internal dimensions.
• Elevations — external views of each face of the building, showing height, roof form, cladding and finishes as they’ll appear from outside.
• Sections — vertical “cuts” through the building, showing floor-to-ceiling heights, floor build-ups, roof pitch and how different levels relate to each other.
• Detail drawings — large-scale close-ups of specific junctions, like a window head, a stair or a waterproofing detail, where the general drawings don’t have room to show enough information.
• Structural and services drawings — engineering drawings for structure (footings, slabs, framing) and services (electrical, hydraulic, mechanical), usually issued as a separate, cross-referenced set.

Every drawing is produced at a stated scale — a fixed ratio between a measurement on the page and the real dimension on site — so anyone with a scale rule can measure directly off a printed drawing. Digital plan sets increasingly carry stated dimensions rather than relying on scaling at all, which is both faster and far less error-prone.

The golden rule of reading plans is that a written dimension always overrides anything you measure or scale off the drawing yourself. Drawings get resized, printed at the wrong scale, or bear only loosely on the actual measurements shown, so scaling should only ever be a fallback for a dimension that’s missing altogether — never a substitute for a stated figure.

Grid lines, running in a lettered and numbered pattern across structural and floor plans, give a fixed reference frame for locating any element precisely — especially useful on larger or more complex buildings, where a verbal description like “the wall near the kitchen” stops being precise enough.

Construction drawings rely on a shorthand of symbols and abbreviations to pack a huge amount of information onto a page without cluttering it with full text. Learning the common ones is one of the fastest ways to read a set of plans confidently.

• FFL (Finished Floor Level) and FGL (Finished Ground Level) — the completed height of the floor and the ground once landscaping is finished.
• NGL (Natural Ground Level) and RL (Reduced Level) — the existing ground height and a height measured relative to a fixed survey datum.
• SSL (Structural Slab Level) — the top of a structural slab, before finishes like tiles or flooring are added.
• DP (Downpipe) and SW (Stormwater) — drainage elements shown on site and services plans.
• BAL (Bushfire Attack Level) — a rating that determines construction requirements in bushfire-prone areas.
• WC — the standard abbreviation for a water closet, or toilet, on a floor plan.

Every properly issued drawing carries a title block in one corner recording the project name, drawing number, scale, revision letter or number, and the date it was issued. Before you measure or price anything, checking that block is the single fastest way to avoid working from an outdated design.

Plans are revised constantly as a design develops — a council condition, an engineering requirement or a client change can all trigger a new revision. An estimator who prices from an earlier revision when a later one has already been issued risks measuring rooms, openings or structural elements that no longer exist in the current design.

• Check the revision letter or number against the latest issue you’ve been sent, not just the date on the sheet.
• Look for an issue status such as “For Tender” or “For Construction” — a preliminary or “For Information” issue may still be subject to change.
• Keep a simple register of which revision of each sheet you actually priced from, so it can be checked later if the scope is disputed.

Plans show what and where; the specification says how and to what standard. Reading one without the other leaves real gaps — a floor plan shows where the tiles go, but the specification says which tiles, what adhesive, and to what Australian Standard the waterproofing must be installed.

This is also where a Bill of Quantities earns its place in the process: it draws the measured quantities from the plans and the quality and inclusion requirements from the specification into one priced document, so nothing gets measured from the drawing alone without checking what the specification actually calls for on that item.

• Plans vs specification — plans show location, dimension and general arrangement; the specification defines material standards, quality and performance requirements.
• Plans vs schedules — a door, window or finishes schedule lists every individual item by a reference tag shown on the plan, with its own specific size, type and finish.
• Plans vs Bill of Quantities — a BOQ measures the plans into priced quantities, cross-checked against what the specification requires for each item.

Most measurement and pricing errors trace back to a handful of recurring habits rather than genuinely ambiguous drawings.

• Scaling a dimension off a printed or PDF drawing instead of using the stated figure, especially after a drawing has been resized or printed at the wrong scale.
• Pricing from an old revision because a later issue was never checked, or was missed in an email chain.
• Reading a floor plan in isolation without cross-checking the matching section or elevation for heights and build-ups that aren’t shown in plan view.
• Missing information hidden in notes, legends or the specification rather than shown directly on the drawing itself.
• Not accounting for items shown only on structural or services drawings because the trade drawings were reviewed in isolation from each other.