Construction drawings are the language of building. Before construction starts, contractor, inspector, and owner all need to be reading the same drawing — interpreting symbols, scales, dimensions, and notes the same way. Misreading a drawing causes the kitchen island to be built 12 inches too short or the wall to land 6 inches off — expensive mistakes traced back to a misread plan.

This guide is a homeowner-friendly primer on reading typical residential construction drawings: site plans, floor plans, elevations, sections, and detail drawings. By the end, you should be able to follow your renovation drawings without needing to ask the contractor.

Before you start

Three things to settle:

1. Drawings come in a set, not as one drawing. A typical residential drawing set: cover sheet (with index), site plan, floor plans (one per level), elevations (4 sides of the building), sections (cutaways), and details (close-ups of important assemblies). Each drawing has a sheet number (A1, A2, etc.) referenced from other sheets.

2. Scale matters — measure with a scale or read dimensions. Drawings are scaled (1:50, 1:100, 1/4 inch = 1 foot). Don't 'measure' off a printed drawing with a regular ruler — printers distort. Use a dimension call-out (the labeled number) or an architect's scale.

3. Symbols are standardized but vary by drafter. Common symbols: arrows for direction, hatching for cut materials, circles with letters for door/window types, triangles for elevation references. Most drawings include a 'Legend' or 'Symbols Key' on the cover sheet — read it first.

What you'll need

Tools

Architect's scale or engineer's scale (for measuring)
Highlighter (for marking up your copy)
Tape measure (for verifying real-world dimensions)

Materials

Set of construction drawings (PDF or printed)
Pencil for notes
Reference: AIBC or OAA standards documents (online if needed)

Always read dimensions, not visual measurement

Drawings are reduced to fit on paper. The dimension call-outs (e.g., '3000 mm' or '10 ft 0 in') are accurate; visual measurement is not. If a dimension doesn't appear, ask the drafter to add it — never assume.

Construction drawings in Ontario typically use metric (mm) per OBC and design office standards.

Step-by-step instructions

Read the cover sheet first

Cover sheet typically includes: project name, address, drafter info, date, sheet index (list of all drawings).

Notes about scope, code references, and overall project parameters appear here.

Read this first to understand what you're looking at.

Understand the site plan

Top-down view of the property, showing the house, lot lines, setbacks, north arrow, easements.

Used by inspector to verify the addition or work is within zoning setbacks.

Should include: lot dimensions, house dimensions, distance from house to lot lines, north orientation.

Read the floor plans

Floor plans show the layout from above: walls (lines or hatching), doors (arc swings), windows (double-line breaks in walls), fixtures (toilets, sinks, etc.), dimensions, room labels.

One floor plan per level (basement, main floor, second floor).

Existing-vs-proposed: most renovation drawings show both — verify which is which.

Interpret elevation drawings

Elevations show the exterior of the building from each side: north, south, east, west.

Used for visual approval and for verifying exterior changes (windows, doors, siding).

Show: roof line, window/door openings, siding pattern, exterior finishes.

Understand section drawings

Sections are vertical cutaways through the building, showing what you'd see if you sliced the house with a giant knife.

Show: floor structure, wall composition, ceiling height, roof structure.

Used by inspector to verify framing, insulation, and other hidden assemblies.

Find detail drawings

Details are close-ups of specific assemblies: typical wall section, typical foundation detail, typical window detail.

Show fasteners, layers of materials, dimensions of small parts.

Reference numbers connect detail drawings to floor plans and sections.

Decode common symbols

Arrow with circle: section cut indicator (with sheet reference).

Triangle with number: elevation reference.

Circle with letter: door or window type (matched to schedule on a separate sheet).

Hatching patterns: indicate material type (concrete, wood, insulation, etc.).

Dashed lines: hidden objects (above the cut) or future/optional elements.

Check schedules and notes

Door schedule: list of all doors with type, size, finish.

Window schedule: similar for windows.

Finish schedule: room-by-room flooring, paint, ceiling spec.

General notes: code references, structural specs, contractor responsibilities.

These supplement what's on the drawings — read them.

Mark up your copy and ask questions

As you read, highlight items you don't understand or want to verify.

Compile questions for the designer or contractor.

It's much cheaper to clarify a drawing question than to fix a misbuild.

Common mistakes that cost you

Measuring printed drawings with a ruler. Printer distortion makes measured values inaccurate. Use dimensions or architect's scale only.
Assuming standard sizes. Doors and windows come in many sizes. Check the schedule, don't assume 32×80.
Ignoring notes. General notes contain critical info: structural details, finish requirements, code refs.
Confusing existing vs proposed. Renovation drawings show both. Read carefully; proposed walls are usually shown differently (heavier line, different hatching).
Not asking questions. If something's unclear, ask. Designer can answer in 5 minutes; misbuild costs days.

Frequently asked questions

What's the difference between a designer's drawing and an architect's drawing?

BCIN-certified designer: qualified to draw most residential under OBC Section 9 (typical houses). Less expensive than architects.

Architect: full architectural license, required for larger commercial or institutional buildings.

For typical Ottawa residential renovations, a BCIN designer is appropriate and most cost-effective.

Why are dimensions in millimetres?

Ontario Building Code uses metric. Construction drawings in Ontario default to mm.

Conversion: 1000 mm = 1 m = 39.37 inches. Common: 2400 mm wall = 8 ft, 600 mm = 2 ft.

Some plans use feet/inches; usually marked clearly.

Where do I get a copy of my renovation's drawings?

From your contractor or designer. They typically provide a PDF set at project start.

If you pull your own permit, you keep the drawings.

Building department archives drawings for permit history; you can request copies if needed.

When to call us instead

We provide clear, well-marked drawings on every project. Pre-construction walkthrough with drawings ensures everyone is reading them the same way.

Book a free 60-minute site visit →

Related Ottawa services

If you're starting a renovation, our team includes BCIN-designer drawings as part of the fixed-price scope. Book a free 60-minute consultation.