Chapter 2 Notes: Measurement Systems, Scales, and Line Types

Scale

The term scale refers to the proportional shrinking or enlarging of an object. Construction drawings are drawn to scale.

Scale Size

The scale used for producing construction drawings depends on the size of the object, the level of detail required, the size of the plotting paper, and the measurement system. A large building may require a larger scale reduction; the drawing type (detail vs. elevation) and the paper size influence readability; Imperial and metric systems use different reduction scales.

Two Systems of Measurement

Imperial and metric are the two systems of measurement. Building codes are in metric. Materials are manufactured in either system (e.g., plywood and drywall commonly in imperial sheets like 4′ × 8′; blocks more often in metric sizes like 200 mm). Residential drawings may be imperial or metric depending on region, while commercial drawings are usually metric.

Block and Layout Sizes

Metric blocks are standard but are often referred to in imperial units. For example, a 200 mm block with a 10 mm mortar joint is often called an 8″ block. This can create mismatches when renovating or restoring older structures.

Comparison of Layout Sizes

Standard spacing for studs, joists, rafters, and trusses is defined in the NBC using a hard conversion. Imperial spacing is traditional and still common because panel goods are manufactured in imperial sizes.

Tape Measure Comparison

There is a noticeable difference between 16″ and 400 mm spacings. The 19.2″ OC spacing (diamond mark) is becoming more popular and divides evenly into 8′.

Simple Mathematical Conversion

A metric tape makes conversion straightforward. Core rule: $1\ \mathrm{in} = 25.4\ \mathrm{mm}$. To convert 10″ to mm: $10\ \mathrm{in} \to \mathrm{mm} = 10 \times 25.4 = 254\ \mathrm{mm}$. To convert back, multiply by 0.03937 or divide by 25.4, since $1\ \mathrm{mm} = 0.03937\ \mathrm{in}$. For feet and inches, first convert everything to inches: e.g., 4′6″ = 54″, then convert to mm by multiplying by 25.4. First-principles understanding is essential.

$1 \mathrm{in} = 25.4 \mathrm{mm}$
$10 \mathrm{in} = 254 \mathrm{mm}$
$1/4 \mathrm{in} : 12 \mathrm{in} = 1/48 \mathrm{ft}$
$1 \mathrm{ft} = 12 \mathrm{in}$

Practice Examples

Convert the following: 20″ to mm; 2′6″ to mm; 10′ to mm; 254 mm to inches; 7350 mm to inches; 9240 mm to feet and inches.

Metric Scale Reading

Metric scale reading is covered in the Metric Scale Reading assignment; refer to Chapter 2 for practice questions and readings.

Imperial Scale Reading

The architectural scale is the most common imperial scale for drawings and is based on portions of 12. For example, 1/4″ : 12″ corresponds to 1/48th of a foot.

$\frac{1}{4} \mathrm{in} : 12 \mathrm{in} = \frac{1}{48} \mathrm{ft}$

Common scales shown include 1/8″ and 1/2″, which are used for different architectural drawings and uses.

Use of Scales

Reasons not to scale drawings include photocopying reducing accuracy, enlargements without scale, difficulty reading small scales, or designer-drawn changes not scaled accurately. When dimensions are missing, confirm with the designer.

Scaling Drawings (Digital Tools)

Digital scales with touch screens and estimating software can be used for estimation and data entry, but caution is advised when scaling drawings to ensure accuracy remains.

Reading and Dimensioning on Drawings

Examples of how frame construction dimensions are indicated include center lines for doors/windows/walls in wood-frame construction and edge references for masonry. Always note where dimensions are measured from and to, as practices can vary between drawings.

Cutting-Plane Line

A cutting-plane line is used to cut through an object to show a cross-sectional view, highlighting internal components. Without the cross-section, the 3D relationships may be unclear.

Doncaster Example: Cutting-Plane and Detail Designation

A detail designation marks the area of interest where a cross-section is shown; compare with the following slide to see how the cutting plane is applied in practice.

BIM and Modern Practice

Residential builders from coast to coast are adopting BIM components. The level of BIM adoption (3D–6D, etc.) depends on the type of work and the financial benefits expected.

Scaling Drawings (Estimation and Digital Workflows)

Digital scales with touch screens or estimating software can input data into spreadsheets, but scaling should be used cautiously to avoid inaccuracies.

Chapter 2 Key Terms

Key terms include: Break line; Center line; Cutting-plane line; Dashed line; Descriptive line; Detail designation; Dimension line; Extension line; Floor joists; Hard Conversion; Imperial system of measurement; Leader line; Metric system of measurement; Not to scale; Object line; Scale; Soft conversion; Studs; Sub-floor.