Design and Human Factors: Composition, Form, Proportion, Space, Circulation, Anthropometrics, Accessibility and Bye-laws

Form is the shape together with the three-dimensional structure and mass of a building. It is the building's primary identifying characteristic, while space is what the form encloses and shapes. The primary solids (sphere, cylinder, cone, pyramid and cube) are regular forms that are stable and easy to read, and they give designers a vocabulary to transform.

• Dimensional transformation: one or more dimensions change and the form keeps its identity, so a cube becomes a prism.
• Subtractive transformation: volume is removed, as in a notch, a corner cut or a courtyard, and the form stays readable if enough of the original remains.
• Additive transformation: forms are added to the original. The additive types are centralised (a dominant centre with secondary forms around it), linear (a row), radial (a core with linear arms), clustered (grouped by proximity or a shared trait) and grid (held by a modular three-dimensional grid).

The properties of form are shape, size, colour, texture, position, orientation and visual inertia, the degree of stability, which depends on the geometry and on the orientation relative to the ground, to gravity and to our line of sight. A triangle resting on its base is stable; the same triangle standing on its apex is dynamic. Form is read through the light that falls on it, so the same form looks different with each hour and each viewpoint.

Ratio compares two quantities and proportion is the equality of two ratios. A proportioning system is a consistent set of ratios that relates every part of a building to the others and to the whole, which is the source of visual order. It is internal to the design, unlike scale, which relates the design to the human body or its surroundings.

• Vitruvius's body proportions and the classical orders, in which every part is a fixed multiple of a module such as the column diameter.
• Renaissance harmonic ratios such as 1 : 2, 2 : 3 and 3 : 4, borrowed from musical consonance and applied to room and façade proportions.
• Le Corbusier's regulating lines, diagonals drawn across a façade to confirm that its parts are similar rectangles.
• Body-based modules of Indian śilpa texts (aṅgula, hasta, tāla) and the Japanese tatami mat, about 2 : 1, used as a module for room sizes.

• Golden section of a 10 m wall: 10/1.618 = 6.18 m and 10 − 6.18 = 3.82 m.
• Golden rectangle of width 4 m: length = 4 × 1.618 = 6.47 m. A √2 rectangle of short side 3 m: long side = 3 × 1.414 = 4.24 m.
• Modulor: 183/113 = 1.62 and 113/70 = 1.61, both close to φ.

Scale in design is the apparent size of a building or element compared with a reference: either the human body (human scale) or the other elements around it (generic scale, size relative to the context). Proportion is internal, part to whole, whereas scale is external, so a building can be perfectly proportioned and still be out of scale. Do not confuse it with the scale of a drawing, the representative fraction of the previous chapter.

Scale cues are familiar elements such as the door, step, rail, window and brick course. Exaggerate them and the building looks smaller or larger than it is, which is false scale, and a large building is given human scale by breaking it into parts of familiar size. In urban space the ratio of the width of the space D to the height H of its enclosing walls governs the sense of enclosure. D/H = 1 gives strong enclosure, the eye angle to the top of the opposite wall being 45°; D/H = 2 gives a comfortable enclosure (27°); D/H = 3 a weak one (18°); and enclosure fades as D/H rises further.

Worked: a street 12 m wide between buildings 12 m high has D/H = 1 and an eye angle of tan⁻¹(H/D) = 45°. Widen it to 24 m and D/H = 2, so the angle falls to tan⁻¹(0.5) = 26.6°, about 27°.

Space is shaped by the base plane (floor), the overhead plane and the vertical planes, and by the openings and thresholds that control how enclosed or connected it feels. Organising space means arranging spaces by function, privacy, hierarchy, access, view and climate. Ching describes four spatial relationships: a space within a space, interlocking spaces, adjacent spaces, and spaces linked by a common space.

Plan logic: zone spaces by privacy (public, semi-public, private) and by use (day and night areas), and show hierarchy through size, shape and position. Keep the servant spaces (stairs, toilets, kitchens, shafts) together so that the served spaces (living and working rooms) stay open and flexible, which is Louis Kahn's served and servant idea. Test adjacency with a bubble diagram or a relationship matrix before drawing walls. In Indian practice the open-to-sky courtyard is a classic organiser of spaces and of climate.

A plan is the orthographic projection, on a horizontal plane, of the part of a building that lies below an imaginary horizontal cutting plane, seen from above. The cut is taken high enough to pass through doors and windows, commonly about 1.2 m above the floor, above the sill and below the lintel, so that openings show. An elevation is the orthographic projection of an exterior face on a vertical plane, with no cut, and it is named by the direction the face looks towards: the north elevation is the face that looks north. A section is a vertical cut, viewed in the direction of the arrows at the ends of the section line, and it shows what plan and elevation cannot, namely heights and levels.

Conventions: cut walls and columns carry the heaviest line or a solid poché; elements beyond are lighter; elements above the cut are dashed; doors show their swing arcs. A section line with direction arrows is marked on the plan, and one section is normally taken through the staircase to show headroom. A sectional elevation is a section drawn together with the exterior elevation of what lies beyond the cut. The drawings are projected from one another: vertical lines carry widths from plan to elevation, and horizontal lines carry levels from section to elevation.

Worked: with a floor-to-floor height of 3.0 m and a 150 mm slab, the clear height between structural surfaces is 3.0 − 0.15 = 2.85 m, from which the floor finish and any false ceiling are still to be deducted. On a 1 : 100 section the 3.0 m storey is 30 mm high.

Circulation is the path of movement to and through a building. Its parts are the approach, the entrance, the path configuration (linear, radial, spiral, grid, network or composite), the path–space relationship (passing by spaces, passing through them or terminating in them) and the form of the circulation space (closed corridor, open on one side, open on both sides). A good plan gives movement that is legible, direct and safe, and it keeps the share of floor area given to circulation modest.

Horizontal circulation uses corridors (single-loaded with rooms on one side, double-loaded with rooms on both), lobbies, galleries and ramps. Width follows the flow to be carried, the need for two people or a wheelchair to pass, and evacuation. In the National Building Code exit width is counted in units of 500 mm, so width = (persons ÷ persons per unit) × 0.5 m, with the capacity per unit taken for the occupancy and element. Planning efficiency is net usable area ÷ gross area: if circulation takes 22% of a 1200 m² floor, the usable area is 0.78 × 1200 = 936 m².

Vertical circulation uses stairs, ramps, lifts and escalators. In a stair the riser R is the vertical step and the tread T the horizontal one. Blondel's rule 2R + T ≈ 600 to 650 mm (about R + T ≈ 450 mm) gives a comfortable stair, with R commonly 150 to 180 mm and T 250 to 300 mm. The number of risers = floor-to-floor height ÷ R, rounded to a whole number with R recomputed; treads = risers − 1 in a flight, because the floor above forms the last tread; and the horizontal length of the flight (its going) = treads × T. Codes cap the risers in one flight (about a dozen in housing), require landings at least as wide as the stair, and require clear headroom (about 2.2 m). The usual stair types are straight, dog-legged, open-well, quarter-turn, half-turn, spiral and helical.

A ramp's gradient is rise : run, written 1 : n, so the run = rise × n. For accessibility the gradient is no steeper than 1 : 12, with level landings at the top and bottom and where the run is broken, handrails on both sides and a non-slip surface. Lifts are the main vertical transport of multi-storey buildings, planned as a core with a lobby wide enough for waiting and passing; a lift is not counted as a means of escape in fire, which is the job of the stairs, although tall buildings carry special fire lifts. Escalators and travelators move large flows in public buildings.

• Stair: 3.0 m floor-to-floor with R = 150 mm gives 20 risers and 19 treads. A dog-legged stair of two equal flights has 10 risers and 9 treads per flight, so with T = 300 mm each flight is 9 × 300 = 2.7 m long in plan (2R + T = 600 mm).
• Ramp: a 0.75 m rise at 1 : 12 needs a run of 0.75 × 12 = 9.0 m, plus any level landings; the length along the slope is √(0.75² + 9.0²) = 9.03 m, but the plan length is the run.

Anthropometry is the measurement of the human body. Structural (static) dimensions are taken in fixed postures: stature, sitting height, elbow height, hip breadth, knee and popliteal height. Functional (dynamic) dimensions are taken in motion: reach envelopes and ranges of movement. They vary with age, sex, region and generation, so the data must come from the user population (Neufert's Architects' Data, Panero and Zelnik's Human Dimension and Interior Space, Dreyfuss's The Measure of Man). Tables give the mean, the standard deviation and percentiles: for a normal distribution P50 is the mean, P5 = μ − 1.645σ and P95 = μ + 1.645σ, and the 95th percentile means 95% of people are smaller.

Ergonomics (human factors) fits the task, equipment and environment to the people who use them. Its domains are physical (posture, load, reach), cognitive (information, controls, wayfinding) and organisational, and it covers the lighting, thermal, acoustic and air environment. Applications: seat height near the user's popliteal height, and seat depth shorter than the buttock–popliteal length so that the edge does not press behind the knee; desk height set from the seated elbow height, with knee clearance for large users; a kitchen work triangle linking sink, cooker and refrigerator that is compact and free of through traffic; reach zones, with the normal work area inside the forearm sweep and the maximum area inside the full-arm sweep; heavy work below elbow height and fine work at or above it. Proxemics (E. T. Hall) names interpersonal distances: intimate (up to about 0.45 m), personal (to about 1.2 m), social (to about 3.6 m) and public (beyond).

Worked: for a group with mean stature 1650 mm and standard deviation 60 mm, P95 = 1650 + 1.645 × 60 = 1748.7 mm and P5 = 1650 − 98.7 = 1551.3 mm. Headroom and door heights are set from P95 plus an allowance for shoes, hair and movement, and switch and shelf heights from the reach of the P5 user.

Barrier-free (accessible) design removes the physical, sensory and informational barriers that stop persons with disabilities and elderly people from using buildings and open spaces, and it works from standards for specific needs. Universal design, a term associated with Ronald Mace, goes further: it designs environments to be usable by all people, to the greatest extent possible, without adaptation or specialised design. The aim is one solution for everyone, such as a step-free main entrance that every visitor uses, in place of a separate disabled entrance.

• The seven principles of universal design: equitable use, flexibility in use, simple and intuitive use, perceptible information, tolerance for error, low physical effort, and size and space for approach and use.
• The Rights of Persons with Disabilities Act, 2016, which replaced the 1995 Act, makes accessibility a right and ties the approval of building plans and the retrofitting of existing public buildings to accessibility rules.
• The Accessible India Campaign (Sugamya Bharat Abhiyan, 2015) set targets for built environments, transport and information. The technical provisions are in the Harmonised Guidelines and Standards for Universal Accessibility in India (Ministry of Housing and Urban Affairs, 2021, building on the 2016 guidelines) and in the National Building Code of India, 2016.

The common thread is a continuous accessible path of travel from the site entrance and parking to every public space, with no abrupt change of level, slip-resistant surfaces, tactile warning at the head of stairs and at hazards, doors that open with one hand, and information given in more than one way (sight, sound, touch). Features must also be maintained, since a locked accessible lift or a blocked tactile path is as much a barrier as a missing one.

Building control in India works through a hierarchy. State town and country planning Acts empower the planning authority; the master plan and zoning set land use; development control regulations and building bye-laws, adopted by the municipal or development authority, are the statutory, enforceable rules, and a building permit is issued only if the plan complies. The National Building Code of India (NBC), published by the Bureau of Indian Standards (editions of 1970, 1983, 2005 and 2016), is a comprehensive model code: it is recommendatory until an authority adopts it in its bye-laws or a law makes it binding. The Town and Country Planning Organisation's Model Building Bye-Laws (2016) is a model for states and cities.

NBC 2016 is arranged in parts; for this heading the important ones are Part 3 (development control rules and general building requirements), Part 4 (fire and life safety) and Part 11 (approach to sustainability). Indian Standards (IS codes), also from the Bureau, give specifications and codes of practice for materials and design: IS 456 for plain and reinforced concrete, IS 875 for loads, IS 1893 for earthquake-resistant design and IS 13920 for ductile detailing of reinforced concrete. In short, bye-laws are the law of a place, a code such as the NBC is a body of recommended practice and a standard fixes the quality or method of a material or work.

Bye-laws also fix the minimum areas, widths and heights of habitable rooms, kitchens and bathrooms, the light and ventilation openings, stair and exit widths, fire-safety measures, parking, accessibility provisions, sanitation and rainwater harvesting, and the extent to which projections such as chajjas and balconies may enter the setbacks. Worked: a plot of 20 m × 30 m with setbacks of 5 m front, 3 m rear and 2 m on each side has a buildable envelope of (20 − 4) × (30 − 8) = 16 × 22 = 352 m². If coverage is capped at 50% the footprint cannot exceed 0.5 × 600 = 300 m², and at FAR 1.5 the built-up area is 900 m², which is three floors of 300 m².