NZS 3604:2011 timber-framed buildings explained

Is the building inside NZS 3604?

Answer for the building. Each limit is the standard's own; past any of them the building, or that part of it, needs specific design or another standard such as NZS 4229.

Inside NZS 3604

Used as: Importance Level 2: houses and the everyday buildings Table 1.1 lists
External walls: It has external walls
Ground: On good ground
Lowest ground to top of roof: 6 m from the lowest ground to the top of the roof, within 10 m
Steepest roof plane: 25°, within 60°
Storeys: One storey, timber framed; it may have a part storey in the roof space or a part basement
Plan floor area: 150 m²: any plan area, every storey being timber framed
Floor load: 1.5 kPa floors, within the main tables
Wind zone: High wind zone
Snow load: Snow up to 1 kPa, which every table already allows for
Masonry veneer: No masonry veneer

What to know about the project

Every part of the building reads these. The ones the project keeps are set once and every page and tool picks them up; the rest are asked where they are read.

Wind zoneIn the project: From the wind region and lee zone on the map, the ground roughness, the site's exposure and its topography, through Table 5.4. NZS 3604:2011 5.2.1, Tables 5.1 and 5.4, Figure 5.1Read by: Wall bracing, Lintels, Studs and plates, Roof framing
Earthquake zoneIn the project: Read off the map, Figure 5.4. NZS 3604:2011 5.3.2, Figure 5.4Read by: Wall bracing
Soil classAsked on each page: The site's subsoil class, A rock to E very soft; read as the standard's default where it is not known. NZS 3604:2011 5.3.3Read by: Wall bracing
Snow loadAsked on each page: The site's snow zone, N0 to N5, and its altitude, Figure 15.1: up to 1 kPa, 1.5 or 2 kPa. NZS 3604:2011 1.1.2(d), 15.2, Figure 15.1Read by: Lintels, Roof framing, Scope
Exposure zoneIn the project: Mainly by the site's distance from the sea, harbours and tidal estuaries; it sets the treatment and the fixings. NZS 3604:2011 4.2Read by: Durability
Roof and wall weightsAsked on each page: Light, medium or heavy, by the cladding's mass, as the definitions set them. NZS 3604:2011 1.3Read by: Wall bracing, Roof bracing, Lintels, Studs and plates, Roof framing
Floor loadAsked on each page: 1.5 kPa inside a house, 2 kPa for a deck over a metre off the ground, 3 kPa for an office or communal kitchen. NZS 3604:2011 1.1.2(e), Table 1.2Read by: Wall bracing, Subfloor, Lintels, Studs and plates, Scope
Roof pitchIn the project: The steepest roof plane, which sets the bracing demand and the scope. NZS 3604:2011 1.1.2(i), 5.2.6Read by: Wall bracing, Roof bracing, Scope

How each is worked out

Wind zone

Five answers give it. The wind region, A or W, and whether the site is in a lee zone, both read off the map; the ground roughness, urban or open, from whichever direction is worst; the site exposure, sheltered or exposed; and the topographic class, T1 to T4, from how steep the hill is and where on it the site stands. Together they give one of the five zones below, from Low to Extra high, or send the site to specific engineering design.

Urban means more than 10 houses or 3 m trees to the hectare, and anywhere within 500 m of open country counts as open. A site is sheltered only with two rows of similar buildings on every side; a steep site never is, and one beside playing fields or other open space, a beach, a large river, a motorway or a wind channel over 100 m wide is exposed. A lee zone raises Low to High and Medium to Very high, and anything higher out of the standard.

The wind zones
Wind zone Tables 5.4 to 5.7
	Design wind speed	Demand, times High's
Low	32 m/s	0.5
Medium	37 m/s	0.7
High	44 m/s	1
Very high	50 m/s	1.3
Extra high	55 m/s	1.6

NZS 3604:2011 5.2.1 to 5.2.5, Tables 5.1 to 5.4, Figures 5.1 and 5.2

Earthquake zone and soil

The earthquake zone, one to four, is read off the map. The site subsoil class, A to E, comes from the council's hazard records, a geotechnical completion report or GNS Science's QMAP; where none gives it, the site is Class E, the softest. Zone and soil together set a multiplier on the earthquake demand, from 0.3 on rock in the quietest zone to 1.5 on soft soil in the most active.

Finding out the soil class is often the cheapest saving in the whole design: in zone 2, a site on rock takes 0.5 times the table's demand, and one taken as Class E takes 0.8.

NZS 3604:2011 5.3.2, 5.3.3, Figure 5.4, Tables 5.8 to 5.10

How heavy the building is

Earthquake demand follows weight, so the roof, the walls and any subfloor cladding are each put in a class by the mass of their cladding for every square metre, a roof's sarking counted with it. Only the class is asked, never the mass itself.

Cladding weight classes, kg/m²
Mass of the cladding 1.3
	Light	Medium	Heavy
Roof cladding	up to 20	–	20 to 60
Wall cladding	up to 30	30 to 80	80 to 220

NZS 3604:2011 1.3 Definitions

What to measure

The building's length and width, the floor area of each level, the roof pitch, and two heights: H, from the floor of the level being braced to the apex, and h, the roof's height above the eaves. A roof up to 25° gives its wind demand on the walls' length and width; a steeper one, still within NZS 3604 up to its steepest pitch, on the roof's own length and width, overhangs included.

NZS 3604:2011 5.2.6, Figure 5.3

The sections you will use

What each section settles, and the page here that works through it.

Section 1: Whether a building is covered, and the terms every table reads, such as loaded dimension and good ground.
Section 2: Dimensions, timber grades and fixings; the tables are for SG 8 timber.
Section 3: The site: good ground and its bearing.
Section 4: Durability: exposure zones, the timber's treatment and the fixings for each zone.Durability
Section 5: Bracing: the wind and earthquake demand, the bracing lines and what each element is rated.Wall bracing · Design the bracing in the calculator
Section 6: Foundations and subfloor framing: piles, footings, bearers and subfloor bracing.Subfloor · Design the subfloor in its tool
Section 7: Floors: joists, flooring and slabs on ground.Subfloor
Section 8: Walls: studs, plates, lintels and their fixings.Openings and lintels · Studs and plates
Section 9: Posts and their footings.Roof framing
Section 10: Roof framing: rafters, beams, trusses, purlins and roof bracing.Roof framing · Roof bracing
Section 11: Roof and wall claddings, which the Building Code's E2 takes further.E2
Section 12: Interior linings.
Section 13: Ceilings: battens, trimmers and ceiling diaphragms.Roof framing
Section 14: Floors of 3 kPa: the tables that take the place of Sections 5 to 8's.Subfloor · Openings and lintels · Studs and plates
Section 15: Snow of 1.5 and 2 kPa: the tables that take the place of Sections 8 and 10's.Openings and lintels · Roof framing

Each part of the building

A page for each part: a quick answer for the everyday sizes, or the steps explained where a tool of its own does the design.

Wall bracing
How the bracing demand and lines are worked out, and the makers' systems that carry it.
Design the bracing in the calculator
Roof bracing
How many roof braces, of which kinds, and what may stand in for them.
Design the bracing in the calculator
Subfloor
Piles, bearers, joists and flooring, and the subfloor's bracing, explained.
Design the subfloor in its tool
Openings and lintels
Size a lintel, its ends and its fixing.
Studs and plates
Stud size and spacing, plate build-ups and their fixings.
Roof framing
Purlin and ceiling batten spacing, rafter sizes, and the other roof members.