NCC 2019 Volume One
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Specification J1.2 Material properties

Specification J1.2 Material properties

1. Scope

This Specification lists the thermal properties of some common construction materials.

Intent

To clarify that Specification J1.2 covers the relevant properties attributed to common construction materials, air films and airspaces, and reflective surfaces.

2. Construction Deemed-to-Satisfy

(a)

Table 2a lists the thermal conductivity considered to be achieved by some common construction materials.

Table 2a Thermal conductivity of typical wall, roof/ceiling and floor materials

Material description

Material density (kg/m 3 )

Thermal conductivity (W/m.K)

1. Framing

  1. Steel

7850

47.5
  1. (b) Timber – kiln dried hardwood (across the grain)

677

0.16
  1. (c) Timber – Radiata pine (across the grain)

506

0.10

2. Roof Cladding

  1. Aluminium sheeting

2680

210
  1. (b) Concrete or terra cotta tiles

1922

0.81
  1. (c) Steel sheeting

7850

47.5

3. Wall Cladding

  1. Aluminium sheeting

2680

210
  1. (b) Autoclaved aerated concrete

350

0.10

900

0.27
  1. (c) Cement render (1 cement : 4 sand)

1570

0.53
  1. (d) Clay bricks

(i) Clay brick – 2.75 kg

1430

0.55

(ii) Clay brick – 3.25 kg

1690

0.65

(iii) Clay brick – 3.75 kg

1950

0.78
  1. (e) Concrete blocks

(i) 190 mm dense or 90 mm dense solid

1100/2200

1.1

(ii) 140 mm dense or 190 mm lightweight

1250/910

0.85

(iii) 90 mm dense hollow or 90 mm lightweight solid

1650/1800

0.75

(iv) 140 mm lightweight

1050

0.67

(v) 90 mm lightweight

1360

0.55
  1. (f) Fibre-cement

1360

0.25
  1. (g) Gypsum plasterboard

880

0.17
  1. (h) Pine weatherboards

506

0.10
  1. Plywood

530

0.14
  1. (j) Solid concrete

2400

1.44
  1. (k) Steel sheeting

7850

47.5
  1. (l) Prestressed hollow core concrete panel

1680

0.80

4. Flooring Materials

  1. Carpet underlay

-

0.04
  1. (b) Carpet

-

0.05
  1. (c) Prestressed hollow core concrete planks

1680

0.80
  1. (d) Particleboard

640

0.12
  1. (e) Plywood

530

0.14
  1. (f) Timber – kiln dried hardwood (across the grain)

677

0.16
  1. (g) Timber – Radiata pine (across the grain)

506

0.10
  1. (h) Solid concrete

2400

1.44
  1. Vinyl floor tiles

2050

0.79

5. Other Materials

  1. Clay soil (10% moisture content)

1300

0.6
  1. (b) PMMA (polymethylmethacrylate)

1180

1.00
  1. (c) Polycarbonates

1200

0.2
  1. (d) Sand (6% moisture content)

1800

1.64
  1. (e) Soda lime glass

2500

1.0

Notes to Table 2a :

  1. For materials which incorporate cores or hollows in regular patterns (such as cored brickwork, hollow blockwork and cored floor or wall panels), the tabulated material densities and thermal conductivities are based on the gross density (mass divided by external dimensions).
  2. The R-Value of a material is determined by dividing the thickness of the material in metres by the thermal conductivity in W/m.K.
(b)

Table 2b lists the R-Valueconsidered to be achieved by air films and airspaces.

Table 2b Typical R-Values for airspaces and air films

Position of airspace

Direction of heat flow

R-Value

1. Airspaces non-reflective unventilated

In a roof with a pitch of not more than 5°

Up

0.15

Down

0.22

In a roof with a ceiling that is parallel with a roof with a pitch more than 5° and not more than 15°

Up

0.15

Down

0.21

In a roof with a ceiling that is parallel with a roof with a pitch more than 22° and not more than 45°

Up

0.15

Down

0.18

In any roof space with a horizontal ceiling, with a pitch more than 5°

Up

0.18

Down

0.28

In a wall

Horizontal

0.17

2. Airspaces non-reflective ventilated

In any roof with a pitch not more than 5° and 100 mm deep airspace

Up

Nil

Down

0.19

In any roof space with a horizontal ceiling, with a pitch more than 5°

Up

Nil

Down

0.46

In a wall

Horizontal

0.14

3. Air films – Still air

On a surface with a pitch of not more than 5°

Up

0.11

Down

0.16

On a surface with a pitch of more than 5° and not more than 30°

Up

0.11

Down

0.15

On a surface with a pitch of more than 30° and not more than 45°

Up

0.11

Down

0.13

On a wall

Horizontal

0.12

4. Air films – Moving air

Not more than 3 m/s wind

Any direction

0.04

More than 3 m/s wind speed and not more than 7 m/s wind speed

Any direction

0.03

Note to Table 2bR-Values are for a temperature of 10°C and temperature difference of 15 K.

(c)

The thermal properties considered to be achieved by reflective surfaces are—

(i)

within a wall—

(A)

with an inner reflective surface of 0.05 emittance and a 20 mm airspace to the wall lining, an added R-Value of 0.48; and

(B)

with an inner reflective surface of 0.05 emittance and a 70 mm airspace to the wall lining, an added R-Value of 0.43; and

(C)

with an inner reflective surface of 0.05 emittance and a 70 mm airspace to the wall lining and an outer anti-glare reflective surface of 0.20 emittance and a 25 mm airspace to the wall cladding, an added R-Value of 0.95; and

(D)

with an outer anti-glare reflective surface of 0.20 emittance and a 35 mm airspace to the wall cladding, an added R-Value of 0.50; and

(ii)

within a roof where the reflective insulation is laid directly under the roof, those in Table 2c.

Table 2c Typical thermal properties for reflective surfaces with airspaces in roofs

Emittance of added reflective insulation

Direction of heat flow

R-Value added by a reflective surface

Pitched roof (>10°) with horizontal ceiling

Flat, skillion or pitched roof (≤10°) with horizontal ceiling

Pitched roof with cathedral ceiling

Ventilated roof space

Non- ventilated roof space

15° to not more than 25° pitch

more than 25° to not more than 35° pitch

more than 35° to 45° pitch

0.2 outer

Downwards

1.21

1.12

1.28

0.96

0.86

0.66

0.05 inner

0.2 outer

Upwards

0.59

0.75

0.68

0.72

0.74

0.77

0.05 inner

0.9 outer

Downwards

1.01

0.92

1.06

0.74

0.64

0.44

0.05 inner

0.9 outer

Upward

0.40

0.55

0.49

0.51

0.52

0.53

0.05 inner
(d)

A ventilated roof space is a roof space with—

(i)

gable vents, ridge vents, eave vents, roof vents or the like that—

(A)

are evenly distributed to allow an unobstructed flow of air; and

(B)

are located to ensure, where practicable, there are no dead airspaces; and

(C)

have an aggregate fixed open area of not less than 1.0% of the ceiling area; or

(ii)

not less than 2 wind-driven roof ventilators having an aggregate opening area of not less than 0.14 m2 in conjunction with gable vents, ridge vents, eave vents, roof vents or the like having an aggregate fixed open area of not less than 0.2% of the ceiling area; or

(iii)

a tiled roof without sarking-type material at roof level.

Intent

To detail the relevant properties attributed to common construction materials, air films and airspaces, and reflective surfaces.

The values provided in Table 2a are material density values and thermal conductivity (k) values for materials. Tables 2b and 2c list the R-Values of airspaces and films and expected added R-Values provided by a reflective surface. All except the material density can be used in determining the Total R-Value of a roof, wall or floor system.

The term surface density suggests mass per unit volume but in this context is the mass of the full thickness of 1 square metre of wall surface area.

Clause 2(d) explains the meaning of a ventilated roof space.