Building with earth - Gernot MINKE (1)

Solid loam Lightweight loam
2.31
U-value (W/mK)
0 0.2 0.4 0.6 0.8 1.0 1.2
2.30
Clayey loam (clay = 28%, silt = 34%, sand = 38%)
Silty loam (clay = 12%, silt = 78%, sand = 56%)
Sandy loam (clay = 15%, silt = 29%, sand = 56%)
Straw loam 450 kg/m 3
Straw loam 750 kg/m 3
Straw loam 950 kg/m 3
Straw loam 1250 kg/m 3
Loam with expanded clay 800 kg/m 3
Loam with expanded glass 500 kg/m 3
Loam with expanded glass 750 kg/m 3
Clayey loam plaster
Silty loam plaster
Cowdung-loam-lime-sand plaster (12/4/3/20)
High hydraulic lime plaster
Lime plaster
Lime-casein plaster (10/1)
Lime-linseed oil plaster (20/1)
( ) Volumetric proportion
2.28
specific
weight
(kg/m 3 )
Water content (g/dm 3 )
Vapour diffusion resistance coefficient µ (–)
0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0
on the inside due to the vapour barrier.
In this case, the wall remains damp for a
longer period than it would without a
vapour barrier.
Influence of heat
The common perception that earth is a
very good material for thermal insulation is
unproven. A solid wall of rammed earth
without straw or other light aggregates has
nearly the same insulating effect as a solid
wall of baked bricks. The volume of air
entrained in the pores of a material and its
humidity are relevant for the thermal insulation
effect. The lighter the material, the
higher its thermal insulation, and the greater
its humidity level, the lower its insulating
effect.
The heat flowing through a building element
is defined by the overall heat transfer
coefficient U.
Thermal conductivity
The heat transfer of a material is characterised
by its thermal conductivity k [W/mK].
This indicates the quantity of heat, measured
in watts/m 2 , that penetrates a 1-mthick
wall at a temperature difference of
1°C.
In 2.31, the different k-values according to
DIN 4108-4 (1998), indicated by a 1, are
shown. 2 are measurements of Vanros,
3 and 4 of the BRL.
At the BRL, a lightweight straw loam with
a density of 750 kg/m 3 gave a k-value of
0.20 W/mK, whereas a lightweight expanded
clay loam with a density of 740 kg/m 3
gave a value of 0.18 W/mK.
Specific heat
The amount of heat needed to warm 1 kg
of a material by 1°C is called its “specific
heat,” represented by c. Loam has a specific
heat of 1.0 kJ/kgK which is equal to 0.24
kcal/kg°C.
Thermal capacity
The thermal capacity (heat storage capacity)
S of a material is defined as the product of
specific heat c and the density r:
S = c . ρ[kJ/m 3 K]
The thermal heat capacity defines the
amount of heat needed to warm 1 m 3 of
material by 1°C. The heat storage capacity
Qs for a unit area of wall is S multiplied by
the thickness s of the element:
Q s = c . ρ . c [kJ/m 2 K]
1 Spruce, planed
2 Limba, planed
3 Earth block, clayey
4 Earth block, silty
5 Cement plaster
6 Lime-cement plaster
7 Lime-casein plaster
8 Silty loam plaster
9 Clayey loam plaster
10 Solid brick
11 Clinker brick
12 Porous brick
13 Lime-sand brick
14 Porous concrete
Relative humidity (%)
Heat intake and release
The speed at which a material absorbs or
releases heat is defined by the thermal diffusivity
b which is dependent on the specific
heat c, density r and the conductivity k:
b = √c . ρ . k [kJ/Km 2 h 0.5 ]
The larger the b-value, the quicker the penetration
of heat.
31
Properties of earth