Building with Earth: Design and Technology of a Sustainable Architecture

Condensation
In moderate and cold climatic zones, the
water vapour contained in indoor air diffus-
es through the walls to the exterior. If the air
is cooled down in the walls and reaches its
dew point, condensation occurs. This damp-
ness reduces thermal insulation capacity and
may lead to fungus growth. In such cases, it
is important that this humidity be transport-
ed quickly by capillary action to the surface
of the walls, where it can evaporate. There-
fore, materials like loam with a high capillari-
ty are advantageous.
In order to reduce the danger of condensa-
tion in walls, vapour transmission resistance
should be higher inside than outside. On
the other hand, resistance to heat transfer
should be higher outside than inside.
Though the above principles normally suf-
fice to inhibit the formation of condensation
in walls, it is also possible to create a vapour
barrier on the inside by utilising paints or
sheets.
It should be mentioned, however, that
vapour barriers have two important disad-
vantages.

• Vapour barriers are never fully sealed in
  practice, especially at joints, as in walls with

doors, windows and in ceilings. Harmful

condensation can occur in these joints.

• With monolithic wall sections, water pene-
  trates in the rainy season from the outside
  into the wall, and then cannot evaporate

30 Properties of earth

1 Sandy loam 1900 kg/m^3

2 Silty loam 1950 kg/m^3

3 Straw loam 1200 kg/m^3

4 Straw loam 550 kg/m^3

5 Straw loam 450 kg/m^3

6 Mineral loam 750 kg/m^3

7 Mineral loam 600 kg/m^3

Water content (g/m

3 )

1 Solid brick 1850 kg/m^3

2 Hollow brick 1200 kg/m^3

3 Lime-sand brick 1800 kg/m^3

4 Porous concrete (Hebel) 600 kg/m^3

5 Porous concrete (Ytong) 450 kg/m^3

6 Cement concrete M25 2200 kg/m^3

Water content (g/m

3 )

Drying time (d)

1 Straw loam 450

2 Straw loam 850

3 Straw loam 1200

4 Loam with expanded clay 450

5 Loam with expanded clay 550

6 Loam with expanded clay 700

7 Expanded clay particles

8 Expanded glass particles

9 Rye straw

1 Clayey loam

2 Silty loam

3 Sandy loam

4 Granular clayey loam

5 Loam brick

6 Kaolinite, pulverized

7 Bentonite, pulverized

Water Content W (%)

Relative humidity (%)

Water Content W (%)

Relative humidity (%)

2.27

2.29

2.27 Drying period of

loams and other building

materials

2.28 The vapour diffu-

sion coefficient μ of differ-

ent loams and plasters

according to the German

standard DIN 52615, wet

method

2.29 Absorption curves

of solid (left) and light-

weight (right) loams

2.30 Equilibrium mois-

ture content of different

loams and other building

materials

2.31U-values of loam

0.5

0.4

0.3

0.2

0.1

0.0

0.5

0.4

0.3

0.2

0.1

0.0

Drying time (d)