7S7X0 – Materialization of facades and roofs
Lecture 1 Physical properties of materials in buildings
Physical properties
Density
𝑚𝑚 [𝑘𝑘𝑘𝑘]
⋅ Bulk density [1] 𝜌𝜌 =
𝑉𝑉 [𝑚𝑚3 ]
⋅ Specific density Density of material itself (i.e. without pores) (apparent density)
Really dense materials like Aluminium have a Buk and Specific density which are the same.
Aerogel can be made with enormous amounts of air, resulting in a very low Bulk density.
Porosity
𝜌𝜌 𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏
Porosity calculation [2] 𝑃𝑃 = 1 − ∗ 100 Density known
𝜌𝜌 𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑐𝑐
𝑉𝑉 𝜌𝜌
[3] 𝑃𝑃 = 1 − ∗ 100 Volume known
𝑉𝑉 𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡
Open pores and closed pores.
A. Porous, non-permeable
B. Porous, permeable
C. High porosity, low permeability
D. Low porosity, high permeability
Air cavity Interrupting water (leakage) transfer into inner leaf
Allowing two-sided drying of applied outer material
Ventilation of transferred indoor vapor
Effecting Pressure Equalization
Water transfer
2 Water transfer mechanisms Suction transfer (Water affinity of the applied materials)
Driving forces (Gravity force, wind pushing/pulling)
H2O has a negative end towards the Oxygen. This results in an attraction between the dipole of water and
the polarity of clay material. All ionic bond materials attract water. Hydrophilic and hydrophobic materials
also work with these bonds (Surface chemistry of the material: OH- and OHx).
Water absorption
Bricks 1-35% water absorption, depending on capillary porosity (=amount of open pores)
Suction rate Approx. 1.5 kg/m2/minute
Vapor diffusion Vapor diffusion is the transport of vapor molecules through permeable materials.
Test: Solutions of salt and water, with a given RH inside a pot, measures the vapor
barrier.
,Moisture and thermal movement – Clay brick
Movement joints have to be applied to cope with moisture and thermal movement. Movement joint per 10-
15 m. In practice: 1 mm/m brickwork
Reversible moisture movement 0.02%
Reversable thermal movement 0.03% * *a = 5-8 * 10-6 / °C
Retrofit movement joints 1. Cracking resulting from expansion
2. Cavity tie installation to restrain brickwork
3. Expanded polyethylene foam filler
4. Priming prior to installing sealant
5. Application of sealant
6. Finished movement joint
Thermal properties
λ ∗𝐴𝐴∗ ∆𝑇𝑇
Thermal conductivity [4] 𝑞𝑞 =
𝑑𝑑
q Heat flow [W]
λ Thermal conductivity [W/m.K]
A Cross sectional area [m2]
∆T Temperature difference [K]
d Thickness [m]
Thermal resistance [5] ∆𝑇𝑇 = 𝑅𝑅 ∗ 𝑄𝑄
∆T Temperature difference [K]
R Heat resistance [K.m2/W]
Q Heat flow density [w/m2]
If an object is made of different materials, its heat resistance = sum of all heat resistances of every material (per unit
of surface).
Monolithics demand no vapour control, as a free flow is allowed, and no condensation will occur.
Examples: Straw bales, aerated concrete blocks (no impermeable layer, let material breathe)
Insulation Aluminium foils reduces heat loss (or gain) through radiation
Closed seams (by tape) reduce heat loss, but (mostly) cannot stop vapour
Sound insulation Effective barrier to airborne sound = ca. 1000 – 3000 Hz
𝐸𝐸
Heat capacity [6] 𝐶𝐶 =
∆𝑇𝑇
C Heat capacity [ J/K]
E Total energy [J]
∆T Temperature difference [K]
Passive buildings South oriented apertures
Increase of specific heat/thermal mass of structures
, Water for high thermal mass (possibility for cooling) (PCM)
Good insulation
New insulation materials
Emergent (rational) Ecological (natural)
⋅ Cellular materials (manufactured on nano scale) ⋅ Natural fibre materials, like hemp, sisal...
⋅ Improved light weighted, foamed plastics ⋅ Reed and straw based materials...
⋅ Foamed gypsum, foamed aluminium, foamed ⋅ Wood wool, sheep wool...
clay, foamed concretes...
𝑘𝑘
Thermal diffusivity [7] 𝛼𝛼 =
𝜌𝜌 ∗ 𝐶𝐶𝐶𝐶
𝛼𝛼 The rate of transfer of heat of a material from the hot end to the cold end [m2/s]
k Thermal conductivity [W/m.K] (λ in Eq. 4)
𝜌𝜌 Density [kg/m3]
Cp Heat capacity [J/kg.K]
Material with a high thermal conductivity and low heat capacity, will hence have a large thermal diffusivity,
like steel.
𝑀𝑀𝑀𝑀
Emissivity [8] ∈=
𝑀𝑀𝑀𝑀 0
∈ Capacity of a surface to emit energy as thermal radiation (e.g. visible light)
Me Radiant exitance of a surface
Me0 Radiant exitance of a black body at the same temperature as that surface
Gloss/shine is comprised in the property of Emissivity
Timber properties
Physics of timber Organic and hygroscopic material
Not homogeneous
Anisotropy (property values reflect orientation differences)
Affinity to water (-OH bonds)
Two kinds of open capillary porosity: Cell walls and Lumens
𝑤𝑤𝑤𝑤𝑤𝑤𝑤𝑤ℎ𝑡𝑡 𝑜𝑜𝑜𝑜 𝑤𝑤𝑤𝑤𝑤𝑤 𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠−𝑑𝑑𝑑𝑑𝑑𝑑 𝑤𝑤𝑤𝑤𝑤𝑤𝑤𝑤ℎ𝑡𝑡 𝑜𝑜𝑜𝑜 𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠
Moisture content [9] 𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀 𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 = ∗ 100
𝑑𝑑𝑑𝑑𝑑𝑑 𝑤𝑤𝑤𝑤𝑤𝑤𝑤𝑤ℎ𝑡𝑡 𝑜𝑜𝑜𝑜 𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠
Biology of timber
a. Open cells, stretched in longitudinal direction (rays)
b. Hollow space in cell, lumen
c. Vessel: sap transfer in deciduous wood
Timber grows from pith sideways; heartwood and sapwood are used for a.
construction. Bast and bark barely (only for cork).
b. c.
c.
, Cell wall of timber consists of multiple layers. 1) Cellulose grants strength to the timber. 2) Lignin is the
cement between all cellulose molecules (hydrophobic material). 3) Hemicellulose is distributed around
rays.
Cellulose alongside z-axis = stiff material.
Cellulose alongside another axis = elastic material
Moisture saturation Saturation of lumens (last wet, 1st dry)
Saturation of fibres (1st wet, last dry)
Water content in timber 20% - Timber rots
30-35% - Fibre saturation
Shrinkage of timber Axial/longitudinal oriented cells resist shrinkage best
Radial oriented next best, but shrinkage is higher
Tangential oriented are worst in shrinkage
Heat will influence the expansion , but when it heats up, natural timber will dry automatically. Heat expansion
will be compensated by hygroscopic shrinkage.
Thermal conductivity 0.14 W/m.K (No thermal bridges)
Because fibres are saturated first, no air is removed from the lumens and the thermal property of the
wood/material is barely changed.
Timber is not waterproof, unless very thick and continuous.
