Civil Engineering Reference
In-Depth Information
Disadvantages include cost and durability, depending on the quality and vapour-tight-
ness of the metallic film around the panel. VIPs are currently supposed to last for at least
20 years.
Multi-foil reflective insulation systems
Thin multi-foil insulation is composed of reflective layers—generally aluminium foil—
spaced by separating layers like wadding, foam, etc. Its insulating properties are based
on limiting reflection (infrared waves), convection (still air is present in the cavities) and
conduction. These insulating systems work properly when installed in cavities, alone or as
a complement to traditional insulation.
On-site measurements show good insulating performances of these thin compound
systems, making them suitable for refurbishment.
3.1.1.2 Cladding Materials
Recent developments in materials and manufacturing processes are delivering
solutions that have the potential to transform the building from a net burden on the
environment to an active producer of energy and even an environmental filter.
Advancements in nanotechnology and surface science are opening up new pos-
sibilities to improve (or find new) performances of traditional construction materi-
als. The past decade has seen a remarkable revolution in our understanding and
mimicking of natural processes at a chemical, physical and atomic structural level
(Turney
2009
). This is translating to innovative products that make buildings more
interactive with the surrounding environment and easier to maintain.
Progress in self-cleaning surfaces is significant and is based on three alternative
strategies (ibid.):
• easy physical removal of dirt through superhydrophilic ilms of water which
thoroughly wet the surface;
• prevention of residual dirt adhesion with superhydrophobic surfaces where
water droplets readily roll off a surface, collecting dust particles on the way;
• removal of organic or biological surface ilms by photocatalytic oxidation.
The first two strategies are already applied in commercial products such as glass
and coatings (e.g. external render and textiles) that can be cleaned under the sim-
ple effect of rainwater. The photocatalytic effects of TiO
2
coatings have been
applied into a wide range of paints, glazes and cements. Besides being self-clean-
ing (TiO
2
has superhydrophilic properties), nanoparticulate titanium dioxide is a
potent catalyst under near-UV radiation and can thus be used for the control of air-
borne pollutants (Diamanti et al.
2008
). In the future, the use of TiO
2
coatings may
find feasible applications for the control of odour in indoor environments provided
there is sufficient UV light intensity.
Recent laboratory developments in thermocromic VO
2
coatings could form the
basis for thermally responsive materials. Vanadium dioxide undergoes a marked
change in optical transmittance and reflectivity in the IR region, associated with an
insulator-to-metal phase transition: in principle, such coatings would absorb IR radi-
ation until they reach the transition temperature, and then become strongly reflecting.
