Retrotec USACE - Manual (Page 395)

Appendix K K7
The analysis of these old envelopes mainly shows an important sensitivity
to moisture, and specifi c energy properties for thermal comfort. In new in-
dustrialized buildings, the walls are generally tight. Their foundations and the
materials are dry and protected against humidity.
In old buildings, the walls often have a strong sensitivity to moisture that
mainly comes from the porosity of the materials used and from specifi c build-
ing techniques. Among these techniques is a lack of capillarity barrier at the
base of walls and a lack of rain drainage systems. The moisture fl ow is more
important in old buildings. Indoor and outdoor surface coatings have to be
selected with great care.
The surface coatings present specifi c thermal properties. A surface coat has
to weather outside climatic variations and to protect the support from it. Con-
sequently, it is not a sustainable layer. The coatings consist in mortars of lime,
plaster, or a mixture of lime and plaster. The binders between stones, bricks
and other materials consist in mortars mainly made of clay, plaster, lime or are
only mixed. The coatings show the following characteristics: vapor permeabil-
ity, low water permeability, dimensional stability, capability to distort without
cracking, and good adherence to the support.
The energy properties of old envelopes are diffi cult to evaluate in situ. The
thermal role of each wall depends on its situation, its exposure, its building,
and its size. The design of each old building is complex:
Used local materials have ignored characteristics: the theoretical or sta- ■
tistical values such as thermal conductivity of a wall must be considered
with caution. The conductivity is a variable and depends on local materi-
als and climatic conditions.
Old walls are heterogeneous: several materials may be used in the same
■
wall or fl oor, and so on.
K.4.1 Recommendations
It is necessary to protect the existing moisture barriers in old buildings:
Do not destroy string course, bad molding, or cornice, which are both ■
decorative and protective elements in a façade, as they minimize the
run-off of rainwater over the wall surface.
Do not shunt a cut of capillarity in substructure by adding a coating.
■
It is necessary to preserve different fl ows through the old walls:
Do not add a vapor-tight coating on old masonry. ■
Do apply put air-tight coating (paint, etc.) without installing an effi cient ■
ventilation system on the premises.
In old buildings, the indoor coatings and traditional binders are made of
plaster. These plaster constituents are very sensitive to water and provide sig-
nifi cant regulation of indoor humidity.