Thermal insulation and mechanical fixing
THERMAL INSULATION: products having a thermal
conductivity coefficient (lambda ?) < 0,1 Kcal/mh °C are defined as
insulation materials. Further to the thermal characteristics, insulation
materials must be resistant to ageing, pressure and fire and must show good
dimensional stability. The types available are either of organic and inorganic
nature. The inorganic ones have higher stability, but are less effective as
insulation than the organic ones. (see table). The right thickness is calculated
according to the thermal conditions needed to be maintained in the enclosed
rooms or spaces and to the characteristics of the insulation itself. The
insulation material is normally used in the form of prefabricated panels, mainly
to allow ease of application of the layers, using oxidised bitumen as an
adhesive. Laying should be made placing the panels in staggered rows; when the
thickness exceeds 4 cm, it is advisable to lay the insulation in double layer,
taking care to position the upper layer offset to the first one. The two layers
must be bonded using hot bitumen. When the conditions require a bonding strength
greater than the one offered by the oxidised bitumen, mechanical fastening can
be used.
MECHANICAL FIXING is necessary in situations where the use of partial bonding alone cannot guarantee the safety of the application. Mechanical fasteners can be either nails or straps of stainless metal. The layout and distribution of fasteners must be carried out uniformly across the overlap areas of the sheets. The number of nails depends on the type of substrate, the type of membrane and on environmental conditions: it may vary from a minimum of 2 to a maximum of 4 per square meter in case of traditional substrates; it must be increased in case of corrugated metal roofing. It is important to remind that nails and metal straps must always be covered with a further layer or strip of membrane which will be fully bonded to the lower one.
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