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Impact resistance
The test for fragility of roofing assemblies’ ACR (M) 001: 2005 consists of a 45kg bag being dropped from a height of 1200mm onto a fixed sample of roofing. It is intended to provide information about whether the roof can support the instantaneous loads imposed on it by persons stumbling or falling onto it. A roof is classified as fragile if the bag passes through the roof assembly.
If the bag is retained on the test assembly and no other drop tests are carried out, the assembly shall be classified as Class C non-fragile assembly. AS6 sheets meet this requirement.
Sound insulation
When tested in the critical frequency range of 100-3150Hz, the profiled sheeting achieves the following mean airborne sound reduction:
AS6 & Farmscape single skin 26 decibels
Breaking strength
The minimum breaking strength for fibre cement sheets is defined under BS EN 494.
AS3:
The minimum lengthways breaking load is 1400N/m whilst the minimum transverse bending moment at rupture is 40Nm/m.
AS6 & Farmscape:
The minimum against grain breaking load (purlin to purlin) for is 4250N/m. The minimum with grain bending moment at rupture (ridge to ridge) for is 55Nm/m.
Density
Minimum density for AS3 is 1400kg/m³ in accordance with BS EN 494.
Installed weight
The approximate installed dry weight of single and double skin profiled sheeting with fixings and the required side and end lap is as follows:
AS3 single skin approx. 14.5kg/m². This includes fixings, 150mm end lap and 131.2mm side lap.
AS6 & Farmscape single skin 17.0kg/m²
Fire
External fire exposure: the sheets have a P60 (external SAA) rating to BS 476: Part 3: 1975, and can be classified Class 0 in accordance with the Building Regulations.
Water tightness
Fibre cement complies with BS EN 494: Clause 5.3.4.
Water absorption
Average water absorption +25% of dry weight after complete immersion for 24 hours.
Moisture content
When new, fibre cement sheeting has a relatively high moisture content. If humid conditions prevail, damp patches (without formulation of droplets) may appear on the underside of the sheets. This phenomenon is in no way detrimental to performance, and will disappear within 12 months, in the course of natural exposure.
Condensation
In the absence of proper ventilation, water droplets may condense on the underside of the sheeting, especially on cold, clear nights when the roof radiates heat to the sky. Whilst not harmful, the effect is undesirable and adequate ventilation should be provided.
Effects of chemicals
Over the years chemical and industrial atmospheric pollution will cause a slight softening of the surface of natural finish fibre cement sheets. The acrylic paint finish provides added protection against many acids, alkalis and solvents normally found in the atmosphere.
The polyester/alkyd finish to the metal liner tray is corrosion resistant in normal industrial atmospheres. However, in more aggressive environments, a fibre cement liner tray is recommended. Where fibre cement is to be used in particularly aggressive atmospheres, with higher than normal concentrations of acids, alkalis, fats or salts, please contact the Technical Department for advice.
Biological
All the profiled sheets are vermin and rot-resistant, but lichen may grow on the outer surface. For advice on removal, please contact the Technical Department.
Effects of low and high temperature
The profiled sheeting is designed to be minimally affected by frost or climatic temperature changes.
For buildings in which higher than normal temperatures occur, or in areas which are expected to be subjected to sudden changes in temperature, special considerations may be necessary. (Consult the Technical Department for recommendations).
Thermal and other movements
The amount of movement is negligible, but it is necessary to provide movement joints in association with the structural framework. The co-efficient of linear expansion for profiled sheeting is 8 x 10-6m/mK.
Thermal conductivity
The profiled sheeting has only low thermal conductivity when compared with other sheet roofing products. This serves to reduce heat build up in summer and heat loss in winter.
Thermal conductivity (k) = 0.48W/mK.
Thermal transmittance (U value)
When constructed as detailed in this compendium, all insulated systems will exceed a U value of 0.25W/m²K. (This is the standard U-value required by Building Regulations Approved Document L2 for roofs with integral insulation on buildings other than dwellings.)
Durability
The profiled sheeting may be regarded as having a normal life of at least 50 years, but the durability of the fixing accessories should be taken into account.
Atmospheric pollution is not normally sufficiently concentrated to be harmful. Measures should be taken to prevent corrosion of the fixing accessories, e.g. by the use of plastic washers and caps.
The profiled sheeting is resistant to most forms of atmospheric attack but with age becomes less elastic and a small deflection will be experienced, which may make it less resistant to impact. Its transverse strength, however, is maintained. |
