Cladding - Structural Forms.

In addition to visual and aesthetic requirements, one of the fundamental roles  of the cladding system is to provide not only the weatherproofing for the building but also the insulation requirements suited to both the building  and the environment.

Cladding profiles are roll-formed and produced in volume, so giving excellent economy, and this means that, apart from an extremely rare occasion, the chosen profile will be from a manufacturer’s published range.The loads that the profile can withstand are determined by the manufacturer and published in his brochure.Until
recently they would have been determined by test, but calculation methods have been developed which are satisfactory for trapezoidal shapes. These give slightly conservative answers but, in general, profiles that are walkable will have capacities in excess of those required. Sheeting can be erected satisfactorily without the need to walk indiscriminately over the whole area. The crowns at mid-span are the most susceptible to foot traffic but these positions can easily be avoided, even if crawl boards are not used.

In double-skin construction it is normal to assume all loads are taken on the outer sheet, and the inner liner merely has to be erectable and stiff enough to prevent noticeable sag once installed.

The specifier, therefore, has to select the profile appropriate to  the design requirement and check the strength and deflection criteria against the manufacturer’s published load tables. Care must also be taken to ensure the fasteners are adequate.

As mentioned briefly previously above, the use of higher specification cladding systems, by default, reduces the emissions of greenhouse gases; the pressing need to reduce such gases is an almost internationally accepted goal.

In recognition of this, the UK pledged, at the Kyoto summit, to reduce greenhouse gases by some 12% by 2010. In addition, the government’s own manifesto included a commitment to reduce CO2 emissions by 20%.

Consequently, in order to achieve this goal, significant changes have been pro- posed to the Building Regulations (England & Wales) – Approved Document Part L for Non-Domestic Buildings, since it was recognized that a significant proportion of the UK’s emission of greenhouse gases arises from energy used in the day-to-day use of building structures.

The significant changes are outlined below:

• Increase thermal insulation standards by use of improved U values
• Introduce an air leakage index
• Introduce as-built inspections
• Introduce whole building design by integrating the building fabric with heating, cooling and air-conditioning requirements
• Introduce the monitoring of material alterations to an existing structure
• Introduce operating log books and energy consumption meters.

1 Improved U values   Approved Document Part L embraces significant changes to the insulation requirements of the building fabric that will impact on the use of fuel and power. The intended reduction in...

2 Air leakage index   It will be mandatory for buildings to be designed and constructed so that an air leakage index will not be exceeded. This index will be set at a  specific value of volume of air leakage per hour per square...

3 ‘As-built’ inspections   In order that the revised insulation standards are adhered to, it will be necessary to ensure that the provision of insulation within the fabric itself does not exhibit zones...

4 Whole building design   As the title of this subsection suggests, the building should be designed taking due account of how the constituent parts interact with each other. To this end, insulation...

5 Material alterations   Material alteration is intended to cover substantial works to existing buildings that were designed and constructed prior to the changes in Approved  Document Part L...

6 Building log books and energy meters   The building owner will initially be provided with details of all the products that constitute the building, including a forecast of annual energy consumption based  on...

7 Cladding systems   A variety of systems is available to suit environmental and financial constraints.The most common are listed below. Single-skin trapezoidal roofingThis was widely used in...

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