External walls– Twin skin metal cladding
  
Built-up cladding systems are assembled on site.
 
The inner and outer metal sheets are separated by zed sections with a thermal breakstrip or by rail and bracket system. The cavity between the two cladding sheets is filled with Rockwool Cladding Roll to provide maximum thermal performance.

Cladding Roll is located against the inner metal lining panel and between the spacers, with all insulation edges tightly butted. With rail and bracket spacer system, the rail holds the insulationtightly to the internal sheets.

The inner cladding sheets should be fixed as soon as possible after the insulation to avoid exposure to weather.
 
The building fabric should be constructed so that there are no significant thermal bridges or gaps within the insulation layers and various elements of the buildings fabric. Particular importance are the joints between elements and at the edges of elements, such as those around window and door openings.

Further guidance is given in the MCRMA Technical Note 14, ‘Guidance for the design of metal cladding and roofing to comply with Approved Document L  BRE ‘Limiting thermal bridging and air leakage.
 
Insulation thickness to achieve U value requirements, may vary depending on the cladding system used. Confirmation of U values should be obtained directly from the individual cladding system manufacturer.