Laying and Fixing Procedures

Laying of Single Skin and Built Up Insulation Systems

The pitch of the roof should be chosen to maintain efficient rain water drainage. Care should be taken to avoid reducing the pitch to produce minimal drainage conditions which could produce ‘ponding’ or, with driving winds, negative drainage.

Where corrugated profiles are used we recommend the roof pitch should not be less than 10 degrees. Using trapezoidal profiles the pitch can be reduced to 6 degrees. Where shallower pitches are envisaged we recommend that technical advice should be taken at the design stage to ensure that all necessary precautions are taken.

Sheet laying procedure

Cutting

The following points should be observed if any profiled sheets have to be cut on site:

  • Burning through with oxyacetylene (or similar) torches is completely unacceptable. It is almost impossible to cut a clean line and the coating is invariably damaged.
  • Cutting with an abrasive disc is not recommended. It is not easy to get a clean line and the coating can be damaged by the heat generated or by a carelessly held disc.
  • Using a sheet nibbler is highly recommended. This gives a very clean edge and causes no damage. It is also easy to cut complex-shaped holes through the sheet.
  • Use of a reciprocating saw for on-site cutting of composite panels is recommended.

It is also necessary to remove all swarf and other debris as roof erection proceeds since they can cause discolouration and corrosion.

Fixings

Apart from just attaching the sheets to the framework and supporting their self weight, the fixings have to withstand  considerable wind pressures and be weather-proof and durable. It is also important that the fixings are visually compatible with the cladding.

Probably the most popular fixings are the N.W.S.S. range of self-tapping / self-drilling screws. They are neat, strong and applied completely from the outer face of the cladding. They are available with colour coded, moulded heads or separate snap-on plastic caps in colours to match the cladding and incorporate a sealing washer under the head. A crown fixing with saddle washers is also possible.

Steel Sheet Fixings
Steel Sheet Fixings

End Laps, Use of Sealants and Side Lap Fasteners

   ROOF PITCH (Degrees)  EXPOSURE
 SEVERE MODERATE
 End Lap Side Lap
Fast Centres		  End Lap  Side Lap
Fast Centres
 Over 15  150 300 150 450
 10 – 15  150 300 150 450
 6 – 10  200 300 200 450
WALLS 150 As Necessary 100 450
NOTE: Side and End Lap Sealant on roof pitches below 15°, walls with severe exposure Side Lap Sealant required.