The packs can be off-loaded directly to the roof, or to a storage area, which should be dry and well away from traffic. Packs may be stacked using suitable wooden bearers and packers. Bearers should be placed above each other.

Handle AS profiles carefully to avoid marking weather sheets or liners. Lift sheets from the pack - do not drag them. Observe site health and safety procedures and the results of manual handling and other assessments.

Preparation
Before fixing any sheets check the squareness and accuracy of the steelwork. Determine the direction of the prevailing wind. Check sheets for damage before fixing.

Installation
There are two methods for installing the AS twin skin
system:

• working across the roof building up the whole system in one pass, or
• laying the liner across the whole roof, then laying the
  insulation and weather sheet. Using 0.7mm AS20/1000 or AS30/1000 as a liner will give a non-fragile roof which makes the rest of the installation process safer, and enables a higher standard of installation.

The following installation guidance presumes the second method.

Roofs - general sequence
Observe the general installation sequence:

1. Lay liner sheet (see laying sequences for sheets below). Seal side laps with 50 x 1mm polyband tape.
2. Assemble and fix support rails and brackets.
3. Lay insulation in a continuous layer.
4. Lay and fix weather sheet (see laying sequences for sheets below).
5. Fix flashings. Use foam filler pieces and butyl sealant to form weather tight junctions.

Roofs - single tier laying sequence
The following sequence applies to weather sheets on single tier roofs:

1. Lay the first sheet with the female edge to the gable, away from the prevailing wind. Use a string line to lay the sheet straight and true. Fix the sheet.
2. Apply butyl sealant along the top of the male crown. The surfaces receiving the sealant must be dry: joints in the sealant must be lapped by 25mm not butted.
3. Lay the second sheet with its female crown over the male crown of the first sheet. Fix the sheet.
4. Stitch the lap with self-drilling fixings.
5. Continue to lay sheets across the roof, checking the alignment of the sheeting and correcting any deviations.

Roofs - double tier laying sequence - liner sheets
On a double tier roof lay the liner sheets in the order shown in figure 40.

1. Lay liner sheet one with the female edge to the gable, away from the prevailing wind. Use a string line to lay the liner sheet straight and true. Fix the liner sheet at every purlin except the top one.
2. Apply a single run of 4mm diameter butyl sealant to the head of liner sheet one (figure 41).
   
3. Lay liner sheet two with its female edge to the gable and the tail lapping the head of sheet one. Fix the liner sheet.
4. Lay liner sheet three with its female crown lapping the male crown of sheet one. Fix the liner sheet at every purlin except the top one.
5. Apply a single run of 4mm diameter butyl sealant to the head of liner sheet three (figure 42).
6. Lay liner sheet four with its female crown lapping the male crown of sheet two and its tail lapping the head of sheet three. Fix the liner sheet.
7. Apply a run of 50mm polyband sealant tape along the side lap of liner sheets one and three and liner sheets two and four (figure 43).
8. Continue to lay the liner along the roof, checking the alignment of the sheeting and correcting any deviations.

Figure 41

Figure 42

Figure 43

Roofs - double tier laying sequence - weather sheets
On a double tier roof lay the weather sheets in the order shown in figure 40.

1. Lay weather sheet one with the female edge to the gable, away from the prevailing wind. Use a string line to lay the sheet straight and true. Fix the sheet at every purlin except the top one.
   
2. Apply two runs of 6 x 5mm butyl sealant to the head of weather sheet one and a run of butyl sealant to the male crown for the length of the lap (figure 44).
3. Lay weather sheet two with its female edge to the gable and the tail lapping the head of sheet one. Fix the sheet.
4. Apply a run of butyl sealant to the male crown of sheets one and two (figure 45).
   
5. Lay weather sheet three with its female crown lapping the male crown of sheet one. Fix the sheet at every purlin except the top one.
   
6. Stitch the side lap with self-drilling fixings.
   
7. Apply two runs of 6 x 5mm butyl sealant to the head of weather sheet three and a run of butyl sealant to the male crown for the length of the lap. Ensure the sealant laps the run on the male crown of sheet two (figure 46).
   
8. Lay weather sheet four with its female crown lapping the male crown of sheet two and its tail lapping the head of sheet three. Fix the profile.
   
9. Stitch the side lap with self-drilling fixings.
   
10. Continue to lay the sheet along the roof, checking the alignment of the sheeting and correcting any deviations.

Figure 44

Figure 45

Figure 46

Walls - general sequence
Observe the general installation sequence:

1. Fit liner sheets with temporary screws (see sequences for liner sheets above).
2. Assemble and fix support rails and brackets.
   
3. Fit insulation in a continuous layer: clip in place until the weather sheets are installed.
   
4. Fit and fix weather sheets (see sequences for weather sheets above).
   
5. Fix flashings. Use foam filler pieces and butyl sealant to form weather tight junctions.
   

Walls - laying sequence
The following sequence applies to weather sheets on walls:

1. Set sheet one upright against the framing at the corner of the building with the female edge to the corner. Make sure the profile is vertical.
   
2. Fix with one fixing in alternate valleys at each rail.
   
3. Apply a run of butyl sealant along the male crown.
   
4. Set sheet two upright with its female edge lapping the male edge of sheet one.
   
5. Fix the sheet.
   
6. Stitch the lap with self-drilling fixings (weather sheets only).
   
7. Continue to lay sheets along the wall, checking the alignment of the cladding and correcting any deviations.

Cutting profiles
Where profiles have to be cut on site:

• Use a powered reciprocating saw or circular saw. Do not use an abrasive wheel.
  
• Support the profile along the line of the cut.
  
• Protect the pre-coated finishes of the profile.
  
• Clean any swarf or debris from the pre-coated finish of the profile immediately.

Completion
When all the sheets have been installed check:

• All fixings are correctly fitted and tightened;
  
• The fixings do not distort the profile;
  
• All fixing caps are fitted;
  
• Minor scratches have been treated;
  
• The surface of the roof is clean and free of any swarf or debris.