Dual Roofing System


In today’s environment of conservation, the reduction of energy consumption, the importance of environmentally friendly, cost effective products is ever increasingly recognised.

The savings and benefits in supplying natural daylight in the workplace and in recreational facilities can be maximised at a fraction of the cost of dual glazing with Zammit Roofing’s Dual Roof System. This system provides good, evenly diffused natural light, eliminates condensation, and reduces transmitted heat.

The Zammit Roofing Dual Roof System utilises the fundamental principles of double glazing in an innovative manner suited to the Australian climate; simplicity and ease of installation set it apart from complicated and costly double glazed skylights originally designed for overseas countries with cooler climates. Dual Roof is not unique in theory, in practice it provides long term cost savings with valuable benefits both to users and the environment.

Sports stadiums and multi-purpose halls where condensation quickly forms on the skylight panels due to internal warm moist air meeting with the cold skylight surface, have been quick to embrace the Zammit Roofing Dual Roof Anti Condensation Skylighting System to solve the problem.


Condensation will form on any surface having a temperature below the dew point temperature of the air under consideration. The relative humidity (amount of water vapour in the atmosphere) within a sports stadium can change rapidly with large numbers of occupants. At normal ventilation rates, a body of air will absorb moisture from the occupants at the rate of 50 – 60g/person/hour. This may result in the moisture content exceeding that of the external air by about 2g/kg of dry air. Therefore the risk of condensation forming on cooler surfaces increases dramatically.

Independent engineer’s testing has established that the Zammit Roofing Dual Roof Anti Condensation System displays superior thermal properties to conventional single sheet skylighting systems. Effectively this means better insulation.


  • Eliminates condensation.
  • Great energy savings.
  • Cost Effective.
  • Can Be combined with Webglas GC or ClearSlide which allows for longer sheet lengths.
  • Effective thermal insulation.

Available Profiles


Most current and superseded roofing profiles can be used with the Dual Roof System. Please contact your nearest Zammit Roofing Office for details.


Zammit Roofing premium Industrial grade “Dual Roof” fibreglass is manufactured in strict accordance with AS/NZS 4256 parts 1 & 3: 1994. Standards Licence No.986.

N.B.”Dual Roof” incorporates gel coat surface protection as used for “Wonderglas GC” premium grade sheeting. The highest quality materials available and the very latest resin technology are used in the manufacturing process.

Spanning Capacity

Industrial Standard and Premium Grades
Series 2400 (1.4mm) 3050 (1.75mm) 3660 (2.1mm) 4270 (2.45mm)
5 Rib 1500mm 1700mm 2000mm 2300mm

The above spans are recommended for wind loads up to 1 kPa.

For information regarding recommended spans in high wind and cyclonic regions please contact your local Zammit Roofing office.

Sheeting Grades

Series Weight (Kg/m2)
2400 2.4
3050 3.05
3660 3.66
4270 4.27
4880 4.88

Important: Heavier grades give the specifier the option to use Zammit Roofing sheeting in cyclonic zones, or match the span of the nominated steel roofing material (see ‘Spanning Capacity’).

Fixing Allocation

Installation information

The following table gives the recommended rib allocation for Dual Roof Spacers.


Screw length includes Weatherlok washers. All screws are 12#, Type 17 fixing to timber or Metal Tek fixing to steel. The use of Clearfix Industrial or Fibreglass Teks both with 32mm Weatherlok washers are recommended. These screws cut an oversize expansion hole as they drill.

Profile Fixing Rib Timber Screw Metal Screw
5-Rib Every rib 85mm 75mm
ClearSlide Every rib 45mm
Corrugated Ribs 2, 5, 8, 11 75mm 65mm
Decking 700 Every rib 95mm 85mm
Kliplok 700 Every rib 100mm 90mm
Longspan Ribs 2, 4, 5, 7 85mm 75mm
Megaclad Every rib 85mm 75mm
Spandek 700 Ribs 2, 4, 6, 8 80mm 70mm

Other profiles can be used – please consult an Zammit Roofing office for further information.


The following installation procedures are recommended by the product manufacturers — Zammit Roofing Australia Pty Ltd.

These recommendations closely follow the Australian Standard: Design and installation of Sheet Roof and Wall Cladding, Part 3: Plastic. AS 1562.3-2006

Where wire safety mesh is incorporated under the fibreglass sheeting and over a purlin, a protective purlin strip must be installed to prevent fracturing. Zammit Roofing manufacture a 65 mm wide self adhesive fibreglass strip which, when viewed from below is not visible.

In roofing applications, fixings shall be fitted through the crest of any profile. Oversize screw holes from 10 mm up to 15 mm must be drilled at all points of fixing. Only 32 mm ‘Weatherlok’ seals should be used. These seals are large enough to cover the oversize hole and are sufficiently flexible to contour to any corrugation (or rib) when medium pressure is applied. Medium pressure means that the ‘Weatherlok’ seal is contoured to the shape of the corrugation (or rib), but rib or corrugation must retain its shape without any sign of buckling.

Contractors must make sure that the fixing is located in the centre of the oversize hole, or the benefit of the larger hole is lost. To ensure accuracy, Zammit Roofing recommends the following:

  1. Fasten fibreglass sheeting in the same manner as metal.
  2. When Job is completed, remove fasteners on fibreglass section.
  3. Using the existing screw hole as a guide, drill an oversize hole, swap neoprene washer (used in step 1) with ‘Weatherlok’ seal and reinstall the fastener.

Zammit Roofing design and recommend the fibreglass sheets to be installed on top of metal roofing on both sides. The sheet rib can still go over and under when fibreglass sheets are installed side by side.

Where fibreglass sheets are end lapped including those with dissimilar materials, two lines of Lapseal Tape or a flexible sealant shall be placed across the full width of sheet. Each strip is placed approximately 150 mm apart with one line located 25 mm from the end of the fibreglass sheet. Zammit Roofing recommends the use of 25 mm Lapseal Tape as silicone sealants can harden and cure due to exposure to daylight. The over-lapping sheets then become locked together as one sheet, effectively stopping movement between the sheets, and possibly causing buckling. With decking profiles install Lapseal Tape in the tray only or use a flexible sealant.

Fibreglass sheeting is not easily reshaped after manufacture, and will require special weather seals to be provided at all flashing and capping points. Typically, a foam closure strip matching the profile of the fibreglass sheet should be bonded to the pans or valleys with a flexible weatherproof sealant. Ideally it should be fitted at least 100 mm behind the turn down of the flashing.

Zammit Roofing fibreglass sheeting (with the exception of Webglas GC) is a non-trafficable material. Sheets should be handled with care to avoid damage to the surface coating which is either Melinex film or Gel Coat according to the grade. Guarantees will not apply to sheeting that has been damaged in handling, or mechanical damage due to foot traffic.

Furthermore, unless the above instructions are strictly adhered to, Zammit Roofing Australia Pty Ltd cannot accept any responsibility for consequent leakage problems, caused by sheets buckling or “ocean waving”.