Polycarbonate Roof Sheeting Technical Info

Polycarbonate is one of the newer plastics to be used in the construction industry around the world. by Hough Group has been closely involved in the distribution and manufacture of profiled Polycarbonate roof sheets during the past 10 years in South Africa.

The highest grade POLYCARBONATE polymer available from the leading manufacturers in the world, is used by Hough Group. Modern co-extrusion technology is used in the manufacture of Polycarbonate Roof Sheets, ensuring a high product quality and allowing for any transportable length of sheet to be made.

A layer of highly UV stabilised POLYCARBONATE is co-extruded on the weathering side of all Hough Group Polycarbonate Roof Sheets. This layer will not crack or delaminate, and ensures years of clear performance in the harsh South African climate.

A range of colours is manufactured with the standards being clear, white (opal 50) and bronze. Silver (Heat Stop), blue and green are also available subject to order quantity.

All the generally used profile shapes in South Africa, to match those of other non-translucent roofing and cladding sheets, are manufactured by Hough Group in any transportable length.

New or additional roofing profiles can be manufactured by Hough Group, but it must be noted that the time and cost incurred is considerable.

Nominal Thickness

The internationally accepted unit of measurement, as used by Hough Group, for polycarbonate sheeting is the nominal thickness of the sheet.

This nominal thickness should be established by representative measurements (by vernier or micrometer) at various points across the full width of the sheet.

Owing to the inherent variances of tolerance which are experienced when profiling a thermoplastic extrusion, it will be found that the actual thickness will vary slightly from one point to another on the sheet.

Hough Group’s polycarbonate manufactures two nominal thickness specifications:

• 1.25 mm Nominal Thickness
• 1.00 mm Nominal Thickness

A layer of UV protection PC is co-extruded on the weathering side of all polycarbonate roof sheets.

1.25 mm Nominal Thickness is deemed to be the Standard Weight Specification for all industrial installations. This specification will meet the rigorous conditions found in an industrial environment – particularly that of deflection under load (positive and negative), handling on site, spanning capabilities and general robustness of profile.

1.00 mm Nominal Thickness is manufactured as a light weight PC sheet to be used mainly in those applications where exposure to wind is less, spanning requirements are less than normal, and generally lighter domestic-type applications.

The 1.00 mm nominal thickness products are restricted to certain profiles only. Refer to the profile list for details.

Light and Solar Energy Transmission

Different applications using translucent polycarbonate sheeting call for varying levels of light transmission. With different colours these levels change.

Not only does the natural (or visible) light level vary, but the amount of solar energy (heat) also varies.

Polycarbonate is a thermoplastic with a high degree of clarity. Therefore the direct transmission of solar energy is considerably higher than that of a diffused panel. Consideration for the appropriate colour should therefore be carefully weighed up.

The diagram below depicts the approximate transmission of the various wavelengths of the light spectrum for a clear PC sheet.

More than 70 % of the heating effect of the sun is carried between 350 and 800 nanometres (generally, the visible light spectrum) and we can see that these wavelengths are generously transmitted through a clear polycarbonate sheet – more than 85 %.

Why does heat build up in a room?

As illustrated, a high percentage of the visible short wave radiation has been transmitted through a polycarbonate clear sheet.

This radiation is absorbed by surfaces inside the room, and these surfaces become heat radiators. The heat emitted from these “radiators” is long wave radiation which is not so readily transmitted out of the room through the polycarbonate sheet. The result is that the trapped heat builds up in the room. This is also known as the “greenhouse effect”.

An effective method of combating heat build-up in a room is to have good through ventilation. This can also be improved by selecting the most appropriate polycarbonate roof sheet.

The table below shows the various percentages of transmitted light and solar energy, and also that amount of light and solar energy which is reflected and absorbed by the different coloured polycarbonate sheets.

Heat Stop

Heat Stop is an innovative development in polycarbonate translucent roof sheeting. This product effectively eliminates 60% of the radiated heat of the sun, resulting in a cool shaded environment.

Heat Stop is a polycarbonate profiled extrusion, manufactured in South Africa, which has a co-extruded layer of UV stabilised surface protection on the weather side. Microscopic reflective particles are incorporated in the core material which create the silver colour and the reflective qualities of the product.

If an application for a translucent roof sheet or skylight requires a minimum heat build-up under the natural light panel – Hough Group offers a polycarbonate solution. It should be remembered, however, that a lower level of light transmission is achieved with Heat Stop. The appropriate surface area of translucent roof sheets must therefore be used to achieve the required interior light levels.

Heat Stop offers the following properties:

• All the excellent physical properties of polycarbonate.
• UV surface protection on weather side.
• Exciting new colour – silver.
• 20 % light transmission.
• It is available in 1 mm and 1.25 mm profiles:
  – IBR
  – Corrugated
  – Nurib
  – Grecca
• Price – the same as the normal tint price.

ColorQUEST Colorimeter Test Results

Hough Group’s Polycarbonate Translucent Roof Sheets

Notes:

• Shading coefficients are used for comparing solar heat transmission properties of different glazing materials to that of clear float glass 3 mm to 4 mm thick, the glass being given a value of 1. To be used for comparative purposes only.

• For practical purposes, our PC sheets do not transmit harmful UV rays.

ColorQUEST Colorimeter Test results

Notes:

• Shading coefficients are used for comparing solar heat transmission properties of different glazing materials to that of clear float glass 3 mm to 4 mm thick, the glass being given a value of 1. To be used for comparative purposes only.

• For practical purposes our Heat Stop does not transmit harmful UV rays.

Weatherability

Polycarbonate roof sheeting is manufactured using modern co-extrusion technology to create a highly UV stabilised weathering surface on the sheet.

This UV layer will not crack or delaminate, and ensures years of trouble-free performance in the harsh South African weather conditions.

As with almost all plastics, UV attack from the sun will, over a period of time, adversely affect polycarbonate roof sheets. This process is called photodegradation.

What occurs during this process is the following:

The aggressive short wavelength UV rays are absorbed into the polymer. They “excite” the chemical molecular bonds, causing them to separate, resulting in a slight yellowing and a reduction of physical properties such as tensile strength and impact resistance.

This process is significantly reduced in the polycarbonate sheet because of the excellent protection offered by the UV co-extruded layer which incorporates UV stabilisers and UV absorbers. Over a prolonged period, a slight yellowing or hazing will be detected in a polycarbonate sheet.

With outside exposure in normal conditions in South Africa, it is expected that a clear polycarbonate sheet with UV protection will not increase in yellowness more than 9 yellowness index units within ten years from date of sale.

The determination of the yellowing index will be made on samples subjected to pre-test cleaning and conditioning according to our test procedures, and the yellowness index shall be determined according to ASTM D-1925-70 as measured with Hunter Colour-Quest colour Spectrophotometer.

A Polycarbonate sheet will retain virtually all its physical properties, and remain structurally sound over this period of time, under normal conditions.

Corrosion and Medical Resistance

Our Polycarbonate sheets will resist chemical attack and corrosion in most industrial and marine environments.

Tests have found the following:

• Our Polycarbonate sheets is highly resistant to corrosion and high concentrations of mineral acids, many organic acids, oxidising and reducing agents, neutral and acid salt solutions, many oils and fats, saturated aliphatic and cyclo-aliphatic hydrocarbons and alcohols.
• Our Polycarbonate sheets are not resistant to strong acids and alkalis, methyl alcohol, aromatic hydrocarbons and chlorinated hydrocarbons nor to lengthy immersion in hot water.
• Our Polycarbonate sheets must not be used in conjunction with plasticised PVC. This will result in stress corrosion cracking and cause damage to the Hough Group’s Polycarbonate PC sheet.
• Hough Group’s Polycarbonate sheets are ideal for coastal applications.

The resistance to chemical attack varies with a wide range of chemicals, detergents, polishes and cleaning agents. This resistance chart refers to certain chemicals and the reaction of PC under certain conditions.

……………..……………..……………..+ resistant …………….. – non-resistant

Physical and Mechanical Properties

Note that the very high impact resistance of Hough Group’s Polycarbonate sheets makes them virtually unbreakable, and therefore makes them particularly suitable for use in high risk areas where damage from hail, high wind loads or vandalism is likely.

Notes:

• All sheets have a co-extruded UV protection layer on weather side.
• All dimensions are nominal.
• Other profiles available subject to order quantity.

Download Polycarbonate Profiles Guide