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:

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.

ColorQUEST Colorimeter Test Results

Hough Group's Polycarbonate Translucent Roof Sheets

VISIBLE SPECTRUM (380 nm - 700 nm)            
% Light Transmission 90 65 40 50 40 25
% Light Reflectance 13 10 10 42 8 74
SOLAR ENERGY (350 nm - 2100 nm)            
% Rejected 13 26 41 41 40 67
% Direct Transmission 87 68 47 57 47 31
% Direct Reflectance 11 8 8 34 7 63
% Absorption 3 24 44 9 46 7
% Total Transmission 88 74 59 59 60 33
SHADING COEFFICIENT 1.00 0.86 0.68 0.68 0.69 0.37


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.

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:

ColorQUEST Colorimeter Test results

VISIBLE SPECTRUM (380 nm - 700 nm)  
% Light Transmission 22
% Light Reflectance 32
SOLAR ENERGY (350 nm - 2100 nm)  
% Rejected 60
% Direct Transmission 27
% Direct Reflectance 27
% Absorption 46
% Total Transmission 40


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.


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:

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

6 DAYS / 23 °C
+ resistant - non-resistant
Acetic acid, 10 % in water
Hydrochloric acid, 10 % in water
Sulphuric acid, 10 % in water
Nitric acid, 10 % in water
Phosphoric acid, 1 % in water
Citric acid, 10 % in water
Sodium carbonate (soda), 10 % in water
Sodium chloride, saturated / aqueous solution
Sodium nitrate, 10 % in water
Ammonium nitrate, 10 % in water / neutral
Iron (III) chloride, saturated / aqueous solution
Potassium hydroxide 1 % in water
Sodium hydroxide (caustic soda), 1 % in water
Ammonia, 0.1 % in water
Benzine (free from aromatic compounds)
Butyl acetate
Dibutyl phthalate
Diethyl ether
Dioctyl phthalate
Ethanol (pure)
Ethylene glycol, 1:1 with water
Ethylene chloride
Ethyl acetate
Isooctane (2.2.4-trimethyl pentane), pure
Isopropanol (pure)
Methylene chloride
Methyl ethyl ketone
Ozone, 1 % in air
Paraffin, paraffin oil, (Vaseline), pure / free from aromatic compounds +
Perhydrol (hydrogen dioxide), 30 % in water
- (30°C)
Silicone oil
Carbon tetrachloride
Tricresyl phosphate
Triethylene glycol
Xylene Swells

Physical and Mechanical Properties

Tensile Strength
72 MPa - ASTM D-638
Flexural Strength
+92 MPa - ASTM D-790
Modulus in Flexure
+2400 MPa - ASTM D-790
Thermal Movement
+Coefficient of linear expansion (clear) 67 X 10-6m/°C. - ASTM D-696
Water Absorption 0.36% by mass after 24 hours at 20°C - ASTM D-570
80 (°Shore D)
Drop Dart Impact Strength
25 Nm (Gardner)
Thermal Conductivity
0.2. W/mK - ASTM C-177
V2 when tested to UL94 ratings. Whilst Hough Group's Polycarbonate sheets do burn, they are self-extinguishing and will not promote fire or assist spread of flame.

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.


Download Polycarbonate Profiles Guide