How To Specify Your Rooflight

The range primarily reflects the level of thermal efficiency (U Value) and hence its suitability for particular applications. It is recommended that the appropriate range be selected first, followed by required size, shape and glazing, then options and accessories - so building up the specification. Cross referencing to our Technical Specification Guide will prove helpful in guiding you through the specification process.

Glazing Colour

The various glazing layers in Xtralite rooflights can be supplied in four types or colours: clear, opal, bronze or diffused - with the characteristics described below. For information on the light transmission of different types of polycarbonate rooflight glazing in various configurations, refer to Properties of Glazing Materials and Configurations In addition, all ranges are 'Non-fragile, Class B' rating classified to ACR[M]001:2005 'Test for Non-Fragility of Profiled Sheeted Roofing Assemblies', Edition 3 - the "Red Book".


• High light transmission
• Placement where glare may occur is a consideration
• Allows full vision of views and objects


• Maximises privacy
• High levels of light transmission in to a building
• Diffuses light transmission and so avoids glare and shadows
• Prevents vision of views and objects


• Maximises privacy
• Diffuses light transmission and so avoids glare
• Prevents vision of views and objects


• Reduces solar heat gain
• Reduces light transmission into a building



Xtralite offers a range of security options to prevent unauthorised access, depending on the level of security required and product range selected. Intruder grid systems may be added to all rooflights in the Xtralight range. They are positioned between the glazing and roof opening and consist of a 3mm diameter, solid steel fully welded mesh in a 75mm grid. This system will resist entry even when the rooflight has been compromised or removed.


Each of Xtralite's rooflight ranges has a wide array of options. To aid specifiers in the selection process Xtralite has created a simple-to-follow guide, designed to help formulate the rooflight configuration required.

By following the advice in this manual and referring to the CAD database on the Xtralite website in the downloads section, specifiers can see the options available and configure individual roof light specifications.

When specifying, it is not essential to use the product codes which denote the different glazing, ventilation and roof attachment options available, specifying using text descriptions is acceptable. However, providing the correct codes may assist in accurately specifying the desired rooflight configuration.

If further assistance is required in determining the rooflight configuration, please call Xtralite on 01670 354157.

Step 1—Before the detailing begins

Consider the following two key elements:
• Most rooflight specification is driven by Part L and consequently U value performance. So select the rooflight that meets your particular project requirements from the X-One to X-Five range.
• If glazing only (X-Glaze) is required go to step 7. For units that require an attachment or ventilation zone go to step 2.

Step 2—Understanding the rooflight construction

Rooflight construction is broken down into three key areas:
•Attachment zone
•Ventilation zone
•Glazing zone
You will need to work from the bottom up so firstly—the attachment zone.

Step 3—The Attachment Zone

The attachment zone covers three elements;

1. The shape of the opening—rectangular, square or circular
2. The various attachment options
3. Security—the inclusion of an intruder grid

Further information regarding these details is available in the individual product sections within the product portfolio.

  Code X-One X-two X-Three X-Four X-Five

Roof Opening Shape













Kerb with Variable Metal Foot A      
Kerb with Variable Metal Foot 
to Suit Kerb-to-Falls Insulation
Kerb Direct to Roof C
Adaptor Kerb D  
Sleeve Over F  


Intruder Grid IG


Step 4—The Ventilation Zone

Xtralite’s range of options gives the specifier considerable scope to satisfy the ventilation requirement.

  Code X-One X-Two X-Three X-Four X-Five
Unventilated 00
Hit and Miss 01    
Rotary Vent 02    
Wormgear 03  
Access Hatch with Gas Spring 04G    
Access Hatch with Restriction Stay 04F  
Access Hatch with Electric Motor 04E      
Smoke Vent/AOV with 90° Opening 0590      
Smoke Vent/AOV with 140° Opening 05140      
Smoke Vent/AOV with Dual-Pitch Opening 05DP        
Linear Motor 06  
Emergency Opening Gas Spring 07    
Permanent Vent 08        
Control Louvre 09        
50% Louvre 10        
Electromagnet 11      
Electric Sliding Opener 12E        
Manual Sliding Opener 12M        
Extract Vent 13        
Trickle Vent 14      


Step 5—Sizing the Rooflight

lite has the ability to manufacture bespoke-sized modular rooflights up to; rectangular 1500 mm x 2400 mm, circular 1800 mm (diameter). The following is a selection of common standard sizes. For larger rooflights see the continuous rooflights, panelised glazing and specialist glazing sections.

Material*       X-One X-Two X-Three X-Four X-Five
Square 600x600 
Rectangular 600x900
Circular (Diameter) 600


Step 6—The Glazing Zone

Within the glazing zone there are four options to consider, material, shape, colour and security. Unless otherwise specified the glazing will be 3 mm polycarbonate for each skin.

Material*   Code X-One X-Two X-Three X-Four Xfive
Polycarbonate Single 1        
  Double 2        
  Triple 3  
Glass** Single GL        
  Double IGL  
Polycarbonate Pyramid PY  
  Dome DM  
Glass Flat Glass
Solid Flat Solid
Glazing Colours              
Polycarbonate Clear Clear
  Diffused Diffused
  Opal Opal
  Bronze Bronze
Glazing Security              
Security Screws   SS
Security Frame   SF  
*Glazing options are only those that we recommend to achieve the U value figures shown in step 1. Other options are available on request.
** For your glass specification, please contact Xtralite to review the options available.


Step 7—Specifying Glazing Only (X-Glaze)

For those situations where a pre-constructed builder’s kerb already exists, Xtralite provide a polycarbonate glazing only option. A security screw attachment is available and if further security is required an intruder grid can be fitted. U values vary depending on whether single, double or triple glazing configurations are used. For sizing guidance please refer to step 5.

  Code   Configuration  

Triple Skin
(Code 3)

Double Skin
(Code 2)

Single Skin
(Code 1)
U Value
(2.2 required for Part L)
  1.8 2.9 4.0
Polycarbonate Options        
Dome DM
Pyramid PY
Trapezoid TR
Colour Options        
Clear Clear
Diffused Diffused
Opal Opal
Bronze Bronze
Security Options        
Security Screws SS
Intruder Grid IG


Step 8—Required Information for Bespoke Rooflight Sizes

To ensure that each bespoke rooflight is correctly manufactured, the measurements required are clarified in the descriptions and accompanying diagrams below and overleaf.

Glazing only (X-Glaze) and Adaptor Kerbs

To fix X-Glaze (domes and pyramids) and rooflights with adaptor kerbs to a kerb that has been pre-built the measurements required are shown in the diagram and itemised below.

Overall finished kerb sizes including all added insulation and weatherproofing finishes.

Internal finished sizes including all well liners.

* Min 150 mm from finished roof surface.

Rooflights that Include a Kerb Supplied by Xtralite

Care must be taken to ensure the fixing point of the rooflight kerb locates onto solid ground to ensure a secure fixing.

The measurements shown in the diagram and itemised below are the required details.

A & B
The roof opening size.