Thermal Efficiency

Xtralite X-Range rooflights, are available with polycarbonate glazing but also glass glazing in metal frames. As the leading independent rooflight manufacturer, Xtralite offers the widest range available, suitable for all applications and building types. All Xtralite rooflights are individually manufactured in the UK to order and so are effectively bespoke products, offering the widest possible flexibility. However, to help designers build up specifications to suit their specific needs, products are organised into X-Ranges as summarised in the table below. Options and accessories for each model are illustrated with relevant product codes.

Categorisation by Thermal Efficiency

The range primarily reflects the level of thermal efficiency (Ud value) and hence its suitability for particular applications. It is recommended that the appropriate X-Range be selected first using its Ud value as a guide, followed by the required size, shape and glazing, then options and accessories—so building up the rooflight specification.

X-One

X-Two

X-Three

X-Four

X-Five

Ud Value

(2.2 required for Part L)

Thermal Efficiency U<sub>d</sub> Value 1.3 Thermal Efficiency U<sub>d</sub> Value 1.8 Thermal Efficiency U<sub>d</sub> Value 2.2 Thermal Efficiency U<sub>d</sub> Value 2.2 Thermal Efficiency U<sub>d</sub> Value 4.0

Shape

Rectangular
Circular

All Glazing Colours

Glazing Material

Polycarbonate Single
Double
Triple
Glass Single
Double

Ventilation

Security

Security Screws
Security Frame
Intruder Grid

Kerbs

PVC
Metal
GRP Circular

Flexible Base Adapter

 

X-One Rooflight

The Lowest Ud Value — X-One Rooflight

New Zones With an exceptionally low Ud value of 1.3, exceeding Part L requirements, this latest model from Xtralite represents the future of rooflights. The X-One rooflight also benefits from high thermal performance. Unlike other rooflights, the X-One rooflight is designed and constructed in three distinct zones to clarify specification and maximize performance and flexibility:

  • Glazing Zone
  • Ventilation Zone
  • Attachment Zone

 

Waterproof Glazing System

The X-One is triple glazed as standard and formed from enhanced UV protected polycarbonate with breathing airspaces between the glazing elements. The integral cascade water management system ensures that moisture drains to the outside of the building removing risk of leakage.

 

Accessory Frame

The accessory frame is the key element which ensures Part L compliance and gives X-One its unique environmental efficiency. The frame is constructed from a single, highly complex, PVC profile designed to efficiently ‘dock’ between the glazing module and either the kerb adaptor profile or the kerb, creating a secure, weathered and warm connection with no cold bridges.

The accessory frame arrangement is flexible depending on the specifiers requirements. For example it can include a unique continuous hinge, facilitating manual or electrical opening, allowing for high volume air ventilation.

The cylindrical profile protects it from the outside elements using a continuous cowl feature and integral insect mesh. The vent design ensures that no cold bridging occurs between the outer and inner surfaces. When the vent is closed it forms a virtual triple skin chamber with very low air leakage and exceptional sound reduction performance. The ventilation system is simply operated by rotating the operating handle.

 

Flexible Rooflight Attachment

Xtralite have developed unique rooflight mounting systems to aid attachment and make the process of incorporation easy.

A versatile metal foot will allow for a variety of thicknesses of roof insulation, whilst allowing ‘flexible’ matching of rooflight to roof opening as well as ‘cut to falls’ variable depth insulation systems.

Fixing direct to the roof deck allows for the kerb to be attached direct to the supporting structure which could be above the insulation layer or by using a kerb adaptor direct to any pre-constructed builders kerb.

The kerb has three main insulating chambers ensuring compliance with Part L regulations and with projected future changes, by the addition of high performance insulation to the chambers. The kerb is designed to be equally suitable for, and compatible with, both polymeric and PVC roofing membrane systems, bituminous membrane and mastic asphalt systems.

The rooflight assembly includes a unique termination detail to ensure that the ‘top edge’ of the roofing membrane is fully protected. A special ‘key’ finish to the PVCu kerb increases roof membrane fixing options and ensures that the PVCu kerb is torch-on system friendly. Simplified assembly allows the roofing finish to be applied to the upstand prior to clipping the Glazing Section and Accessory Frame into position. This procedure minimises damage and the need for protection, and eliminates dressing around the vents.

 

X-Two Rooflight

X-Two Rooflight

This model also meets and beats the requirements of Part L with an impressive 1.8 Ud value using ‘all thermoplastic construction’ for outstanding thermal efficiency, high resistance to weathering and low maintenance. The X-Two rooflight is formed from enhanced UV protected polycarbonate with vented airspaces. The integral cascade water management system ensures that moisture drains to the outside of the building and air leakage meets Part L criteria. Key features include:

  • Aluminium trim and extruded gasket sections
  • Steel security insert within the PVCu section
  • Rooflights easily removed and replaced with keys
  • Available in four versions—fixed; worm-gear opening; hit and miss;access hatch.

A 2 mm thick wall thickness ensures weld strength and a weather seal on all opening rooflights maintains weather-tightness. A special ‘key’ finish to the PVCu kerb assist adhesion of membrane and the PVCu kerb torch-on system friendly. X-Two can be delivered in two parts for easy handling and more efficient installation.

 

X-Three Rooflight

X-Three Rooflight

This thermally broken, metal rooflight offers considerable flexibility whilst complying with the maximum allowable Ud value (under Part L) of 2.2. Frames and kerbs are finished in white—standard colour—coloured kerbs are also available. X-Three rooflights can have double glazed or triple glazed polycarbonate. The integral cascade water management system ensures that moisture drains to the outside of the building and air leakage meets Part L criteria. A security frame is also available as an option.

 

X-Four Rooflight

X-Four Rooflight

This GRP kerbed system is designed for circular rooflights whilst also complying with the maximum allowable Ud value (under Part L) of 2.2. X-Four rooflights are triple glazed as standard with enhanced UV protected polycarbonate and vented airspaces, and air leakage meets Part L criteria.

 

X-Five RooflightX-Five Rooflight

This metal system offers considerable flexibility for unheated areas where thermal insulation is not an important criterion. White frames and kerbs are as standard but coloured kerbs are also available. X-Five rooflights can be square, rectangular or circular and single glazed as standard with enhanced UV protected polycarbonate or glass. A security frame is also available as an option.

Ud Value Calculation

The Ud value of a rooflight is calculated by dividing the heat transfer across the system (measured in Watts) by the environmental temperature difference across the test element (measured in degrees K) multiplied by the area of the aperture in the surround panel—called the projected area (measured in m²). This latter dimension is equivalent to the opening in the building envelope. One consequence of this is that the ‘Ud’ value of the product will increase as it gets deeper, despite the thermal properties of the individual components staying the same.

The building energy software SBEM uses the actual area (often called the developed area) of the product, to calculate the heat transfer through the product.

To show what this value is, a “supplemental” Ud value has been calculated using developed area and it is this relevant value that we quote in this document.