Standards Development

Scope

This document specifies methods for the determination of the thermal transmittance of rooflights and roof hatches intended for the use on upstand in flat and slightly inclined roofs, with and without an upstand.

This document takes account of:

- different subfamilies of rooflights as there are individual plastic rooflights, continuous plastic rooflights, individual glass rooflights, continuous glass rooflights and roof hatches due to their product scopes

- different construction of rooflights with and without framing profiles

- different types of transparent fillings sealed or vented (e.g. glass or plastic; single or multiple glazing; with or without low emissivity coatings, and with spaces filled with air or other gases or gel, multiwall sheets of plastics),

- different types of opaque elements

- different constructions of upstands

This document excludes:

- thermal bridge effects at the rebate or joint between the rooflight and the rest of the building envelope

- effects of solar radiation,

- heat transfer caused by air leakage,

- Calculation of condensation.

The document does not apply to roof windows, windows and curtain walling

The scope may be adjusted while drafting the document

Purpose

CEN/TC 128, Roof covering products for discontinuous laying and products for wall cladding, has asked CEN/TC 89 to develop a standard concerning the thermal transmittance of rooflights. The purpose of the new EN is to define the method for the determination of the thermal transmittance for rooflights. The thermal transmittance of rooflights is a mandated characteristic in the relevant product standards.

At the moment there are two published product standards for rooflights: EN 1873:2014+A1:2016, Prefabricated accessories for roofing - Individual rooflights of plastics - Product specification and test methods, and EN 14963: 2006, Roof coverings - Continuous rooflights of plastics with or without upstands - Classification, requirements and test methods.

Note 1: The 2016 version of EN 1873 was not published in the OJEU. Therefore the version EN 1873:2005 of this standard has to be used at the moment for the CE marking.

Note 2: EN 1873 and also EN 14963 are currently under revision. Draft documents of EN 1873-1 and EN 14963-1 were published in 2020.

Note 3: Additionally, 2 established work item for new standards for subfamilies of products are currently in drafting stage WI00128190 for prEN1873-2 for individual glass rooflights and WI00128191 for prEN1873-3 for roof hatches.

Note 4: In future the drafting of a standard for continuous glass rooflight is planned and should be covered by the future standardization request. 

In EN 1873:2014+A1:2016 the general method currently used for assessment of the thermal transmittance of rooflights is specified. The latest version of the revised documents FprEN14963 and FprEN1873-1 include some improvement of the methods due to the feedback of notified bodies using it.

Major Technical topics to be discussed:

- General approach for the determination of the thermal transmittance of individual rooflights with translucent parts made of plastics or glass, of continuous rooflights with translucent parts made of plastics or glass and of roof hatches

- The methodology should be mainly based on the calculation of the thermal transmittance of the complete product. Measurement method of the complete product may be specified if necessary and possible. The calculation method should consider also the thermal transmittance of components determined by measurement.

- The horizontal orientation of rooflights shall be reflected

- Specification of the relevant area of the product types rooflights or roof hatch without upstand and rooflight for roof hatch with upstand and for the relevant components for the determination of the thermal transmittance.