Pilkington has welcomed the Government’s latest proposed revisions to Part L of the Building Regulations, especially the introduction of Window Energy Ratings (WERs), which indicate that Pilkington’s K glass could still be an acceptable low-E glass in the UK market.

Window Energy Ratings combine different aspects affecting the energy performance of a window into a single number or Rating. These aspects are heat loss, solar gain and ventilation. They are linked by an equation, which has been developed so that the Rating reflects the effect the window has on the energy consumption of a typical house throughout the year. Compliance for replacement windows will be achieved if the window achieves a Rating of minus 40 (which is Band E) or better.

It will, however, still be possible to satisfy the requirement by the old U value route. The proposal recommends that the current U value for replacement PVC-U and timber windows remain unchanged and the maximum U value of 2.0 will now apply to metal windows as well (compared to the current 2.2), with the option of complying through a centre pane U value of 1.2 staying the same.

A significant amendment is the proposal of dropping individual U value requirements in new build. The only route to compliance would be to calculate the CO2 emissions for the proposed building as a whole and to show that these meet the prescribed level. This means the Elemental and Target U value methods will no longer be permissible. ‘Backstop’ U values of 2.2 will still be required for windows, meaning that developers will no longer be able to get away with using standard double glazing through trade-off options, thereby requiring the use of K Glass or alternative low-E products in each new development.

Rick Wilberforce, Pilkington Market Development Manager for Europe, comments:

‘It is possible that some or all of the proposed measures could change as a result of the consultation process, however, as things stand, they are extremely encouraging for those who wish to see a continuation of current window specification and practice. The introduction of Window Energy Ratings and whole building CO2 targets rewards solar gains and makes the precise U value of an IGU less relevant.’

Additional proposals mean that conservatories will now be covered under the obligations of Part L, although the glazing requirements will be exactly the same as for replacement windows. The proposed requirement for extensions is for a maximum window U value of 1.8 or a Window Energy Rating of minus 30, however, trading off is permitted, which means that higher U value windows could also be acceptable.

Following a period of consultation, the Office of the Deputy Prime Minister will publish the new Part L in the summer of 2005. It is expected to become law at the start of the following year.

Source

Glass Age