Energy Efficiency Frames

WER Testing

The test for a PVCu window is carried out on an industry universal size of 1230mm x 1480mm side hung next to a fixed light frame using small outer frame, mullion Z/T, internally glazed sash with both ogee & flat beading and does not account for any additional ancillaries - cills & add-ons etc. This is by using the standard reinforcing guidelines. Additional reinforcing is then included for foiled options, it should be noted the main reason for inclusion is for expansion/contraction and not for structural strength within the frame - this not necessary for the U70 multi-chambered profiles. 

When calculating U- Values for doors it should be noted that the standard door size used and widely accepted (as in BFRC reports) is 1230mm x 2180mm with a Midrail section - the same criteria applies as stated above.

General Installations - Pre 2010

April 2002 brought changes to the window and door industry. This was in the form of the `Approved Document L’ - Building Regulations covering England and Wales (concerning the conservation of fuel and power). It required PVC-U windows & doors sold into the domestic home improvement market, to achieve a minimum U value of 1.9 W/m2 deg K. There was exclusion for replacement doors with less than 50% glazing. It also included specifics to fire escape facilities to first floor habitable rooms and certain criteria relating to ground floor dwellings i.e. bungalows. 

‘New build’ Projects - Pre 2010

These were slightly different with three areas to consider, basically there was a ‘trade off’ between different building elements and a Target U Value relating to the actual building. In most cases it was only the centre pane U value of the glass unit - although Document L1A stipulated 2.0 W/m2K.

Current Requirements - 2010 onwards

October 2010 legislation (Document L1B) has realigned the criteria for replacement windows & new build schemes by stipulating that all windows ordered on or after this date must have an energy rating of at least band C in England & Wales (C Compliance) or a combined U value of 1.6 W/m2K, and doors to be 1.8 W/m2K or less.

Trickle Vents:

The regulations have allowed for the introduction of Trickle Vents as they form part of Document F Ventilation - in the case of U70 the T/V can be fitted into top rail section of large outer frame without reducing the energy rating index. However, it is always more practical to locate these within the sash.

Decorative Glass:

Glazing features - Astragal /Georgian bar grilles and Lead work designs are deemed acceptable as long as the perimeter seal (i.e. the glass, SwissVSpacer & Argon) remains as the original composition.

Laminated Glass:

There is a reduction in the index rating for frames which incorporate laminated glass on the outer pane (i.e. security criteria) where by in most cases the original rating is lowered - this can in some instances be compensated in changing certain components e.g. profile or the glass composition - please check at point of order.


Questions are sometimes raised in relation to shaped e.g. raked / arched designs as to their energy index rating, if they are a small amount within a large number of other frames within the job, then the WER which has been specified will remain the same. However, if the entire contract is solely made up of special designs then further clarification (possible costs involved) would be required.

Note - Metal blinds within glass units do not carry any index energy rating