FENSA, Document L & The Building Regulations?
The new regulations only apply to 'new or replacement windows' and therefore replacement sashes are not subject to these new requirements. Replacement sashes are simply a repair to an existing window and so can be supplied either single or double glazed. Authentic replica sashes do not require any local authority planning permissions or FENSA certification.
Complete window replacements do however require compliance, with some exceptions for conservation areas and listed properties.
All new windows must now meet minimum thermal standards, expressed as a 'U' Value. To achieve the required U value in the case of new sash windows then they must be double glazed, incorporating a low 'E' glass with an Argon gas filled void. The size of the void between the panes must also be increased, likewise several changes must also be made to the window construction. Inevitably these additional requirements have significantly increased the cost of replacing whole windows, making repair work the preferred option when possible.
We are not a FENSA registered company as the majority of our work is restoration and not replacement. Currently building permissions must be obtained by the home owner, from the local authority, for any complete replacement window required.