Carrying out unauthorised works to a listed building is a criminal offence, and the owner of the building and any individual or company that has undertaken the construction, can be prosecuted. A planning authority can insist all work carried out without consent is reversed at the owner’s cost. An owner will have trouble selling a property with no consent for work undertaken.
Repair or reinstatement
Consent for listed buildings is typically granted on a ‘like for like’ basis, unless the applicant is able to satisfy certain conditions, such as ‘that the building is not of special architectural or historical interest’ – more likely with a Grade II than a higher listing. For listed buildings of special architectural or historical interest, the planning officer will require the applicant to reinstate and re-use as much of the original material and detail as possible. This may involve scarfing in new sections of timber, freeing sashes, replacing draught proofing, repairing or replacing hardware, re-glazing (possibly using original glass) and fresh decoration. The original colour may also need to be maintained. If repair is not possible, the replacement details will need to replicate the existing design details, including mouldings, glazing method and use of historic glass.
Improvements to energy efficiency
A single-glazed window can have a u-value worse than 5 W/m2 K. Improvements to the energy performance of single-glazed windows and doors are limited to: • The simple addition of draught-proofing strips • Renovation, with bead adjustment and the addition of draught-proofing strips • Curtains, blinds and shutters (effective only at night) • Secondary glazing, which, as noted, can affect the reflection of the windows and the appearance of the interior of the property, as well as presenting condensation and cleaning challenges. Today’s double-glazed timber windows can achieve a BFRC A energy rating or a u-value of 1.4 W/m2 K.
cylinder unfolded into a flat sheet. Cylinder glass displays a distinctive character of faint parallel ripples. For the repair and reinstatement of windows in listed buildings of special architectural or historic interest, the glass should, ideally, be preserved and reused. New float glass may not be acceptable due to its uniform, flat, reflective surface. Alternatives It is possible to imitate historic crown and cylinder glass using hand or machine drawn glass. These types of glass are often used as the outer layer in a doubleglazed unit to add character and reduce visibility of the inner layer.
However, depending on how close the replacement needs to be to the original, a less expensive 3mm ‘period style’, or horticultural, glass may be acceptable. This has a wavy reflection without having the same quality as hand blown glass.
Crown glass 14th to mid-19th century Molten glass is gathered on the end of a blowpipe and a ‘balloon’ shape blown. The blowpipe is removed and a rod attached. The glass is spun until a disc is formed. The outer glass is cut into small panes and the central section of the spun glass becomes the bull’s eye or bullion. Crown glass can be identified by its concentric ripples and air bubbles.