Door and windows replacement is one of the most difficult design problems. The following comments apply both to doors and windows for extensions and their replacement in existing buildings. Householders often receive leaflets promoting double glazed systems. Like most large ranges of standard products stocked by DIY warehouses, these are wholly unsuitable for traditional houses in conservation areas.

You should first consider whether any replacement is necessary. It may be possible to repair windows. Skilled joiners can make repairs to or replicas of timber windows without difficulty. Many properties have leaded light windows with small panes joined by lead strips called cames. These windows can be repaired and the leads renewed. Traditional leaded lights have a sparkle due to the slight irregularity if the individual panes. This is lost in modern substitutes where thin lead strips are stuck to the surface of a single sheet of glass. This will generally unacceptable substitute. Interwar Suburb houses often had ‘Crittal’ steel windows, with either traditional small panes or ‘moderne’ horizontal proportioned panes, and curved corners on bays. It is possible to repair these or obtain replica replacements which are galvanised, thus overcoming the big problem of rust. The Trust and Barnet Council can supply the names of specialist manufacturers of steel-framed windows.

Householders often wish to put in double glazing. If the original windows are retained, their frames can be made more efficient by proper weather stripping to exclude draughts. Secondary glazing can be fitted internally.

Although this is not ideal, there a minimum change to the external appearance of the building. It should be remembered that only a small proportion of heat loss is through the roof which can often easily be insulated.

Replacement windows and those for new extensions should match the originals in the way they are subdivided into opening and fixed lights. The frame material, overall style, pane subdivision, mullion and transom widths and glazing rebate should de repeated.

Colour coated aluminium and UPVC replacement windows have been extensively marketed over the past twenty years. The Trust and Council have yet to see a product which is acceptable for installation on the Suburb. Their use, without consent, is likely to result in enforcement proceedings, by both the Trust and Barnet Council. The current practice of including a plastic grid between the two panes of the double glazing to imitate a glazing bar has an unacceptable effect on the property. The lack of depth gives a thin and artificial appearance.The recent use of external glued-on plastic grids which attempt to reproduce ‘puttied’ glazing bars is also unsatisfactory. Applications for the substitute windows of the types described above, or for their installation in new extensions will usually be unacceptable.

In the past some front doors have been replaced by unsuitable patterns, resulting in inconsistency of design. In the original designs front doors might be of different types, but a group of cottages or a group of larger houses would be consistent in style. One type consists of vertical timber boards often in oak and generally with a small area of leaded light. Others had six or eight small panes of glass over a boarded panel or three narrow moulded panels. Other larger houses had ‘Country Georgian’ panelled doors with or without glass.

In the 1960s some house holders wanted natural light and put in fully glazed doors. Nowadays the demand for greater security means hat glass is out favour. In fact the traditional doors were generally quite robust and had a reasonable combination of timber and high level glazed area. We will encourage designs which are more compatible with the early styles and repair, retention or replication of the originals where they still survive. If replacement is desirable, we expect exact copies of the original doors. We will discourage varnished hardwood doors unless this was the original style. In other cases doors may be made of hardwood for extra strength but should be painted. Mass-produced doors are almost always unsuitable, particularly those with a semi-circular fanlight in the door itself. This style is alien to Suburb buildings and will be resisted.