Original details

Windows were timber double-hung, installed in the plane of the wall as single or twin units or installed into a bay window form (see Figures 1 and 2 for common design variations and figures 3-9 for construction details). Width varied according to location – the window in a service room was usually smaller.

Bay windows

The bay window was typically installed under a gable roof, but a wide range of variations occurred such as: a flat roof to the bay window; a hipped roof over the bay; the main roof constructed as a hip or faceted; and a shed or single slope roof over.

A bay may consist of:

  • a single sash installed into a framed and clad angled bay – typically the walls adjacent to the windows were clad in weatherboard
  • a square bay with a wide central sash with a narrower sash each side and narrower return side sashes installed as a unit.


Common sash widths included:

  • 1’ 2” (350 mm) – side lights to the main sash
  • 1’ 9” (550 mm) – sashes to the angle clad wall of a bay
  • 2’ 9” (850 mm) – service rooms 
  • 3’ 3” (1010 mm) – single sash in bedrooms or the main sash to a bay or multiple sash windows. 

Fixed sashes adjacent to doors were typically 9½” (240 mm) wide.

Typically, the overall window heights (and particularly to bay windows) was 6’ (1.8 m).


Glazing was generally:

  • a single pane in each sash
  • a single vertical glazing bar to give two rectangular panes.

Early glass was imported and produced by the cylinder process. The largest pane size available was 3⅓ x 1⅔’ (1000 x 500 mm). This accounted for the widespread use of four-pane double-hung windows. Glass had ripples and many imperfections. The original glass may still remain in a number of existing villas.

Coloured glass was popular in the 1870–80s. It was either flash glass (clear glass dipped into coloured glass) or cast. 

Sash horns

Top sash horns – possibly introduced to improve the racking resistance of the sash – are one way of indicating the age of the original windows:

  • Concave and convex horns – early 19th century.
  • Ogee – mid to late 19th century.

Horn details varied around the country, with an angled cut horn being used in the Wairarapa.

The shape of the glazing beads used can also indicate age.


Windows were finished with 4¾” (120 mm) wide facings that were commonly profiled. The junction between the jamb.

Design variations

Variations in window design included:

  • a top light above the double-hung sashes
  • curved top to the top sash
  • a flat pediment over the centre window
  • a curved or angled pediment over the centre window.


The top of the head facing was often finished with an inclined flat board to form a cap to the window over which the flashing was installed (Figure 10).

Galvanised iron head flashings were installed to the facing or to the timber cap and fitted behind the lap of the weatherboard above.

A sill tray in galvanised iron was used and the underside of the sill was finished with either:

  • sill blocks
  • a scalloped edge board running the full width of the sill. 

Window construction

Window construction consisted of:

  • jambs housed into the sill and the head
  • sash rail to stile joints constructed using a pinned (timber dowel) mortice and tenon joint
  • glazing puttied into place.

Another feature of villa windows is the occasional use of a small lean-to roof supported on timber brackets installed over the window head to provide shading and weather protection.

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Where new aluminium-framed single-glazed windows have been fitted, it is often immediately obvious because they are out of character. Better options include wooden-framed windows, composite frames (with aluminium on the outside and timber inside), PVC or fibreglass frames in the style and proportion of the original double-hung windows. If the existing timber frames are in good condition and have the right thickness, replacing the single glazing with double-glazed units in the existing frames is a possibility. This will require some alteration to the sash weights.

When replacing glazing, carefully consider thermal performance of the replacement glazing. One tool that can help with this is the Window Energy Efficiency Rating System (WEERS), a 6-star rating system for assessing the thermal performance of new residential windows.

Safety should always be a prime consideration during alteration or replacement of windows. NZS 4223.3:2016 Glazing in buildings – Part 3: Human impact safety requirements sets out the rules.

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Weathertightness and moisture

When windows are being replaced or modified, care must be taken to ensure that the replacement window is weathertight. See moisture.


Original and replacement windows are most likely single glazed and relatively air leaky, which makes them inefficient in terms of retaining heat within the building. See insulation for options.

Matching original glass

It’s difficult to match original glass profiles and colours. There are several ways to deal with this problem. Read More.