History of the double hung sash window
Double hung sash windows were distinctly English development if the late seventeenth century and the eighteenth century. Because this development took place during the colonial times double hung sash windows were introduced to the American colonies and subsequently to Australia and New Zealand. In these and other English speaking countries, double hung sash windows have continued to be used in certain circumstances and mainly in the Auckland central region where Villas and Bungalows dominate the streets.
Because of these early connections, the double hung sash window has come to be associated with Georgian and American colonial styles in buildings, particularly when Georgian type multi pane sashes and proportions are used.
How double hung sash windows work – Advantages and disadvantages
Double hung windows in which upper and lower sashes slide vertically, have special advantages in some situations.
- They are relatively wind-tight and weather-tight as the junction between the sash and frame is covered by facing or beads on the outside as well as on the inside. Villa windows draught proofing services can drastically improve these early practices. Contact us for a free quote.
- They can provide efficient ventilation at high and low levels and so do not require the addition of air-conditioning or ceiling fans. Moreover, in storm conditions, when windows must be closed, a small amount of indirect ventilation at the meeting rails can be obtained by raising the lower sash about 20mm.
- When open the sashes do not project either inwards or outwards to cause obstruction, nor are they exposed to twisting strains from high winds.
- Both surfaces of the glass can generally be cleaned from inside the building, although not as easily or as safely as when sashed are hung on friction stays, special hinges, or pivots.
Double Hung windows have some limitations and disadvantages:
- Maximum opening is limited to somewhat less than half the window area and to achieve this amount of opening meeting rails must occur about the middle of the window. Over time these meeting rails become out of alignment, Villa windows operational service will set the meeting rails back to the original position maximizing the sash window to its full potential.
- The free running of the sashes or freedom from rattles is not always easy to maintain. Villa windows draught proofing services can help minimise the amount of rattle by adding a brush pile to the sash window.
Double hung sashes balanced by counterweights
Early double hung sash windows were produced by counterbalanced weights suspended on cords. Villa windows sash cord replacement
can replace any broken cords to get your sash moving freely again.
Traditionally, double hung sashes were fitted to boxed frames or cased frames – so named because the jambs were built up out of comparatively thin members, which formed boxes to accommodate the counterbalancing weights and cords. Box mullions were used when two sets of weights of adjoining double hung windows had to be accommodated. Metal sash pulleys were fitted to the stiles of the frames and these members became known as pulley styles.
Sash cords used in New Zealand were usually braided cotton, This eventually led to breakages due to the hash New Zealand sun perishing the cords. Villa windows sash cord replacement
use only 100% cotton fiber cords that will withstand the test of time.
Cotton sash cords are made in different gauges between 6 and 8 mm diameter. The thicker cords require larger pulleys and the following table indicates the size of the pulleys recommended.
Sash cord sizes 6 7 8 10
pulley diameter (mm) 50 57 65 75
Sash weights are made of cast iron or lead in round and square section, although round section cast iron weights of 40 mm diameter are normally used. They are made in various weights to suit sashes of different sizes. Weights are chosen to balance the sash and at the same time to ensure that the sash will tend to close rather than open if vibrated by the wind. The combined weights for the upper sash is made 0.5 to 0.75 kg heavier than the sash, and the combined for the lower sash 0.5 to 0.75 kg lighter than the sash. Villa windows operational service
will ensure your balance weights are weighted correctly for your sash window.
Spiral spring balances for double hung windows
Spiral balances incorporating helical torsion springs were introduced into New Zealand during the nineteen forties and they have largely replaced counterweights and cords for balancing double hung windows. Most of the spring balances used in New Zealand are Unique patent spiral balances.
Although they may not be as free running as counterweights and chains or cords in perfect condition, spiral balances have many advantages over the older systems. Among these advantages are:
- Because spaces do not have to be left to provide for hanging weights, jambs and dividing mullions can be made much narrower; greater space can be allowed for glazing and wide mullions can be avoided.
- Frames are simpler and cheaper to make and the counterbalances are easier to fit.
- Danger, expense and inconvenience caused by cord breakage are eliminated.