Contrary to what many people think, choosing and buying proper windows is not to be rushed into. Apart from aesthetics, which is important, energy efficiency should be on your list of guidelines, too. 40% of the heat energy in a home can be lost and up to 87% of the heat can be gained if you do not choose the right window.


  • Single- and double-hung: the bottom sash slides upwards/both sashes slide vertically
  • Single- and double sliding: one sash slides/both sashes slide horizontally
  • Awning: hinged at the top, opens outwards
  • Casement: hinged at the sides, opens outwards
  • Hopper: hinged at the bottom, opens inwards
  • Tilt and turn: opens outwards like a casement window and tilts like a hopper window

Awning, casement, hopper and tilt and turn windows have the sash, which is pressed against the frame when closing and because of that they have a low air leakage rate.


  • Aluminum: durable, low maintenance needs, may be subject to condensation
  • Timber: the most common frames, not very durable, high maintenance needs
  • uPVC: durable, the colour range is limited, darker colours can fade
  • Aluminum and timber (composite): expensive, low maintenance for aluminum, a range of colours possible
  • Fiberglass: expensive, durable

Aluminum has poor energy efficiency unless a thermal break is installed. uPVC, fiberglass and timber frames have great overall thermal performance. Composite frames are less energy efficient than timber frames unless a thermal break is installed.


  • Single-glazing: only one pane
  • Double glazing: two panes create a gap filled with air, or gas
  • Low-e: reduces glare and UV transmission
  • Laminated: improves safety (hard to break), excellent noise reduction, reduces UV transmission, water exposure can lead to deterioration
  • Toned glass: reduces heat, decreases visibility
  • Window film: reduces heat, reinforces windows

Comparing all types of window glass, only a retro-fitted double glazing option comes with all the benefits, including insulation both in summer and winter, noise reduction and reduction of UV transmission. The Solar Heat Gain Coefficient (SHGC) of double glazing windows is lower than the SHGC of single glazing ones. The lower the SHCG, the cooler the house in summer. The U-value of these windows, which measures the amount of heat escaping during winter is lower than the U-value of their single-glazed counterparts. In a recent chat with NZ’s experts for double glazed windows, I learned that this solution is usually opted for when renovating, as they can be custom-installed without installing replacement windows.


Choose windows depending on the architectural style of your home. For instance, contemporary homes can have floor-to-ceiling windows, while if you have a traditional home, you can opt for bay windows. Interior aesthetics is important as well, especially if you want to consider window treatments. Decide whether you would like to have skylight windows, or maybe accent windows, including transoms and fanlights. The colour of window frame should be taken into consideration. As it was shown above, not all window frames come in all colour ranges. The type of frame can influence which accent colour and/or mullions you will choose.

Energy Efficiency

Compare energy efficiency of different windows by visiting the official website of the Window Energy Rating Scheme (WERS). Every commercial and residential window has its own ID. You can find which type of glazing a window has. If you see three figures, it means that a window is double-glazing as three figures signify the width of the outside pain, the thickness of air gap and the width of the inside pain respectively. You can also identify the U-value, the SHCG, the amount of air leakage (air infiltration, AI) and the visible transmittance (VT). Cooling and heating starts indicate how energy efficient a window is. Improvement figures show the performance of a window compared to a 3mm clear glass window in an aluminum frame.

To conclude, the proper windows are crucial for the overall design of both exterior and interior as well as for thermal insulation. Choose a window contractor who can explain to you all the options for your home.