It was an exciting day on site on last Tuesday when Nulook CHB delivered the first lot of our Aluminium Joinery to site. During the design phase of the project, we invested a lot of time selecting products that would ensure that Habitat would be a would be warm, dry and comfortable home. The technical way this is measured is through ‘R Value” – a rating which measures how well insulation can resist heat flow. ‘R’ stands for thermal resistance.

  • R-Value depends on a number of things such as type of material, its density and thickness.
  • Higher R-Value = Better insulation

While insulation (in walls, ceilings and floors) plays a large part in this, another critical factor is the window and door joinery. Windows and doors are often the weak link within the thermal performance of a building. It is far easier for heat to escape through them than thick, solid walls. However, not all doors and windows are created equally – there are a range of options to choose from to upgrade the R-Value of your aluminium joinery.

The following chart compares the R-Values of various Aluminium Joinery upgrades:

  • Glazing – Double glazing is currently standard in NZ. It is also known as an insulated glass unit or IGU. An IGU limits heat transfer by conduction and convection due to the resistance of the air between the panes of glass. Triple glazing is available in NZ, but many of the units are imported from overseas – it is only something we would consider for a particularly cold climate. Single glazing is generally not supplied anymore due to its low thermal performance, but is still an option for warmer climates, though not recommended.
  • Thermally Broken – This means there is an insulating strip between the inside and outside of the aluminium frame. This significantly reduces the transfer of heat through the frame, resulting in less overall heat loss/gain from the building. Upgrading from standard to thermally broken aluminium is expensive. It can add approximately 30% to the cost of the joinery*.  While this is beneficial if budget allows, the most ‘bang for your buck’ in terms of overall heat loss and R- Value for the building will come from general floor/wall/roof construction upgrades.
  • Low-E Glass – This means low emissivity. It consists of a very thin metallic coating, that reflects radiation off the glass from inside or outside the house. This limits excess heat coming in and out through the glass by radiation. The performance of the low-e can improve a little further further with the addition of a window tint. This is a relatively cost effective upgrade (approximately 5-10% of window costs*) when you consider the increase in R-Value it gives.
  • Argon Gas – The space in between glass panes, is commonly filled with dry air. Using argon gas instead, can increase the R-Value of the window by up to 20%, as it is a better insulator than air. Argon gas is non-toxic, clear and naturally occurring. Like thermally broken aluminium, argon gas is expensive, and would not be something we would usually specify in a North Island climate (excluding Central Plateau), unless there was a significant budget allowance made available.

While mitigating heat loss is a major consideration, in many climates mitigating excess heat gain is equally important. While high R-Values will also work to keep the house cool in summer, there are other ways that joinery choice can help to reduce overheating. To aid with cooling in the Wairarapa’s hot summers, we have specified panels of louvres at critical points in the home to assist in cross-flow and general ventilation. The beauty of louvres is their versatility – they can be opened only a small amount or completely – and they are ideal for keeping a home securely ventilated over night or when the owners are out. We have also ensured there is a good balance of large, sliding doors and smaller windows for added ventilation depending on conditions.

In the coming weeks we look forward to getting the windows installed, and cladding underway – keep an eye out for further updates.

Our Tip: All of these ‘upgrades’ come at a cost, and can sometimes be an area where compromises need to be made if the budget is being pushed. At a building consent documentation stage, as long as the sizes of the joinery units are confirmed, you can choose to make ‘upgrades’ after consent if budget allows. For example; a specified standard aluminium frame with double glazing can be upgraded to a thermally broken frame with low e and argon. Usually Council can simply note this as a minor addition to the plans. Downgrading joinery units on the other hand can have knock on effects to the amount of insulation required, and would usually require an official amendment to the consent.

*Please note these figures are based on our own anecdotal experiences of pricing aluminium window joinery – for more precise and up to date cost information please refer to your local aluminium joinery company.