Understanding The R Rating – New Zealand Building Code

The H1 building code regulates the energy efficiency standards within building environments. The standard sets out the requirements new builds must be constructed to. The purpose of this is to ensure kiwi homes have an adequate degree of energy efficiency, thermal resistance and limit uncontrollable airflow. The H1 building code sets physical conditions for energy performance, known as the R value. The R value is the minimum thermal performance required under the NZBC H1 Energy Efficiency and dictates the minimum requirements for insulating walls, floors, and ceilings, as well as ensuring the thermal performance of doors and windows.

“Many products which theoretically meet new H1 requirements will be creating thermal bridging and condensation both inside the house as well as inside the walls.” – Koffman

What is the R value?

R value, or ‘thermal resistance rating’ measures the effectiveness of a product or material in slowing down the transfer of heat. The larger the R-value, the more effective a product is at slowing down the rate of heat transfer. Put simply the higher the R-value, the better the material is at insulating your home.

What is the U value?

U value measures thermal transmittance, the rate of heat loss or gain through a structure or material. The lower the U value, the better the material is at stopping the transfer of heat and the better insulated the material is. The value can be denominated Ug, Uf, and Uw, representing glazing, frame, and window.

Ug = Glazing values

Uf = Frame values

Uw = Windows including the glazing, frame, glass etc.

What is the difference between the R value and U value?

The R value measures thermal resistance through a material, the U value measures thermal conductivity. They are mathematically inverse of one another.

U = 1/R

R = 1/U

R = How much heat the window resists

U = How much heat the window lets through (insulation)

Both values are used to measure energy efficiency however, the U value is used to measure insulated glass units as it takes into account convection and radiation heat losses whereas the R value takes into account the performance rating across the whole unit.

How is the R value measured?

There are three ways the R value can be measured.

Schedule method: Based on a table of R values for different building elements. The building meets the threshold if the building elements such as walls, windows, doors, skylights, floor etc meet or exceed the R-value. There are rules as to when the schedule method can be applied.
Calculation method: This method has a lot more flexibility, it includes calculations of which a building can have different insulation combinations, as long as the thermal performance is comparable to or better than the reference building, which is insulated in accordance with the schedule method. This method usually saves on unnecessary insulation. For example, if your windows achieve a higher R value, you may find that you require less insulation in the ceiling. This calculator can be used to determine the rates. There are rules to determine whether the schedule method can be applied such as “the window area of the building can be no greater than 40% of the total wall area.”
Modelling method: This takes into account the orientation and location of the building to predict its space heating loads and cooling loads. It assesses how all components work together and ensures outcomes like overheating are picked up in the design process. This method is used if the window area of a building is greater than 40%.

What R value is required?

The New Zealand climate has been split into 6 zones. Each climate zone determines the R value the building or materials must achieve.

In zones 1 – 4 the R value for vertical windows and doors is required to be R=0.46

In zones 5 – 6 the R value for vertical windows and doors is required to be R = 0.5

Despite the recent improvement, New Zealand’s housing standards still lag behind other comparable climates resulting in draughty, damp, and mould-prone homes, even when meeting code requirements. It’s important to remember the R value is the minimum thermal performance required under the NZBC H1 Energy Efficiency Clause and should not be the benchmark for quality and efficient homes.

Is the building code the best it can be?

No. A survey in 2022 out of 2000 Kiwi kids found 60% to be living in homes with temperatures and humidity levels outside the World Health Organisation recommended range. Kiwi homes are still damp, cold, draughty, and sometimes mouldy despite achieving building code.

“A new house built in Sydney or Brisbane, for example, must have more insulation than one in Invercargill, while a new build in Dublin requires almost double the amount of insulation of one in Dunedin – despite the two cities having similar climates.” – Marcus Hogan -Professional practice director at Te Kāhui Whaihanga New Zealand Institute of Architects.

Is excess insulation a waste? Where should I place priority in my home?

No, excess insulation is not a waste of money. Some experts might say that adding extra insulation in the ceiling does not yield enough of a benefit to justify the cost and in some cases, they are right. If you are on a tight budget, you should prioritise your spend where it is going to yield the highest return and this is often in windows. Windows yield the highest return because they are the lowest-performing building element and can account for up to 50% of heat loss. The gains from increasing your window insulation versus increasing your insulation in your ceiling are far more significant.

How is heat lost through your windows?

Heat is lost by a process called “radiation through glazing”, this means one pane absorbs radiation (internal heat) and it travels through the glass and reaches the outer window pane. Heat can also be lost by convection through the cavities and conduction through the frame of the window. This is the reason on a cold day if you touch the windows inside your home, despite having the heat pump or heating on, the surface of the windows can still feel cold, and wet with condensation.

Why do my windows still get condensation and feel cold despite having double glazing?

It’s important to understand that not all double glazing is the same. Aluminium is a strong building material, requires low maintenance, and has a sleek look; however, it is a highly thermally conductive building material.

If your aluminium double or triple-glazed windows are not thermally broken or installed correctly (recessed so the line of thermal barrier in the window and wall are connected), they are going to let a lot of heat out and cold in.

What is a thermally broken window?

A thermally broken window has a non-thermally-conductive material inserted into the aluminium frame in a way that disrupts the transfer of heat by breaking the thermal bridge between the interior and exterior of the building. By interrupting the flow of heat through the frame, thermally broken aluminium windows significantly reduce heat loss during the colder months and heat gain during the warmer months.

What is the correct way to install your windows?

Windows should be recessed into the wall where the thermal barrier of the window is connected to the thermal barrier of the wall. Typically windows are installed so they overhang the cladding which causes a cold draught or heat to be lost through the window frame.

If your windows are not installed correctly, despite purchasing thermally broken aluminium or highly insulated uPVC windows, which either have a thermal break or are multi chambered to disrupt the transfer of heat through the frame, the windows may still underperform giving:

Condensation
Heat loss through the edge of the window
Cold draughty feeling
Potential for mould to grow

Recessed installation does not require specific builders, tools, or any extra certifications. The reason why most windows aren’t recessed installed is because there is a lack of awareness and readiness to change from old methods.

How are Koffman windows different?

Koffman windows are built using the latest European technology with the best materials on the market. The windows can achieve an R value of up to 2.7 times higher than the minimum threshold required, with triple-glazed windows achieving an R value of 1.35. This saves on energy costs and keeps your house warmer during winter and cooler during summer. Double and triple-glazing at Koffman uses argon gas filling the space between the glass panes. These glass panes are also fitted with a Low-e coating. Triple glazing is the best option as it is 3 panes of glass with 2 argon gas-insulated spaces, increasing the barriers of heat transfer and making it better than double glazing at stopping heat from escaping your home.

Argon is a dense gas that slows down the rate of heat transfer through the panes of glass acting as a thermal insulator. Some companies offer a range of Low E coatings on their glass however, they are not always the best. At Koffman, we only use the best. Low E glass is important as it reflects a higher percentage of heat back into your home than standard uncoated glass.

In summer, it reflects heat from the sun back outside, helping keep the interior cool. In the winter, it reflects heat back into the room, helping to keep it warm.

What are passive houses and why are becoming popular?

Passive houses are a type of building design that prioritises energy efficiency and comfort through a set of design principles and construction techniques. Passive Houses are built to maintain a comfortable indoor climate throughout the year without relying heavily on traditional heating or cooling systems. Passive houses can save up to 75% on energy costs when compared with average new builds.

Passive houses are gaining traction in New Zealand as the demand for energy-efficient housing continues to grow.

Is it important to understand the building code?

Yes, it is important to understand the building code and R values to ensure you can build or renovate your home to be as energy efficient as possible. While the R value requirements in New Zealand do not match the standards in regions with comparable climates and leave much to be desired in the standard of New Zealand homes. By understanding the R values, you can significantly maximise your homes energy efficiency by upgrading the areas that lose the most heat, such as your windows. Koffman delivers highly energy efficient windows and doors, using the best materials and latest technology.