The Green Rate team recognize that a NatHERS certificate can be confusing to interpret, even for seasoned industry professionals.
While a good sustainability consultant will ensure that the requirements of your energy rating are communicated to you, it’s good to have an understanding of how to read and interpret the important information contained within the certificate. The below is written as a guide to help when reviewing the NatHERS Certificate for your project.
Please note, the below is written as a guide only with aspects deliberately simplified and only select sections discussed. If you have any questions, please feel free to contact the team at Green Rate for site specific advice.
The above image shows the property details. It’s important to ensure that all details are correct as this is the basis of the NatHERS Certificate and is important from a compliance perspective.
The image below shows the star rating that was achieved by the design and selected insulation and glazing. It’s clear to see that a star rating of 7.1 stars was achieved. Less clear are two additional criteria, being the heating and cooling loads. To be compliant, the modelled heating and cooling loads must be below the load limits. In this example, we can see that both the modelled heating and cooling loads are below the load limits and as such, are compliant.
The next section that is important to review is the Window and Glazed Door summary. As we can see from the image below, the section is presented in two parts. The first is the windows which have been used in the model, with their respective performances (U-Value and SHGC). The second section shows the Window ID that was chosen for each individual window. While the below example is simplistic, these sections can be quite convoluted.
When providing your NatHERS Certificate to your builder or glazing supplier, it’s important to note that it is the U-Value and SHGC Values which must be achieved, not the window descriptor. Window and glazed door performances can vary wildly and as such, as long as the U value and SHGC range is achieved, the glazing is considered compliant.
The next section summarizes the external wall types which were modelled within the assessment. In this case, it was a framed wall with a fibre cement cladding on the outside. It’s important to check that the wall types modelled match your design. Also important to check is the bulk insulation R-value which generally will range from R2.0 – R2.7. This specifies the level of insulation required to be installed.
The following section summarizes the floor type, covering and insulation required. In the below example, a suspended timber floor has been modelled with R2.5 batts added to areas that are above an open space. Again, it’s important to check the correct floor type, covering and insulation values that have been used match your design.
Finally, the image below shows the ceiling/roof type and insulation values modelled. In this example, a pitched, metal roof with a flat ceiling has been selected. R5.0 batts have been modelled to the ceiling with an R1.3 blanket modelled under the roof.
Being able to review the construction types, insulation and glazing requirements is important to ensure a thermally efficient and comfortable home. Ensuring that these requirements are incorporated into your design early on will help avoiding nasty surprises later.
