Can’t get a straight answer as to how much a NatHERS assessment will cost? Why do assessors always want to see the house plans before providing a quote? In this blog, we look at the key reasons why prices can vary so much between different house designs.
Complexity of design:
Not surprising, the number one reason there isn’t a one price fits all option can be attributed to the complexity of the design. To model a house in accordance with the NatHERS guidelines, you must include every detail from the materials used in construction, to where the neighbours are located in relation to the house. Whilst an assessment for a single storey project-built home may be able to be reproduced at a certain price point time and time again, an architectural three storey masterpiece with floor to ceiling windows throughout will require significantly more time and effort to achieve the required thermal performance.
A concrete slab on ground versus a suspended timber floor will have a very different impact on the thermal performance of a home. An experienced accredited assessor will know what construction methods rate well and what methods rate poorly.
The use of construction methods that rate poorly in one area of a home will mean that other areas of the home and other design options will need to be reviewed to improve their thermal performance. Achieving the perfect balance in heating and cooling loads across the home can take quite some time and as we all know, time is money! In the example below, we have modelled a simple house design (exterior envelope light weight cladding), on the left (a) we have modelled the home with a concrete slab and on the right (b), with a suspended timber floor. Note the difference in the star rating achieved and the heating and cooling loads.
The number of windows:
Windows are one of the largest sources of heat transfer in a buildings’ envelope. The more windows a home has, the more difficult it will be to achieve thermal efficiency. To improve the thermal performance of windows, a relatively easy fix is to specify Low E, thermally broken frames or double-glazed windows. This can be very costly to you, the client. An accredited assessor should look at other areas of the design first to see if there are more cost-effective ways of improving a homes’ overall energy rating.
The external envelope is the first line of defence against heat transfer, getting this wrong will severely compromise the thermal performance of a home. A home that is constructed from brick veneer has significantly more thermal mass and therefore, will rate better than a home constructed from metal gladding. In the example below, we have again modelled a simple house design (concrete slab), on the left (a) we have modelled the home with brick veneer exterior walls and on the right (b), metal clad exterior walls. Note the star rating and heating and cooling loads. The brick veneer achieves the 6 star rating, but the metal cladding does not.
Ball park figures:
The below pricing information is a guide only, but may give you an indication of what costs you can expect when engaging a NatHERS assessor.
|Single storey (estate style)||$250-600|
|Double storey (estate style)||$350-700|
|Single storey (designer)||$350-800|
|Double storey (designer)||$500-1200|
|Single storey (complex)||$500-1500|
|Double storey or more (complex)||$800-2500|
These are just some of the factors a NatHERS assessor must consider before providing a quote to thermally assess a home. Without viewing the working plans, an accurate quote for an energy assessment cannot be provided. Someone who provides the cheapest quote, or a quote without seeing the plans, may choose to not spend as much time working on the model to achieve the highest thermal performance possible. This in turn, could cost you, the client more money, not only in construction costs, but also in your heating and cooling costs over the life of the home.