Since Hero v3.1, to facilitate the introduction of steel-frame thermal-bridging modelling in NatHERS 2022 assessments, you can model the Structure Option of a Wall, Floor or Ceiling.
You can watch the Hero v3.1 Webinar section on Thermal-Bridging & Structure Options at the 10:54 timestamp below:
The selected Structure Option applied to a Wall, Floor or Ceiling can thermally-bridge a material layer (such as an insulation material) and reduce their effective R-value & thickness in the simulation.
The article below breaks down how these are introduced into Hero via the Structure Options, then explains some of the settings available, the calculation methodology, and viewing and editing structure options in the Wall Assembly Library.
Structure Options are similar in concept to each Assembly having various Insulation Options that can represent different variants of the assembly based on a selected insulation choice. Likewise each Assembly can have several Structural Options that represent different ways that the Assembly might be built with different structural materials, such as different timber-stud sizes or spacing, or steel-framing of varying thicknesses and types. It is these structure materials that are the secondary materials that "thermally bridge" other primary materials such as insulation layers.
Again, similar to Insulation Options, you can create as many Structural Options as desired for each Wall Assembly in the Wall Library, and then apply them into your project on selected walls, floors or ceilings in the Data-Grid or Summary View as detailed below. For Ceilings and Floors, you currently can only model the default structure options that have been provided for you.
The image above shows the new Structure column of the Wall, Floor and Ceiling Data-Grid tabs, showing a range of Structure Options that can be applied to these walls, including timber and various steel-frame options.
Likewise the Wall, Floor and Ceiling Summary View tables contains a similar Structure column that can be selected to show and group Summary data by their Structural Options as per the image below.
Note that Ceilings have both Ceiling Structure & Roof Structure - the Ceiling Structure bridges any Ceiling Insulation entered, and the Roof Structure bridges any Roof Insulation such as roofing blanket.
Note that air-gap materials aren't effected by any thermal-bridging effects in NatHERS.
In Hero v3.1 the Default Wall, Floor & Ceiling Assemblies come with a pre-populated list of Structure Options available, but any previously created Custom Assemblies will require their own Structure Options list created for them, so if your Structure Options list in the Data-Grid or Summary-View is empty, please remember you must create your Structure Options first in the Construction Library prior to applying them in the Data-Grid or Summary-View.
Thermal Bridging Settings
The Structural Options set on any Walls, Floors or Ceilings in Hero will effect the simulation by reducing the effective R-Value/Thickness of any bridged materials, depending on the Thermal Bridging Settings which are detailed below.
There are three settings that determine how Structure Options and Thermal Bridging are considered in your Project. These settings get applied in the Project Data-grid tab and are:
1 - None
This Thermal Bridging setting means that regardless of any applied Structure Options in your model, no thermal-bridging R-value reduction will be applied to any floor, ceiling or wall materials.
This setting can be an easy way to turn off thermal-bridging without removing it from every wall/floor/ceiling, or to model and use Structure Options for other purposes than thermal-bridging (such as embodied energy calculations).
Projects targeting NatHERS 2019 compliance can leave the Thermal Bridging setting in this default None setting regardless of whether the project has steel-framing (unless otherwise advised).
You cannot use this setting for a NatHERS 2022 project containing steel-frame walls, floors or ceilings (unless otherwise advised).
2 - NatHERS
This is the default setting for NatHERS 2022 projects that use steel-frames in any Walls, Floors or Ceilings.
In NatHERS setting, Thermal-Bridging effects will be only be applied to Walls, Floors or Ceilings with Steel-frame Structure Options in areas that meet NatHERS Tech Note conditions, and compensated against an equivalent Timber-framed wall.
Table 5 of the NatHERS Tech Note shows where thermal-bridging must be applied.
In the NatHERS Thermal Bridging mode, you can enter your Structure Options in as per the project plans, and then Hero will automatically work out whether the thermal-bridging effects should be applied as per the Tech Notes based on their type and locations. E.g. Steel-frame Structure Options get ignored if they are an External Wall of a Garage in NatHERS setting, and Timber-frame structure options in walls, floors or ceilings will be ignored automatically.
For example if a project had a 90x40 steel-frame structure option applied to external walls of a garage or to internal walls between two conditioned zones, because this does not require thermal-bridging in NatHERS Tech Notes, and so no thermal-bridging effect will be applied to any insulation in this area.
If it was to a normal zone's external wall, or any other appropriate situation as per the Tech Notes (such as a roofspace or subfloor adjacent wall etc), then thermal-bridging effects from the selected Structure Option would be applied.
In addition, when in NatHERS Thermal Bridging setting, the calculation of the steel-frame wall's overall R-value & thickness get referenced against an equivalent timber-frame. This is because timber-framed walls don't have any thermal-bridging effects calculated upon them in the NCC2022, and so steel-frames are only "punished" to the degree they are worse than an equivalent timber-frame. So in effect, a steel-frame wall is only rated in terms of it's reduction impacts based on it's reduction against a timber-frame wall.
3 - Full
The Full Thermal Bridging setting in Hero is an optional beyond-compliance setting where all Structure Options including Timber frames and regardless of location, are modelled for thermal-bridging effects in all situations, and no reference compensation against a Timber frame effect is applied (as discussed above).
In this mode, regardless of where the Structure Option is (such as on an internal wall) it will apply a thermal-bridging effect, so it goes beyond NatHERS Tech Note requirements.
This setting is more accurate and aligned with NZ4214 and can be used for better design and research purposes.
Thermal Bridging effects and calculation method
Thermal bridging effects in Hero follow the NatHERS thermal bridging methodology that mostly aligns with standard NZ4214:2006, with a few differences. Please see the NatHERS Thermal Bridging page for further information and where the full NatHERS thermal-bridging calculation methodology is detailed.
In brief, for each material layer in an assembly (e.g. a 110mm brick or a 90mm insulation batt or 10mm plasterboard layer), there can be an additional secondary material in that layer (such as a steel or timber frame stud that disrupts the main wall insulation batt material layer). This secondary material will effect that layer's R-value and thickness in the assembly. The total R-value of this bridged assembly is then the sum of the individual bridged layers.
Structure Options can be viewed, created, edit and removed in the Wall Assembly library.
A Material Layer can now have a Structural Material that is that secondary material, and which disrupts the continuity of the primary material. You can add multiple Structural Materials to all materials (i.e. all rows) of the Wall Assembly - for these assemblies with multiple structural materials, Hero just creates a Structure Option that is based on having those two Structural Materials applied into the assembly.
For example in the image above we see a 90mm R2 insulation batt bridged with a 92mm x 36mm x 0.75mm steel frame at 600mm centres will reduce that insulation's effective R-value from R2 to R1.6. In Chenath this will thereby be modelled at a 70.4mm thickness instead of 88mm and thereby dropping the overall R-value of the wall assembly from 2.93 to 2.52.
Viewing, Creating & Editing Structure Options
In the Wall Assembly library you can see how wall assemblies get effected by the various structure options that can be applied to them. The below image outlines how Structure Options are utilised throughout the Wall Assembly Builder.
1 - Thermal Bridging Visual Setting
This is a way to visualise the effect thermal-bridging settings have on Assemblies within the Construction Library. Note this is a visual only setting for the Construction Library that allows you to quickly see the impacts of various settings on an Assembly but it does not relate to the Project's Thermal-bridging setting set in the Project Data-grid tab.
2 - Currently shown Structure Option
An Assembly can have many Structure Options available to be easily applied to it in the Data-Grid or Summary View. The "Current Structure Option" is the one selected in the Combo-box at (2), or via selecting the Structure Option in the list shown in the Library section at (6).
The dropdown selection will show the other available Structure Options created and ready for use in the Assembly (similar to what is shown in the list at (6)), so you can easily switch between different structure options and see what effects they'd have if applied to a Wall.
3 - Structure Column - New Structure Material column of the Wall Assembly table, showing where structural materials are in the assembly. In the example image there is only one Structural Material bridging the Insulation at row index 3.
4 - Structural Material - A Structure Material bridging the insulation layer at row index / position 3. You can change the type of Structural Material applying to that row by using the dropdown selector at (4).
5 - Create Structure Material - You can either Drag and drop a new Structural Material onto your Assembly by dragging and dropping the "Structure" button and dropping over the material-row that you'd like to apply the Structural Material to. Or alternatively, you can select the row and click the "+" button to the right of the Structure button.
6 - Structure Options list in Assembly Library - The Structure Options list of a Wall Assembly are shown both here (similar to what is shown in the dropdown of (2)). You can select the current Structure Option by clicking this row, or select a Structure Option and hit Clone/Copy to create a new Structure Option based off the previously selected one, or alternatively you can hit Delete on a selected Structure Option to remove it.
7 - Create/Clone new Structure Option - Create/clone a new Structure Option based off the existing, or delete an existing Structure Option from an Assembly's Structure Options list.
Check the Construction Code, your local state regulatory authority, your NatHERS AAO to find out whether there are thermal-bridging variations in your state.