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Assemblies and products ​

An assembly is an element's layer build-up: the framing, insulation, linings, cladding and cavities that give a wall, roof or floor its construction R-value. This page covers building your own assemblies, choosing products, and swapping products live from the H1 page.

You started with a sample - now build your own ​

Every element needs an assembly, so Thermly ships sample assemblies for walls, roofs and floors to get you a result immediately. They appear alongside your saved assemblies and are read-only - open one to see its build-up, and click Make a copy for an editable copy of your own. When you are ready to reflect the real construction, you build your own. It is the same short, layer-by-layer form.

Open the Assembly Builder from the nav or from New assembly on the Dashboard, or start from a Template (Wall / Roof / Floor) and adjust it.

Add layers ​

Build the element up layer by layer (the order is preserved and shown on the report). Each layer is one of:

  • Simple layer - a single material: a lining, a cladding, a rigid board, an air gap. Pick a Product from the catalogue, or choose Custom R-value and type an R directly.
  • Bridged layer - insulation between framing, calculated by the isothermal-planes method. You set an insulation product and a framing product (or custom Rs) and the framing fraction - the proportion of the layer's face taken up by framing. This is the standard timber- or steel-framed wall, or a rafter or joist layer.
  • Vented cavity - a drained and vented cavity behind cladding, handled per NZS 4214 §5.3.2.

Surface resistances (the internal and external air films) are added by Thermly automatically at the compliance values - you do not enter them. The layer card shows a running R-value as you complete it, and the header shows the assembly total.

The framing fraction and the 38% rule ​

For a framed wall, H1/AS1 6th edition sets a default: assume a wall framing fraction of no less than 38% unless a lower fraction is demonstrated for the building (§2.1.3.1(a)(i)). Timber conducts far more heat than the insulation between it, so understating the framing overstates the wall's R-value.

The Assembly Builder helps you get this right:

  • A one-click H1/AS1 min (38%) button sets the compliant default.
  • A built-in framing-fraction calculator works it out from member spacing, width, dwangs or blocking and an openings-and-junctions allowance (a single-bay estimate), or as an area-weighted average across wall panels.
  • If you set a wall below 38% without a demonstration, Thermly warns: "Below the H1/AS1 6th edition 38% framed-wall assumption. Use 38% unless project records demonstrate a lower framing fraction is appropriate."

Roof and floor framing is not subject to the 38% wall rule and uses the framing you enter.

Steel framing is supported: add a light-gauge steel section (base metal thickness, flange width, section depth) and Thermly applies the NZS 4214 metal-frame method. Where a steel batten bridges continuous insulation (a top-hat or Z-girt over rigid board), Thermly warns that the one-dimensional transform is optimistic and that a two-dimensional determination (THERM / ISO 10211) is required for a compliance figure. See How Thermly calculates compliance.

Choosing products ​

The Product picker searches the sourced NZ catalogue by name, manufacturer, category and common aliases (batts, foam, brick, and so on). A Brand filter narrows to one manufacturer. Reference materials (generic boards, timbers, and air gaps from the standards) appear alongside branded products, badged Reference.

Where a product's R-value is not published, choose Custom R-value and enter the figure yourself with its basis. Catalogue R-values are sourced from manufacturer datasheets and reference tables - see Product sourcing and provenance - and should be checked against the manufacturer's current datasheet before use.

The Product Catalogue: sourced products, each with a "Show source" link.

Swapping products live from the H1 page ​

You do not have to leave the H1 page to try a different product. Each element on the compliance page carries its own copy of its assembly, so you can swap a product in place and watch the verdict recompute immediately.

This is a capability the plan-linked workflow gives you: experiment freely. Try a higher-R batt, a different lining, a thicker cavity board; the heat-loss check updates live ("Recalculating…"), and you can see at a glance whether a change brings a failing element into compliance or buys headroom. It is the fastest way to find a build-up that works for the building.

Because the swap lives on this report's copy, it does not disturb your saved assembly library. The panel keeps the genealogy honest:

  • unchanged: "a copy of [assembly] · swaps stay local to this report";
  • changed: "modified from [assembly] · this report owns its own copy".

You can rename the copy so the construction name on the report stays truthful after a swap. Some layers are marked Fixed and cannot be swapped: a vented cavity (resistance is method-derived), steel framing (sized by the NZS 4214 method), or an externally-determined R that governs its layer.

Save and reuse ​

Save an assembly to reuse it across elements and projects; find your saved assemblies on the Assemblies tab of the Dashboard. A saved project keeps a snapshot of the assemblies it used, so an old report stays reproducible even after you refine the library.

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