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.

Start from a standard build-up

The fastest way to a real assembly is the guided Start from a standard build-up flow next to the assembly name: choose Wall, Roof or Floor, then a construction group, then the specific build-up. The library holds 34 build-ups in eight groups - Timber frame, Steel frame and Mass and panel walls; Roof space, Skillion and Low slope roofs; Suspended and Slab on ground floors - and every entry's name carries the things that change the answer: the cavity state (a drained cavity triggers a different calculation from a direct-fixed wall) and the framing material (steel routes through a different method from timber). Framing depth is not a separate build-up to hunt for - you pick the member on the layer, and all timber and LVL depths are available in walls, roofs and floors alike.

Every insulation slot ships empty, deliberately: a build-up is a starting point, not a claim about what is in your building, so no entry pre-selects an insulation product or promises an R-value in its name (and no manufacturer appears anywhere in the shipped library). The slab-on-ground entry is a signpost rather than a build-up - a slab's R-value is dominated by ground coupling, not a layer stack, so it routes you to the Appendix E wizard (see Supplied floors and rafts).

Applying a build-up works as a guided template. The scaffold layers it pre-fills - cladding, underlay, lining, cavities - are locked read-only, while the decision layers (your insulation pick and framing configuration) stay open and are marked "Your choice". A Customise layers control unlocks the whole stack at any time for free editing, and the assembly keeps a build-up breadcrumb showing where it started, including after saving and reopening.

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.

A layer of continuous insulation over the framing - a rigid board or insulated rigid air barrier running across the studs - is not simply added in series. H1/AS1 6th edition §2.1.3.2 requires it to be carried inside the framed portion (its R counted in both the framing path and the insulation path), a layer between two framed portions to be split half into each, and a pliable membrane or underlay to be treated as if it were not there. Thermly applies all three, and each affected layer says so on the report - so a wall insulated over the top of its frame is credited the way the Acceptable Solution prescribes.

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. Completed layers collapse to a one-line summary (products, framing fraction, R-value) - click to expand - and any advanced setting that changes the calculation shows as a small chip on the layer header, so nothing is hidden by collapsing.

A note on colour: a computed R-value shows green only when the engine returned it unflagged. A total that carries a caution (for example, a configuration the one-dimensional method can only treat as indicative) takes the amber or red of its warning, so a number in doubt never reads as reassurance.

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 Common layouts menu fills the bay calculator from a named configuration (for example 45 mm studs @ 600 + dwangs @ 800) and applies the derived fraction in one click. Wall layouts always include a 10% openings-and-junctions allowance, so the one-click figure is an all-timber estimate rather than the bare single-bay minimum.
• A built-in framing-fraction calculator works it out from member spacing, width, dwangs or blocking and an openings-and-junctions allowance, or as an area-weighted average across wall panels. Its bare single-bay result is labelled "Single bay (select set)" - the minimum framing set, not a compliant wall value.
• 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." A sub-38% figure taken from a bare single-bay calculation with no openings allowance carries the same caution, because a single bay excludes the extra timber that packs up around openings, corners and junctions.
• If you genuinely hold a lower figure - a frame-and-truss supplier's timber-percentage report for this build, or a whole-wall take-off from the consent drawings counting lintels, sills, trimmers, corners and junctions - you can record the demonstration under the caution. It is deliberately not a checkbox: you write what the evidence is (a nominal bay layout does not qualify, and the form says so), and that text prints verbatim in the report's framing-fraction declaration. Changing the fraction afterwards clears the declaration, since a demonstration is of a specific figure.

The report declares every framed layer's fraction and its basis - declared geometry, the 38% default, or a typed value - and, where an air gap or continuous insulation was folded into the layer, prints the exact equation the engine evaluated, so the printed inputs reproduce the printed R.

Roof and floor framing is not subject to the 38% wall rule; H1/AS1 sets no framing default for them, so a roof or floor fraction is only as good as the geometry behind it - which is why the built-in roof and floor build-ups carry their take-off (member width, spacing, bay length) as data the report can state.

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. The 38% wall floor applies to steel-framed walls exactly as to timber - clause 2.1.3.1(a)(i) names framed walls, not a material - and a section missing a dimension reports no R-value at all rather than quietly falling back to something else. 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.

Separately from the framing rules, H1/AS1 §2.1.2.11 sets a minimum construction R-value for every envelope element (roof R2.6, wall R1.0, suspended floor R1.3). An assembly below its minimum raises a blocking finding - stronger than a caution, because the figure is trustworthy and still not good enough, in any climate zone, with no way to trade it back elsewhere. It leads the warning rail in the builder and the Critical review items on the report.

Advanced NZS 4214 inputs

A bridged layer's occasional inputs live behind its Advanced menu; each is off by default, applies only when its values are complete and in bounds, and shows as a chip on the layer header while active:

• Steel section - the light-gauge steel transform described above, with a checkbox to declare a ventilated through-bridge (NZS 4214 §5.7.2): a member passing through a vented cavity, such as a top-hat batten spanning a drained cladding cavity. Thermly computes the value but raises the note that the one-dimensional method does not apply to that case.
• Still air gap on the insulation path - an enclosed gap counted in series with the insulation between the framing.
• Bounding enclosed air gap (§5.7 / Appendix F2) - an unventilated cavity sitting directly against the bridged layer (the brick-veneer case), folded into both the framing and insulation paths rather than counted as its own layer. Presets cover the wall (R0.17) and roof/ceiling (R0.14) cases.
• Chord penetration (§5.7) - where framing only part-penetrates the insulation (say 90 mm truss bottom chords under a 330 mm ceiling blanket), only the penetrated depth is bridged; the remainder counts as a continuous overlay in series.
• Compression check (NZS 4214 C2) - enter the insulation's nominal (labelled) thickness and the depth it is actually installed into; when the label exceeds the space, the insulation R is derated and the compression caution appears on the result and the report. Simple layers carry the same check.
• 2-D / measured override (§5.1.1(b)) - enter a THERM / ISO 10211 or measured (guarded hot box) effective R with a provenance note, and it supersedes the calculated value for that layer. The layer is marked externally determined on the report, carrying its provenance - the supported route for a configuration the one-dimensional method cannot certify.

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 leads it - narrowing to a manufacturer is usually the first step, so it sits first in reading and tab order. Reference materials (generic boards, timber framing, and air gaps from the standards - including reflective foil-faced cavities at set widths) appear alongside branded products, badged Reference. Picking a product shows its catalogue R-value right on the layer row, and a slot only offers products that can actually be that layer - sheet linings (plasterboard, fibre-cement, plywood) are available as an outer skin too, which is what the garage side of an internal wall is made of.

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.

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. On any row with an assembly, the "Build-up · N layers" line opens the editor directly - swap products, set custom R-values, rename the assembly and its layers - with each layer's computed R contribution shown inline ( Edit assembly… in the row's ⋯ menu is a second route). A row whose assembly leaves a product slot unset shows an amber "Product not set" chip; click it to jump straight to the layer, because until a product (or custom R) is set that layer contributes no R.

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.

Next

• Supplied floors and rafts - proprietary rafts and supplied-R floors.
• Generating your H1 report.