Hardie Gravis, the 2026 Design Forecast, and an Honest Cavity Debate

We had James Hardie present at our Monday Mastermind this week, and it was genuinely one of the more useful sessions we have run. A new product, a set of free tools most builders are not using, their 2026 design forecast, and a properly good debate about cavities. Here is what stood out, builder to builder.

One note before I start: Gravis is a brand new product and James Hardie were upfront that the manual is a first version being actively updated, so treat the technical detail below as a starting point and confirm the current specifics against their own documentation before you build.

The free tools in My Hardies

My Hardies is a free web platform (not an app, though you can save it to your phone’s home screen). Most builders I know are not using it, and there is real value sitting in there:

• A visualiser to preview different cladding styles and colours on preset house types, handy for helping a client picture the look.
• A free takeoff service. You send your plans and their team returns a bill of quantities, right down to paint and nails, plus your plans marked up to show sheet layouts and minimise waste. Roughly two to three days for residential, one to two weeks for larger commercial, and it comes back as an Excel spreadsheet.
• Installation guides that are always current and region-specific. This one matters. Search the open web and you will find guides that are years out of date, or the New Zealand version with slightly different details. The platform keeps you on the right one.
• Technical details you will not find on the public site, like tiling externally over their products, or junction details between one Hardie product and another.
• New interactive 3D installation guides for their ten most popular cladding products, so you can rotate and step through a connection detail instead of squinting at a 2D sheet.

The new product: Hardie Gravis

Gravis is James Hardie’s new autoclaved aerated concrete (AAC) panel. It is a lightweight concrete, made from cement, lime, gypsum and water and cured so it fills with tiny air pockets, with anti-corrosion steel mesh embedded for strength. It feels like masonry but installs much lighter.

	Detail
Material	Autoclaved aerated concrete, steel-reinforced
Wall panels	50mm (up to 3m high) or 75mm (up to 3.3m high)
Floor panel	75mm, 1800 x 600
Fire (FRL)	Up to 120 on the 50mm, up to 180 on the 75mm wall; up to 90/90/90 floor
Warranty	25 years, exterior
Fixing	Screwed onto horizontal steel top hats, on timber or steel frame

Where it genuinely opens up options compared with fibre cement:

• It can sit in the ground, and you can pour concrete straight up against it (with an Ableflex base gap), instead of managing ground clearances.
• It achieves deep window reveals, either 50mm or 75mm, which was always hard with fibre cement.
• It can be curved, faceted down to a minimum 270mm radius at the narrowest point.
• It is certified to NCC 2025, and James Hardie say it is the only AAC product currently carrying that certification.

The cavity debate

This was the best part of the session, and it is worth laying out honestly because it matters for how you would actually build with it.

Gravis does not use a ventilated and drained cavity. James Hardie’s technical position is sound: rather than the deemed-to-satisfy pathway that requires a drained cavity (the one they use for fibre cement), Gravis complies with the NCC’s condensation requirements through a verification method, simulating the wall across a range of Australian locations and demonstrating the mould index stays within limits. The horizontal top-hat system it fixes to physically blocks vertical drainage, so a vented cavity would mean a completely different system with vertical top hats and weep holes.

The room pushed back, and I was with them. Cavity construction has become standard best practice for most of us, and as one builder put it, basically everyone in the group runs a ventilated cavity now. Another was blunt: if adding a cavity batten voided the warranty, he simply would not use the product. James Hardie’s answer on warranty was that adding third-party battens behind their top hats is a grey area, any failure caused by that third-party component would sit outside their warranty, though the Gravis product warranty for its own workmanship and defects still stands.

To their credit, they took the feedback well, and the group’s clear ask was for James Hardie to develop a ventilated-cavity installation option. My honest view is the same: I would want my Hardie products on a vented cavity too, because that is where the industry has moved. It is a genuinely good product, and a vented-cavity guide would make it an easy yes for a lot more builders. Worth raising with your own rep if it matters to you.

Meeting seven stars

With the move to a 7-star NatHERS minimum for new homes and renovations (timing varies by state), a chunk of the session covered what actually moves the needle. James Hardie ranked the eight levers by impact:

1. Orientation
2. Windows and glazing
3. Shading
4. Insulation and thermal mass
5. Wall cavities
6. Ventilation
7. Reflectivity
8. Colour

In their Sydney case study, upgrading the glazing was the single biggest factor, taking a home from 5.5 to 7.1 stars. There is also the Whole of Home rating to hit (a 0 to 100 scale, minimum 60, covering appliances and solar). James Hardie publish a free energy efficiency guide, and have a partnership with assessor Energy Advance offering discounted assessments through the My Hardies portal, including running the same design across different orientations and material comparisons.

The 2026 design forecast

The part I found most interesting for the design-minded end of the trade. James Hardie’s Modern Homes Forecast, now in its third edition, is built on research with global trend forecaster WGSN. It identifies eight modern home styles, and there is a design handbook for each one on their website, covering not just cladding but roof lines, windows and how to achieve the whole look. They make a great client-facing tool.

Style	Signature look
Modern Classical	Curved parapets and facades, archways, aluminium window hoods
Box Modern	Parapet lip, textured panelling, bold picture-frame windows
Modern Farmhouse	Board and batten, deep window recesses, chimneys as a feature
Modern Heritage	Original facade kept at the front, contemporary at the rear
Barn	Slim corner detailing, expansive windows, decorative battens
Mid-Century Modern	Stone chimneys, blade walls, deep fascias
Modern Coastal	Hood awnings, aluminium battening, outdoor tiling
Japandi	Timber junctions, warm tones, deep fascias

Barn and Modern Farmhouse are the most popular right now, but the one they flagged as the strongest emerging style is Japandi, a blend of Japanese and Scandinavian warmth, heavy on timber junctions and calm, natural tones.

The thread running through the whole session was mixing materials. You rarely see a single-cladding house any more, and the point James Hardie were making is that with their expanding range, including Gravis, you can now achieve a mixed-material facade from one manufacturer with one warranty behind it.

A genuinely useful morning, and exactly the kind of thing our Future Builder mastermind exists for: real products, real questions, and builders sharpening each other.

Cheers Luke