StoTherm Insulation for Timber and Steel Frame
For architects, specifiers, and builders working on timber or steel frame construction, StoTherm Armat wraps the building's external envelope in continuous, thermally-resistant insulation — addressing the thermal bridging that stud-cavity insulation alone can't reach. StoTherm Armat holds BRANZ Appraisal No. 478, giving architects and specifiers a documented compliance pathway alongside the energy performance benefit.
This page explains how the StoTherm Armat insulation system works for timber and steel frame construction, what makes up a complete installation, and what it means for a project's energy performance and long-term facade durability.
What Is StoTherm Armat?
A StoTherm Armat installation is an external wall insulation system (EWIS) — insulation applied over the outside of the frame, rather than fitted only between the studs. The difference matters: cavity insulation between studs still leaves the studs themselves as a direct thermal path to the outside, since timber and steel both conduct heat far more readily than insulation does. Those studs become thermal bridges no matter how well the cavity itself is insulated. StoTherm Armat addresses this directly by wrapping the entire structure in a continuous external thermal envelope, rather than insulating between the frame and leaving the frame itself exposed.
The StoTherm Armat Insulation System's nine layers — from building wrap and cavity batten through to the finished coloured render.
Who This Matters For
This system is relevant wherever thermal performance, energy rating compliance, or long-term facade durability is a genuine consideration on timber or steel frame construction — new residential, multi-unit, commercial, and institutional builds, as well as refurbishment projects where an existing facade needs both a performance upgrade and a new finish. It's a particularly practical fit for projects targeting a specific energy rating under the NCC, and for refurbishment projects where re-cladding and re-insulating in the same pass avoids the cost of doing each separately.
Panel Options
StoTherm Armat insulation is available in two panel types, selected to suit a project's specific thermal performance requirements. Both are EPS (expanded polystyrene) panels, available from 40mm up to 100mm and over in thickness.
The StoTherm+ Panel improves on the standard StoTherm Panel's insulation properties, delivering R-values up to a further 20% higher at the same thickness — a meaningful gain where a project's energy rating targets call for higher thermal performance without adding further wall thickness.
StoTherm Panel (left) and StoTherm+ Panel (right) surface texture.
Indicative R-values by panel thickness:
| Thickness | StoTherm Panel | StoTherm+ Panel |
|---|---|---|
| 50 mm | 1.30 | 1.60 |
| 60 mm | 1.57 | 1.93 |
| 80 mm | 2.10 | 2.58 |
| 100 mm | 2.63 | 3.22 |
How the System Works
Every StoTherm Armat installation is engineered as a complete, layered system rather than a collection of independent products.
- Substrate — timber or steel frame construction, with building wrap.
- Cavity batten — a vented, self-adhesive cavity batten.
- Insulation — StoTherm or StoTherm+ EPS panel, 40mm to 100mm and over.
- Impact and screw fixing — StoTherm Anchor.
- Basecoat — a lightweight, EPS-bead mineral plaster render with good build properties and machine-application characteristics.
- Reinforcement render — StoArmat Render: organic, cement-free, weather-resistant, high-impact render, with crack resistance up to six times higher than standard cement-based plasters.
- Mesh — Sto glass fibre mesh, meeting crack, stress, and alkalinity resistance requirements.
- Coloured finishing render — Stolit Renders: organically bound, weather-resistant, hard-wearing, impact-resistant, pre-coloured finishing renders.
- Facade paint — StoColor coating.
Thermal bridging matters most at the fixing points — every screw or anchor that penetrates the insulation layer is a potential thermal bridge in its own right, and a facade that gets the panels right but the fixings wrong hasn't actually solved the problem. StoTherm addresses this with two anchor types for timber and steel frame construction: the StoTherm Impact Anchor, for face-fixed panels up to 80mm, and the StoTherm Counter Sunk Anchor, which cuts and compresses the panel to a depth of 20mm before the anchor is capped with an insulation cap — eliminating the thermal bridge at the fixing point entirely and leaving a smooth, homogeneous surface ready to render.
The StoTherm Anchor installation sequence on timber frame: drilled, countersunk, capped, and ready to render.
Why Choose StoTherm Armat
Thermal bridging isn't just an energy-efficiency statistic — it shows up as cold walls, condensation, and mould in the finished building. A correctly installed StoTherm Armat system keeps the substrate warm and dry by keeping it above the dew point, addressing the underlying cause rather than just the symptom.
That performance is backed by more than 50 years of system development — StoTherm was the first EIFS subjected to reliability and long-term material quality testing from the outset, with over 150 million square metres installed worldwide. Installation is carried out exclusively by Sto-registered contractors, with the added protection of the StoArmat Warranty and StoService Assurance, and BRANZ Appraisal No. 478 gives architects and specifiers a documented, independently verified compliance pathway rather than a manufacturer claim alone.
From Specification to Completion
Specifying StoTherm Armat follows the same process as any Sto system: an initial consultation to discuss substrate, climate exposure, and energy performance targets; panel and thickness selection matched to the target R-value; specification support including plan review, mockup assistance, and Sto's CAD/PDF detail library; installation exclusively by Sto-registered contractors; warranty activation on correctly specified and installed systems; and ongoing StoService Assurance, with scheduled inspections, cleaning, and minor repairs every 2.5 years. Sto operates on a custom, quote-based model rather than a published price list, consistent with a specification-led approach where substrate, panel thickness, and project scope all affect cost.
What to Expect
Timelines vary by project scope and substrate, but most projects move from initial technical consultation to a confirmed specification within a matter of weeks, not months — plan review and mockup assistance run alongside the broader design process rather than delaying it. Because installation is carried out exclusively by Sto-registered contractors, the specification and the on-site outcome are directly connected: what's documented in the plan review is what gets installed, reducing the gap between specification intent and built reality that can otherwise erode facade performance.
Proven in Practice
StoTherm Armat has been specified on a genuine range of timber and steel frame projects. Aorangi House in Wellington used the system as part of a full facade refurbishment, specified by Studio Pacific Architecture. North Methodist Church in Christchurch specified StoTherm Armat as part of a new-build design by Dalman Architects. Residential applications across Stuttgart demonstrate the same system performing in a genuinely different climate again.
Frequently Asked Questions
What's the difference between StoTherm and StoTherm+ panels?
Both are EPS insulation panels available from 40mm up to 100mm and over in thickness. The StoTherm+ Panel delivers R-values up to a further 20% higher than the standard StoTherm Panel at the same thickness, making it the better choice where a project's energy rating targets call for higher thermal performance without increasing wall thickness further.
Does StoTherm Armat eliminate thermal bridging completely?
StoTherm Armat is specifically engineered to address thermal bridging, including at fixing points, where the StoTherm Counter Sunk Anchor eliminates the thermal bridge created by face-fixed anchors entirely. Combined with continuous external insulation over the full wall assembly, this gives a facade a genuinely continuous thermal envelope.
Is StoTherm Armat BRANZ appraised?
Yes. StoTherm Armat insulation for timber and steel frame construction holds BRANZ Appraisal No. 478, covering insulation panels from 40mm to 100mm finished in a selected Sto plaster system — an independently verified compliance pathway under the National Construction Code.
Can StoTherm Armat be used on masonry substrates too?
No — this specific system and its BRANZ Appraisal No. 478 apply to timber and steel frame construction only. Sto offers a separate system, StoTherm Armat Masonry, purpose-built and separately BRANZ appraised for solid masonry substrates.
How much can StoTherm Armat reduce heating and cooling costs?
Insulating the facade alone can reduce heating and cooling costs by a substantial margin — commonly cited in the 30–40% range — since a significant share of a typical building's energy loss occurs through poorly insulated walls and the thermal bridging points within them.
Who installs StoTherm Armat systems?
Installation is carried out exclusively by Sto-registered contractors. This keeps the warranty valid and ensures the system is applied to the specification BRANZ Appraisal No. 478 is based on.
Last updated September 2026
