How the two differ in kind
Continuous insulation earns its name by crossing the structure without interruption, which is what makes it so much more effective per unit thickness than insulation between framing. How the cladding is then held off it decides how much of that continuity is left.
Z-FURRING is a folded metal section fixed through the insulation to the structure behind, with the cladding fixed to its outer flange. It is simple, familiar, cheap, and it is a CONTINUOUS metal path running the full length or height of the wall, in contact with the structure at one end and with the cladding at the other. That is precisely the geometry continuous insulation exists to eliminate, and the penalty is not marginal: a wall with a nominal insulation value can end up with an effective value a large fraction lower once the furring is accounted for. The exact degradation depends on the section, its spacing and the insulation's own value, which is what a bridging calculation quantifies — and the result is routinely larger than people expect.
CLIPS AND RAILS break the line. A clip is a point fixing, usually incorporating a thermal break where it meets the structure, and it carries a rail standing clear of the insulation face. The metal crossing the insulation is then a small area at intervals rather than a continuous ribbon, so the bridging penalty falls sharply. Systems vary in how far they take this — some isolate the fastener itself, some use a low-conductivity clip body, some do both — and their published performance reflects those differences.
The trade is that a clip system is engineered rather than assumed. Clip spacing is not a convention: it is determined by the weight of the cladding it carries, the wind load it has to resist, and the insulation thickness it spans, and it comes from the manufacturer's tables for that system with that cladding. It is also more expensive per square metre, and it requires the fixer to follow a layout rather than run furring at a familiar centre.
The factors that actually differ
Show
| Clips and rails | Z-furring | |
|---|---|---|
| Geometry of the bridge | Point fixings at intervals, usually with a thermal break at the structure. | A continuous metal line from structure to cladding, running the full height or length. |
| Thermal penalty | Modest, and quantified by the system's published data. | Substantial — enough that a nominal insulation value can be degraded by a large fraction. |
| What sets the spacing | Cladding weight, wind load and insulation thickness, from the manufacturer's tables. | Convention and the cladding's own fixing requirement, which is why the thermal question gets skipped. |
| Cost | Higher per square metre, and more components to order and place. | Cheap, familiar and widely stocked. |
| Installation | To a layout, with each clip located and each fastener to a specified embedment. | Run at centres, which is faster and needs less thought. |
| Insulation thickness it suits | Thick. Clip systems are made in depths for substantial insulation, which is where the thermal argument matters most. | Thin to moderate. Deep Z sections are unwieldy and the bridge worsens with depth. |
| Drainage and ventilation behind cladding | A rail on clips leaves a continuous cavity, which is what a rain screen needs. | A horizontal Z section can interrupt drainage down the cavity unless it is detailed to allow it. |
| Compressing the insulation | Avoided by design — the clip sets the standoff and the insulation is not the load path. | A real risk. Over-tightened fixings crush the insulation, reducing its thickness and its value. |
| Fastener design | Specified for withdrawal and shear at the clip spacing, into a known substrate with a known embedment. | Often chosen by habit, and a long fastener through thick insulation is a lever arm the substrate has to resist. |
| Verification | The system's tested thermal and structural data, applied at the specified spacing. | An effective-value calculation, which is the step that reveals what the furring costs. |
Which one, and when
Choose clips and rails when…
- The insulation is thick and its performance is the point of the assembly.
- A performance standard has to be met on the EFFECTIVE value rather than the nominal one.
- It is a rain screen needing a continuous drained and ventilated cavity behind the cladding.
- The cladding is heavy enough that the support system needs engineering anyway.
Choose z-furring when…
- The insulation is thin and the bridging penalty is correspondingly small.
- Cost and familiarity dominate, and the thermal target is undemanding.
- The cladding's own fixing requirements suit continuous support rather than point support.
- It is what the system being installed specifies — some clad wall assemblies are tested with it.
Now run your own numbers
This page holds no prices on purpose — a national average is wrong for almost every real project. Quantify both options with your dimensions and your local quotes.
Frequently asked questions
- How much does Z-furring actually cost thermally?
- More than intuition suggests, because metal conducts hundreds of times better than insulation and the path is continuous. A Z section runs unbroken from the structure to the cladding, so heat crossing the wall has a metal route that bypasses the insulation entirely — and in a parallel-path assembly, the best conductor dominates. Published effective-value calculations for steel Z-furring through continuous insulation routinely show a large fraction of the nominal insulation value lost, with the penalty worsening as the insulation gets thicker, because the better the insulation the more the bridge stands out. That last point is the one that matters for design: adding more insulation behind continuous Z-furring delivers progressively less, which is the same diminishing-return mechanism that applies to cavity insulation past a certain depth.
- What makes a clip system better?
- Breaking the continuous line into small interrupted areas, and where the system provides it, inserting a low-conductivity material at the point where the clip meets the structure. A point fixing at intervals presents a fraction of the cross-sectional area that a continuous section does, and heat crossing it has to spread through insulation on either side rather than running along a ribbon. Systems differ in how thoroughly they do this — some isolate only the fastener, some use a clip body of low-conductivity material, some use both — and their published effective values differ accordingly. The important discipline is to use the SYSTEM's data at the SPACING actually installed, rather than assuming that any clip is thermally negligible; a closely spaced steel clip with no break is considerably better than furring and is not free.
- What decides clip spacing?
- Structural demand, not thermal preference, which is why it comes from the manufacturer's tables rather than from a rule of thumb. Each clip carries a share of the cladding's dead weight in shear and resists wind load in tension and compression, through a fastener into whatever substrate is behind — and the insulation thickness matters because it sets the lever arm between the cladding plane and the structure. So the spacing depends on the cladding weight, the design wind pressure for that building and that zone of the facade, the insulation depth, and the substrate's own fastener capacity. Corners and parapets see the highest wind pressures, so spacing usually tightens there. Widening the spacing to reduce the thermal penalty is not available as a design move; it is a structural decision the manufacturer's data governs.
- Can the fixings crush the insulation?
- Yes, and it is one of the more common site failures because it is invisible once the cladding is on. Fixings driven through insulation into the structure behind can be over-tightened, compressing the board between the cladding support and the substrate. That does two things: it reduces the actual thickness of insulation at that point, and for some insulation types it damages the material's structure so it does not recover. The result is a wall built with a specified thickness that has substantially less at every fixing. Clip systems generally avoid it by design, since the clip sets the standoff and the insulation is not in the load path. With furring and with through-fixings, the protections are a specified torque or a depth stop, and choosing an insulation with adequate compressive resistance for the application.
- How is the effective value calculated?
- By accounting for every parallel path through the assembly rather than adding up the layers in the middle of a panel. A simple layer-by-layer calculation gives the value at a point where nothing crosses the insulation, which is not representative of a wall with metal through it. The methods in use — area-weighted parallel-path calculations, the isothermal planes approach, and for complex geometries a two- or three-dimensional thermal model — each account for the bridge and for the way heat spreads around it, and the choice of method matters because the simpler ones can understate a highly conductive bridge. For a specific proprietary clip, the manufacturer's tested or modelled figure at a given spacing is the most reliable input. What is never adequate is the nominal insulation value with a note that there is some bridging.
- Does this apply to rain screens specifically?
- It applies to any clad wall with continuous insulation, and rain screens add a second requirement the support system has to satisfy: a continuous drained and ventilated cavity behind the cladding. Vertical rails on clips create that naturally, since the cavity runs uninterrupted from the base to the head. Horizontal sections — including horizontal Z-furring — sit across that path and can dam water running down the cavity and interrupt the airflow, unless they are detailed with drainage and ventilation provision. That is a durability question rather than a thermal one, and it is why rain screen support systems are usually specified as systems rather than assembled from generic sections: the thermal performance, the structural performance and the cavity behaviour are all properties of the arrangement rather than of any one component.
- Is exterior insulation worth it if the fixings bridge it anyway?
- Yes, comfortably, and the comparison that matters is against the alternative rather than against a theoretical ideal. Even with Z-furring, insulation outside the structure still covers the studs, the plates, the lintels and the junctions that cavity insulation cannot reach — so it improves the assembly substantially compared with putting the same material between framing. It also warms the structure, which reduces condensation risk within the wall. The argument for clips is not that furring makes the exercise pointless; it is that having paid for the insulation, the support method decides whether you receive most of what you paid for or a fraction of it. Since the support system is a small part of the wall's cost and a large part of its performance, that is usually a straightforward decision once the numbers are on the table.
- What should I ask a supplier for?
- Three things, in writing. The system's effective thermal performance at the spacing you will actually install, not at a demonstration spacing and not for the insulation alone — with the method or test behind the figure named. The structural capacity per clip in shear and in tension for your cladding weight, your insulation depth and your design wind pressure, with the fastener and the substrate stated, since a clip's rating is meaningless without the fastener that anchors it. And the installation requirements: fastener type and embedment, torque or depth control, spacing at corners and parapets, and the detailing at openings and terminations. A supplier who can produce all three is selling a system; one who can only produce a catalogue picture and a price is selling components you will have to engineer yourself.