Closed Panel System (CPS) Explained

At a glance

HebHomes’ Closed Panel System (CPS)—developed with Donaldson Timber Systems using Sigma® II—delivers lower U-values (≈0.13–0.15 W/m²K as standard), faster erection, and fewer follow-on trades than SIPs or standard timber frame. It uses hydrophobic recycled glass-wool blown fibre (no oil-based rigid foam), has BOPAS+ & BBA approvals with a 60-year assurance, and arrives ready for first-fix electrics.

Deeper wall (≈235 mm insulation zone) for superior performance and better architectural proportions.
Minimal cold bridging via double-stud geometry; OSB both sides, ventilated cavity outside.
Factory-fitted external breather membrane & airtightness detailing—no internal membrane to fit.
No insulated plasterboard needed to hit target U-values; less material, fewer trades.
Faster programme: typical HebHome reaches wind & weathertight in ~7 working days.
Stronger, stiffer racking performance and robust quality control.

CPS versus SIPs (in practice)

Thermal performance: CPS delivers ≈0.13–0.15 W/m²K as standard. A 150 mm SIP panel is commonly ~0.21 W/m²K; with extra internal layers some SIP builds reach ~0.16 W/m²K—still typically higher (worse) than CPS.

Fewer follow-on trades: CPS arrives with breather membrane & air layer resolved and a built-in service zone. SIPs usually need vapour control foil, internal service battens and often insulated plasterboard to match CPS U-values.

No oil-based rigid foam: CPS uses recycled glass-wool blown fibre (hydrophobic) rather than polyurethane/PIR cores typical in SIPs.

Adaptability on site: CPS is more forgiving for late changes and first-fix routing; SIP penetrations risk compromising the OSB/air layer.

Assurance & lending: CPS is BOPAS+ & BBA approved with a 60-year assurance, which lenders and valuers recognise for Modern Methods of Construction.

Crane requirements: Because CPS panels are heavier, the system often requires a larger crane than SIPs, which can make erection more expensive or impractical in some locations.

How CPS is built

Double-stud Sigma® II frame with separated C-studs.
Blown fibre insulation filling the deep cavity (≈235 mm).
OSB sheathing both sides; factory-fitted external breather membrane.
Internal service zone & foil-backed plasterboard—no internal VCL install required.
External ventilated cavity and cladding (timber/render/metal/masonry).

Programme & site benefits

Rapid erection: trained crew typically achieves wind & weathertight in ~7 working days (type/season dependent).
Ready for first-fix electrics: service zone avoids chasing and preserves the air layer.
Less weather risk, less waste thanks to off-site manufacture and integrated membranes.

Reviewed by Alasdair Stephen, Managing Director, and Neil Stephen RIAS, Director.

Common Questions

What is a Closed Panel System (CPS)?

CPS stands for Closed Panel System — panels are delivered closed with insulation and sheathing factory-installed, improving speed, airtightness and quality.

What U-values can CPS achieve compared with SIPs?

CPS typically achieves ≈0.13–0.15 W/m²K as standard. A 150 mm SIP panel is typically around ~0.21 W/m²K; with added internal insulation many SIP builds reach ~0.16 W/m²K. CPS usually outperforms SIPs without needing insulated plasterboard.

What insulation is used in CPS panels?

No. CPS uses hydrophobic recycled glass-wool blown fibre insulation, avoiding the polyurethane/PIR rigid foam cores common in many SIPs.

Does CPS need an internal vapour control layer fitted on site?

Not with CPS. The external breather/air layer is factory-fitted and the internal lining is designed so you don’t need to install an internal VCL on site.

Does CPS require insulated plasterboard?

No. CPS achieves its target U-values without insulated plasterboard, saving time, material and trades.

How strong is the CPS structure?

CPS provides excellent racking strength and robust fixity via its double-stud/OSB build-up, with testing and certification under BOPAS+ and BBA.

How does CPS reduce thermal bridging?

The double-stud geometry separates inner/outer studs so timber does not form a continuous path through the insulation, dramatically minimising thermal bridges.

Can I get a mortgage and warranty for a CPS HebHome?

Yes. CPS is BOPAS+ & BBA approved with a 60-year assurance, recognised by major lenders and warranty providers.

Is CPS faster to build with than SIPs?

In practice, yes. While SIP shells can go up quickly, they typically need more follow-on trades (VCL, service battens, insulated plasterboard) to hit target performance. CPS arrives closer to finished, so projects reach weathertight and first-fix faster. However, CPS will require a larger crane.

What is the difference between CPS and SIP construction?

Both deliver excellent performance. Choice depends on budget, detailing and lead time. We’ll recommend the best system for your project.
Compare: CPS vs SIP