Open joint rainscreens use deliberate gaps between panels to promote ventilation and pressure equalisation, enabling rapid drainage and drying. Closed joint rainscreens use interlocking profiles, gaskets or baffles to minimise water ingress and airflow through joints.
Both rely on a drained and ventilated cavity, selection hinges on water management, fire strategy, acoustics, aesthetics, climate, and maintenance.
Open joint systems excel for ventilation, continuous air flow drying for the removal of moisture and bacterial growth such as mold, whilst providing a visually striking shadow-gap aesthetic.
Closed joint systems prioritise water tightness and sealing of the construction, providing a seamless, continuous façade that can mimic traditional systems.
This article compares open vs closed joint rainscreen systems across performance, compliance, and lifecycle.
Table of Contents
Rainscreen Fundamentals
A rainscreen is a layered façade strategy that manages water, air, and heat using an outer weathering surface separated from the primary wall by a ventilated and drained cavity. A typical build-up includes: cladding panels, a cavity with subframe, fire barriers, continuous insulation, and an air/water control layer (AWB/AVCL) on the sheathing or structure.
Unlike curtain wall systems, rainscreens are not airtight at the outer layer; they intentionally allow a small amount of water behind the cladding, where it is controlled, drained, and dried by the continuous airflow throughout the cavity.
Performance depends on pressure equalisation (to reduce water drive through joints), robust drainage, compartmentalisation, structural integrity under wind load, and compliance with fire regulations.
Whether the joints are open or closed, the cavity must be carefully detailed and tested to CWCT methods to confirm resistance to wind-driven rain and dynamic water.
What Is an Open‑Joint Rainscreen?
Open‑joint rainscreens use intentional gaps, commonly 6–12 mm, between panel edges to create crisp, continuous shadow lines. These gaps permit air movement within the cavity, encouraging pressure equalisation across the cladding and rapid drying after rain events.
When compartmentalised, the system functions as a pressure-equalised rainscreen (PER), limiting wind pressures and reducing water penetration. Key components include a UV‑stable, breather membrane behind the joints for visual uniformity and weather protection. Where needed, they incorporate open‑state cavity barriers (OSCB) to maintain ventilation while providing fire integrity at compartment lines. They require a well-aligned subframe, and continuous insulation to reduce thermal bridging.
With open joints, the membrane can be intermittently exposed to sunlight, so UV resistance ratings and warranty coverage is critical. An insect mesh and robust drainage paths at the base of the cladding help manage ingress risks.
Open joint systems offer excellent cavity ventilation and drying, sharp architectural expression, and faster installation with fewer or the removal of gasketing components.
Detailing for Open Joints
- Specify a UV‑stable breather membrane.
- Maintain tolerances when installing the subframe to ensure panel flatness and a uniform joint aesthetic.
- Compartmentalise for PER using vertical and horizontal baffles when needed; set maximum bay sizes by calculation and test evidence.
- Provide insect mesh where appropriate; ensure unobstructed drainage paths and movement joints at transitions.
What Is a Closed‑Joint Rainscreen?
Closed‑joint rainscreens minimise direct pathways through joints using interlocking/shiplap profiles, rebated edges, or EPDM gaskets and baffles. The joints are tighter, visually more “closed”, yet the system still relies on a drained and ventilated cavity behind the cladding.
Reduced airflow through joints can lower perceived water ingress and limit UV exposure to the membrane, while still allowing the cavity to function as a pressure‑moderated space. Typical assemblies incorporate precision‑formed edges (e.g., shiplap or rebated panels), clip and rail subframes, compressible gaskets or baffles at joints, and standard cavity and barrier elements behind the cladding.
Detailing focuses on tolerance management and maintaining clear drainage routes to avoid trapping water within profiles. Where gaskets are used, material selection, service life, and replacement access are key maintenance considerations.
Detailing for Closed Joints
- Select durable EPDM or equivalent gaskets with tested longevity, weather/UV resistance, and documented replacement procedures.
- Manage tolerance stack-ups carefully; use systems that maintain joint integrity.
- Maintain drainage continuity within interlocks; incorporate pressure‑moderation details to reduce water drive.
Technical Comparison: Open vs Closed Joints
Water Management and Pressure Equalisation
Open‑joint systems, when compartmentalised, facilitate pressure equalisation within each bay, reducing differential pressure across joints and limiting wind‑driven rain penetration. Detailing must include vertical and horizontal baffles with maximum bay dimensions validated by calculation and CWCT test data.
Closed‑joint systems restrict direct paths for water entry via profiles or gaskets; they can perform strongly in hose and dynamic water tests when drainage and tolerances are meticulously managed.
Both system types require a robust drainage plane and properly lapped membranes to direct water to safe discharge points.
Airflow, Drying, and Hygrothermal Behaviour
Open joints encourage higher airflow, accelerating drying after wetting events and reducing time‑of‑wetness on materials. This can improve hygrothermal behaviour by lowering moisture accumulation risk. The designer must ensure compartmentalised techniques to eliminate wind‑washing effects that could potentially reduce the insulation performance.
Closed joints reduce airflow, which may help limit wind‑washing but also slows drying rates; careful selection of non‑hygroscopic insulation and moisture‑tolerant sheathing becomes more important.
Thermal Performance and Energy
Thermal continuity is governed more by subframe design and insulation strategy than by joint type. Both systems should minimise thermal bridges via thermally broken brackets and continuous insulation.
In hot‑humid climates, limiting moisture retention and solar heat gain is crucial.
In wet climates, open joints can aid drying and reduce interstitial moisture risks.
Energy modelling should reflect local climates and façade orientation.
Acoustic Performance
Ultimately, acoustic performance is driven by the total designed through-wall solution.
The materials selected and the quality of the installation will influence the acoustic performance. The combination of the used insulation density, the cavity depth and the internal wall construction, all play a combined factor.
The façade joint design influences flanking paths and correct detailing should be followed to achieve the desired acoustic performance.
Detail penetrations and slab edge methods to prevent acoustic flanking should be implemented as well.
Fire Safety and Regulations
In the UK, non‑combustible materials either A1 or A2-s1,d0 to EN 13501‑1 standard, are required on buildings above 18 meters in height.
Open‑state cavity barriers (OSCB) are used with open joints to preserve ventilation while achieving fire compartmentation; closed joints still require compliant cavity barriers at prescribed locations. System‑level fire performance may be demonstrated via BS 8414 testing.
Durability and Maintenance
Open joints expose the breather membrane to UV; therefore, membranes must have proven UV stability for the expected exposure fraction.
Closed joints shift maintenance toward gasket and silicone integrity; periodic inspection and potential replacements are necessary.
Both systems benefit from durable external finishes such as light weight stone panels, vitreous enamel and glass panels with rear ceramic‑coatings. These exterior cladding options offer exceptional durability, scratch, chemical, and graffiti resistance.
Aesthetics and Design Freedom
Open joints deliver strong shadow lines and crisp module expression with minimal joint hardware, ideal for contemporary façades.
Closed joints provide a more monolithic aesthetic, with flush interlocks and reduced visual recess.
Both approaches support variable panel formats, perforations, curved geometries, and rich colour/print options, provided the subframe and fixings are engineered accordingly.
Cost, Programme, and Return on Investment.
Open joints typically reduce parts and can accelerate installation, improving programme and labour costs.
Closed joints may increase material and labour due to interlocks/gaskets, higher tolerance demands, and QA checks.
Consider lifecycle costs: open‑joint membranes vs closed‑joint gasket replacement cycles, cleaning access, and potential downtime. Prefabricated, lightweight panels can reduce structural demands and transport costs, improving ROI.
Sustainability
Lightweight panels and ventilated façades reduce structural loads and can improve operational energy when paired with continuous insulation.
Open joints may shorten drying time and mitigate moisture‑related degradation, supporting long service life.
Closed joints can reduce direct UV and dust exposure to membranes and cavities, potentially lowering cleaning frequency. Select A1/A2 materials with robust EPDs and consider disassembly strategies for end‑of‑life.
Side‑by‑side summary table
| Criterion | Open‑Joint | Closed‑Joint | Best For |
| Water management | Relies on PER + drainage; higher airflow | Interlocks/gaskets reduce direct ingress | Closed‑joint in high exposure; open‑joint with proven PER |
| Drying behaviour | Fast drying; lower time‑of‑wetness | Slower drying; check materials | Open‑joint for hygrothermal resilience |
| Thermal/wind‑washing | Mitigate via compartmentalisation | Lower airflow; potential benefit | Climate‑specific decision |
| Acoustics | More flanking risk if under‑detailed | Improved perceived tightness | Closed‑joint in noise‑sensitive uses |
| Fire strategy | Requires OSCB at compartment lines | Requires compliant barriers | Both: A1/A2 materials; test evidence |
| Maintenance | Membrane UV inspection | Gasket condition/replacement | Project‑specific O&M |
| Aesthetics | Strong shadow gaps | Monolithic/flush look | Architectural intent |
| Programme/cost | Fewer parts; faster install | More parts; tighter tolerances | Open‑joint for speed; closed for exposure |
Codes, Testing, and Compliance Pathways
Compliance begins with material fire classifications (EN 13501‑1), typically A1 or A2 for external walls on relevant buildings in the UK. System‑level fire performance may be demonstrated via BS 8414 large‑scale façade testing with BR 135 assessment criteria.
Open‑joint façades require open‑state cavity barriers (OSCB) at prescribed locations to maintain ventilation while achieving compartmentation; closed‑joint systems require standard cavity barriers. Detailing must also address floor slab edges, openings, and interfaces.
CWCT testing verifies structural adequacy and weathertightness: wind resistance, impact resistance (hard/soft body), static water, hose, and dynamic water tests. Pressure‑equalised bays should be sized and baffled according to CWCT guidance and validated by test data.
In high‑exposure environments, dynamic water testing becomes particularly important for both open and closed joints.
For critical infrastructure and transportation projects, blast‑resistant performance like ISO 16933:2007 can be specified alongside fire and acoustic requirements for public saftey.
Documentation should include declarations of performance, EPDs, CWCT test reports, fire classifications, and any large‑scale fire or blast test certifications for the proposed build‑ups.
Design and Detailing Checklist
- Climate, exposure category, and building height
- Joint strategy (open vs closed), joint width, and tolerances
- Fixing strategy (visible vs secret‑fix), clip/rail compatibility
- Membrane specification and UV resistance (open joints)
- Gasket/baffle materials and service life (closed joints)
- Cavity depth, ventilation strategy, and PER compartment size
- Fire barriers: open‑state cavity barriers and standard barriers at prescribed lines
- Drainage continuity: base, openings, and intermediate weeps
- Acoustic targets and flanking control at slabs and penetrations
- Structural movement, thermal expansion, and seismic/blast allowances
- Cleaning access, replacement strategy (membrane/gaskets), warranties
- Testing and approvals: CWCT, EN 13501‑1, BS 8414/BR 135, Local country approvals
Quick specification checklist
| Item | Requirement | Notes |
| Joint type | Open or closed | Align with exposure, fire, acoustics |
| Joint width | 6–12 mm (open typical) | Project‑specific tolerances |
| Membrane | UV‑stable | UV rating and warranty duration |
| Gaskets/baffles | EPDM or equivalent | Service life and replacement access |
| Cavity barriers | OSCB + standard barriers | Locations per code and design |
| Subframe | Thermally broken brackets | Minimise thermal bridging |
| Testing | CWCT + fire compliance | Dynamic water, BS 8414 (if applicable) |
| Maintenance | Inspection plan | Membrane UV or gasket cycles |
Applications and Contextual Guidance
- High‑rise residential/office: Prioritise A1/A2 materials, robust cavity barrier strategy, and CWCT‑proven details. Open joints can be used with OSCB and PER, provided wind exposure and water testing support the design. Closed joints may simplify stakeholder acceptance on high‑exposure façades.
- Transport/infrastructure: Consider abuse resistance, cleaning, and security.
Tested bomb blast systems our mandatory in some countries to ISO 16933. Future proofing the design can eliminate the requirement to update the façade later to meet increased security design that is being implemented globally.
Healthcare/education: Durability, hygiene, and low maintenance drives material choice. Vitreous enamel and ceramic‑coated glass offer anti‑graffiti and chemical resistance, supporting long‑term OPEX reduction and easy cleaning and sanatory requirements.
Climate notes:
- Manage wind‑driven rain and freeze‑thaw; open joints can enhance drying.
- Balance the joint strategy with programme, maintenance access and lifecycle cost.
- Fully tested and certified systems reduce risk and potential future costs.
How Dynamic Cladding Supports Project Needs
Dynamic Cladding manufactures lightweight, prefabricated panel systems engineered as open-joint ventilated rainscreen façades, ensuring moisture resistance, durability, and fire safety.
- DynaPanel Glass: A1 non-combustible ceramic-coated glass on a cementitious backer. Extensive RAL, metallic, and photorealistic print options deliver precise colour control for ventilated façades.
- DynaPanel Stone: A2 s1 d0 natural stone veneer (4–6 mm) bonded to a cementitious backer, up to 50% lighter than traditional stone cladding, available in polished, honed, brushed, or flamed finishes.
- DynaPanel Vitreous Enamel: A1, exceptionally durable with anti-graffiti and chemical resistance, suitable for high-traffic and public infrastructure.
All systems are CNC-engineered for tight tolerances and are secret-fix solutions. The system can be integrated with open-state cavity barriers and other project-specific detailing.
For high-security environments, the DynaPanel systems are tested to ISO 16933:2007 for both PBIED and VBIED blast resistance.
Our technical team provides project and product information. We support the complete project process, from specification writing to on-site training. We can provide design services covered by PI Insurance. Our offering is a full solution from concept to installation, accelerating delivery while maintaining compliance. Request a project-specific review and samples to validate the optimal project strategy, performance testing, and cost plan for your façade.
FAQs
Are open‑joint rainscreens watertight enough for high‑exposure sites?
Yes, when designed as pressure-equalised rainscreens (PER) with validated compartment sizes, robust membranes, and CWCT dynamic water test evidence. Detailing must ensure effective drainage and correctly placed cavity barriers.
Do open joints reduce thermal performance?
No, open joint ventilated rainscreen facades are designed to improve thermal performance. The open joint system creates a ventilated air gap between the cladding and the building’s exterior wall. This gap helps to cool the building during hot summer months and provides insulation in cooler weather. To work effectively in various climates and seasons, the system requires careful design.
When are open‑state cavity barriers required?
OSCBs are typically used with open‑joint systems to maintain ventilation while providing fire compartmentation at slab edges and prescribed lines. They expand in fire to close the cavity, meeting the required period of integrity/insulation.
Locations and product selection must align with local codes and tested details, regardless of the joint type.
Will UV degrade the membrane behind open joints?
Without proper specification, yes. Select a membrane with documented UV resistance for the anticipated exposure fraction, validated by third‑party testing and backed by warranty.
Do closed joints eliminate the need for a breather membrane?
No. Closed joints reduce direct pathways but do not create a fully sealed outer leaf. A breather membrane (or AWB behind insulation) still manages incidental moisture and air movement and is part of the tested assembly. Drainage and ventilation provisions remain essential.
Which joint strategy is better acoustically?
Either strategy can meet the acoustic targets with system appropriate wall build‑ups. Acoustic performance is primarily driven by the mass and continuity of the backing wall, cavity depth, insulation density, and detailing at interfaces.
