The PHS Sd Variable Plus Airtight Membrane is a robust, flexible, and high-performance membrane designed to create a fully airtight building envelope while dynamically controlling vapour diffusion. Its variable Sd value from 0.4 to 35m allows the membrane to adapt to changing environmental humidity, ensuring optimal moisture control and preventing condensation build-up that can lead to structural damage and mildew growth.
Ideal for flat roof builds, retrofits, and applications using air-injected insulation or insulation mats, the PHS Sd Variable Plus is made from triple-layer non-woven polypropylene (PP) fabric with a reinforced mesh, providing both durability and tear resistance. It is suitable for ceilings, walls, floors, and loft spaces, and can be used across multiple construction types including block, steel frame, and timber frame buildings.
Key Features & Benefits
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Robust and Flexible – Durable membrane that adapts to structural movements.
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Highly Tear-Resistant – Reinforced mesh fabric ensures long-term reliability.
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Variable Diffusion Resistance – Adjusts Sd value between 0.4–35m depending on humidity levels.
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Moisture-Adaptive – Prevents condensation build-up and moisture damage.
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Compatible with Insulation – Works with air-injected insulation and insulation mats.
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CE-Approved Quality – Suitable for professional construction projects and retrofits.
Applications
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Internal installation to create a reliable airtight envelope
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Particularly suited for flat roofs and retrofit projects
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Ceilings, internal walls, floors, and loft spaces
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Compatible with block, steel frame, and timber frame buildings
Technical Specifications
| Property |
Specification |
| Colour |
Grey graphics on white |
| System |
Airtight, Retrofit |
| Elongation Longitudinal |
24% |
| Elongation Transverse |
24% |
| Mass Per Unit Area |
103 g/m² |
| Material |
Airtight Membrane |
| Resistance to Fire |
Class E |
| Roll Area |
75 m² |
| Roll Weight |
7.7 kg |
| Water Vapour Resistance – Sd Value |
0.4–35 m, Variable |
| Size |
1.5 m × 50 m |
| Tear Resistance Longitudinal |
230 N |
| Tear Resistance Transverse |
230 N |
| Tensile Strength Longitudinal |
387 N/50mm |
| Tensile Strength Transverse |
387 N/50mm |
| Thickness |
0.27 mm |
| Water Penetration Resistance |
Class W1 |
| Application Area |
Ceiling, internal wall, loft space |
| Type of Build |
Block, steel frame, timber frame |
| Airtightness |
<0.01 m³/(m²·h·50Pa) |
| Approx Coverage |
67 m² |
| μ-Value |
48,148 |
Installation Guide
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Lay the membrane with the printed side facing the fitter.
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Align sheets parallel or perpendicular to rafters, ensuring at least 10cm overlap.
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Ensure flush-mounted bay insulation, with no cavities between insulation and membrane.
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The translucent membrane allows easy visibility of markings, measurements, and fixtures.
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Fit the membrane without tension and avoid creases.
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Seal all overlaps, component joints, and penetrations using PHS sealing products, including tapes and sealants.
Why Choose PHS Sd Variable Plus
The PHS Sd Variable Plus Membrane offers a dynamic, moisture-adaptive solution for airtightness and vapour control in modern building envelopes. Its variable Sd value, robust construction, and compatibility with insulation make it ideal for flat roofs, retrofits, and complex interior installations, ensuring long-term protection against condensation, drafts, and heat loss while improving energy efficiency.
