Description
Visqueen Gas Barrier NF-400
Visqueen Gas Barrier NF-400 is a 0.4mm (400 micron) co-extruded, multi-layer thermoplastic gas membrane designed to provide protection against the ingress of harmful levels of methane, carbon dioxide and radon in buildings. The membrane has a blue upper surface and white underside and is supplied as a 2.4m x 43.5m roll.
Suitable for use above or below reinforced cast in situ concrete floor slabs, including ground-bearing, suspended and raft slabs, as well as above precast suspended segmental subfloors such as beam and block floors. It can also function as a high-performance radon membrane and damp proof membrane, providing a versatile solution for ground gas and moisture protection.
Key Benefits
- 0.4mm (400 micron) multi-layer thermoplastic gas membrane
- Designed to provide protection against methane, carbon dioxide and radon
- Suitable for all Characteristic Gas Situation (CS) ground gas regimes
- BDA Agrement Certificate BAB-24-339-P-A-UK
- Complies with the methane gas transmission rate, mass per unit area and thickness requirements of BS 8485:2015 + A1:2019
- Complies with NHBC Foundation NF94 guidance for Type A membrane locations using a non-foil system
- Conforms to the specification requirements of NHBC Amber 1 and Amber 2 applications
- Conforms to the specification requirements of BR 211:2023
- UKCA, UKNI and CE to EN 13967:2012
- Can also be used as a radon and damp proof membrane
- Suitable for installation above or below reinforced concrete floor slabs
- Can be jointed by heat welding or taping, depending on the project specification
- High elongation and tear resistance
- Passes watertightness testing at 2kPa for 24 hours, including after ageing and alkali exposure
Applications
Visqueen Gas Barrier NF-400 is designed for ground gas protection in a wide range of building applications, including:
- Ground-bearing concrete floor slabs
- Suspended concrete floor slabs
- Raft foundations
- Beam and block floors
- Precast suspended segmental subfloors
- Radon protection
- Methane gas protection
- Carbon dioxide protection
- Damp proofing applications
- Type A membrane locations in accordance with the stated NHBC NF94 guidance
The membrane can also be used around complex detailing areas such as internal and external walls, corners, doorway thresholds, service pipes, party walls and structural columns, using suitable detailing components to maintain continuity of the gas protection layer.
Technical Information
| Property | Specification / Result |
|---|---|
| Product | Visqueen Gas Barrier NF-400 |
| Product type | Co-extruded, multi-layer thermoplastic gas membrane |
| Nominal thickness | 0.4mm (400 micron) |
| Roll dimensions | 2.4m x 43.5m |
| Approximate roll area | 104.4m² before allowance for laps and detailing |
| Colour | Blue upper surface / white underside |
| Mass per unit area | >370g/m² |
| Tensile strength – machine direction | 26.3 N/mm² |
| Tensile strength – cross direction | 29.4 N/mm² |
| Elongation at break – machine direction | 607% |
| Elongation at break – cross direction | 921% |
| Joint strength – taped joint | 217 N/50mm |
| Joint strength – welded joint | 405 N/50mm |
| Watertightness at 2kPa for 24 hours | Pass |
| Resistance to impact | 400mm |
| Low temperature flexibility | -20°C |
| Methane gas transmission rate – membrane | 13.2 ml/m²/day/atm |
| Methane gas transmission rate – welded joint | 15 ml/m²/day/atm |
| Carbon dioxide gas transmission rate | 22 ml/m²/day/atm |
| Radon gas transmission rate | <3.0 x 10⁻⁹ m/s |
| Puncture CBR | 1620 N |
| Water vapour permeability | 0.08 g/m²/d |
| Water vapour resistance factor | 1,140,000 |
| Water vapour diffusion equivalent air layer thickness | 459m |
Technical values above are taken from the manufacturer's August 2026 datasheet.
Approvals and Standards
Visqueen Gas Barrier NF-400 has BDA Agrement third-party accreditation, certificate BAB-24-339-P-A-UK. The datasheet states that the product complies with the methane gas transmission rate, mass per unit area and thickness requirements of BS 8485:2015 + A1:2019, is suitable for all Characteristic Gas Situation ground gas regimes, and complies with the stated NHBC Foundation NF94 guidance for Type A membrane locations.
The membrane also conforms to the specification requirements of NHBC Amber 1 and Amber 2 applications and BR 211:2023, with UKCA, UKNI and CE marking to EN 13967:2012.
Application Guidance
Visqueen Gas Barrier NF-400 should be installed with the blue side facing upwards onto a smooth, continuous substrate. Suitable substrates include grouted beam and block floors, compacted sand blinding and smooth concrete blinding. The substrate should be free from sharp protrusions, loose aggregates, voids, projections and mortar deposits.
The membrane should be loose laid with sufficient overlap to allow the specified jointing method. The manufacturer recommends on-site welding of lap joints using hot wedge or hot air welding. For hand welding, an approximately 100mm overlap and approximately 35mm weld are normally achieved.
Where taped joints are specified, the sheets should be overlapped by approximately 100mm and bonded using VisqueenPro Double Sided Jointing Tape, with the joint subsequently sealed using Visqueen NF-60 or NF-150 Lap Tape as appropriate to the project specification.
Installation should be carried out by a competent contractor experienced with this type of product, and the manufacturer states that installation should be subjected to third-party validation in accordance with BS 8485:2015 + A1:2019 and CIRIA C735.
After installation, the membrane should be protected from following trades and prolonged UV exposure using an appropriate protective layer. Care should be taken to prevent the membrane from being punctured, stretched or displaced.
When taped lap joints are used, the air temperature should not be below 5°C or falling. Where ambient temperatures exceed 25°C or are rising, the barrier should be covered immediately after installation.
Important: Visqueen Gas Barrier NF-400 is not intended for applications where there is a risk of hydrostatic pressure. For CS4 and above site or zone characteristic gas situations, the manufacturer advises contacting the Visqueen Technical Office.
System Components
Suitable system components listed by the manufacturer include:
- VisqueenPro Double Sided Jointing Tape, 50mm x 10m
- VisqueenPro Detailing Strip, 300mm x 10m
- Visqueen TreadGUARD 1500, 1m x 2m
- Visqueen TreadGUARD 300, 2m x 75m
- Visqueen Ultimate Top Hat Units
- Visqueen NF-Detailing Strip, 300mm x 10m
- Visqueen NF-60 Lap Tape, 60mm x 45m
- Visqueen NF-150 Lap Tape, 150mm x 10m
FAQs
What is Visqueen Gas Barrier NF-400 used for?
It is a ground gas membrane designed to help prevent the ingress of harmful levels of methane, carbon dioxide and radon. It can also be used as a radon and damp proof membrane.
What size is a roll of Visqueen Gas Barrier NF-400?
Each roll measures 2.4m x 43.5m, providing approximately 104.4m² of membrane before allowing for laps, joints and detailing.
Which way up should Visqueen NF-400 be installed?
The membrane should be installed with the blue side facing upwards onto a smooth, continuous substrate.
Can Visqueen NF-400 be welded or taped?
Yes. The datasheet provides both heat-welded and taped jointing methods. The correct method should be determined by the project specification.
Is Visqueen Gas Barrier NF-400 suitable for hydrostatic pressure?
No. The manufacturer's datasheet specifically states that the barrier is not intended for use where there is a risk of hydrostatic pressure.
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