Visqueen Gas Venting Systems

Design Service & Complete Gas Ventilation Solutions in accordance with BS8485; 2007

Gas Venting Systems

0845 302 4758 visqueenbuilding.co.uk

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Background

Visqueen Airbrick

BS 8485:2007 Code of Practice

Visqueen Gas Fitting Index

Passive Venting Solution & Design

Complete System

Visqueen Gas Vent Mat

Product Installation

System Overview - Gas Flow Fittings and Outlets

Technical Support

Visqueen Flood Resistant Gas Vent Box

Visqueen Gully Vents

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15

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18

6

21

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24

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Table of Contents

Permission to reproduce extracts from BS 8485:2007 is granted by the British Standards Institution (BSI). No other use of this material is permitted. The complete British Standard can be purchased from the BSI online shop: http://shop.bsigroup.com/en/ProductDetail/?pid=000000000030149737

The information given in this brochure is based on data and knowledge correct at the time of printing. Statements made are of a general nature and are not intended to apply to any use or application outside any referred to in the brochure. As conditions of usage and installation are beyond our control we do not warrant performance obtained but strongly recommend that our installation guidelines and the relevant British Standard Codes of Practice are adhered to. Please contact us if you are in any doubt as to the suitability of application.


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The hazards of ground gases must be taken into account when designing and constructing new developments. Ground gas can be drawn into a building by the pressure difference that exists between the inside and outside of the building (warm indoor air is less dense than cold outdoor air). Ground gases can enter buildings through:

1. Cracks in solid floors2. Construction joints3. Cracks in walls below ground4. Gaps in suspended concrete or timber floor5. Gaps around service pipes6. Cavities in walls7. Soil and vent pipes

Background

1


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Common ground gases and contaminates

HydrocarbonsHydrocarbons can be highly toxic and are aderivative of the petrochemical industry.Hydrocarbons are prevalent in areas such asdisused petrol stations and post industrial sites.Most hydrocarbons are carcinogenic and potentially flammable.

MethaneAn odourless flammable gas that is explosivewhen released to the atmosphere at levels aslow as 5% and exposed to a source of ignition.Methane is formed wherever there is below-grounddegradation of organic substances e.g. landfillsites, sewage treatment areas, mining localitiesand peat bogs.

Carbon DioxideCarbon Dioxide is a colourless, odourless gas that in high concentrations can result in asphyxiation.The gas is formed by the oxidation of carboncompounds such as in landfill sites. When carbondioxide levels reach concentrations of 3%symptoms of headaches and shortness of breathcan occur, becoming severe at 5%, with loss ofconsciousness at 10%. It’s potentially fatal at concentrations of 22% and above.

RadonRadon is a naturally occurring radioactive gasthat is odourless and colourless. It is formedwhere uranium and radium are present. It migrates into any building that is built over the source. If it accumulates in a building at unacceptably high concentrations it will increase the potential risk of the occupants developing lung cancer.

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The standard is broken down into the following key elements:

1. Site categorisation and investigationA desk study should provide sufficient information on sources, pathways and receptors for these to be investigated. Once any potential gases have been identified a full ground gas investigation must be undertaken using borehole testing and analysis.

2. Risk assessment objective – Determining the gas flow rateThis sets out how the data collected during site monitoring visits that measure hazardous gas emis-sions from specific monitoring points can be assessed and used to arrive at one value that repre-sents the whole site (or set of values if a large site would be best split up into zones). After determin-ing the gas flow rate it is then characterised in the table below:

BS 8485:2007 Code of Practice for the characterisation and remediation of gas contiminated land in affected developments

This standard is intended to provide a framework that will allow designers to judge the adequacy of ground gas and related site investigation data, providing an approach to determining appropriate ground gas parameters. This can be used to identify a range of possible construction solutions that will mitigate the presence of ground gas on a development site.

3

Qhg = Chg

100q

Terms and definitionsFor the purposes of this document the following apply.NOTE: These terms are not to be confused with similar terms in other referenced documents.

Ground gaspotentially hazardous gas, generated below ground NOTE: The most common ground gases are methane and carbon dioxide.

Measured flow rateqtotal gas flow from a borehole measured in volume per unit time (typically litres per hour)

Measured hazardous gas concentrationChg

concentration of a specific hazardous gas measured as a percentage ofthe total gas volume from a borehole

Calculated hazardous gas flow rateQhg

calculated flow rate of a specific hazardous gas from a boreholereading, i.e.


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Table 2.

Characteristicgas situation

NHBCtraffic lightVery low

Required gas protection

Non-managed property, e.g.private housing

Public buildingCommercialbuildings

Industrial buildings

123

GreenAmber 1Amber 2

034

033

022

01 C)

2

456

Red 6 D) 5 D)

6 E)

457

346

NOTE Traffic light indications are taken from NHBC Report no.: 10627-R01 (04) [3] and are mainly applicableto low-rise residential housing. These are for comparative purposes but the boundaries between the traffic lightindications and CS values do not coincide.

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3. Solutions – Recommended gas protectionHaving ascertained the characteristic gas situation, as the final part of the process, the appropriate gas protection measures should be selected for the building. There are a great number of existing designs and component elements available in the current market (and others being developed constantly); Table 2 and Table 3 give a guide as to the relative performance of the various types of designs and systems available today. Given the combined design gas regime and risk factors, a guidance value for the required gas protection in the range 0 to 7 should be obtained from Table 2. Then, a combination of ventilation and/or barrier systems should be chosen from Table 3 to meet that requirement using a point scoring mechanism.

NOTE: The side characteristic hazardous gas flow rate is synonymous with the “gas screening value” inCIRIA C665 and NHBC Report no.: 10627-R01 (04) [3].

Table 1.

Characteristicgas situation

Hazard potential

Site characteristic hazardous gas flow rate, Qhgs lh

–1Additional factors

1 Very low <0.07 Typically ≤1% methane concentration and ≤5% carbon dioxide concentration (otherwise consider an increased characteristic gas regime)

2 Low ≥ 0.07, <0.7 Typical measured flow rate <70 l/h (otherwise consider an increased characteristic gas regime)

3 Moderate ≥ 0.7, <3.5

4 Moderate to high

≥ 3.5, <15

5 High ≥ 15, <70

6 Very high ≥70


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b) Barriers

Floor slabsBlock and beam floor slabReinforced concrete ground bearing floor slab

Reinforced concrete ground bearing foundation raft with limited service penetrations that are cast into slab

Reinforced concrete cast in situ suspended slab with minimal service penetrations and water bars around all slab penetrations and at joints

Fully tanked basement

0

0.5

1.5

1.5

2

It is good practice to install ventilation in all foundation systems to effect pressure relief as a minimum.

Breaches in floor slabs such as joints have to be effectively sealed against gas ingress in order to maintain these performances.

c) Membranes

Taped and sealed membrane to reasonable levels of workmanship/in line with current good practice with validation

Proprietary gas resistant membrane to reasonable levels of workmanship/in line with current good practice under independent inspection

Proprietary gas resistant membrane installed to reasonable levels of workmanship/in line with current good practice under CQA with integrity testing and independent validation.

0.5

1

2

The performance of membranes is heavily dependent on the quality and design of the installation, resistance todamage after installation, and the integrity of joints.

d) Monitoring and detection (not applicable to non-managed property, or in isolation)

Intermittent monitoring using hand held equipment

Permanent monitoring and alarm system

Installed in theunderfloor venting / dilution system

0.5

2

1

Where fitted, permanent monitoring systems ought to be installed in the underfloor venting/dilution system in the first instance but can also be provided within the occupied space as a fail safe.

Installed in the building

e) Pathway intervention

Pathway intervention — This can consist of site protectionmeasures for off-site or on-site sources

Table 3.

Protection Element/ System Score Comments

a) Venting/dilution (see Annex A)

Passive sub floor ventilation (venting layer can be a clear void or formed using gravel, geocomposites, polystyrene void formers, etc.)

Very goodperformance

2.5 Ventilation performance in accordance with Annex A.

If passive ventilation is poor this is generally unaccept-able and some form of active system will be required.

There have to be robust management systems in place to ensure the continued maintenance of any ventilation system. Active ventilation can always be designed to meet good performance. Mechanically assisted systems come in two main forms: extraction and positive pressurization.

Assumes car park is vented to deal with car exhaust fumes, designed to Building Regulations Document F [5] and IStructE guidance [6].

Good performance

1

Subfloor ventilation with active abstraction/pressurization (venting layer can be a clear void or formed using gravel, geocomposites, polystyrene void formers, etc.)

Ventilated car park (basement or undercroft)

2.5

4

5


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Current UK construction practice adopts the concept of multiple gas protection measures to form a gas control system, typically protection measures increase in number and robustness as the potential risk increases. The gas protection solution is based on the point scoring system from BS 8485:2007.

Visqueen has developed a comprehensive passive venting solution to facilitate the dilution and dispersal of dangerous gases. Used extensively across the UK, the system comprises of:

• Visqueen Gas Vent Mat

• Visqueen Gas Flow Fittings

• Visqueen Gas Vent Outlets including the unique Flood Resistant Gas Vent Box

• Visqueen Gas Membranes & Gas Resistant DPCs

Specification

To determine what system is required we would require a copy of the site investigation report, foundation layout and perimeter sections for the purpose development. If venting is required, in accordance with the guidance provided within BS8485: 2007, Visqueen Technical Support Team will specify the most cost effective solution.

Visqueen Gas Vent Mat can be laid in various methods:

• Blanket Coverage: Covers the entire floor area, usually required on more heavily gassing sites

• Percentage Coverage: Installed in strips to cover specific percentage area of the building’s footprint

• Bespoke: Installed in strips at predetermined centres

Passive Venting Solution & Design

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Visqueen Gas Vent Mat• Lightweight and easy to install

• High gas flow capacity

• Creates a de-pressurisation zone for collection of ground gases

• Cost effective compared to traditional below slab perforated pipework and fill Description

The Visqueen Gas Vent Mat comprises a cuspated HDPE (High Density Polyethylene) core bonded to a non-woven polypropylene geotextile filter membrane. Visqueen Gas Vent Mat is 25mm thick and supplied in 900mm x 50m roll format.

Installation Information

The Visqueen Gas Vent Mat is designed to be installed with the geotextile filter side of the product in contact with the ground.

The product can be laid as single strips at predetermined centres beneath a ground bearing slab or raft foundation to create a strip effect or butted together to create a blanket.

When installing in strip format, careful consideration should be given to the foundation and super structure design in order for the vent mat to be positioned accordingly to avoid over complex detailing. Please consult with the Visqueen Technical Support Team for assistance when designing and detailing a strip venting design system.

Jointing

Where a venting blanket is required, unroll the mat into position. The next roll should be placed in a similar way to the first so the dimpled cores butt together. The geotextile filter membrane extends beyond the width of the dimpled HDPE core at one side; this creates an overlap. Continue installing further rolls in a similar manner to create the blanket.

Technical Data

Characteristic Units ValueWidth mm 900Length m 50Thickness mm 25Compressive Strength N 3000Roll Weight kg 80Roll Diameter m 1.3In-plane air flow capacity with soft/hard platens @ 20 mm and 100kPa l/m/s 155

Shear Strength kN 1

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System OverviewGas Flow Fittings and OutletsVisqueen offer a variety of solutions to disperse gas from beneath buildings. The type of passive venting outlet and fitting to disperse gases is dependant on the building type and the amount of gas flow - Please consult Visqueen Technical Support Team for further information. Visqueen’s complete outlet system consists of the following options:

• Flood Resistant Gas Vent Box

A high performance ground level vent provides an unobtrusive method of venting around the perimeter of a building. Typical building applications are curtain walling and glazing where the ducting cannot be taken through a perimeter wall. The Flood Resistant Gas Vent Box is available with a variety of lid types providing options for different levels of airflow, appearance and safety.

Visqueen also offer Gully Vents in two options; Circular and Rectangular, please refer to page 13.

• Airbricks

The UV stabilised polypropylene airbricks are available in a variety of colours to blend into masonry walls. Airbricks can also provide a cross ventilation method beneath suspended beam and block floor type constructions.

• Vent Bollards

Visqueen’s Gas Vent Bollards are available in a variety of finishes for an aesthetic yet functional means to terminate the venting. Typical applications include commercial buildings, retail parks, warehouses and distribution centres.

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Airbrick

Flood Resistant Gas Vent Box

Vent Bollard


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• Unique design reduces the risk of water flooding into the void

• Releases harmful gases safely into atmosphere

• Supplied with a variety of lids to suit most applications

• Part of the Visqueen Gas Venting System

Visqueen’s unique high performance Flood Resistant Gas Vent Boxes provide an alternative to passive periscope vents and airbricks in masonry for subfloor ventilation. When fixed to connecting pipe work and geocomposite void formers they provide controlled release and dispersal of gas from the ground to the surrounding atmosphere and reduce the risk of flooding into the void below.

Visqueen Flood Resistant Gas Vent Box

Description

Visqueen Ground Vent boxes comprise of a High Density Polyethylene (HDPE) base with two 110mm pipe connections; the first to connect to the venting system and the second to connect to the stormwater / land drainage system. There are various options of slotted and perforated lids manufactured from a variety of materials, from stainless steel to plastic, to ensure gas collected from beneath the building is harmlessly vented to the atmosphere. Provision is also made for a side connection to the vent box.

Application

Typical building applications are curtain walling and glazing where the ducting cannot be taken through a perimeter wall. Visqueen flood resistant gas vent boxes provide an alternative to passive periscope vents in brick and blockwork for subfloor ventilation. When fixed to connecting pipe work and geocomposite void formers they provide controlled release and dispersal of gas from the ground to the surrounding atmosphere.

High Airflow = 19,200mm² free air capacity

High or Low Airflow Lid Options

The Visqueen Flood Resistant Gas Vent Box is supplied with varying lid options to suit most applications including:

• High airflow (slots) - for general use in pavements, non road or landscaped areas. Free air capacity 19,200mm2.

500mm

300mm

150mm

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Gas Flow Fittings

Visqueen offers various fittings that connect the vent mat to the Visqueen Flood Resistant Gas Vent Box thus ensuring the gas is efficiently dispersed from beneth the building.

Please see next page for a typical detail.

Low Airflow: 6mm perforations = 5,994mm² free air capacity

Gas Vent MatGas Vent Pipe (Cut) (VT008)

90o Bend (VT002)

Gas Vent Mat Connector with Pipe (VT011)


The lids are available with various finishes including:

• Stainless steel

• Galvanised steel

Please note all vent box options are only suitable for pedestrian traffic. Should a road traffic rated vent be required please contact the Visqueen Technical Support Team for further advise.

Installation

The vent box should be placed on a minimum of 150mm deep, 20mm diameter shingle. The unit should be surrounded with 150mm of concrete to the top of the box and smoothed level to allow the gully grate lid to be positioned on top of the unit.

Visqueen Flood Resistant Vent Box Product Options:

• Low airflow (perforations) - specifically designed for safety e.g. child friendly lids within a school environment. Free air capacity 5,994mm2.

Product Reference Product Description

VT020A Flood Resistant Gas Vent Box Stainless Steel High Airflow

VT020B Flood Resistant Gas Vent Box Stainless Steel Low Airflow

VT020C Flood Resistant Gas Vent Box Galvanised Steel High Airflow

VT020D Flood Resistant Gas Vent Box Galvanised Steel Low Airflow

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Typical Flood Resistant Gas Vent Box System Detail

1

2

3

4

Geocomposite Vent Mat 25mm

VT011 Gas Vent ConnectorVT008

Gas Vent Pipe

VisqueenFlood Resistant Gas Vent Box and Lid

VT002 90o Bend

Stormwater Drainage

GL150

FFL

Key: Visqueen Gas Protection Membranes/ DPC :-

1 Visqueen Gas Barrier

2 Visqueen Zedex High Bond DPC on HP Tanking Primer

3 Visqueen 100mm Double Sided Tape

4 Visqueen 150mm GR Lap Tape

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75

300

125

125

500

125

125

1:60 fall

Drip

Stainless steel perforated lid secured using 4 no. counter sunk threaded allen bolts

Perforations to be 6mm or slots with 8mm

110mm vent & drain pipe spigots

Connect vent to sub-floor ventilation layer or vented void

Connect drain to stormwater / land drainage system

Drain pipe outlet to have 10 mm removable mesh cover to preventdebris from entering / blockingthe system

Internal catchment tray to fall 1:60to centre of box

Drip along exposed edge

Provisions is also made for side connection to the vent box.

Line of catchment tray above

Section

Plan

Isometric

Vent

Dra

in


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Visqueen Gully Vents• Releases harmful ground gases safely into atmosphere

• Available in circular or rectangular options

• Fully compatible with the Visqueen gas venting system

• Costeffective ground level option

Visqueen's Rectangular and Circular Gully Vents provide an alternative to passive periscope vents in airbricks in masonry for subfloor ventilation. When fixed to connecting pipe work and geocomposite void formers they provide a controlled release and dispersal of gas from the ground to the surrounding atmosphere.

Description

Visqueen's Rectangular and Circular Gully Vents comprise of a High Density Polyethylene (HDPE) base with a 110mm pipe inlet and a galvanised steel lid. The rectangular vent box is available with two lid options comprising of both perforated and slotted finishes.

Application

Typical building applications are curtain walling and glazing where the ducting cannot be taken through a perimeter wall. Visqueen gully vent boxes provide an alternative to passive periscope vents in brick and blockwork for subfloor ventilation. When fixed to connecting pipe work and geocomposite void formers they provide controlled release and dispersal of gas from the ground to the surrounding atmosphere.

Circular Gully Vent

Free Airflow Capacity 7,000mm²

SectionPlan

13

320mm*

50mm

690mm

320mm

*Bespoke heights available


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Installation

The gully vent should be placed on a minimum of 150mm deep, 20mm diameter shingle. The unit should be surrounded with 150mm of concrete to the top of the box and smoothed level to allow the gully grate lid to be positioned on top of the unit.

Rectangular Gully Vent

Visqueen's Rectangular Gully Vent has two lid options to suit most applications.

These are the following:

• Low airflow (6mm holes) - specifically designed for security e.g. child friendly lids within a school environment. Free air capacity 6,840mm2.

• High airflow (6mm wide slots) - for general use in pavements, non road or landscaped areas. Free air capacity 18,100mm2.


VT021 Circular Gully Vent Stainless Steel

VT022A Rectangular Gully Vent Stainless Steel High Airflow

VT022B Rectangular Gully Vent Stainless Steel Low Airflow

Low airflow (6mm perforations)= 6,840mm2 free air capacity

High airflow (6mm wide slots)= 18,100mm2 free air capacity

SectionPlan

14

320mm*

50mm

690mm

320mm

*Bespoke heights available


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Visqueen Airbricks are made from UV stabilized polypropylene and are available in various colours. The robust interlocking airbricks have a textured finish while installation is fast with airbricks replacing external masonry. The free airflow capacity is 6,000mm².

Colour Options

• Black

• Terracotta

• Anthracite

Airbrick and Connections Solution

Gas flow fittings

Visqueen offer various fittings that connect the vent mat to the airbricks thus ensuring the gas is efficiently dispersed from beneath the building to the atmosphere. A typical system build up is illustrated below.

Gas Vent Mat Gas Vent Mat Connector (VT010)

Extension Sleeve (VT015) Airbrick Terracotta (VT024B)

Adjustable Z Vent (VT014)


VT024A Airbrick Black*

VT024B Airbrick Terracotta*

VT024C Airbrick Anthracite*

70mm

57mm

210mm

* To be used in conjunction with Adjustable Z Vent (VT014) to connect to vent mat to air brick. Adjustable air vent can be adjusted vertically to a height between and adjusted horizontally using extension sleeve VT015.

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Our range of gas venting bollards include self finished stainless steel, powder coated steel (as shown) and HDPE. They provide an aesthetic yet functional solution for dispersing ground gases into the atmosphere, particularly when a vent pipe with a high free air capacity is required. The bollards are made to a high standard and are easy to install. The Gas Venting Bollard is 1200mm in height, allowing for a standard 800mm-900mm above external ground finish level. The 110mm diameter gas venting bollard allows for a 25,000mm² free air flow.

Bollard Size (height x diameter):

1200mm x 110mm

Free Air Capacity

25,000mm²

Material finishes:• Stainless steel• Powder coated steel (as shown)• High Density Polyethylene (HDPE)

Visqueen Vent Bollard

Gas flow fittings

Visqueen offer various fittings that connect the vent mats to the bollard thus ensuring the gas is efficiently dispersed from beneth the building. A typical system is illustrated to below.

Gas vent mat

Gas Vent Pipe (Cut) (VT008)

90o Bend (VT002)

Gas Vent Mat Connector with Pipe (VT011)


VT023A Gas Vent Bollard Stainless Steel

VT023B Gas Vent Bollard Powder Coated Steel

VT023C Gas Vent Bollard HDPE

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Typical Visqueen Gas Vent Bollard Detail

150

1

2

3

4

Geocomposite Vent Mat 25mm

VT011 Gas Vent Connector

VT008Gas Vent Pipe

VT008Gas Vent Pipe

VT023 (A, B or C) Gas Vent Bollard

VT002 90o Bend

GL

150

FFL

Key: Visqueen Gas Protection Mebranes/ DPC :-

1 Visqueen Gas Barrier

2 Visqueen Zedex High Bond DPC on HP Tanking Primer

3 Visqueen 100mm Double Sided Tape

4 Visqueen 150mm GR Lap Tape

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Gas Fittings Index

VT002 90o Bend*

VT005 Solid Carrier Pipe VT006 Slotted Carrier Pipe

VT009 Flexible Connector PipeVT007 Slitted Carrier Pipe VT008 Gas Vent Pipe

VT004 End Cap

VT003 Coupling* ***PVC

**Multifit option also

available see Product index.

VT001 ‘T’ Fitting*

330mm220mm

3m

990mm

1.5m

220mm200mm

3m

120mm

40mm

I.D 108mm

I.D 108mm

I.D 119mm

70mm

60mm

70mm

3m

All buried fittings and pipes are HDPE (High Density Polyethylene) unless stated

Twin Wall Smooth

*PVC *PVC

1.5m

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All buried fittings and pipes are HDPE (High Density Polyethylene) unless stated

Twin Wall Smooth

VT010 Gas Vent Mat Connector

VT012 Gas Vent Mat Connector with Pipe

VT014 Adjustable Z Vent

915mm

336mm50mm

100mm

915mm

50mm

200mm

100mm

330mm

243mm

VT015 Extension Sleeve**Also available as vertical extension sleeve see product index

550mm

220mm290mm

210mm

70mm

VT013 Vent Pipe Adaptor

215mm

105mm

42mm

VT011 Gas Vent Mat Connector Slotted

990mm (Slot)

1130mm

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Gasflow FittingsProduct Reference Product Description Compatibility

VT001 T Fitting VT005,006 & 007

VT002 900 Bend VT005,006 & 007

VT003A Standard Coupling VT005,006 & 007

VT003B Multi Fit Coupling VT005,006 & 007

VT004 End Cap VT005,006 & 007

VT005 Solid Carrier Pipe (Coupler Included)

VT006 Slotted Carrier Pipe

VT007 Slitted Carrier Pipe (Coupler Included)

VT008 Gas Vent Pipe

VT009 Flexible Connector Pipe VT005, 006 and 007

VT010 Gas Vent Mat Connector Vent Mat 25mm; VT014 & 015A

VT011 Gas Vent Mat Connector Slotted Vent Mat 25mm; VT005 & 006

VT012 Gas Vent Mat Connector with Pipe Vent Mat 25mm; VT005

VT013 Vent Pipe Adaptor VT005 & VT014

VT014 Adjustable Z Vent VT010, 13, 015 & 024

VT015A Extension Sleeve (Horizontal) VT010, 013 & 014

VT015B Extension Sleeve (Vertical) VT014

Visqueen Gas Venting Product Index

OutletsProduct Reference Product Description Compatibility

VT020A Flood Resistant Gas Vent Box Stainless Steel High Airflow VT002

VT020B Flood Resistant Gas Vent Box Stainless Steel Low Airflow VT002

VT020C Flood Resistant Gas Vent Box Galvanised Steel High Airflow VT002

VT020D Flood Resistant Gas Vent Box Galvanised Steel Low Airflow VT002

VT021 Circular Gully Vent Stainless Steel VT002

VT022A Rectangular Gully Vent Stainless Steel High Airflow VT002

VT022B Rectangular Gully Vent Stainless Steel Low Airflow VT002

VT023A Gas Vent Bollard Stainless Steel VT002

VT023B Gas Vent Bollard Powder Coated Steel VT002

VT023C Gas Vent Bollard Plastic VT002

VT024A Airbrick Black VT014

VT024B Airbrick Terracotta VT014

VT024C Airbrick Anthracite VT014

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Gas Barrier Membranes

In accordance with the recommendations of BS 8485:2007, a passive venting system can also require a gas barrier membrane. Visqueen offer an extensive range of gas barriers to suit most applications as shown by our product selector below. Table below indicates suitability of membrane type to resist specific ground gases.

Complete system

Radon CO2 Methane Hydrocarbons

GX Geomembrane & GX Flexi HC Barrier

Gas Barrier Membrane

Gas Resistant Self Adhesive Membrane (GR SAM)

Liquid Gas Membrane (Liquid GM)

Low Permeability Gas Membrane (LPGM)

Radon Membrane

Accessories

A full range of accessories including pre-formed units, top hats, tapes and gas dispersal fittings are available from Visqueen Building Products: see website for details.

GX Membrane Liquid GM

Radon Membrane

Gas Barrier

LPGM

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How to lap and joint a membrane above a floor slab

How to joint the cavity tray to the membrane at the floor perimeter

Product Installation

Remove loose debris from the surface of the floor slab and unroll the first sheet of membrane. The surface of the slab should be smooth and free from projections or indentations – if very rough,apply a sand blinding.

Remove the protective paperfrom one side of the appropriate jointing tape and apply it to the first sheet, starting about 50mm from the edge. Ensure that all surfaces are dry for maximum adhesion.

Unroll the second sheet along the joint, overlapping the first by at least 150mm. Press firmly onto the double sided tape, gradually removing the protective paper.

Seal the edge of the overlap with appropriate sealing tape.

Install the DPC starting fromthe outside of the external wall, over the inner masonry leaf and finishing at least 200mm from the wall.

Just before the floor topping is applied (or floor slab is cast), clean any mortar droppings, or other debris from the DPC. Remove the protective paper from theappropriate jointing tape and apply the tape to the DPC,Starting about 50mm from the edge.

Lay the membrane over thefloor slab (or subfloor blinding), overlapping the DPC by at least 150mm. Press firmly onto the appropriate jointing tape, gradually removing the protective paper.

Seal the edge of the overlap with appropriate sealing tape.

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Service Pipe Penetrations

How to install a top hat

Cut a circular hole in the membrane as close as possible to the pipe, or pipe socket. Ensure that pipe penetrations do not occur at joints in the membrane.

With the pipe in position, slide the Visqueen Preformed Top Hat Unit over the pipe (various diameters are available – 110mm being the most common).

Mark the extent of the square horizontal skirt over the membrane and also mark the line of the top of the top hat unit around the pipe.

Raise the top hat unit and cut four lengths of Visqueen Double Sided Jointing Tape, one for each side of the horizontal skirt. Allowing for an overlap at each corner. Cut one length to go round the pipe.

Start to remove the protective paper from the double sided tape around the pipe and raise it up at an angle so that it will project above the top hat unit when it is stuck to the membrane.

Gradually remove the remainder of the protective paper from the double sided tape around the pipe.

Release the protective paper from each of the four lengths of double sided tape. Lower the top hat unit, ensuring that the free end of the protective paper around the pipe is reachable, and seal the horizontal skirt to the membrane.

Seal the junction of the horizontal skirt and the membrane with the appropriate sealing tape and secure the top hat unit to the pipe with a jubilee clip.

Damp proof and airtight seals should beformed around all service entry points.Visqueen Top Hat Units are available forsealing around pipe units. The full systemconsists of:

• Rigid preformed pipe sleeve (top hat) unit – available for either 110mm, 135mm or 160mm

• External diameter pipes.

• Flexible preformed pipe sleeve (Top Hat) unit – supplied to suit pipe.

• External diameter as required.

• Double sided jointing tape.

• Girth lap tape.

• Foil lap tape – for gas applications.

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1

2

3

3

5

4

47

Key1 Preformed Pipe Sleeve 5 Jubilee Clip

2 Visqueen Gas Barrier 6 Visqueen TreadGUARD 1500

3 Visqueen Double Sided Tape 7 Visqueen Vapour Barrier

4 Visqueen GR Lap Tape 8 Smooth Sand Blinding Layer


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For more than 50 years Visqueen Building Products, part of British Polythene Industries PLC, has been recognised as the leader in the development, production and supply of high performance, high quality construction products including best selling damp proof membranes, damp proof courses and gas protection systems.

For high quality protection against gas and damp ingress on increasingly demanding site conditions, only Visqueen Building Products offers you a complete solution.

Gas Venting Design Support

Visqueen offer an unrivalled technical and design service. To determine what system is required we require the site inspection report, foundation layout and perimeter sections. On receipt of this information Visqueen’s technical design team can provide an outline drawing of a cost effective venting solution.

Please contact our technical helpline on 0845 302 4758 for further information. Venting systems should be designed on a site specific basis.

Quality and Environmental Assurance

Visqueen’s products are manufactured under strict quality guidelines. As part of our commitment to the highest standard of quality and service, Visqueen is registered to ISO 9002, 14001 and 18001.

CPD Seminars

Visqueen’s Continuing Professional Development (CPD) seminars are designed to provide critical up-to-date information on the latest building regulations and guidance affecting those in the construction sector.

Presented by our highly qualified and experienced technical consultants, Visqueen’s one hour interactive seminars provide key advice and support for architects, specifiers and anyone involved in new-build construction or refurbishment.

Visqueen offer two CPDs:

• Structural Waterproofing

• Gas Protection

To arrange your free CPD seminar please complete our online from the link below or call us on

0845 304 2567

visqueenbuilding.co.uk/cpd.asp

Technical Support

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http://www.visqueenbuilding.co.uk/cpd.asp

Visqueen Gas Venting Systems

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