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Visqueen Gas Venting Systems

Transcript of Visqueen Gas Venting Systems

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

    Gas Venting Systems

    0845 302 4758

  • 0845 302 4758


    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













    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:

    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.

  • 0845 302 4758

    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



  • 0845 302 4758

    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%. Its 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.


    Qhg = Chg


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

    Calculated hazardous gas flow rateQhgcalculated 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


    GreenAmber 1Amber 2




    01 C)



    Red 6 D)5 D)

    6 E)



    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.


    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

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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






    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.




    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




    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