Correct Specification and

Detailing forProtection fromHarmful Ground

Gases

CI/SfB (13.9)

Uniclass L681

September 2015

Z-LED RANGE

Gas Risk Assessment - Traffic Lights with Typical Maximum Concentrations and GasScreening Values

Ground Gas Protection Measures Required for theTraffic Lights

Correct Specification and Detailing for Protection from Harmful Ground Gases

Harmful soil gasesHarmful ground gases such as methane, carbon dioxideor radon entering buildings can pose serious health risks.They can enter properties by many different routes:through cracks in floors and walls, construction joints,wall cavities and around service pipes.

Government planning policy statement (PPS3) requiresthat at least 60% of new housing should be provided onpreviously developed land (often referred to as brownfieldsites). Owing to environmental considerations there is apreference for all developments to be constructed onpreviously developed land wherever possible, whichmeans that many more buildings will need protectionfrom ground gases.

Methane, carbon dioxide and radon are formed by avariety of means, including rock formation, coalmeasures, landfill sites, sediments from rivers and lakesand many more natural or man made causes. Groundgases can also be found on greenfield sites owing todeposits of peat, coal or even river silt.

Methane is a colourless, odourless, explosive andasphyxiating gas.

Carbon dioxide is a colourless, odourless, non-flammable but asphyxiating and toxic gas.

Radon is a naturally occurring colourless, odourlessradioactive gas, more prevalent in certain areas.Exposure to radon for long periods increases the risk ofdeveloping lung cancer. For further information on radonaffected areas and geographical maps see UKradon.org.

Protection from these ground gases is a specificrequirement of the Building Regulations Part C forEngland and Wales. “Preparation of site and resistanceto contaminants C1 (2) Reasonable care should be takento avoid danger to health and safety caused bycontaminants on or in the ground covered by the buildingand any land associated with the building.”

Detailed guidance is given in the following publications.Building Research Establishment BR 211, Radon,Guidance on protective measures for new buildings; BR 212, Construction of new buildings for gascontaminated land; BR 414, Protective measures forhousing on gas-contaminated land and CIRIA C665Assessing risks posed by hazardous ground gases tobuildings.

From BR 414 the NHBC have produced their ownguidance for low rise developments and housing inconjunction with RSK Group plc which works on asimple traffic light system with Green requiring noprotection and Red not suitable for residentialdevelopment. CIRIA C665 adopts a similar system forboth residential and non-residential development. Bothset minimum requirements for protection but state thatBR 414 must be followed when detailing protectivemeasures. See tables

Land is assessed on the concentration and flow rates ofground gases. Calculations for both methane and carbondioxide have to be carried out and the worst caseadopted to establish the necessary protection measure.

Correct Specification and Detailing for Protection from Harmful Ground Gases

Routes by which ground gases entera building The primary cause of gases entering a building is owingto pressure differences between the inside and outsidedrawing gas into the building by either the stack effect orthe venturi effect.

This replacement air is drawn in through routes of leastresistance, so a damaged or badly sealed gas barrierwould allow gas laden air to enter the habitable part ofthe property.

Gas control measures generally consist of a gas resistantbarrier across the whole building footprint above anextraction (or ventilation) layer from which the gases canbe dispersed and vented to the atmosphere.

Gas protection schemes for new houses should onlyincorporate passive ventilation, not mechanical andtherefore houses should only be constructed on siteswhere the level of gas will remain relatively low. In ahouse an ignition source will nearly always be presentand therefore an increase in indoor methaneconcentration as a result of mechanical failure cannot beallowed. The method of constructing floors for housescan be used for larger buildings too. For gas protectiveschemes, which include mechanical extraction and gasdetection, further specific guidance should be sought.

The gas resistant membrane is a critical component inproviding protection against harmful ground gases but itsperformance can be significantly reduced if is torn,punctured or not adequately lapped and sealed. Withunreinforced membranes the thinner the material thegreater risk of damage during construction. Small tearscan be repaired but this requires a high standard ofworkmanship on site. As stated in BR212, the mainconsideration with a gas proof membrane is whether itcan withstand the construction process, because oncetorn or damaged the membrane ceases to operate as aneffective barrier.

Independent tests (INSPEC) commissioned by Glidevaleshow the methane permeability of its Z-Led ProtectGDB10 gas membrane compared to a typical 1200gauge polythene membrane. Copies of the test report are available on request.

Product Volume Permeation Rate

Typical 1200 gauge polythene sheet 418 ml/m2/day

Protect GDB10 gas protection barrier No permeation detected after test duration of 8 hours. < 1.5 ml/m2/day

Using a reinforced membrane, which is independentlycertified for use as a gas protection membrane and theuse of specialist contractors for installation, cansignificantly reduce the risk of damage on site. Thehealth and safety of the occupants of the buildingdepend on its performance. The use of preformedproprietary components to maintain protection at wallcavities, corners, pipe and service entries removes theneed to form difficult shapes on site giving a simpler andmore reliable installation.

Through cracks in solid floors

Through construction joints

Through cracks in wallsbelow ground level

Through gaps in suspended

floors

Through cracks incavities and walls

Through gapsaround service

pipes

12 x 2mm butyl strip

Z-Led RPS1 UniversalPipe Seal

Jubilee clampZ-Led 50mm foil-facedJoint Protection Tape

Exposed edge protected by Z-Led 50mmfoil-faced Joint Protection Tape

150mm minimum overlap

Z-Led Protect GDB10membrane

Blinded substrate

Z-Led 50mm double-sided Gas Jointing Tape

Z-Led 50mm foil-faced JointProtection Tape

Z-Led MV650 Universal Weep Ventat maximum 450mm centres

Z-Led polypropylene Cavity Barrier and combined Cavity Tray

12 x 2mm butyl strip

Z-Led 50mm double-sidedGas Jointing Tape

Z-Led polypropylene Slab Edge Protection Tray

Slab and edge protection

Z-Led Protect GDB10 membrane jointing

Slab edge and cavity wallService pipe penetration of membrane

Radon ventilation

Ventilation of underfloorvoid with porous fill

Radon laden air escapingnaturally by convection

Glidevale RPS1 Universal Pipe Seal

Z-Led Protect GDB10 membrane

Porous fillmaterial

RS Radon Sump

Glidevale Z-LedCavity Tray

MV250 Airbrick

MV251 Periscope

Membrane

Underfloor ventilation

Typical details for installation of a gas protection membrane

Typical underfloor ventilation solutions

Correct Specification and Detailing for Protection from Harmful Ground Gases

GLIDEVALE LIMITED2 Brooklands Road, Sale, Cheshire M33 3SS Tel: 0161 905 5700 Fax: 0161 905 2085

Email: info@glidevale.com Web: www.glidevale.com

ReferencesBR 211, Radon, Guidance on protective measures fornew buildings.

BR 212, Construction of new buildings on gascontaminated land.

BR 414, Protective measures for housing on gascontaminated land.

CIRIA C665 Assessing risks posed by hazardous groundgases to buildings

NHBC/RSK GROUP PLC, Guidance on evaluation ofdevelopment proposals on sites where methane andcarbon dioxide are present.

The Glidevale Z-Led SolutionGlidevale Z-Led range of ground floor protectionproducts offer a complete solution. The gas protectionrange includes a universal barrier membrane forprotection against methane, carbon dioxide, radon anddamp penetration from the ground. Z-Led ProtectGDB10 is a multi-layer reinforced polyethylene/polypropylene membrane with an integral continuousaluminium foil. BRE certified for use as a gas protectionmembrane, it is tough and durable with excellent tensilestrength and is puncture and tear resistant. Used inconjunction with the Glidevale cavity and slab edgeprotection system it provides a complete solution forbuilding on gas contaminated land.

A complementary range of underfloor and cavity wallventilation products enable the regulatory requirementsfor ventilation to be met.

For further advice or detailed information regarding aspecific project please contact our Technical ServicesTeam on 0161 905 5700.

A CPD seminar on Correct Specification and Detailing forProtection from Harmful Ground Gases can be providedon request, subject to numbers. Please contact our Marketing Team for furtherinformation.

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