{"title":"Ground Gas Venting","description":"\u003cp\u003eGround gas venting systems disperse hazardous ground gases from beneath and around a building, working alongside a gas barrier membrane to form a complete gas protection strategy. \u003c\/p\u003e\n\u003ch3 class=\"text-text-100 mt-3 -mb-1 text-[1.125rem] font-bold\"\u003eWhat is a ground gas venting system?\u003c\/h3\u003e\n\u003cp class=\"font-claude-response-body break-words whitespace-normal\"\u003eA ground gas venting system is a network of components installed beneath and around a building to collect hazardous ground gases and disperse them to atmosphere before they can accumulate. On contaminated or gassing ground, a gas barrier membrane alone prevents gas entering the structure, but on higher-risk sites the gas beneath the slab must also be actively managed. The venting system provides that route, creating a void beneath the floor slab through which gas is collected and channelled away, either passively or, where required, with mechanical assistance.\u003c\/p\u003e\n\u003cp class=\"font-claude-response-body break-words whitespace-normal\"\u003eA complete system has three stages: a collection layer beneath the slab, a network of pipework that carries the collected gas, and external outlets that release it safely to atmosphere at the building perimeter or within the surrounding landscaping.\u003c\/p\u003e\n\u003ch3 class=\"text-text-100 mt-3 -mb-1 text-[1.125rem] font-bold\"\u003eWhen is a gas venting system required?\u003c\/h3\u003e\n\u003cp class=\"font-claude-response-body break-words whitespace-normal\"\u003eThe level of gas protection required on a site is determined by the ground investigation and the risk characterisation carried out in accordance with BS 8485:2015+A1:2019. On lower-risk sites a gas barrier membrane may be sufficient on its own. As the characteristic gas situation increases, a venting layer is added beneath the slab to relieve pressure and dilute gas concentrations, reducing the load on the barrier and providing a second line of defence.\u003c\/p\u003e\n\u003cp class=\"font-claude-response-body break-words whitespace-normal\"\u003eMethane and carbon dioxide are generated by decomposing organic material and are a particular risk on brownfield land, former landfill and made ground. Radon is a naturally occurring radioactive gas found across parts of the UK, and volatile organic compounds are associated with former industrial sites. Where the ground investigation identifies elevated gas concentrations, a venting system designed to the specific site conditions forms part of the protective measures required before construction of the ground floor slab.\u003c\/p\u003e\n\u003ch3 class=\"text-text-100 mt-3 -mb-1 text-[1.125rem] font-bold\"\u003eGround gas venting system components\u003c\/h3\u003e\n\u003cp class=\"font-claude-response-body break-words whitespace-normal\"\u003eThe venting range covers each stage of the system, from collection beneath the slab through to the external outlet.\u003c\/p\u003e\n\u003ch4 class=\"text-text-100 mt-2 -mb-1 text-base font-bold\"\u003eGas collection\u003c\/h4\u003e\n\u003cp class=\"font-claude-response-body break-words whitespace-normal\"\u003eThe gas vent mat is a cuspated geocomposite laid beneath the reinforced concrete floor slab to create a shallow venting void. Gases collected across the mat are drawn towards the pipework for dispersal. On sites requiring a defined collection route, slotted carrier pipe is laid within the venting layer to gather gas along its length and feed it into the solid pipework. Mat connectors provide the transition between the collection layer and the pipe runs.\u003c\/p\u003e\n\u003ch4 class=\"text-text-100 mt-2 -mb-1 text-base font-bold\"\u003eVent pipework and fittings\u003c\/h4\u003e\n\u003cp class=\"font-claude-response-body break-words whitespace-normal\"\u003eSolid vent pipe carries the collected gas from the collection layer to the external outlets. The pipework is built and routed using preformed HDPE fittings: couplings to extend straight runs, bends to change direction, T fittings to form branch junctions, end caps to close runs, flexible connectors to take up alignment and movement, and adaptors to connect to outlet components. The smooth internal bore of the fittings maintains consistent gas flow through the network.\u003c\/p\u003e\n\u003ch4 class=\"text-text-100 mt-2 -mb-1 text-base font-bold\"\u003eExternal outlets\u003c\/h4\u003e\n\u003cp class=\"font-claude-response-body break-words whitespace-normal\"\u003eAt the building perimeter, the collected gas is released to atmosphere through an external outlet. Gas vent boxes are set into paths, patios and trafficked ground, with a heel-safe locking lid suitable for pedestrian areas. Gas vent bollards provide an above-ground outlet where the dispersal route cannot be taken through a perimeter masonry wall, such as at curtain walling or glazed elevations. Airbricks, fitted with an adjustable vent and extension sleeve, release gas through the external wall face while blocking wind driven rain and insects.\u003c\/p\u003e\n\u003ch3 class=\"text-text-100 mt-3 -mb-1 text-[1.125rem] font-bold\"\u003ePassive and pressurised venting\u003c\/h3\u003e\n\u003cp class=\"font-claude-response-body break-words whitespace-normal\"\u003eMost low-rise and residential applications use passive venting, where gas disperses through the system under natural pressure differences and airflow, without mechanical assistance. This is the simplest and most maintenance-free approach and is suitable for the majority of sites where a venting layer is required.\u003c\/p\u003e\n\u003cp class=\"font-claude-response-body break-words whitespace-normal\"\u003eOn higher-risk sites, or where the building footprint and layout limit natural airflow, a mechanically assisted or pressurised system may be specified, using fans to actively draw gas through the venting layer and out through the outlets. The choice between passive and pressurised venting is a design decision based on the site gas regime, the building type and the guidance in BS 8485:2015+A1:2019.\u003c\/p\u003e\n\u003ch3 class=\"text-text-100 mt-3 -mb-1 text-[1.125rem] font-bold\"\u003eChoosing the right venting components\u003c\/h3\u003e\n\u003cp class=\"font-claude-response-body break-words whitespace-normal\"\u003eThe venting system is specified as part of the overall gas protection design for the site, and the components required follow from that design. The gas vent mat provides the collection layer; the number and type of outlets follow from the free air flow capacity required and the building perimeter; and the pipework and fittings are selected to build the runs that connect them. Because the system works in conjunction with the gas barrier membrane, the two should be specified together against the site gas assessment. Where you need help matching components to a gas protection design, our team is available to assist.\u003c\/p\u003e","products":[{"product_id":"visqueen-gas-vent-mat-vt-m1","title":"Visqueen Gas Vent Mat VT M1","description":"\u003cp class=\"font-claude-response-body break-words whitespace-normal\"\u003eVisqueen Gas Vent Mat VT M1 is a geocomposite void former comprising a cuspated HDPE core bonded to a nonwoven polypropylene geotextile filter membrane. Laid beneath reinforced concrete ground floor slabs, it creates a 25mm deep void through which hazardous ground gases, including methane, carbon dioxide, radon and volatile organic compounds, are collected and dispersed to atmosphere via a designed arrangement of Visqueen connectors and venting components.\u003c\/p\u003e\n\u003cp class=\"font-claude-response-body break-words whitespace-normal\"\u003eWhere high gas concentrations have been recorded, the mat is laid in blanket format with individual mats butted together. Where concentrations are lower or pressure relief is the priority, it is laid in strip format at predetermined spacings, reducing material use without compromising performance.\u003c\/p\u003e\n\u003cp class=\"font-claude-response-body break-words whitespace-normal\"\u003e \u003c\/p\u003e\n\u003cp class=\"font-claude-response-body break-words whitespace-normal\"\u003e\u003cstrong\u003eBenefits\u003c\/strong\u003e\u003c\/p\u003e\n\u003cul\u003e\n\u003cli class=\"font-claude-response-body break-words whitespace-normal\"\u003eLarge format rolls allow rapid installation across large slab areas\u003c\/li\u003e\n\u003cli class=\"font-claude-response-body break-words whitespace-normal\"\u003eReduces the volume of contaminated soil requiring removal compared to traditional pipe and gravel venting systems\u003c\/li\u003e\n\u003cli class=\"font-claude-response-body break-words whitespace-normal\"\u003eCompatible with a full range of Visqueen system components for exhausting collected gases to atmosphere\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cp\u003e \u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eGood to know \u003c\/strong\u003e\u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003eAchieves between 0.5 and 1.5 points when assessed to BS 8485:2015+A1:2019\u003c\/li\u003e\n\u003cli\u003eWhere high gas concentrations have been recorded, the mat is laid in blanket format with individual mats butted together.\u003c\/li\u003e\n\u003cli\u003eWhere concentrations are lower or pressure relief is the priority, it is laid in strip format at predetermined spacings, reducing material use without compromising performance.\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cp\u003e \u003c\/p\u003e","brand":"Visqueen","offers":[{"title":"Default Title","offer_id":57947463811404,"sku":"BM06641","price":908.73,"currency_code":"GBP","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/1046\/6715\/2716\/files\/visqueen-ground-gas-venting-visqueen-gas-vent-mat-vt-m1-1246866006.jpg?v=1782999649"},{"product_id":"visqueenpro-gas-vent-box","title":"VisqueenPro Gas Vent Box","description":"\u003cp class=\"font-claude-response-body break-words whitespace-normal\"\u003eThe VisqueenPro Gas Vent Box is the external termination point of the Visqueen gas venting system, releasing collected ground gases safely to atmosphere at the building perimeter. It comprises a base with a 110mm pipe inlet and adjustable feet, allowing it to be levelled and secured within the concrete surround, with the lid held down by locking bolts.\u003c\/p\u003e\n\u003cp class=\"font-claude-response-body break-words whitespace-normal\"\u003eThe lid is heel-safe and suitable for use in pedestrian areas, so the vent box can be set into paths, patios and other trafficked ground without creating a trip hazard. Its design also manages surface water at the vent point, reducing the risk of rainwater entering the void beneath and diluting the effectiveness of the system.\u003c\/p\u003e\n\u003cp class=\"font-claude-response-body break-words whitespace-normal\"\u003eChoose from a galvanised steel base (VT020A) or a stainless steel base (VT020B) to suit the exposure and durability requirements of the installation.\u003c\/p\u003e\n\u003cp class=\"font-claude-response-body break-words whitespace-normal\"\u003e\u003cstrong\u003eBenefits\u003c\/strong\u003e\u003c\/p\u003e\n\u003cul\u003e\n\u003cli class=\"font-claude-response-body break-words whitespace-normal\"\u003eSuitable for all ground gas venting applications including VOCs\u003c\/li\u003e\n\u003cli class=\"font-claude-response-body break-words whitespace-normal\"\u003eTested to BS EN 1433:2002, suitable for loads up to 12.5 tonnes\u003c\/li\u003e\n\u003cli class=\"font-claude-response-body break-words whitespace-normal\"\u003eHeel safe lid suitable for use in pedestrian areas\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cp\u003e \u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eGood to know \u003c\/strong\u003e\u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003eWater management design reduces the risk of rainwater entering the void\u003c\/li\u003e\n\u003cli\u003eAvailable in galvanised or stainless steel to suit the application\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cp\u003e \u003c\/p\u003e","brand":"Visqueen","offers":[{"title":"Galvanised","offer_id":57947617132876,"sku":"BM06642","price":545.67,"currency_code":"GBP","in_stock":true},{"title":"Stainless Steel","offer_id":57947617165644,"sku":"BM06643","price":706.89,"currency_code":"GBP","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/1046\/6715\/2716\/files\/visqueen-ground-gas-venting-galvanised-visqueenpro-gas-vent-box-1246866005.png?v=1782999633"},{"product_id":"visqueen-vt014-adjustable-z-vent","title":"Visqueen VT014 Adjustable Z Vent","description":"\u003cp class=\"font-claude-response-body break-words whitespace-normal\"\u003eVisqueen Adjustable Z Vent VT014 is manufactured from black polypropylene and provides a clear airflow passage from the underfloor void to a Visqueen Airbrick fitted at the external wall face. It forms the connecting stage of the Visqueen gas venting system, carrying collected ground gases from beneath the slab out to atmosphere.\u003c\/p\u003e\n\u003cp class=\"font-claude-response-body break-words whitespace-normal\"\u003eThe vent is sold separately from the airbrick and extension sleeve, so it can be paired with whichever combination suits the wall build-up and cavity depth on site.\u003c\/p\u003e\n\u003cp class=\"font-claude-response-body break-words whitespace-normal\"\u003e\u003cstrong\u003eBenefits\u003c\/strong\u003e\u003c\/p\u003e\n\u003cul\u003e\n\u003cli class=\"font-claude-response-body break-words whitespace-normal\"\u003eFunctional solution for exhausting ground gases from underfloor voids\u003c\/li\u003e\n\u003cli class=\"font-claude-response-body break-words whitespace-normal\"\u003eManufactured from durable black polypropylene\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cp\u003e \u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eGood to know\u003c\/strong\u003e\u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003eUsed with a Visqueen Airbrick and, where required, a Visqueen Extension Sleeve\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cp\u003e \u003c\/p\u003e\n\u003cp\u003e \u003c\/p\u003e","brand":"Visqueen","offers":[{"title":"Default Title","offer_id":57947922465100,"sku":"BM06655","price":5.77,"currency_code":"GBP","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/1046\/6715\/2716\/files\/visqueen-ground-gas-venting-visqueen-vt014-adjustable-z-vent-1246866004.jpg?v=1782999616"},{"product_id":"visqueen-vt015-extension-sleeve-horizontal-vertical","title":"Visqueen VT015  Extension Sleeve (Horizontal \u0026 Vertical)","description":"\u003cp class=\"font-claude-response-body break-words whitespace-normal\"\u003eVisqueen Extension Sleeve VT015 is manufactured from black polypropylene and extends the reach of the Visqueen Adjustable Z Vent, both vertically and horizontally. This allows the vent to bridge greater wall thicknesses or offset positions between the underfloor void and the external airbrick without compromising the venting path.\u003c\/p\u003e\n\u003cp class=\"font-claude-response-body break-words whitespace-normal\"\u003eIt is sold separately from the vent and airbrick, so it only needs to be specified where the wall build-up requires the extra reach.\u003c\/p\u003e\n\u003cp class=\"font-claude-response-body break-words whitespace-normal\"\u003e\u003cstrong\u003eBenefits\u003c\/strong\u003e\u003c\/p\u003e\n\u003cul\u003e\n\u003cli class=\"font-claude-response-body break-words whitespace-normal\"\u003eExtends vent reach both vertically and horizontally\u003c\/li\u003e\n\u003cli class=\"font-claude-response-body break-words whitespace-normal\"\u003eUsed alongside the Visqueen Adjustable Z Vent and Airbrick\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cp\u003e \u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eGood to know \u003c\/strong\u003e\u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003eIt is sold separately from the vent and airbrick, so it only needs to be specified where the wall build-up requires the extra reach.\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cp class=\"font-claude-response-body break-words whitespace-normal\"\u003e\u003cbr\u003e\u003c\/p\u003e","brand":"Visqueen","offers":[{"title":"Default Title","offer_id":57948005105996,"sku":"BM06656","price":12.22,"currency_code":"GBP","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/1046\/6715\/2716\/files\/images_926d75b2-9b86-485e-82ac-81c4f0657195.jpg?v=1783003221"},{"product_id":"visqueen-gas-vent-bollard-stainless-steel-plastic","title":"Visqueen Gas Vent Bollard | Stainless Steel \u0026 Plastic","description":"\u003cp class=\"font-claude-response-body break-words whitespace-normal\"\u003eThe Visqueen Gas Vent Bollard is a 110mm diameter bollard with a total height of 1400mm, of which between 800mm and 900mm sits above external ground level. It provides an alternative outlet for the Visqueen gas venting system where the gas dispersal route cannot be taken through a perimeter masonry wall, such as curtain walling or glazed elevations.\u003c\/p\u003e\n\u003cp class=\"font-claude-response-body break-words whitespace-normal\"\u003eThe bollard can be positioned close to the building perimeter or set within the surrounding landscaping, for example adjacent to pathways, giving flexibility where wall-mounted outlets aren't practical.\u003c\/p\u003e\n\u003cp class=\"font-claude-response-body break-words whitespace-normal\"\u003eChoose from a stainless steel body (VT023A) for a durable, rust proof finish and higher free air flow, or a plastic body (VT023C) as a lower-cost alternative where the higher capacity is not required.\u003c\/p\u003e\n\u003cp class=\"font-claude-response-body break-words whitespace-normal\"\u003e\u003cstrong\u003eBenefits\u003c\/strong\u003e\u003c\/p\u003e\n\u003cul\u003e\n\u003cli class=\"font-claude-response-body break-words whitespace-normal\"\u003eSuitable for all ground gas venting applications including VOCs\u003c\/li\u003e\n\u003cli class=\"font-claude-response-body break-words whitespace-normal\"\u003eAvailable in rust proof stainless steel or plastic to suit the specification\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cp\u003e \u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eGood to know \u003c\/strong\u003e\u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003eSlotted venting design eliminates the need for a sub-base soakaway\u003c\/li\u003e\n\u003cli\u003eHigh free air flow capacity reduces the number of units required\u003c\/li\u003e\n\u003c\/ul\u003e","brand":"Visqueen","offers":[{"title":"Stainless Steel","offer_id":57948530835788,"sku":"BM06657","price":1053.14,"currency_code":"GBP","in_stock":true},{"title":"Plastic","offer_id":57948530868556,"sku":"BM06658","price":310.79,"currency_code":"GBP","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/1046\/6715\/2716\/files\/shopping_e13378e2-a2b5-4515-ae3e-2407ddea5f09.webp?v=1783003228"}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/1046\/6715\/2716\/collections\/visqueen_gas_vent.jpg?v=1782987851","url":"https:\/\/www.constructionsuppliesuk.co.uk\/collections\/ground-gas-venting.oembed","provider":"Construction Supplies UK","version":"1.0","type":"link"}