To fulfil its needed function a gas evidence membrane must have both a reduced permeability to landfill gases and sufficient strength characteristics to prevent tearing or puncturing during laying and subsequent construction activities. Secondary criteria influencing the choice of membrane are cost and ease of handling.
Factors that determine the permeability and strength of the membrane are the thickness and sort of material employed for its manufacture.
All design ought to be carried out with due consultation with government environmental regulating officers. For that reason, the following might not be suitable for your use.
Perhaps the most commonly recommended membrane is a 2.0mm thick High Density Polyethylene (HDPE). However, a 1.5mm really Lower Density Polyethylene (VLDPE) membrane has comparable puncture and tear resistance and although its gas permeability is higher it’s still very small and consequently acceptable. The VLDPE membrane has the advantage of getting slightly cheaper and much more effortless to handle in confined spaces and to lay more than irregular shapes.
Either kind is preferable to the use of PVC which doesn’t possess the essential criteria and, despite getting inexpensive, will need to not be utilized as a gas proof membrane. Gas resistant aluminium membranes can be utilized in buildings above the floor slab, but will require a screed or protection boards laid over the top to ensure protection.
It’s futile to bear the additional costs of installing a gas proof geomembrane if this membrane is incomplete or punctured. For that reason, the membrane will need to be integral with the damp proof course which must also have low gas permeability and all providers should ideally enter the constructing above the membrane.
Each effort should be made to design and style the building so that toilets and kitchens etc. are located adjacent to outside walls to ensure drains can pass directly via the walls and any manholes, rodding eyes etc. is usually positioned outside the foundation slab area.
The drains themselves need to be gas tight and also the layout should make sure that any subsequent ground settlement doesn’t open any joints in the drain pipes or pipe connections. Where providers puncturing the membrane cannot be avoided then these will need to be suitably sealed or puddle flanged.
Provision ought to also be made for service trenches and service ducts to be vented or sealed prior to the services enter the developing. The annulus within a duct has to not act as a conduit which will otherwise permit gases to enter the building structure.