apour Barrier and Waterproof Thermal Insulation Aluminium Foil Membrane - Suitable for use in Walls, Floors and Roofs - 1.5m x 50m (75 SQ/M) - 110 G/SM - Free Next Day UK Delivery - Large Discounts Available on Multi Pack (1)

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Firstly, starting with the basics, when you insulate walls you create a temperature gradient across them with the warmest being on the inside and coolest on the outside during the winter months. You can imagine a graph of the temperature showing a fairly steady decrease in temperature as you move from the inside to the outside surface of the wall. Allen, Edward; Iano, Joseph (2013). Fundamentals of Building Construction: Materials and Methods (6thed.). Wiley. ISBN 978-1-118-42086-7. Vapour barriers are waterproof, vapour proof and help to prevent mould and dampness from accumulating in a property over time. At Insulation Superstore, we have a modest range of thermal vapour barriers, with products to suit every budget. Prevents the ingress of water/moisture and the passage of wind-blown snow and dust into the interior of the building

The International Residential Code (IRC) classifies materials by their permeability. They measure this in a unit called a "perm". As clarified in a study published by the University of Alaska Fairbanks (UAF) Cooperative Extension Service: If a material has a perm rating of 1.0, we know that in 1 hour, when the vapour pressure difference between the cold side and the warm side of the material is equal to 1 inch of mercury (1 inch Hg), 1 grain of water vapour will pass through 1 square foot of the material. One grain of water is equal to 1/7,000 of a pound. Lstiburek, Joseph (October 24, 2006). Building Science Digest 106: Understanding Vapor Barriers (PDF). 2006 Building Science Press. Archived from the original (PDF) on October 30, 2012 . Retrieved December 1, 2011. Advanced Polyethylene vapor retarders that pass the ASTM E 1745 standard tests ≤0.3USperm (17SIperm). A vapour barrier (sometimes referred to as vapour retarder) is typically a plastic or foil sheet used for damp proofing to prevent interstitial condensation from forming in various building assemblies such as walls, roofs, foundations and floors. In a typical commercial building or home, vapour barriers or vapour diffusion retarders can improve energy efficiency and comfort, while also preventing problems from moisture and dampness. (Source: U.S. Department of Energy.) Having both an air barrier and vapour retarders is important in more southern warmer climates to prevent humid air from the outside entering the cooler wall cavities.However, you can buy vapour resistant paint and some paints will even display the perm rating on the label. This definition characterizes a region that is similar to the ASHRAE definition of hot-humid climates where one or both of the following occur: Materials such as rigid foam insulation, reinforced plastics, aluminium and stainless steel can also be used as they are relatively water resistant but should also be sealed at the joints.

Experts say that most condensation problems occur because of air leakage, not vapour diffusion, so be sure you properly seal penetrations (such as flashings) for air leakage using an air barrier. A bonus to vapour barriers is that they can make your home more energy efficient, lowering your household bills. The biggest advantage of aluminium foil as a vapour barrier is that it is easy to process. It is very cheap compared to other materials. At the same time, the aluminium foil ensures that the thermal insulation is increased in the case of a vapour barrier. Zone 4 (marine) requires a Class II (or lower) vapor retarder on the interior surface of insulation in insulated wall and floor assemblies where the permeance of the exterior sheathing/cladding assembly is less than or equal to 1.0 perm and greater than 0.1 perm as tested by Test Method B (the “wet cup” method) of ASTM E-96).The IRC divides North America into eight climate areas for the purposes of determining when a vapour barrier might be needed in a building. Semi-permeable (1-10USperm, or 57-570SIperm) – such as unfaced expanded polystyrene, fiber-faced isocyanurate, heavy asphalt-impregnated building papers, some latex-based paints); a 67 degree F (19.5 degrees C) or higher wet bulb temperature for 3,000 or more hours during the warmest six consecutive months of the year; or Different construction and insulation materials cope differently with this condensation. Some materials, such as masonry, can absorb and release it again once the weather warms without too much damage. However, when using vapour impervious insulations in timber frame construction, any condensation forming in the walls tends to be absorbed by the timber, a process that can cause rot. Additionally, during the winter months when this condensation tends to occur, driving rain may also enter the fabric of the building, further increasing moisture levels in walls. It is therefore very important to prevent this condensation process occurring in walls, for the longevity of the building.