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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Kunzel, H.M.; WUFI: PC Program for Calculating the Coupled Heat and Moisture Transfer in Building Components; Fraunhofer Institute for Building Physics, Holzkirchen, Germany, 1999. In areas below foundation level ( subgrade areas), particularly those formed in concrete, vapor retarder placement can be problematic, as moisture infiltration from capillary action can exceed water vapor movement outward through framed and insulated walls.

Vapor retarder paints (for the air-tight drywall system, for retrofits where finished walls and ceilings will not be replaced, or for dry basements: can break down over time due to being chemically based). Applicability – Limited to mixed-humid, hot-humid, mixed-dry, hot-dry and marine regions – can be used with hygro-thermal analysis in some areas in cold regions (Zone 5, but not Zone 6; see Side Bar 2)- should not be used in very cold and subarctic/arctic regionsIf you live in a warmer climate the vapour barrier should be on the outside side of the installation. Water can come in several phases: liquid, solid, vapor and adsorbed. The liquid phase as rain and ground water has driven everyone crazy for hundreds of years but can be readily understood - drain everything and remember the humble flashing. The solid phase also drives everyone crazy when we have to shovel it or melt it, but at least most professionals understand the related building problems (ice damming, frost heave, freeze-thaw damage). But the vapor phase is in a class of craziness all by itself. We will conveniently ignore the adsorbed phase and leave it for someone else to deal with. Note that adsorbed water is different than absorbed water (see Kumaran, Mitalas & Bomberg, 1994). A true vapour barrier is one that completely prevents moisture from passing through its material, as measured by the "moisture vapour transmission rate." If even a small amount of permeability is in the material but the barrier still provides protection from moisture, this is called a vapour diffusion retarder. (Source: U.S. Department of Energy.) Each of the recommended building assemblies were evaluated using dynamic hygrothermal modeling. The moisture content of building materials that comprise the building assemblies all remained below the equilibrium moisture content of the materials as specified in ASHRAE 160 P under this evaluation approach. Interior air conditions and exterior air conditions as specified by ASHRAE 160 P were used. WUFI was used as the modeling program ( Kunzel, 1999).

The IRC recommends builders install a Class-I or -II vapour retarder on the interior side of homes in climate zones 5 (Cold) and north, and in the Marine 4 zone. However, if you air-condition your house in the summer, your might trap condensation in your roof or walls for part of the year. If this is the case, be sure to use a Class-II vapour retarder on the interior of the wall. You also can use a Class-III vapour retarder on the interior paired with spray foam insulation on the interior of the wall or roof. When building in hot, humid climates (zones 1 to 3), you shouldn’t have a vapour retarder on the interior side of the wall. (Source: Fine Home Building.) Permeable (>10USperm, or >570SIperm) – such as unpainted gypsum board and plaster, unfaced fiber glass insulation, cellulose insulation, unpainted stucco, cement sheathings, spunbonded polyolefin or some polymer-based exterior air barrier films. The College of New Caledonia (CNC) in Prince George, B.C., and Twin Maple Group have been collaborating to research the use of the aluminum reflective foil insulation as replacement for vapour barrier in wall building systems. The objective was to quantify the potential energy savings as a result of reducing radiant heat losses. (This research would not have been possible without the support from Natural Sciences and Engineering Research Council of Canada [NSERC] through an Engage Grant for Colleges. This author would also like to express thanks to Twin Maple for its in-kind contribution to this project, with respect to materials and technical expertise. CNC departments participating in the study include the School of Trades & Technology, International Education, Facilities Services, and Applied Research and Innovation.)Lstiburek, Joseph (2004). Vapor Barriers and Wall Design. Building Science Press. Archived from the original on 2015-06-29 . Retrieved 2011-12-01. In the UK and other colder climates where winter temperatures can get colder than 4 degrees you should always install a vapour barrier on the inside of interior insulation. 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. Of these three, air movement accounts for more than 98% of all water vapor movement in building cavities.

Unless you are adding an extension or re-modelling walls it is hard to add a vapour barrier to an existing home. Avoidance of the installation of vapor barriers such as polyethylene vapor barriers, foil faced batt insulation and reflective radiant barrier foil insulation on the interior of air-conditioned assemblies – a practice that has been linked with moldy buildings ( Lstiburek, 2002). The vapor barrier in this assembly is the precast concrete itself. Therefore this wall assembly has all of the thermal insulation installed to the interior of the vapor barrier. Of particular concern is the fact that the thermal insulation is air permeable (except where spray foam is used). Therefore this wall assembly should not be used in cold regions or colder. It has a small moisture storage (hygric buffer) capacity due to the precast concrete construction. The wall assembly does contain water sensitive cavity insulation (except where spray foam is used) and it is important that this assembly can dry inwards – therefore vapor semi impermeable interior finishes such as vinyl wall coverings should be avoided. In this wall assembly the precast concrete is also the drainage plane and air barrier.US Department of Energy. "How Moisture Moves through a Home". Archived from the original on December 29, 2010 . Retrieved January 1, 2011. Part of the problem is that we struggle with names and terms. We have vapor retarders, we have vapor barriers, we have vapor permeable we have vapor impermeable, etc. What do these terms mean? It depends on whom you ask and whether they are selling something or arguing with a building official. In an attempt to clear up some of the confusion the following definitions are proposed: It is however a good idea to consult your local building code as if installed on the wrong side in a certain climates a vapour barrier could end up trapping moisture leading to damp and rot within the walls and roofing. A vapour barrier isn't intended to stop air from flowing or migrating; that's the job of an air barrier. So, although a vapour barrier must be continuous, unlike an air barrier, a vapour barrier does not need to be as tightly sealed. (Source: CMHC, "Canadian Wood-Frame House Construction", p.18.) The SuperFOIL SFTV serves as a comprehensive building membrane for the construction of roofs, walls and floors. It offers both water and vapour resistance while also acting as a foil radiant barrier to minimise solar heat gain during summer and maximise insulation in winter. With two air gaps, this high-performance solution offers an impressive thermal insulation R-value of 0.95 for roofs, 1.42 for walls and 2.8 for floors.