FAQ: The abbreviation FENSA stands for FENESTRATION - SELF ASSESSMENT.
The uk dictionary definition of the word fenestral or fenestrate is " belonging to or like a window" The word fenestration is "the arrangement of windows in a building". FENSA is used by double glazing uk trade companies to certify that their replacement windows and doors installed comply with Building Regulations Document L (and more), actually checking av. 1% of all replacement windows installations.
Did You Know?
How are the two panes of glass 'stuck' together - and does it matter:
The life of a double glazed sealed unit is primarily dependant on the method and materials used to bond the two panes of glass together, followed a close second by the design of the framework it is fitted into, and it is also dependant on the way it is fitted into its framework. With the best will in the world, manufacturers of double glazed sealed units may endeavor to make their units last a lifetime, but in the real world premature failure is all too common.
Let's start with 'Hermetically' sealed units. Good word isn't it?, sounds very impressive and a 'must have', and this description is often used by manufacturers who use the 'hot - melt' method because it is efficient to make, and when made it can be handled and used almost straight away.
Glass bonded together using either 'two part polysulphide' or 2-part polyurethane, although technically still 'hermetically sealed', is the product of a more laboured manufacturing process, and may need to be laid flat to cure, I believe, for some 20 hours.
Another type with a very silly name, called 'swiggle strip', is manufactured in Wigan by Tremco Ltd. This consists of an 'all in one' sealant desiccant and spacer bar that heat seals the two pieces of glass together as it is run through a hot rolling machine. I myself wish such machines were calibrated for several different recognized sealed unit thickness rather than allowing operator coarse adjustment leading to possible unintended odd thickness units. Also I don't like the black colour which attracts heat from the Sun, particularly if the unit is not very deep into the glazing rebate.
With leaded light sealed units real lead strip (either 3mm - 6mm - 9mm wide and either in a flat or oval finish) is normally fixed to both sides of the outside pane. One single pane is used rather than all separate pieces of glass because these would leak and would be unable to be truly hermetically sealed. With real lead exposed to the atmosphere for the first time it will need time to oxidize and form a darkened coating. Until this happens you may expect a certain amount of running marks on the glass, especially showing up when it rains, and this is quite normal. Some manufacturers wipe the lead with a 'patination fluid' which can be obtained at D.I.Y stores but vinegar works just as well.