Double Glazing for Extra Home Warmth
Double glazing is a comfort medium, and may, if the gap between the two panes of glass is deep enough, provide effective sound insulation. Fixed pre-made double-glazed panes can be used, or one of the many types of applied or coupled glazed sashes, which offer a choice of system suitable for use with any type of existing single glazing.
Double glazing is one of the ways of preventing heat loss through the fabric of a building. It has been estimated that up to 20 per cent of heat waste through the fabric is lost through windows and around gaps in badly fitting frames.
It is important to look at double glazing as part of whole-house insulation. Potentially, out of money spent on heating an uninsulated house, 75 per cent is wasted. Loss occurs through walls, roofs, doors and windows, floors and flues.
Opinion varies on the question of how much money is saved by double glazing. Basically, it increases the comfort level but does not usually greatly cut heating costs.
A single sheet of glass is a poor insulator. If used in an exposed condition it can have as high a ‘U’ value as 5.67w/m2 °C or 6.24.
The area around a window is a cold ‘zone’; the nearer you get to the window the colder you find it. When expanding warm air reaches this cold surface, it cools and contracts, causing turbulence which creates a draught. A vacuum, a ‘sandwich’ of air or inertentrapped between two sheets of glass, raises the face temperature of the inner pane, so that warm air is no longer dramatically cooled.
Though double glazing a window area can save up to 80 per cent of the heat lost through the glass, as this usually represents only a small area of the total house fabric, the actual saving, in heat terms, may be as little as 10 per cent.
The amount of thermal insulation provided by double glazing depends on the gap between the two sheets of glass. Basically, the greater the gap, the greater the degree of insulation. A double-glazed unit with a gap of 5mm would have a ‘U’ value of 3.40, while a 13mm gap would improve the value to 2.96.
Before fixing double glazing, it is important to check that heat is not escaping through badly fitting window frames. It is pointless to fit double glazing if heat is escaping and you are prey tofrom outside.
There are various methods of dealing with the problem. If the frame is badly distorted and the wood rotted or warped it may be better to repair or replace the entire frame.
A variety of window draught excluders are available, ranging from sprung-metal stripping, to go around door and window frames,-backed foam-rubber strip to a type in a tube which is squeezed out along the opening and allowed to dry. Before applying an -backed or plastic extruder, first make sure that surfaces are free from grease and dry.
As an aid to sound insulation, double-glazed units do not have very high sound-insulation properties. Domestic glazing units have a gap varying between 5mm and 13mm, but to provide an effective sound barrier this gap needs to be 100mm or more.
A unit like this could not be fitted easily to most domestic windows and would need specially modified window fittings.
The pre-sealed, factory-made unit consists of a double sheet of glass, vacuum sealed or filled with inert gas. This type presents the appearance of conventional glazing and requires no further attention once fitted. With such units problems of condensation on the inner surfaces of the glass are virtually eliminated.
Factory-made units are heavy and may implode if dropped, so get help in handling these. Careful, correct measurement is most important. A rebate at least 13mm deep will be required if the unit is to be glazed into an existing wood or metal frame.
This allows for a 5mm gap between the sheets of glass. Units are made with smaller gaps. Check that the frames are in good condition and adequate to carry the weight of a factory-sealed unit, as this weighs at least twice that of a single sheet of glass.
When fixing pre-sealed units to existing window frames the most satisfactory method of fixing is to use beading, tacked and then painted to match the rest of the framework.
Alternatively, the unit can be glazed, in the conventional way, using a non-hardening glazing mastic.
Pre-sealed units have the added advantage of providing only two surfaces to clean and are neat in appearance.
There are no summer storage problems which apply to other types of glazing units and no ventilation problems. Most suppliers of double-glazed units will supply and fix, or measure for you and then supply for you to fix.
Sealed units are available in over 100 standard sizes but most firms will meet a ‘one-off’ order. As this may take some time, try to anticipate your needs in advance.
10. November 2011 by admin
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