Even the simplest forms of double-glazing can be effective at keeping heat in, and possibly at keeping noise out. But many of these simple types are not very attractive, nor are they very durable.
A short step from some of the simple double-glazing kits is the installation parts of America.
Secondary frames may fit either inside the existing window, or outside it as a coupled window, or a storm window. The frames may be fixed in place—the best solution for a good, tight seal—or sliding or hinged —to give easy access for cleaning and ventilation.
The greatest problem with secondary systems and coupled windows is preventing draughts and condensation. It is essential that your double-glazing system fits the window properly to keep maintenance problems to a minimum. Envisaging problems of this sort, you may prefer to buy a factory-made secondary glazing unit and install this yourself.
The choice ranges from wood, plastics and aluminium glazing frames you fit and glaze yourself, through various forms of factory-made ready-glazed secondary systems , and on to the most expensive option which is a complete replacement window or patio door. These are usually fitted with sealed-unit type double-glazing , but may use conventional glazing if a large-gap airspace for improved sound insulation is required.
If you decide to stick to a secondary glazing system and choose to employ a more rugged and permanent method than that provided by many of the simple kits, a fixed secondary frame is often the answer.
Many firms can make one to a special size if one of the many standard sizes is not suitable and if you can have these glazed inexpensively, this is a very good way of obtaining a professional standard of double-glazing at comparatively low cost.
But although a fixed secondary glazing system is attractive from the point of view of long life, installation is often an involved process. You must take particular care to prevent condensation forming after assembly, and to make provision for cleaning and ventilation.
The secondary frame, once glazed, should be installed on a cold and dry day.
Secondary glazing of this type differs only slightly from that for a coupled window and fitting problems are much the same.
The first major step up from simple systems is the fitting of factory-made ready-glazed secondary systems. Some firms can provide these units for you to fit yourself, whereas others may insist on an all-in professional service.
There is little doubt that these units provide the best compromise as far as performance, cost and looks are concerned, but they are still an extremely expensive proposition if fitted throughout the house. A better idea is to install factory-made frames only in the rooms you use most often.
In most systems, an extruded aluminium frame is attached to existing window framework with a mastic or other suitable sealant used to make good small irregularities and to prevent draughts at the frame edge—a potential cause of condensation.
A brick window opening is rarely truly square and to offset this fact, the better-quality units usually employ a sub-frame. This is fitted first, either to the bare brickwork at the window reveal or to the existing window frame, if this is in good condition. The new frame is then attached to the sub-frame, the fixing screws concealed beneath moulding.
The sub-frame should be made of hardwood to eliminate long-term problems such as warping and splitting. And if the frame is attached to brickwork, it is essential that fitting and construction are of a high standard.
A similar procedure is employed for the installation of complete replacement windows and patio doors. A variation is the use of an additional aluminium sub-frame, which must be carefully fitted to avoid reducing the glazing’s insulating properties and— over the long term—to prevent a buildup of trapped water.
When measuring up for a frame you are constructing yourself or having made to a special size, allow for a small strip of bedding and sealing mastic or putty at the edges.
Other double-glazing options
A number of budget forms of replacement windows are available, some of which combine the maximum use of timber framework with a minimum use of aluminium—contributing greatly to their effectiveness as insulators. The more expensive frames do this by incorporating ‘thermal breaks’—achieved by internal insulation, or by employing a split construction.
This is one name given to double-glazing which consists of two panes of glass sealed together in the factory with a gap between them—sealed units is another name. The gap between the units is filled with dehumidified air or an inert gas to prevent condensation. The units are fitted as replacements for existing single panes, but the window frames must be able to support the additional weight. If the rebate in the frame is not deep enough to take a standard unit, a stepped type can be used.
But you can obtain greater benefits by combining these insulating glass sheets within secondary glazing arrangements, so that triple or multiple glazing results. Multiple glazing is unlikely to be cost-effective in the UK, but may be in Canada and some parts of America.
Used in place of single glazing, insulating glass should—under identical conditions—show a noticeable reduction in the amount of condensation on the inner surface. Claims can seem exaggerated if the influencing factors—relative humidity, surface temperature differences and ventilation—alter: a point worth bearing in mind if you are comparing ready-glazed units with insulating glass.
The sealing methods used for insulating glass—and also for secondary glazing units—are also worth comparing. Choose systems and methods which employ a tight-fitting, but supple, ‘soft’ seal, as this reduces movement and vibration of the glass. Opening windows and doors, and large-area sheets exposed to strong winds are particularly susceptible to trouble of this kind.
Consider using professional help to install a particularly large area of insulating glass as experienced handling and fitting is required to avoid damaging the seal. Take particular care handling stepped insulating glass.
Comfort, safety and security
Draughtproofing and double-glazing can literally seal up a home, so providing adequate ventilation is particularly important. It comes down to striking a happy balance between heating and ventilation from the point of view of comfort, otherwise a buildup of internal humidity will result in severe condensation problems—perhaps far worse than you experienced before double-glazing.
You must provide adequate ventilation for fuel-burning appliances, even if this means going to the lengths of installing a ventilator grille near the appliance once the double-glazing has been installed.
The reduction in heat losses brought about by double-glazing often en-courges greater use of windows and patio-doors—both as a replacement for existing walling and windows, and as part of the design of structural extensions. The resulting increased area of glazing poses safety and security problems which cannot be ignored— even in terms of the single window, where one large area of glass is likely to be used in place of several small ones in individual frames.
Windows near doorways or stairs are particular danger areas. In these and similar instances, the risks of injury can be reduced if you employ safety glass in place of normal float or decorative glass. Safety glass goes through an annealing process which increases its resistance to smashing. And if it does break, the glass fractures into small, comparatively safe pieces rather than splinters.
All forms of glass should be handled with care, using heavy-duty gloves at all times—even on sheets with ground edges. Sharp edges can damage the plastics seals of many of the systems you can glaze yourself. Ask your glass supplier to remove these, or do the job yourself with a carborundum block.
For safety in the event of a fire, ensure that one or more easily accessible windows on each floor can be unlocked and opened quickly.
Take great pains to avoid fitting large sheets of glass in weak or badly supported frames—particularly those of opening windows and patio doors.
Large areas of glass or a window with two sheets of glass instead of one is unlikely to deter an intruder intent on forcing an entry—and quite possibly the reverse will apply. Opening windows should incorporate—or be provided with—locking handles or catches. Recessed locks and safety bolts should feature on all patio doors.
Many of the cheaper types of kit system have no provision for a lock, and you must take care to see that outer windows are properly locked at all times when double-glazing is in use. If possible, though, lock both inner and outer opening windows.
The more expensive your initial installation, the less likely the need for maintenance and running repairs. The seals of insulating glass should be inspected for wear every few years, but faults here are likely to show up in the form of condensation. Carry out these and other checks before really wet and cold weather sets in.
Wood frames can be checked for warping and splitting, and local repairs can be made as necessary.
Cleaning away dust and condensation is likely to be the most frequent maintenance job on most forms of secondary glazing—particularly the cheaper units—but many systems allow for this to be done quickly and efficiently. After you have cleaned the inner surfaces, inspect the various seals for signs of wear and make replacements where necessary.
Choose to spring-clean on a cool, dry day and thoroughly ventilate the room before you refit the secondary glazing to avoid an immediate return of condensation. Never allow condensation which is present to puddle: over a period of time this can rot the frame between the two sheets of glass. If condensation returns quickly in spite of reasonable precautions, suspect damage to the seals between the air gap and inside of the house.
Double-glazed patio door
Professionally installed double-glazing is a major home-improvement expense. A typical job is replacing old French doors with a custom-built unit having sliding doors. A patio door conversion of this nature may require the removal of the low walling on each side of the threshold. This type of structural work is usually carried out by the installers themselves.
The ‘moving’ part of the frame and the fast frame are manufactured with separate inner and outer sections which are secured together by means of a continuous non-conductive material, and the corners are secured by fastenings with secret fixings.
Sealed units of up to 32mm thickness can be accommodated by this design, permitting an air gap of 20mm which is considered the optimum by this manufacturer.
Safety and security are important aspects to consider. With this design —capable of withstanding the strongest gale-force winds—a hook-type lock is employed. ,’