In addition to the refurbishment, the requirement may also be to upgrade existing steel windows (sometimes referred to as "Crittall Windows"). The cost of upgrading must be weighed up against the cost of new steel windows, but generally, the cost of upgrading should always be considerably less than replacing. The type of upgrade should be selected in accordance with the reasons why an upgrade is required.
There are six main reasons why old steel windows might require an upgrade, as outlined below.
Upgrades to the security of existing steel windows and doors can be made using two methods:
• Glazing upgrade to provide a glass that is more secure to vandalism and entry
• Addition of security locks and/or other devices to make windows less accessible during an attack
Existing glass in steel windows, especially in older frames, is usually single glazed annealed glass around 3 - 4mm thick. This offers very little in the way of security and can be broken and accessed very easily. Some style of steel windows include cottage style steel glazing bars leaving only entry points of around 300mm square with the glass out and therefore this style of window is safest. A common misconception is that leaded lights are secure. This is not true and the leads lights are just as, if not more susceptible to breakage and entry.
The way of increasing security to non-leaded larger pane steel windows is to change the glass to a type that is harder to break out. There are two main types of glass that fulfil this requirement. The first is toughened glass and the second is laminated glass. There is little price difference between the two.
Toughened glass is made to be harder to break, but when it breaks it shatters into small shards and leaves an open pane. Laminated glass is made to break as easily as normal annealed glass, but includes a layer of clear transparent material that bonds two separate panes of glass and therefore, holds glass together when broken.
For security, we recommend the use of laminated glass. The usual thickness suitable for a general compromise between cost-effectiveness and security is 6.38mm. This is constructed from 2 sheets of 3mm clear annealed glass with a 0.38mm interlayer. Any existing glass can be removed and replaced with this single glazed sheet as described in the Refurbishment section. All laminated glass is stamped with the laminated mark which also acts as a deterrent to burglars. There are also many thicker versions of laminated glass available which have higher ratings against attack.
Another basic way to increase security is to present to a potential burglar two panes of glass to attempt breakage through instead of one. The retro-fitting of sealed double glazing to existing windows fulfils this requirement. Please refer to "The need for double glazing" section for details.
As well as breaking glass to gain entry, burglars also gain entry via opening windows. Therefore, the ironmongery keeping the window closed should be of a standard to give the best possible security. This can be done in two ways. The first is to replace the ironmongery with new ironmongery which incorporates security devices and the other is to leave existing ironmongery in place and add secondary security devices. The latter would be more preferable to windows utilising ornate ironmongery. There are a number of restrictions on which types of locks can be used on which types of windows and doors. Therefore, types of locks and therefore security attained will depend entirely on the existing type of windows.
If problems are encountered with heat loss, this is usually associated with two causes:
• Gaps in the opening windows - refer to "Draughts" below.
• Single glazing - existing single glazing can be upgraded to double glazing in many cases. Refer to "Double Glazing" section.
Old ironmongery can be given a new lease of life by renovation, straightening, chemical stripping, mechanical polishing and optionally re-coating with a variety of finishes
For existing opening windows that are presently draughty, the windows should firstly be serviced, eased and adjusted (see Renovation Section). This should cut down the majority of the draughts by minimising the gaps around the edge of the moving sashes.
To create a total seal, the windows can be upgraded by silicone draughtproofing (if no existing draughtproofing exists) as described in the "Noise" section. For existing windows which presently include draughtproofing, which is defective, please refer to "Weather Strips" in the Renovation Section.
Existing windows with gaps around the opening sashes should be serviced, eased and adjusted prior to the application of the Silicone Draughtproofing system.
Existing window and door ironmongery can be upgraded for security purposes as described in the "Security" section.
Ironmongery can also be upgraded for aesthetic reasons. There is a wide variety of handles, stays, spring catches and the like available which are in a range of traditional and modern designs and in differing finishes.
Existing steel doors can also have their ironmongery upgraded by retro-fitting additional or replacement door closers, handles and higher-security or differing types of locks.
To upgrade windows for safety purposes, releasable restrictors meeting current regulations can also generally be fitted to existing steel opening windows.
Noise transference through steel windows, especially pre-1965 is very common. After this period, most steel windows included an important item which was a weatherstrip seal between the inner and outer frames of opening windows. This item cuts down a great deal of noise that is transferred through the gaps in the opening windows. Also, double glazing units were starting to be employed into designs which helped a great deal. If the problem is associated with the renewal of existing weatherstrips or double glazing units, refer to the Renovation section.
Existing single glazing can, in many circumstances, be upgraded to double glazing which will help insulate against sound infiltration. Please refer to the Double Glazing section below.
Either the windows can be pre-1965 with no weatherstrip or post this period with no weatherstrips, the below recommendations are made to incorporate weatherstrips into the opening windows. The black neoprene weatherstrips that are used in today's windows are housed into pre-formed grooves in the steel sections (W20 windows) or into pre-fabricated and factory fixed aluminium channels (SMW). Older steel windows that were manufactured before the advent of weatherstripping contained no grooves or mounting points and therefore another method of draughtproofing is used.
The above-described silicone draughtproofing method carried out by SMW provides an excellent seal for the life of the silicone (minimum of seven years) after which time it can be stripped back and re-applied. It works extremely well as it will take up all varying gaps in the steel.
"Stick-on" DIY weatherstrips should never be used on steel windows as these will bow and distort the frames due to the force required to close them.
Silicone draughtproofing is ideally applied to newly-decorated steel windows, decoration, which includes the closing edges of the steel opening windows, in addition to the main faces.
The upgrading of the glazing in existing steel windows can often involve specialised re-glazing of curved panes and multiple-pane windows as demonstrated by this stair window which SWS refurbished and upgraded to safety-rated, and noise-insulating sealed double glazing units.
• Windows should first be serviced, eased and adjusted prior to application to ensure correct setting of opening windows
• Open the steel window
• If the window is not newly decorated, clean down closing edges and apply a coat of primer paint
• Allow to dry
• Apply low tack tape to closing edges
• Apply a bead of silicone (sympathetic colour to window frame colour) to the closing edge of the fixed outer frame
• Close the window fully (Silicone will now compress and run into all areas)
• Apply a removable warning sticker to glass warning not to open window
• Leave window for a minimum 48 hours to allow the silicone to cure
• Return to window
• Remove the sticker from the glass
• Open the window
• Remove tape and clean any excess silicone and residue from opening frame members
• Trim excess silicone level with back weathering leg of outer fixed frame
• Re-set window frame as required and leave all in good working order
NOTE: under no circumstances should the silicone be painted at any time as this would lead to a chemical reaction between the paint and the silicone which leads to the breakdown of the silicone.
There are many very good reasons for upgrading from single glazing to double glazing, notably noise infiltration, heat loss and security. Existing steel windows can, in many cases, have their glazing changed in this way without the need to change the window frames themselves.
There are limitations to which type of steel windows can have their glass upgraded. The 3/8" depth glazing rebates that were used prior to 1965 in commercial buildings cannot accommodate standard double glazing units. This is due to the shallow height glazing legs which would not cover the spacer bar. Inevitable misting up of the unit would follow, after the premature breakdown of the hermetical seal by UV rays. However, in these cases, commercially available premium-priced Slimline or Slimlite warm edge spacer bar height conservation units, with their reduced stack height spacer bars, can usually be used, and these are generally available in overall thicknesses from 12mm (4/4/4) up to 14mm (4/6/4).
Existing single putty glazed SMW windows used from the 1930s can also be re-glazed with these Slimline / Slimlite conservation units with a 12mm thickness. However, if the windows are fitted with horizontal or small-pane glazing bar configurations, then this would be subject to survey, as the fitted glazing bars are sometimes only 19mm from front to back, and these cannot house any type of double glazing unit with an adequate putty seal externally.
The only existing steel windows that can be double glazed with standard type (i.e. standard 11mm- 12mm high spacer bars) double glazing units are windows with a 13mm (Â½") glazing leg depth rebate, and a glazing table (from glass side of glazing back leg to end of table on glazing side) of minimum 26mm. New glazing will involve the redrilling and tapping of all glazing rebates and supply/fix of new beads/corner clips.
Alternatively, in conservation areas or on listed buildings, where there is a need to replicate the existing putty glazing detailing, the units may be bed onto a solid and backfill of silicone mastic, and when cured, can be fronted with standard or rapid set metal casement putty.
Any change to double glazing from single will be rewarded with a significant increase in performance in respect of heat loss, noise reduction and security.
In terms of heat loss alone, single glass has a U value (the measure of heat loss through an element) of around 5.7W/m K centre pane (Ug) as opposed to a conservative low performance Slimlite/Slimline double glazing unit centre pane U value of around 1.9-2.1W/m2 K (Ug). This will result in a more comfortable internal environment, lower fuel bills and a considerably more environmentally friendly installation.
All reglazing would be carried out in the same way as described in the Renovation section.