Window replacement structural safety VIDEO
Provision should be made to ensure that the structural stability of a building is maintained and made no worse as a result of a replacement glazing installation. This usually occurs if the replacement windows are wider than those they replace, or involve the replacement of bay windows, then Building Control will need to be satisfied that proper structural support is provided above the window. In older buildings, the timber frame of the window was often sufficiently strong to carry the load of a wall or roof above it without a lintel. Obviously in these cases either a lintel needs to be installed when the window is replaced, or the new frame carefully reinforced to carry the load.
Bay Windows - appropriate structural support may need to be introduced in some circumstances.
Fire Escape Provision should be made to ensure that means of escape in case of fire is maintained and made no worse as a result of a replacement glazing installation. All first floor windows in dwellings should ideally have opening lights large enough to allow you to escape through them if you were trapped in the room by a fire. This also applies to rooms in bungalows which open into a hall (unless the hall itself has an external door through which you could escape).
It is essential that in dwellings that the existing means of escape in case of fire, is maintained to first floor bedrooms and any room (Inner Room) that only has access through another room (Access Room).
Windows and rooflights Replacement windows to first floor bedrooms and inner rooms should have sufficiently sized and located openings to ensure that means of escape in case of fire is not made any worse than before the replacement glazing was installed or should meet the current requirements whichever is the lesser.
It is recommended wherever possible that escape windows are installed to at least the current minimum size.
If your existing windows do not have opening lights which meet the above requirements, we would strongly recommend for your own safety, that you take the opportunity to provide them in the replacement windows. Where the existing windows already have opening lights which are larger than the above requirements, those in the new windows can be reduced in size provided they are not reduced to less than the dimensions above.
Escape window sizes An opening that is required for means of escape should have a clear unobstructed opening area of 0.33 m² and a minimum width or height of 450mm. For example, if a width of 450 mm is proposed then the height should be at least 733 mm in order to give the area of 0.33 m².
Openings that are required for means of escape should have a maximum floor to sill height of 1100 mm.
Doors Provision of replacement doors should ensure that means of escape is not made any worse than before the replacement glazing was installed. In most dwellings small reductions in the unobstructed width will not be critical.
Non-domestic buildings Existing means of escape in case of fire only occasionally relies upon escape through windows. Where this occurs it is essential that means of escape is maintained.
Windows and rooflights Replacement windows to rooms that rely on escape through windows should have sufficiently sized and located openings to ensure that means of escape in case of fire is not made any worse than before the replacement glazing was installed.
It is recommended where ever possible that escape windows are installed to the current minimum size. Provisions are the same as for dwellings.
Doors Provision of replacement doors should ensure that means of escape is not made any worse than before the replacement glazing was installed. A replacement door, required for means of escape, should have a clear unobstructed opening width of at least that of the existing.
Ventilation Existing windows with a permanent ventilation facility that is required to give air supply to combustion appliances should be maintained and be made no worse as a result of a replacement glazing installation.
All buildings Combustion appliances including some cookers, fires and boilers that draw air from the room in which they are located require a permanent air supply to ensure that they work efficiently and safely. Following any replacement glazing installation the provision of permanent air supply previously provided by an existing window should be not less than that provided by the existing windows or the current minimum standard, whichever is the lesser.
Window replacement prevention from falling Provision should be made to ensure that protection from falling is made no worse as a result of a replacement glazing installation.
Domestic and non-domestic buildings In some situations existing windows act as guarding to prevent building users from falling. In such situations replacement windows should continue to provide appropriate guarding to the bottom edge of a window, opening or otherwise, to ensure protection from falling.
It is recommended wherever possible that guarding is installed to the current minimum size.
Typically accepted standard – current requirements
Ground floors with basement wells or sunken areas next to the building and all upper floors should be provided with ancillary guarding where minimum floor to sill or floor to opening casement heights are less than:
Domestic Windows/rooflights to loft conversions - 600 mm
All other window/rooflights - 800 mm.
Note. Fixed glazing panels below 800 mm may also serve as guarding provided they are sufficiently robust.
Non-domestic All guarding should be at least 1100 mm high.
Windows and Doors (where relevant) Replacement glazing should meet the current minimum standards.
Window replacement conservation of fuel and power The glazing specification should provide an appropriate thermal performance.
Typically accepted standard - Current Requirements
The replacement windows will need to meet the new thermal insulation requirements of the regulations. If the replacement windows have wooden or plastic frames, then the glazing needs to achieve a maximum U-value of 2.0W/m2K while for metal frames a slightly higher U-value of 2.20W/m2K is allowable. Please note that these values are very difficult to achieve and many double glazing units currently on sale will not meet these new standards. Take great care when ordering new windows that your supplier can prove the glazing units used will satisfy this requirement, as the Building Control Officer will need to see this proof before issuing a completion certificate. We would particularly recommend that you leave any labels on the glazing in place until after a satisfactory inspection has been carried out by the Building Control Officer.
In some cases it may be permissible to use glazing units which do not meet the above specifications, but to do so you (or your supplier) would have to submit calculations to prove that the overall insulation requirements of the regulations would still be met. This may be possible if other insulation measures are undertaken at the same time as the window replacement - for example, installing cavity wall insulation or "topping up" loft insulation. The benefits gained by installing this extra insulation can be used to offset the higher losses through the glazing, but this should not be undertaken lightly. We would strongly advise you get any such calculations checked by the Building Control Officer well before the replacement windows are installed, so that expensive mistakes can be avoided.
Window replacement glazing safety Low level glazing (glazed areas within 800mm of floor level) and glazing in doors within 1500mm of floor level should generally be of a type so that if broken, it will break safely. In practice this means such glazing should be either laminated or toughened. Ordinary glazing can still be used in small pane sizes however, provided the glass is sufficiently strong to resist breakage. The Building Regulations gives maximum sizes according to the thickness of glass - for example, in a single pane less than 1.1m square - 8mm glass would be satisfactory.
Typically accepted standard current requirements
Replacement glazing should meet the current minimum standards as in the list below:
Safety glazing specifications should be installed to glazing within the following ‘critical locations’:
Window replacement ventilation Provision should be made to ensure that appropriate ventilation is maintained and is made no worse as a result of a replacement glazing installation. The Building Regulations require that adequate ventilation is provided for people in the building and this should be considered when deciding on the size of opening lights in the replacement windows. For most rooms, one or more opening windows totaling 5% of the floor area, with background "trickle" vents totaling 8000mm2 will be adequate. For kitchens, utility rooms and bathrooms an extract fan is also normally required. In some cases the existing windows may contain a permanent vent to supply combustion air to a heating appliance, although this is now rare. If this is the case however you should ensure that either the replacement window contains a similar permanent vent, or that some other means of providing the required ventilation is installed at the same time.
All buildings Replacement windows should have sufficient openings to ensure that the area of ventilation is not less than that provided by the existing windows or the current minimum standard, whichever is the lesser.
Typically accepted standard - current requirements
Provision should generally meet the requirements appropriate to a new property:
Rapid Area equivalent to 1/20th floor area of the room served
Dwellings Habitable rooms @ 8000 mm² - Kitchens, Bathrooms & WC’s @ 4000 mm²
Background (trickle) - non-domestic
Occupiable rooms up to 10 m² floor area @ 4000 mm² -- Occupiable rooms over 10 m² floor area @ 400 mm²/m² floor area -- Kitchens, Bathrooms & WC’s @ 4000 mm²
Please check with your local building control department before using information contained in this page to ensure that they comply with your local building codes.