Frequently asked questions

If you're thinking of purchasing double glazing, it is always useful to know something about the product. We have included here some FAQs on double glazing, together with some unbiased answers to help you make your decisions.

You'll find more information in our 'how to' guides and Double-glazing Buyers' Guide & Tips section too.

Click a question to reveal the answer.


A. We would suggest a patio awning as these are ideal to protect you from the sun and cover a larger area. Another added attraction is that they can be used at night for entertaining as they can be supplied with lighting. Also, when it's time to go in, simply press a button and your patio awning will fold itself away.

A. Yes, fitting double glazing to your property will certainly improve the sound-proofing. We would suggest that you have B rated sealed units with one side laminated glass as this would drastically cut out the noise from outside.

A. When replacing box sash windows both methods can be used.Some companies believe leaving the original 'box' in place and fitting the new double-glazed sash window within the existing box sash should be perfectly acceptable, providing that the timber is in good condition. This way it will have all the original moulding. Complete replacement is the best option in our view as if the old timber is rotten this would be false economy.

At Falcon we remove the complete boxed sash, stud out inside, plasterboard and skim including fitting a window board. This way it is a much better job and all that is left is the redecoration inside. Alternatively we can fit vertical sliding sashes which are becoming more and more popular and affordable. In our view these are by far the best option, but are slightly more expensive and look just like the old box sash windows including the decorative horns.

A. Yes, there could be restrictions if you live in a conservation area or have a listed building. Our experience has found that it is best to discuss with the local Conservation or Planning Officer what you would like to do and they can let you know whether it's possible.

A. Tempered glass, when broken, shatters into many small fragments and prevents major injuries. Due to these characteristics, tempered glass is used traditionally in applications requiring increased strength such as patio doors, French doors or UPVC windows. However tempered glass should receive the same care as annealed glass.

A. The 'problem' is caused by the fact that the Low E insulating Glass is doing its job so well and reflecting heat back into the room. You would normally expect reduced or no condensation once double glazing was fitted.

External condensation (dew) can occasionally occur on highly insulated units in temperate climates. Such occurrences will only happen on cloud-free nights when there is little or no wind and usually when a warm front follows a dry spell. The amalgamation of quite a few factors, namely external air temperature, localised microclimate and the thermal transmittance of the glazing itself may all add to the formation of external condensation.

A. Customers with children are often concerned about this as it claimed that toughened glass is more dangerous if smashed. The question is - is one more secure than the other?

Both toughened and laminated glasses are forms of 'safety' glass. People often presume toughened glass is extra strong glass.

In our opinion 'break safely glass' - as they are both known - are both safe.

Toughened glass breaks into very small pieces which are very hard to get cut from. Laminated glass cracks when broken as there is a thin layer of perspex in between two panes of glass. Laminated glass is 'thicker - usually 6.4 mm - and as such will offer better insulation and is quieter inside as well due to the different thicknesses of the glass. It is also harder to break in, due to the thin plastic inside the glass

However this thicker glass is also 'heavier' which will in turn means greater wear and tear on opening windows and doors. It is also slightly more expensive than toughened glass.

This is probably one of the reasons why it is not so widely specified in conservatory construction.

Problems with outside condensation on your windows in the cold winter months?

Double-glazing - Quality of Vision

Standards & Regulations

Relevant British & European Standards

  • BS 5588: Part 1:1990 - Fire precaution in the design, construction and use of buildings
  • BS 6206: 1981 - Impact performance requirements for flat safety glass and safety plastics for use in buildings
  • BS 6262: 1982 - Glazing for buildings
  • BS 6375 - Performance of windows Part 1. Classification for weather tightness Part 2. Specification for operation and strength characteristics
  • BS 6399: Part 2:1997 - Loading for buildings Part 2. Code of practice for wind loads
  • BS 7412: 1991 - Plastics windows made from PVC-U extruded hollow profiles
  • BS EN 12608: 2003 - Unplasticised polyvinyl chloride (PVC-U) profiles for the fabrication of windows and doors - Classification, requirements and test methods
  • BS 7950: 1997 - Specification for enhanced security performance of casement and tilt/turn windows for domestic applications
  • BS 8213 - Windows, doors and roof lights
  • Part 1 (1991). Code of practice for safety in use and during cleaning of windows and doors (including guidance on cleaning materials and methods)
  • Part 4 (1990). Code of practice for the installation of replacement windows and door sets in dwellings
  • BS EN ISO 10077-1:2000 - Thermal performance of windows, doors and shutters - Calculation of thermal transmittance
  • Part 1. Simplified method
  • All the above BSI documents can be ordered from 'BSI Customer Services Department on 020 8996 9001'

BPF Windows Group Publications

  • 323/1 COP for the reinforcement of high impact modified PVC-U windows and doors
  • 351/1 Guidelines for the use of PVC-U windows and frames in commercial/light industrial applications
  • 356/1 COP for the installation of PVC-U windows and door sets in new domestic dwellings
  • 357/1 Replacement windows and planning law
  • W362/1 Code of practice for the survey and installation of replacement plastics windows and door sets
  • W363/1 Guidelines for the selection and application of fasteners for the manufacture of plastics windows and door sets
  • W364/1 Guide to the specification and use of plastics windows and door sets Guide to Building Regulations, Building Control and FENSA (CD or booklet)
  • All the above BPF documents can be ordered from 'BPF Publications Sales Department on 020 7457 5000'

Regulations applicable to England and Wales:

  • Part A (England & Wales): Structure The revised edition of this document has been distributed for comment
  • Part B (England & Wales): Fire Safety
  • Part E (England & Wales): Resistance to the passage of sound
  • Part F (England & Wales): Means of Ventilation
  • Part J (England & Wales): Heat Producing Appliances
  • Part K (England & Wales): Protection from Falling, Collision and Impact
  • Part L1 & L2 (England & Wales): Conservation of Fuel And Power Part M (England & Wales): Access And Facilities For Disabled People
  • Part N (England & Wales): Glazing in relation to Impact, Opening And Cleaning

Regulations applicable to Scotland:

  • Part C (Scotland): Structure
  • Part D & E (Scotland): Fire Safety
  • Part F (Scotland): Heat-producing installations and storage of liquid and gaseous fuels
  • Part H (Scotland): Resistance to transmission of sound
  • Part J (Scotland): Conservation of Fuel and Power
  • Part K (Scotland): Means of Ventilation Part P (Scotland): Miscellaneous hazards
  • Part T (Scotland): Facilities for Disabled People