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Double Glazing FENSA Regulations

Double Glazing FENSA Regulations

Double glazing has changed dramatically over recent years. It used to be, that double-glazing meant quality windows. Now however, with improved technology and manufacturing, there are many products on the market which range in quality. Some are adequate to meet minimum building regulations, while others are mid-range in quality right through to extremely energy-efficient, double or triple-glazed.

From the original double glazed sealed units which where simply, two sheets of float glass with a very small spacer bar; today high-spec double/triple glazed sealed units have toughen safety glass, wide spacer bars, argon fill sealed units and Low-E coatings. This combination gives the consumer an efficient window and real value for money.

And its value for money that is so important for consumers. Not only do we all have to cope with increasing energy bills and strident building regulations, but now, new EU legislation means that from 2012 all homes for sale will require an energy efficiency rating to be carried out upfront before a house can even be put on the market. So, we will soon be seeing energy rating labels on all For Sale boards.

On 1st April, 2002, all replacement double glazing window installations became subject to Document L of the Building Regulations. This states that new uPVC or timber double glazed windows should not have a U value higher than 2.0 W/m 2K and metal double glazed windows (aluminium) should not have a U value higher than 2.2 W/m 2K. With so much double glazing being installed in British homes, it has been agreed that the double glazing industry can adopt a self-assessment method for administering the many thousands of installations that take place each week. The self-assessment scheme is referred to as FENSA - Fenestration Self Assessment Scheme. Providing the installer you use is registered with the FENSA scheme, they will certify that the work complies with the relevant regulations and you will not need to notify your local council.

If the installer is not a member of FENSA or you are carrying out the work yourself on a DIY basis, then approval will have to be obtained from the local authority. It is most important to conform to these new double glazing regulations as you will need to provide proof of compliance with Document L, if you wish to sell your property after having installed replacement double glazing windows.

This double glazing window regulation particularly affects the minimum levels of insulation that replacement double glazed windows must achieve when fitted in your home. Levels of insulation are measured as U values. The lower the U value, the better the level of insulation. What was previously referred to as 'normal' double glazing (two panes of glass separated by a spacer bar) is very unlikely to conform to building regulations. To obtain the required level of insulation, look for low emissivity coatings and argon gas filled sealed units.

Its also worth noting that many uPVC or aluminium frames are hollow and that precious heat can be lost through the frame, even though the sealed glazing unit might be efficient. It’s a bit like, forgetting to insulate your loft.

Timber is naturally a very good insulating material, so a timber frame to your sealed glass unit, will stop heat loss and make the whole window energy-efficient. While, triple glazing is now fast becoming the norm and can be more cost-effective at the time of purchase and in savings on your energy bills.

Triple or Double glazing

So what exactly is double glazing? Double glazing is today’s general term used for uPVC windows / replacement windows. The double glazing part of the window is the glass, or sealed unit, this comprises of two panels of glass. Triple glazing has three panes of glass to make up the sealed unit. The glass panes are kept apart by a spacer bar which contains hundreds of tiny silica balls. These same balls can be found in the little bags you find in the packages when you buy electrical goods to keep then dry and free from moisture or condensation. It is these balls which soak up any moisture which exists in the air gap between the panes of glass.

Float glass or safety toughened glass?

Double glazed sealed units will either be normal float glass for small double glazed sealed units or toughen for larger double glazed sealed units, as required by building regulations and the Glass and Glazing Federation.

What is toughened, tempered or safety glass? Tempered glass when broken, shatters into many small fragments, which prevent major injuries. Due to these characteristics, toughened glass is used in applications requiring increased strength such as French or patio doors and windows, which reduces the likelihood of injury in the event of breakages.

Double glazing insulation is affected by;

• The cavity width of the sealed unit.
• The use of argon gas instead of air in between the panes.
• Low emissivity coating that reflects heat back into the room.
  
  

The latest double glazed sealed units offer a greatly improved insulation (as required by FENSA) compared to older traditional double glazed sealed units and single glazing. In addition to their better insulation, double glazed windows are also draught-proof, therefore reducing the amount of heat that can escape, so you can cut down on your heating and save on energy without sacrificing comfort.

The insulation of a double glazed unit is measured in U values (the measurement of heat transfer through the window itself). The following table illustrates some typical sealed unit U values using various combinations of cavity widths, air or argon and Pilkington K Glass, which has a low emissivity coating.

Argon gas sealed units

Argon gas is extremely cost-efficient, and works well with Low-E coated glazing. It is a colourless, odorless, non-flammable, non-reactive, inert gas used to reduce heat loss in glazing sealed units by slowing down convection inside the air space.

When we talk about insulation glass without low-e coating, we refer to double glazing that uses air between panes as a primary source of insulation. Air itself is a good insulator, but filling the gap between the glass panes with a low-conductivity gas such as argon improves window performance by reducing conductive and convective heat transfers. The reason - the density of the gas is greater than the density of the air. Argon is the most commonly used fill gas, due to its excellent thermal performance and cost-efficiency in comparison to other gas fills.

Double glazing windows, patio and French doors and uPVC doors now come under the requirements of building regulations and document Part L which requires that all these products must meet a high standard of insulation.

for more information go to our double glazing or triple glazing standard ranges