How to comply with Building Regulations for replacement windows

To ensure everybody understands the revisions to the Building Regulations for replacement windows and doors for England and Wales, the Glass and Glazing Federation have summarised the requirements and how installers can demonstrate compliance.

building regulations for replacement windows explained

Understanding Building Regulations for replacement windows

Communities and Local Government (CLG) have published the revised Approved Document L Conservation of fuel and power and Approved Document F Ventilation 2010. These will all be implemented for effect from 1 October 2010. There are transitional arrangements, any orders signed before 1 October 2010 can comply with the 2006 requirements as long as the installation work starts before 6 April 2011, all orders taken after 1 October must comply with the 2010 regulations. These regulations still apply as of 2021.

Changes to the U-Values and Window Energy Ratings for 2021

As part of the Government strategy to further reduce energy consumptions, it’s anticipated window energy ratings and U-Values are to get even lower. Therefore, there are anticipated changes to Building Regulations for replacement windows.

Autumn 2021 sees The Ministry of Housing Communities and Local Government (MHCLG) publishing new standards for energy efficiency. There’s more information about The Future Homes Standard, and how it’ll affect the performance of windows in the future.

The key changes to the guidance provided within the Approved Documents:

Replacement windows and doors and windows and doors installed within extensions
All doors and windows will need to meet the requirements of table 1 “Standards for controlled fittings” from Approved Document L1B as shown below:

Window, roof window or rooflightWER Band C or better (see paragraph 4.22) or U value 1.6 W/m²K
Doors with > 50% of internal face glazedU value 1.8 W/m²K
Other doorsU value 1.8 W/m²K

Paragraph 4.22 provides details of the Window Energy Rating formulae and rating bandings; all scheme operators need to use the same methodology as BFRC i.e. a BFRC WER C will be the same grade as a different scheme operators Band C.

BFRC with the WER scheme have the following options available:

WER Licence

A WER Licence – this is when a fabricator has a simulation undertaken on their window and it is registered with BFRC. The current Licence fees are £200/licence/year.

Licence of Addition

If a Licence holder wants alternative or additional glazing solutions; these can be bolted on to the main Licence in the form of a Licence of Addition. The new IGU has to be simulated; the WER has to remain within the same WER band as the original window. BFRC charge a £50 one of fee per addition to a Licence.

Authorised Retailer

If you are buying in frames from a Trade Frame supplier who has a Licence (with or without Licence of additions) you can copy their Licences and have your own BFRC WER with your company name on it by using the Authorised Retailer approach. In addition you can source your own units from your normal unit suppliers (as long as they comply with EN 1279 and are to the same IGU specifications as the original Licences).

FENSA Registered businesses can have up to 10 Licences for £140/year through this route (the annual audit will be undertaken on site by the FENSA inspector at the pre installation assessment). If an Authorised Retailer is not FENSA Registered it will cost £325/year because an additional audit has to be undertaken.

The whole window U value

The GGF are also pleased to see that CLG has included an alternative method of compliance to WER and Building Regulations for replacement windows.  The GGF fully support the WER approach and believe this is the correct way for the industry to go however, there did need to be an alternative for non main stream production. That said, it should be noted that CLG have set a very demanding target of whole window U value 1.6 W/m²K.

An installation company needs to know that the product they install can meet the 1.6 U value; there are a variety of methods available to determine this:

CE Marking Declaration of conformity

CE marking declaration of conformity under EN 14351-1 for thermal performance; this will demonstrate the U value when calculated by a competent body and the manufacturer has made a declaration of conformity when placing the product on the market. Currently CE marking is not mandatory for construction products under the Construction Products Directive. It should be noted that with the Construction Products Regulations (CPR) currently being reviewed by our MEP’s in Brussels CE marking will become mandatory – this is expected to come into effect Q2 2013.

The detailed simulation arriving at Window Energy Ratings and U-Values

Detailed simulation by a certified simulator will provide a very accurate U value for the whole window. BFRC Simulators can provide this service; their details are available on the BFRC web site

What is the U-Value calculator for Building Regulations for replacement windows?

Simplified calculation by using a U value calculator. These use the same logic as the detailed modelling method however; some are more simplified than other which means that the U value achieved will be worse than it actually is in practice.  FENSA are about to launch their U value calculator, this will have a lot of details installed making it very accurate for the window company. To use the FENSA calculator this will be accessed via the FENSA web site, an annual fee of £199 will be charged for unlimited use; details of the frame and the units can be selected and a combined U value determined. A print out will show the frame and components used in the window combination and the u value achieved; this information is required for the auditor to enable inspection to take place.

Understanding default window specifications

The work which has been undertaken by BFRC with the detailed simulation of thousands of window combinations and the resulting whole window U value and WER means we can look at which combinations achieve the 1.6 U value. It is apparent that if you have a timber or PVC-U frame and you use an IGU comprising: soft coat low E glass, 90% gas filled and warm edge spacer bar; you will achieve a 1.6 U value.

We know there are many other combinations of component which can achieve the 1.6 U value however, the above specification is a clear guide for FENSA registered window installers who need a quick guide solution to be prepared for 1 October 2010. Other solutions will achieve the required U value, hard coat low E, non gas filled units and all spacers bars could still be used; these alternative combinations will have to be determined by detailed simulation or by using one of the U value calculators.

The rationale for using this approach has been established since 2002; showing compliance against a 2.0 U value, the window needed to have low E glass and 16mm air gap.

FENSA Registration Explained.

When a window installer registers their installation on line with FENSA; they can continue to use the current approach, provide the details of the site installation and the number of windows installed.

FENSA registered installers who are using the BFRC WER Licence as the method to demonstrate compliance, will have the option to register the Licence numbers with FENSA on line; the homeowner, will then gain an enhanced certificate with the BFRC Licences on the reverse of their FENSA Certificate.

If an installer is using the FENSA calculator to determine the whole window U value; the window specification and the fact it complies with the 1.6 can be registered with FENSA; who will produce a U value registration number. If this registration number is registered with the FENSA on line; FENSA inspectors will know the specification for the window they are assessing and the fact this method demonstrates compliance.

If the WER Licence or the FENSA U value registration number is not referenced when registering an installation; the paperwork demonstrating compliance (U value certificate or WER Licence) will need to be left with the home owner for inspection by FENSA.

Understanding Conservatories and Building Regulations.

Whilst Conservatories are not covered by FENSA; we thought it appropriate to reconfirm the requirements for installing conservatories.

Conservatories are exempt from Building Regulations if they meet the following requirements:

The conservatory meets the definition of a conservatory
The internal floor area less than 30m²
There is separation from the main building by exterior quality doors and windows
There is a separate heating system.

It should be remembered that compliance to Part N (safety glazing) and Part P (electrics) still need to be complied with.

When the statutory Instrument was laid before Parliament on 12 March the Minister made the statement “There was concern, particularly from property owners and occupiers, over the cost and bureaucracy of removing the exemption for allconservatories from Part L and the Government has decided against including this in the 2010 changes”.

Advice on compliance with building regulations for replacement windows from the GGF

The GGF are revising their “A guide to good practice in the specification and installation of conservatories within the United Kingdom” the updated guide explains all the requirements for start to finish for installing conservatories with revisions to Building Regulations and planning permission.  The GGF believe that despite the exemption from Building Regulations for certain conservatories, the glazing and construction should be such that the thermal performance, safety and comfort is achieved to ensure the consumer has a suitable installation and enhances their home.

  • Trickle ventilators within replacement windows.
  • Approved Document F Ventilation has been updated.

Approved Document F 2006 says that where original windows in dwellings are fitted with trickle ventilators, replacement windows should have trickle ventilators (or equivalent means of ventilation). However where the original windows are not fitted with trickle ventilators it would be good practice only to fit trickle ventilators.  The consultation set out the option of requiring the use of trickle ventilators for all replacement windows in dwellings subject to ongoing cost benefit analysis supporting such a change. Although many consultees support the proposals when asked in 2009, they also suggest that the costs in the IA were too low. The GGF have always made a position that a building needs to be able to breath, a completely sealed room will lead to condensation and potential mould growth which could be a health risk.  However, trickle ventilators should only be installed when required otherwise there is no health benefit if not required.  The GGF have been working with CLG and their consultants to determine the cost benefit of making such a requirement mandatory.

The now complete cost-benefit analysis indicates that the total cost of such installation could be £61m.  The benefit measured in terms of Quality Adjusted Life Years (QALYs) attributable to the policy was estimated at just over 600 QALYs. This gave a cost per QALY of around £100,000 and can be compared with the guideline used by the National Institute for Clinical Excellence (NICE) that health treatments costing no more than £30,000 per QALY as being effective. In light of this research and consultation response it has been decided that there is not sufficient evidence to justify a change to the current provisions”.

In summary there is no change in the guidance for the use of trickle ventilators within replacement windows.

The GGF welcome this advice however we do strongly urge that installers carefully consider if trickle ventilators are required.  To assist installers the GGF have produced several publications on trickle ventilators and condensation:

  • Advice to consumers regarding ventilation when replacing windows in dwellings
  • A guide to trickle ventilators
  • GGF Datasheet 6.10 – Guidelines to determine where trickle ventilators should be used within replacement windows
  • Condensation – Some Causes, Some Advice

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