BWF members such as yourselves frequently use our Member and Technical Helplines for assistance on a wide range of Employment, Health and Safety, Pay and Technical issues. We’re putting up a frequently asked question every Tuesday in order to help members and illustrate the type of advice we are able to provide. If you have any questions that you would like to see featured, we would be happy to assist. This question and many others like it can be found in our Question Centre. If you want further advice on any of the issues, don’t hesitate to ring the helpline or browse our extensive publications library, which includes our Fact Cards and guidance on installing timber windows. This week: Basic U-values for Part L Compliance – Some FAQs Since the launch of the Part L Compliance package for the Basic U-value Calculation (ECWINS) software tool on 2nd August, our technical team have been receiving a considerable volume of data from members for their window ranges. Therefore, to help with understanding some of the intricacies of providing the right data, they thought it would be worthwhile giving some answers to your frequently asked questions concerning compliance with Building Regulations Part L from 1st October 2010. Q1 For Replacement Windows, Do I Need To Achieve A U-Value Of 1.6 W/m2k? A1 No, if your windows are Energy Rated to band C or better they will comply. Typically, band C windows have a U-value of 1.5 to 1.8 depending on the solar factor and air leakage values. For new build the maximum area weighted average U-value of all doors and windows should be 2.0 W/m2K. The actual value will be determined by the building designer. Q2 What Type Of Glass Unit Will Generally Enable My Timber Window To Achieve A U-Value Of 1.6 W/m2k? A2 The typical IGU required will be a 24 mm argon filled unit with a softcoat low-e coating on surface 3 and possibly a warm-edge spacer bar. The type of low-e coating, typically 0.05 or 0.03 emissivity, and the type of spacer bar required will be determined by your calculation. Q3 What Happens If I Submit Details Of My Windows And I Do Not Achieve A U-Value Of 1.6 W/m2k? A3 Without obligation, the Technical Team will advise you of any alteration that would be required to enable you to achieve the required U-value. You can then resubmit the data sheets along with payment for the service and we will then calculate the U-value and issue you a certificate stating the window criteria on which the U-value is based. Q4 I Make Tilt And Turn Windows, Fully Reversible Windows And Bespoke Windows, Are These Covered By The BR 443 Model Window? A4 Yes, if your windows use the same sections sizes and glass details then only one calculation is required. If the section sizes differ then separate calculations are needed. These will each be based on the BR 443 model window. Q5 Is ECWINS The Only Software Tool To Calculate U-Values? A5 No, there are software packages provided by other organisations, but the BWF package allows this U-value to be accepted for CE Marking and it covers other characteristics for windows and doors.