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: More FAQs on Basic U-values for Part L Compliance With the new Part L being introduced this Friday (1st October and the launch of the Part L Compliance package for the Basic U-value Calculation (ECWINS) software tool earlier this Summer, our technical team have been receiving a considerable volume of data from members for their window ranges. We have already provided a batch of FAQ’s relating to the new regulations, but since there is still some confusion about the Part L requirements and the best glass to use, out technical team have now provided some more answers to help dispel the myths surrounding the new regulations Q6 What would happen if I do not have my window range checked for its U-value? A6 You are then not likely to know whether your window range would comply with the National Building Regulations Part L from 1st October 2010. Many BWF members who have had a calculation done and received a certificate from BWF will be able to show compliance with Part L and will be using this as a marketing tool to increase their sales, especially amongst their local competitors who may not be aware of the requirements. Q7 I have found that my glass supplier is confused over what is needed to comply from 1st October and have had conflicting advice about whole window U-values and energy rating. How can BWF help? A7 Obtaining an energy rating for your windows is an expensive way to comply with Part L, but for replacement windows a whole window U-value of 1.6 W/m2K can generally be achieved by using glass with a centre pane U-value of 1.2 W/m2K for 24 mm IGU argon filled and warm edge spacer. The two main glass manufacturers Pilkington and Saint Gobain (Solaglass) supply ‘Optitherm SN4+’ and ‘Planitherm Total’ respectively, which both have a centre pane U-value of 1.2 and a soft coat low-E value of 0.05. Saint Gobain also supply ‘Planitherm Ultra N’ of 1.1 W/m2K glass with low-E value 0.03; and ‘Planitherm 1’ giving 1.0 W/m2K glass with low-E value 0.01. Q8 How many calculations are needed for different timber densities? A8 The ECWINS software has a threshold of less than or equal to 500 kg/m3 and greater than 500 kg/m3, so if you state European redwood at 510 kg/m3 then this will cover most of the softwoods and hardwoods you use, so only one calculation is needed for the BR 443 model window at £95 +VAT. Q9 I manufacture a York style window, is this covered by the ECWINS software? A9 This style of window can be modeled using the software for a horizontal slider to give a whole window U-value. Q10 Do doors with less than 50% glass area need to comply with part L? A10 Yes they do. Regulation 4 states that building work, and replacing doors and
windows, is considered to be building work, should be carried out so that, among other considerations, it complies with the applicable requirements of Part L. However, in Part 5 of the Building Regulations, Regulation 12, states that a person who intends to carry out building work is not required to give a building notice or deposit full plans for work listed in Schedule 2B paragraph (h which lists replacing an external door where the door together with its frame has not more than 50% of its internal face area glazed, i.e. a doorset with less than 50% glazed area does need to comply with Part L. This work does not need to be notified to Building Control or to be registered with one of the installation schemes. Q11 I have heard that timber windows will struggle to achieve any Energy Rating of Band C, is this true? A11 No it is not true. On the BFRC website there are twenty-nine timber casement windows listed as having Band C. To achieve this rating the whole window U-values range from 1.2 W/m2K to 1.8 W/m2K and ‘g-window’ varies from 0.3 to 0.47. For Energy Ratings ‘g-window’ is the solar energy transmittance factor at normal incidence (or the g value provided by your glass unit supplier) multiplied by 0.9, which averages the solar energy, and then multiplied again by the frame factor, the ratio of timber to glass in the elevation of the BR 443 model window. Q12 What effect will the changes to Part L have on timber doors? A12 For replacement doorsets to achieve the minimum U-value of 1.8 W/m2K they will need to use similar glass units as windows and make use of insulated panels. Solid timber panels will generally not provide enough insulation and traditional 44 mm thick doors may struggle to accommodate 24 mm glass units unless, perhaps, bolection beads are used. 56 mm hardwood doorsets using glazing and panels with a U-value of 1.2 W/m2K can achieve an overall U-value of 1.8 W/m2K.