I have no wish to defend the shambles of the implementation timetable of Part L, forced on the ODPM by its political masters and the European Union. The development of the Simplified Building Energy Model was part of that sorry process, but to criticise SBEM because it doesn't give the answers you want is hardly fair.

Your piece ("The nightmare has begun", 7 April, page 24) contains at least one major non sequitur, which is that because SBEM permits "all glass buildings" it must be flawed. Glass and facade technology has moved on from the materials that were used in the office towers of the 1960s and 1970s. Facades are now dynamic and multi-skinned. Glass is now made with any number of selective and low-energy coatings, designed to transmit or reject daylight and solar heat according to the needs of the building. Modern glazing contributes positively to the energy balance of a building. How else can you explain why most exemplar low-energy buildings invariably use large amounts of glass (just think of the Integer building, on the BRE's own doorstep)?

The design flexibility introduced into Part L as a result of the whole-building method of compliance should be welcomed. Just because the results might be counter-intuitive to some doesn't invalidate the software. SBEM may or may not have technical shortcomings, but at least it appears capable of modelling the positive energy aspects of glazing.

Rick Wilberforce, market development manager, Europe, Pilkington