On Wed, 18 Apr 2007 20:20:33 +0100 The Natural Philosopher wrote :

Firstly, I would say that they would reach the U value, and secondly,
there is still no absolute requirement in the building regulations that
windows SHOULD have a specific U value, merely a recommendation and a
requirement for OVERALL insulation levels, and thirdly repairs are NOT
subject to FULL building control regulation: 'Like with like and at
least no worse' is the rule IIRC..

2 panes of glass will achieve a U-value of 3.3 - you can't have coated
glass except in a sealed unit. L1B 32 refers to Table 2 which requires a
U-value of 2.0 (or equivalent) for replacement windows. It's true that
this is not mandatory but if you are replacing windows then it is very
hard to argue that it is unreasonable to meet this requirement (an
exception might just be if you were required to have small pane Georgian
style windows for aesthetic reasons).

Where did PVC come from? he was talking having new wood frames made..

" However, the wooden window frames are now deteriorating.

Instead of replacing the whole lot with PVC double glazed units, would it
be feasible to simply replace the wooden frames with either wood or PVC
single glazed windows, "

--
Tony Bryer SDA UK 'Software to build on' http://www.sda.co.uk