Sealed Units

I've done some ringing around and found a very local company that manufactures the units for some of the local window companies. I asked for a number of options on the prices but all following are for 2 units, approx 1000 x 800mm as 4 - 16 - 4 (thats 4mm glass and 16mm space) with Pilkington K glass.

1. Toughened glass, standard spacers £121
2. Toughened glass, "warm edge spacers" £134
3. Standard glass, standard spacers £85
4. Standard Glass, "warm edge spacers" 98.24

The K glass and 16mm space should get me the required U value if I through Building Control regs.
I'll need toughened glass on the lower sash for some of windows, as the cills are low, again part of the regs.
The warm edge spacer sound like a good idea to me, as standard aluminium spacers cold bridge between the glass. At £6.50 difference for each unit I think I'll try it out.

I think I'll leave ordering these until I've started on the painting, there's no sense having big bits of glass laying around our house for longer than neccesary.