Nice post Basil

Its a good approach, but getting the airtightness up to scratch is one of the vital components for a low carbon house. The houses being built at the moment to meet high end efficiency such as the passivhus use a heat recovery system for their ventilation as the whole house is air tight,(when windows closed).

When you mean 'old materials'! Do you mean reclaimed materials or old such as stone. Its great to reuse (its one of the 4 R's of waste minimisation (reduce, reuse, recycle, recover)), but you may need to bring up to standard with building regs. ie reusing a nice old timber window...well its worth putting in double or triple glazing, which may mean modifying the frame a little. But then are there any seals?...probably not, and has the frame got gaps in it? letting the hot air out. etc etc. Maybe in the end cheaper to put in a new window, which you know meets the standard you are aiming for.

So, needs thinking through for each element.