I am currently writing a paper on responsibly retrofitting existing dwellings within the UK. One of the most useful resources has been the Energy Saving Trust who have produced a large range of documents addressing almost anything energy conservation orientated. The most relevant and interesting I found was the Domestic Energy Efficiency Primer, which you can download directly from the EST website here. It looks at every area of a dwelling and suggests what possible improvements can be made, addressing several types of construction common in houses in the UK and advising as to the level of experience needed to undertake each measure.