Comparing the three routes on something other than instinct
The decision between refurbishing, extending and replacing is usually made emotionally and then justified financially, and it repays being taken the other way round. Five factors separate them. Performance is the first: a mid-century house with solid or poorly insulated cavity walls, minimal roof insulation, single glazing and a boiler-based heating system can be improved a great deal, but there is a ceiling on what retrofit achieves within a given budget, and it sits well below what a new building meets as a matter of course. If very low running costs are a primary objective, that materially favours replacement. Plan is the second: extensions add area but rarely fix a fundamentally awkward arrangement — a hall in the wrong place, a stair that lands badly, rooms whose proportions cannot be changed without moving structure — whereas a new building starts from the brief. Risk is the third, and it is the one most often misjudged. Refurbishment and extension carry construction risk: what is behind the plaster, what the foundations are, whether the drainage runs where the drawing says. Replacement carries almost none of that but concentrates the risk in planning, which is binary and known before money is committed to construction. Time is the fourth: refurbishment can often be phased and lived through, while replacement means finding somewhere else to live for a year or more, which is a real cost that belongs in the comparison. Value is the fifth, and on a plot where the land is worth substantially more than the building, the arithmetic frequently favours replacement in a way it does not on a modest plot — but only where planning permits it. The useful output of an options appraisal is not a recommendation but three costed, drawn scenarios with their risks stated, because the right answer depends on how the owner weighs running costs against disruption and certainty against ambition.
