Ask ten builders what an extension costs and you will get ten different answers, mostly because the question is too broad to answer honestly. What follows is how the numbers actually break down for homes in and around Inverness, what pushes a project up the range, and the costs that rarely make it into a first conversation.
Most builders price extensions on a rate per square metre of new floor area, then adjust for what is going inside. In the Highlands, a straightforward single storey extension with a pitched or flat roof, standard windows and a plastered shell currently sits somewhere around £2,000 to £2,900 per square metre for the building work. A kitchen or garden room with large sliding doors, underfloor heating and a lantern roof will land closer to £3,000 to £3,800.
So a 25 square metre kitchen-diner extension is realistically a £55,000 to £85,000 project once fittings are included, and a modest 15 square metre utility or bedroom addition might be £35,000 to £50,000. Two storey extensions look expensive in total but are usually better value per square metre, often £1,800 to £2,400, because you pay for one set of foundations and one roof across two floors. All of these figures exclude VAT unless your builder states otherwise, and new-build extension work does not qualify for any VAT relief.
If you have been reading UK-wide cost guides, you will have seen lower numbers. Those are usually based on urban England, and a few local realities move the figure.
None of this is dramatic on its own, but together it commonly explains a ten to twenty percent difference against a Glasgow or Edinburgh quote for the same drawings.
Scotland has its own building standards system, and this catches people out. You need a building warrant from Highland Council before work starts, not a sign-off afterwards, and the fee is scaled to the value of the work. Budget for the warrant fee plus your designer's drawings and a structural engineer's calculations, which together often come to £2,500 to £5,000 for a typical extension.
Many single storey extensions to the rear fall within permitted development and need no planning application, but the rules depend on size, height, position relative to boundaries and whether you are in a conservation area or on a site with a previous planning condition. Check before you assume. On top of that, allow for a site survey if levels are awkward, drainage alterations, electrical certification, decoration, flooring, and the kitchen or bathroom itself. A kitchen is easily £8,000 to £25,000 and is entirely separate from the build cost.
A number scribbled after a fifteen minute visit is a guess. A quote worth comparing is written against drawings and a specification, and it tells you what is included, what is excluded, and what is allowed as a provisional sum for items not yet chosen. Where ground conditions are unknown, expect a clear statement of what happens if we hit rock rather than silence on it.
When you compare two prices, compare the specification line by line. A cheaper quote is often cheaper because it assumes basic windows, no underfloor heating, or that you are supplying and fitting the kitchen. Ask about the payment schedule, expected programme in weeks, and who is handling the warrant and completion certificate. And keep a contingency of around ten percent of the build cost; on older Highland properties, opening up walls and floors reveals things nobody could have priced in advance.
Often not, as many rear and side extensions fall within permitted development rights, but this depends on size, height, boundary distances and whether your property sits in a conservation area or has planning conditions attached. You will still need a building warrant from Highland Council regardless, and that must be in place before work begins.
For a typical 20 to 30 square metre extension, allow roughly 12 to 18 weeks on site once the warrant is granted, plus two to three months beforehand for drawings, engineering and the warrant itself. Winter starts and difficult ground conditions can extend the programme.
Usually not on a per square metre basis, because converting existing space avoids new foundations and a new roof. A garage conversion or loft conversion is worth pricing first if you have the space and the headroom, and an extension makes more sense when you need a specific ground floor layout such as an open plan kitchen onto the garden.