Cost & Budget
How Much Does a House Extension Cost in Edinburgh?
What really drives the cost of a substantial extension in Edinburgh — and how to set a realistic budget before you speak to a builder.
MJM Joinery & Building ·
It is usually the first question homeowners ask, and the honest answer is that it depends — but not in a vague way. The cost of an extension is driven by a small number of decisions, and once you understand them you can set a budget with confidence.
At MJM we focus on substantial residential projects, typically from around £100,000. This article explains what sits behind that figure and why two extensions of similar size can be priced very differently.
The building itself is only part of the cost
When homeowners compare prices, they often compare the "shell" — foundations, walls and roof. In practice, the shell is only one part of the overall investment. A realistic budget should also account for:
- Structural alterations to the existing house, such as steel beams to open up the rear wall
- Glazing — large sliding doors, roof lanterns and rooflights are often a significant share of the cost
- The kitchen, if the extension is a new kitchen and living space
- Heating, electrics and plumbing, including any upgrades the existing system needs
- Finishes — flooring, joinery, lighting and decoration
- Professional fees for your architect, structural engineer and any other consultants
- Statutory fees for planning permission and the building warrant
- Contingency for the unexpected, particularly in older properties
What makes one extension cost more than another
Structure and ground conditions
Foundations depend on the ground. Sloping gardens, mature trees, drains running under the build area or poor ground can all increase the foundation work. Removing load-bearing walls in the existing house typically needs steelwork designed by an engineer.
Glazing and roof design
A simple flat roof with a couple of rooflights is very different to a full-width glazed wall and a frameless roof lantern. Large-format glazing is one of the biggest single variables in an extension budget.
Specification
Natural stone, bespoke joinery, underfloor heating and high-end kitchens all add to the investment. They also add to the quality of the finished space — the important thing is to decide where you want to spend.
The age and condition of the existing house
Many Edinburgh homes are Victorian or Edwardian. Tying a new extension into an older building often uncovers work that needs doing: dated wiring, old drainage or walls that are not quite where the drawings say they are. A sensible contingency allows for this.
Conservation areas and listed buildings
Much of Edinburgh is within a conservation area. Planning authorities may require specific materials — natural stone, slate or timber windows — which affects both design and cost.
How to set a realistic budget
- Start with the total you are comfortable investing, including fees, VAT and contingency — not just the build.
- Speak to your architect about scope early. It is far easier to adjust a design at concept stage than after planning is approved.
- Ask for an itemised proposal. A clear breakdown shows exactly what is included and makes comparisons meaningful.
- Hold a contingency. For older properties, we would always recommend keeping a contingency in reserve.
Comparing quotes properly
The lowest price is rarely the cheapest outcome. When comparing proposals, check whether each includes the same scope: structural work, glazing, kitchen, finishes, and who is responsible for coordinating trades. Provisional sums and exclusions matter as much as the headline figure.
Talk to us early
If you are planning a significant extension, an early conversation helps. We can discuss your plans, the property and your budget, and give you an honest view of what is achievable. Start your project or read more about our house extensions in Edinburgh.
