How Much Does a House Extension Cost in Perth? 2026 Pricing Breakdown
What Does a House Extension Actually Cost in Perth?
If you're considering extending your home in Perth or Perthshire, the first question on your mind is almost certainly: how much will it cost? It's a fair question — and unfortunately, one that doesn't come with a simple answer.
The truth is, extension costs vary significantly depending on the size, specification, ground conditions, and complexity of the build. But what we can do is give you realistic price ranges based on the projects we've delivered across Perth and Perthshire over the past 15 years.
Average House Extension Costs in Perth (2026)
Here's a breakdown of typical costs for the most common types of house extension in Perth:
| Extension Type | Typical Size | Price Range |
|---|---|---|
| Single-storey rear | 15–30m² | £30,000 – £65,000 |
| Single-storey side return | 10–20m² | £25,000 – £50,000 |
| Two-storey rear | 30–60m² | £55,000 – £110,000 |
| Wrap-around | 25–45m² | £50,000 – £90,000 |
| Over-garage extension | 15–25m² | £30,000 – £55,000 |
| Sunroom / garden room | 10–20m² | £15,000 – £35,000 |
These figures include foundations, structural work, roofing, windows, electrics, plumbing, plastering, and decoration. They assume a mid-range specification — not the cheapest, not the most luxurious.
What Affects the Cost of an Extension?
Size and Footprint
This is the biggest factor. A 15m² kitchen extension is going to cost significantly less than a 40m² open-plan living space. Cost per square metre typically ranges from £1,800 to £2,800 depending on specification.
Ground Conditions
In parts of Perth, particularly around the river and older areas of the city, ground conditions can be challenging. If your site has soft ground, a high water table, or requires deeper foundations, that adds cost. A structural engineer's report (around £400–£600) is always recommended before work starts.
Specification and Finishes
A basic plastered room with standard electrics and a radiator is one price. Add underfloor heating, bifold doors, a fitted kitchen, skylights, and engineered oak flooring and you're looking at a very different figure. The shell of the build typically accounts for 50–60% of the total cost — the rest is all in the finishes.
Access and Logistics
If your property has narrow access, limited space for scaffolding, or requires materials to be carried through the house, labour costs increase. Properties with good side access and space for a skip and materials are cheaper to build.
Planning and Building Warrant
Most extensions in Scotland require a building warrant (around £300–£600 depending on project value). Some also need full planning permission — particularly if the extension exceeds permitted development limits or the property is in a conservation area. Factor in £400–£800 for architectural drawings.
How to Keep Extension Costs Under Control
Get a Detailed Quote — Not Just a Price
A proper itemised quote should break down every element: groundworks, steelwork, blockwork, roofing, electrics, plumbing, joinery, plastering, decoration, and any fitted elements. If a builder gives you a single lump-sum figure with no breakdown, that's a warning sign.
Fix Your Specification Before You Start
The most expensive changes are the ones made mid-build. If you decide halfway through that you want bifold doors instead of French doors, or that you'd like to move the kitchen sink, it creates delays, additional labour, and often waste. At Marshall & Co, we invest significant time in the planning stage to lock down every detail before breaking ground.
Don't Over-Specify for the Area
It's tempting to create a grand design, but if you're spending £120,000 on an extension in an area where houses sell for £250,000, you may not see that investment reflected in the property value. Speak to a local estate agent before committing to a very high specification.
Consider Phased Work
If budget is tight, some elements can be phased. For example, we often build the shell and fit the kitchen and bathroom in phase one, then complete landscaping and decorating in phase two.
What's Included in a Marshall & Co Extension Quote?
When we quote for a house extension in Perth, our price includes:
- Full project management from start to finish
- Groundworks and foundations
- Blockwork, steelwork, and structural elements
- Roofing (tiles, slate, or flat roof systems)
- Windows, doors, and glazing
- First and second fix electrics
- First and second fix plumbing
- Plastering and skimming
- Internal decoration (painting and finishing)
- Building warrant application support
- Site clearance on completion
We don't charge for initial consultations, and our quotes are fixed — no hidden extras or surprise costs.
Planning Permission vs Permitted Development in Scotland
Many single-storey rear extensions fall under permitted development in Scotland, meaning you don't need formal planning permission. However, there are limits:
- The extension must not exceed 50% of the original curtilage
- It must not extend more than 4 metres from the rear wall (6 metres for detached properties in some cases)
- Maximum height restrictions apply
- Materials should match the existing property
Even under permitted development, you still need a building warrant — this is non-negotiable in Scotland. We handle the application process as part of every project.
How Long Does a House Extension Take?
| Extension Type | Typical Build Time |
|---|---|
| Single-storey rear (20m²) | 8–12 weeks |
| Two-storey rear (40m²) | 12–18 weeks |
| Wrap-around (35m²) | 10–16 weeks |
| Over-garage | 8–12 weeks |
These timescales assume no major delays from building control, weather, or material supply. We provide a detailed project timeline at the quotation stage and keep you updated throughout.
Is a House Extension Worth the Investment?
In most cases, yes. A well-designed extension in Perth can add 10–20% to your property value — and that's before you factor in the improved quality of life. An extra bedroom, a bigger kitchen, or a dedicated home office can transform how you live in your home.
The key is getting the design right, choosing the right builder, and making sure the specification suits both your needs and the local property market.
Ready to Discuss Your Extension?
If you're thinking about extending your home in Perth or Perthshire, we'd love to hear from you. We offer free, no-obligation consultations where we visit your property, discuss your ideas, and give you an honest assessment of what's possible within your budget.
Request your free estimate today or call us on 07940 568877.
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