When you need more space, the decision usually comes down to two options: extend your house or build a garden room. Both add usable square footage to your property, but the way they get there — and what they cost in money, time, and disruption — could not be more different.

This is an honest comparison. No sales spin. We manufacture garden rooms, so you might expect us to favour them, but the truth is that each option serves a different purpose. What matters is understanding the trade-offs so you can make the right call for your home, your budget, and your tolerance for building work.

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Cost Per Square Metre: The Numbers

Let us start with the question everyone asks first: what does it actually cost?

A typical single-storey rear extension in the UK costs between £1,800 and £3,000 per square metre, depending on specification, location, and ground conditions. A premium specification with bi-fold doors, underfloor heating, and high-end finishes pushes towards the upper end. For a 20sqm extension, you are looking at £36,000 to £60,000 — and that figure often excludes professional fees, planning applications, and VAT on many elements.

A premium timber garden room from RoomRise sits in the £20,000 to £45,000 range for a completed building including foundations, electrics, insulation, glazing, and interior finishing. That works out to roughly £1,500 to £2,250 per square metre — and because we are the manufacturer, the price you receive is the price you pay.

Here is how the comparison looks side by side:

Factor	Brick Extension	RoomRise Garden Room
Cost per sqm	£1,800 to £3,000	£1,500 to £2,250
20sqm total cost	£36,000 to £60,000	£30,000 to £45,000
Professional fees	£3,000 to £8,000 (architect, structural engineer, party wall surveyor)	Included in quoted price
Planning application	Usually required: £206 to £462	Typically not required (Permitted Development)
VAT	20% on most elements	20% (or 5% if integrated with qualifying residential work)
Groundwork cost	£8,000 to £15,000 (trench foundations, concrete)	£1,500 to £3,000 (steel pile foundations)

The cost differential widens further when you factor in the hidden expenses of an extension. Removing a load-bearing wall to connect the new space to your existing home typically adds £2,500 to £4,500 in structural steelwork alone. Then there is the cost of temporary kitchen arrangements, redecorating disrupted rooms, and the inevitable contingency budget that extension projects consume.

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Disruption: Ten Days vs Six Months

Cost is only part of the equation. The lived experience of each project — the noise, dust, and disruption to your daily routine — is where the two options diverge dramatically.

A Traditional Brick Extension

A single-storey extension typically follows this timeline:

• Weeks 1 to 2: Site setup, demolition of existing structures, and trench excavation. Your garden becomes a building site. Skips arrive, scaffolding goes up, and dust enters the house regardless of how well you seal doorways.
• Weeks 3 to 4: Foundation pours, drainage work, and subfloor construction. Concrete wagons arrive at intervals, and your garden is reduced to mud.
• Weeks 5 to 12: Bricklaying, roofing, window installation. This is the longest phase — trades arrive in sequence, with gaps between each stage. You live with exposed walls, temporary insulation, and unfinished floors for weeks.
• Weeks 13 to 20: First-fix electrics and plumbing, plastering, drying time (at least two weeks for plaster to fully dry), second-fix work, and snagging.
• Weeks 21 to 24: Internal finishing, decoration, and final connections.

Total elapsed time: four to six months, assuming no delays with planning, materials, or trades.

A RoomRise Garden Room

Our build process looks very different because the manufacturing happens off-site in our workshop:

• Day 1: Site preparation and steel pile foundation installation. No concrete wagons, no trench excavation. The piles are driven into the ground using a tracked rig, and the steel frame is bolted on top. Your garden is disturbed only at the footprint of the building.
• Days 2 to 8: The pre-manufactured panels, roof, and glazing arrive and are assembled on-site. The structural shell is weather-tight within 48 hours of delivery.
• Days 9 to 10: Internal first-fix electrics, plasterboarding, and final connections. External cladding is fitted, and the building is handed over.

Total elapsed time: 10 working days, with the vast majority of noisy work confined to the first three days.

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Property Value: How Buyers View Each Option

Both extensions and garden rooms can add value to your property, but buyers perceive them differently — and that perception affects what they will pay for.

Brick Extensions

A well-executed extension that creates an open-plan kitchen-diner or additional ground-floor living space can add 10% to 15% to your property value. This is the gold standard for value addition because the space is integrated into the main house and immediately usable as primary living accommodation.

However, poorly designed extensions can actually reduce value. A dark, poorly insulated single-storey addition with low ceilings and inadequate glazing is a liability, not an asset. Buyers discount heavily for work they will need to redo.

Detached Garden Rooms

Garden rooms add value differently. They do not increase the primary living area of the house, but they create a genuinely separate, flexible space that appeals to a growing market of remote workers, freelancers, and multi-generational households.

Industry data suggests a high-quality, insulated garden room adds 5% to 8% to property value — less than a full extension, but at a fraction of the cost and disruption. The key word here is quality. A garden room built with proper insulation, double glazing, and year-round usability is a genuine asset. A thin-walled summerhouse marketed as a “garden office” adds nothing.

What garden rooms offer that extensions cannot match is flexibility. The same building can serve as a home office, a gym, a teenage retreat, or a guest annexe as your needs change over the years. That adaptability is increasingly valued by buyers who see property as a long-term investment.

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Timeline: From Deposit to Final Coat

Here is a realistic comparison of the full project timeline — not just the build phase, but everything from initial decision to finished space:

Stage	Brick Extension	RoomRise Garden Room
Design and quoting	4 to 8 weeks (architect drawings, structural calculations)	2 weeks (complimentary 3D CAD design consultation)
Planning permission	8 to 13 weeks (if required)	0 weeks (Permitted Development)
Building Regulations	4 to 6 weeks (full application)	0 to 2 weeks (most builds exempt)
Construction	16 to 24 weeks	2 weeks (10 working days)
Total elapsed time	7 to 12 months	4 to 6 weeks

The speed advantage of a garden room is not just about convenience. It is about certainty. A 10-day build has very little that can go wrong. A six-month extension has dozens of potential failure points — weather delays, trade availability, material shortages, structural surprises behind existing walls.

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Which Is Right for You?

There is no universal answer. If you need a larger kitchen, an open-plan living area, or additional bedrooms connected to the main house, an extension is the right choice. That integration with the existing building is something a detached garden room simply cannot replicate.

But if what you need is a dedicated, separate space — somewhere to work, exercise, create, or retreat — a garden room delivers that space faster, cheaper, and with dramatically less disruption. And with 100mm PIR insulation, double glazing, and full electrics as standard, a RoomRise garden room is genuinely usable every day of the year.

The best way to decide is to see the numbers for your specific project. Book a complimentary 3D CAD design consultation and we will talk through your options honestly — including telling you if an extension would actually serve you better.