How Much Does It Cost to Build an Outbuilding? UK Guide

Overview: average cost of building an outbuilding in the UK

When you first speak to builders about the cost of building an outbuilding, the range of figures can feel confusing. One person might quote £6,000 for a basic timber office, while another suggests £20,000+ for what sounds similar.

The reality is that “outbuilding” covers everything from a simple shed to a fully-insulated brick garden room that feels more like a mini-extension. Recent price guides put the average cost of an outbuilding at around £7,500, but with a wide band either side: small modular units from roughly £1,500 and high-spec buildings over £24,000. :contentReference[oaicite:5]{index=5}

As your outbuilding becomes more like “a little house in the garden” – brickwork, high-performance glazing, full insulation, services and sometimes a WC – costs naturally drift closer to small extension levels. That’s why we always recommend cross-checking outbuilding prices against our main guide to extension costs so you can decide which route offers better value for you. :contentReference[oaicite:6]{index=6}

Key differences: timber vs brick outbuilding cost

Material choice is one of the biggest drivers of outbuilding construction cost. Broadly, most projects fall into three categories: modular/lightweight timber, higher-spec timber “garden rooms”, and traditional block or brick outbuildings.

1. Modular or flat-pack timber outbuildings – lowest upfront cost

• Typical budget: from around £1,500–£7,000+ depending on size and quality. :contentReference[oaicite:7]{index=7}
• What you get: pre-designed kit, often with basic insulation and simple joinery.
• Best for: storage, hobby spaces, occasional home office use in milder months.

2. Timber garden rooms & offices – mid-range cost, “room-like” feel

• Typical budget: £7,500–£18,000+ depending on size, glazing and spec. :contentReference[oaicite:8]{index=8}
• What you get: better foundations, upgraded insulation, proper electrics, nicer finishes.
• Best for: regular home working, studios, gyms, kids’ dens.

3. Brick or block outbuildings – highest cost, longest lifespan

• Typical budget: £17,500–£26,500+ for a brick outbuilding, depending on size and finish. :contentReference[oaicite:9]{index=9}
• What you get: robust walls, tiled or slated roof, better sound and thermal performance, easier to blend with the main house.
• Best for: garages, workshops, high-quality garden rooms or studios that feel permanent.

Application types: planning permission & building control for outbuildings

Although this guide focuses on the cost of building an outbuilding, planning permission and building regulations can both affect the budget.

Planning permission or permitted development?

Many domestic outbuildings fall under permitted development (PD) if they’re single-storey, under certain height limits and genuinely “incidental” to the main house (for example, a home office, gym or hobby room rather than sleeping accommodation). If your design is large, in a conservation area, or very close to boundaries, you may need a full planning application instead.

Building regulations routes: Building Notice vs Full Plans

Heavier, more permanent outbuildings – especially those with electrics, plumbing or high-quality insulation – may need building regulations approval. Smaller, detached outbuildings under 15 m² and without sleeping can sometimes be exempt, but it depends on construction, distance from boundaries and use.

You’ll usually choose between:

• Building Notice – quicker but offers less certainty up front; good for simple structures with an experienced builder.
• Full Plans submission – more detailed drawings checked in advance; better if you want cost certainty or your design is complex.

What the cost of building an outbuilding usually includes

When you receive quotes, it helps to understand what’s typically inside the number – and what is often missing.

Commonly included in an outbuilding construction cost

• Site preparation, simple levelling and basic groundworks.
• Foundations or concrete slab (for heavier timber, block or brick buildings).
• Main structure – frame, walls, roof and basic finishes.
• Doors and windows to the agreed specification.
• Basic electrics (lighting, a few sockets, consumer unit connection).
• Plasterboard and simple decoration internally (for higher-spec builds).

Often excluded or only partly allowed for

• Drainage runs for WCs, sinks or showers.
• Upgraded glazing, bifolds or rooflights.
• Heating (electric panel heaters, underfloor heating, air-con units).
• High-performance insulation needed to satisfy building regulations Part L.
• Planning drawings, structural calculations and application fees.
• Landscaping, decking and garden lighting.

Who prepares your outbuilding plans and drawings?

The more solid and “house-like” your outbuilding, the more value you’ll get from proper drawings. Even when planning permission isn’t needed, accurate plans help builders price reliably and avoid on-site disputes.

For most homeowners, the options are:

• Architect or designer: ideal if your outbuilding links visually with a future extension or forms part of a wider re-design.
• Specialist planning & building regs service: a common route if you “just need plans” for a straightforward outbuilding and want someone to handle planning drawings, building regulations plans and structural details together.
• Builder design-and-build service: some companies include basic drawings, but these can be limited to their standard models.

Our team at Plans Made Easy regularly prepares plans for outbuildings, garages, garden rooms and similar structures, making sure they align with both permitted development and building regulations rules so you don’t get tripped up late in the process. :contentReference[oaicite:10]{index=10}

Costs & timelines: how long outbuildings take and what they cost

Once you know what sort of structure you want, you can start to plug in realistic figures.

Remember these numbers usually exclude professional fees (for example, drawings and structural calculations), planning application fees and any unusual groundworks such as retaining walls or moving manholes. Our separate guides on extension build costs and structural calculation costs give useful reference points when you’re comparing options.

Step-by-step: how to plan your outbuilding budget

Here’s a simple process you can follow to keep the cost of building an outbuilding under control from day one.

HowTo checklist – planning the budget for your outbuilding

Pitfalls & “gotchas” that increase outbuilding cost

Most cost surprises come from details that weren’t thought about early enough. Here are the main ones we see with homeowners.

• Underspecified foundations: soft ground, trees or sloping sites can mean deeper foundations or retaining walls.
• Services and drainage: long runs of ducting for power or water, or a new manhole, quickly add hundreds or thousands of pounds.
• Insulation upgrades: if building control is involved, you may need better U-values than the original quote allowed for – see our guide to building regulations U-values.
• Scope creep: extra sockets, better cladding, more glass or a higher-end roof finish all add up.
• Local council quirks: some authorities are stricter about what counts as “incidental”, especially in conservation areas or where there’s a history of outbuildings being used as annexes.

Technical details that affect outbuilding construction cost

A few technical choices can shift your budget significantly:

• Roof type: a simple felted flat roof is cheaper than a warm roof with single-ply membrane, which in turn is usually cheaper than a pitched tiled roof to match the house.
• Thermal performance: if you want a year-round office or studio, you’ll probably be aiming for Part L-friendly insulation levels and decent double (or triple) glazing.
• Fire safety: distances to boundaries affect wall and roof specifications under Part B, particularly for larger or taller outbuildings.
• Services: power, heating and data cabling all need thinking through early, especially if you’re running cables under paths or patios.

FAQs: cost of building an outbuilding

Next steps & useful guides

To dig deeper into costs, permissions and technical details around outbuildings and similar projects, these guides from our library will help:

• In-depth extension cost breakdown – useful if you’re comparing an outbuilding with adding space to the house instead.
• Building regulations approval explained – what triggers it and how the process works.
• Building regulations for garden rooms – how the rules apply to insulated offices and studios.
• Garden rooms guide – planning rules, design options and typical build costs.
• Planning permission – complete homeowner’s guide – ideal if your outbuilding needs a formal application.
• Single vs double-storey extension costs – another benchmark when weighing up your options.

We’ve linked to other in-depth Plans Made Easy resources so you can move smoothly from this Support Stone into the wider Pillar content without needing to search again. :contentReference[oaicite:16]{index=16}

External guidance on outbuildings, planning and building regulations

For official national guidance, it’s always worth double-checking your plans against:

• Planning Portal – national planning guidance and interactive house guide
• GOV.UK – planning permission in England & Wales

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