How Much Does It Cost to Convert a Conservatory Into an Extension?

Quick Cost Overview

• The average cost of converting a conservatory into an extension falls between £15,000 and £25,000, though roof-only upgrades and full rebuilds sit outside this range at either end.

• Prices vary by scope, with a partial upgrade that keeps the existing frame and floor at £8,000 - £15,000 and a full rebuild into a solid brick extension £15,000 - £35,000+.

• The roof specification and the condition of the existing foundations are the two biggest cost drivers, since a shallow conservatory base often needs strengthening before it carries a solid, insulated structure.

A Guide to Converting a Conservatory into an Extension Costs

In this guide, we cover:

1. What Affects the Cost of Converting a Conservatory Into an Extension
2. Average Cost of Converting a Conservatory Into an Extension by Scope
3. Roof Replacement Costs Explained
4. Planning Permission and Building Regulations Costs
5. Labour Costs and Day Rates
6. Additional Costs to Budget For
7. How to Save Money on the Conversion
8. Find an Extension Builder Near You on MyBuilder
9. Frequently Asked Questions

Use the list above to jump straight to the section most relevant to your project, or read on for the full picture.

What Affects the Cost of Converting a Conservatory Into an Extension

The final bill for turning a conservatory into an extension depends on several factors working together, and small differences in scope shift the price by thousands of pounds. Understanding these variables upfront helps set a realistic budget before requesting quotes.

The size of the conservatory is the starting point, since labour and materials both scale with floor area. A small 9m² lean-to costs far less to convert than a 20m² garden room, purely because there is more roof, wall and floor to replace.

The roof type comes next: a polycarbonate or glass roof needs full replacement with a solid, insulated structure, while a conservatory that already has a tiled roof needs less work overall.

Foundations matter just as much as anything above ground. Conservatories are commonly built on shallow slab foundations that were never designed to carry brick walls and a tiled roof, so if the base is not suitable, the builder digs new trench-fill footings or underpins the existing slab, which adds cost and time. Glazing choice also plays a part, since keeping large sections of glass in bifold doors or a roof lantern costs more than switching entirely to brick and standard windows.

Other factors that move the price include:

• The distance between the conservatory and the main house electrics and heating system
• Whether the existing floor slab needs to be dug out and re-laid with insulation
• Regional labour rates, with London and the South East typically running 20% to 30% higher than the North or Midlands
• Access to the site, since a conversion in a tight side passage costs more in scaffolding and material handling than an open rear garden

Average Cost of Converting a Conservatory Into an Extension by Scope

The average cost of converting a conservatory to an extension varies enormously depending on how much of the original structure survives the project. A homeowner keeping the existing frame and floor while upgrading only the roof pays a fraction of what a full rebuild costs, so it helps to think of the job in tiers rather than a single price.

Scope of Work	Typical Cost
Solid roof replacement only	£4,000 to £10,000
Basic upgrade, structure retained	£8,000 to £15,000
Mid-range conversion with partial rebuild	£15,000 to £30,000
Full rebuild into a brick extension	£15,000 to £35,000+

A basic upgrade keeps the existing frame, floor and glazed walls, replacing only the roof with an insulated tiled or panel system. This suits conservatories with sound foundations and frames still in good condition, and it lands at the lower end of the cost of converting a conservatory to an extension.

A mid-range conversion goes further, swapping some glazed panels for brick or block walls, upgrading the roof, and extending the heating and electrics into the space. This tier covers most of what people mean when they search for the average cost of converting a conservatory to an extension, since it delivers a genuinely usable, insulated room without the expense of a total rebuild.

Full Rebuild into a Brick Extension

A full rebuild strips the conservatory back to the slab, or removes it entirely, and constructs a proper brick or block extension with new foundations, a tiled roof and windows matched to the rest of the house. This route makes sense when the existing base is not suitable for a solid structure, or when the homeowner wants the new room to look indistinguishable from the original house. Costs for this tier sit at £15,000 to £35,000, climbing higher in London or for larger footprints, where per-square-metre build costs reach £2,800 to £5,500.

Roof Replacement Costs Explained

The roof is usually the single biggest line item in a conservatory conversion, and the option chosen has a knock-on effect on insulation, heating costs and how the room feels day to day. Three main approaches cover most projects.

Lightweight insulated roof panels fit over the existing glazed or polycarbonate roof structure without major rebuilding work, and cost £2,500 to £6,500 depending on the size of the conservatory and the finish chosen inside. This is the fastest and cheapest way to stop a conservatory feeling like a greenhouse in summer and a fridge in winter.

A full solid tiled roof replacement removes the old roof completely and fits a new timber or steel frame, tiles to match the house, and a plastered ceiling inside. This typically costs £5,000 to £15,000 for an average-sized conservatory, rising towards the top of that range for larger footprints or premium tile finishes.

A guardian-style warm roof system with lightweight tiles sits in a similar bracket, usually £6,000 to £12,000 fitted.

Roof Option	Typical Cost
Insulated panel roof over existing structure	£2,500 to £6,500
Full tiled roof replacement	£5,000 to £15,000

Choosing a roof type early matters because it also decides whether the existing wall frames and foundations need strengthening to carry the extra weight of tiles compared with the original lightweight glazing.

Planning Permission and Building Regulations Costs

Most conservatory to extension conversions fall under permitted development rights, which means formal planning permission is not usually needed, provided the new structure stays within the existing footprint and height.

Conservation areas, listed buildings and conversions that increase the height or footprint of the original conservatory are the main exceptions, and these need a planning application costing roughly £200 to £300 in fees.

Building regulations approval is a different matter and applies to almost every conversion, since removing the thermal separation between house and conservatory changes the room's legal status from conservatory to habitable extension.

Submitting through the local authority building control team costs £500 to £800, while using a private building control inspector typically costs £400 to £600. Combined with any inspection visits, total building control costs usually land between £500 and £1,500.

If the conversion needs planning drawings or structural calculations for a beam or foundation upgrade, an architectural designer prepares what's needed before work starts. MyBuilder's architect fees price guide sets out typical charges for this kind of drawing work.

Find an architectural designer

Labour Costs and Day Rates

Labour typically makes up 40% to 50% of the total cost of a conservatory to extension conversion, since the job draws on several trades working in sequence rather than one team from start to finish. A general builder charges £200 to £350 a day, and a labourer working alongside them adds a further £120 to £180 a day.

Other trades are billed separately. Roofers charge £150 to £250 a day, electricians £180 to £280 a day, and plasterers £150 to £220 a day. A structural engineer, needed when foundations or load-bearing walls change, typically charges a fixed fee of £300 to £600 for a set of calculations rather than a day rate.

Scope of Work	Typical Timeframe
Roof replacement only	1 to 2 weeks
Full structural conversion	3 to 6 weeks

Booking several trades to overlap where possible, rather than one after another, shortens the overall programme and reduces the number of separate site visits a homeowner needs to manage.

Additional Costs to Budget For

Beyond the structural work and roof, a handful of finishing costs turn a shell into a comfortable, usable room, and these are easy to underestimate when budgeting for a conservatory conversion. Most quotes list these separately from the main build price.

• Electrical work to extend sockets, lighting and circuits typically adds £500 to £1,500
• Extending the heating system with new radiators or underfloor heating costs £1,000 to £3,000
• New flooring and plastered finishes across the space add £1,000 to £3,000
• Building control needs to sign off electrics and heating changes before the room counts as habitable all year round

Glazing upgrades sit alongside these costs where large sections of glass remain in the design. Swapping single-glazed conservatory panels for modern double glazing costs £300 to £600 per window, and moving to triple glazing or solar control glass adds a further £1,000 to £2,500 across a typical project.

How to Save Money on the Conversion

A conservatory conversion offers several genuine ways to control costs without cutting corners on safety or building regulations compliance. The starting point is deciding honestly how much of the existing structure is worth keeping.

Retaining sound foundations and a solid frame, and upgrading only the roof and glazing, avoids the far higher cost of digging new footings. Getting several written quotes from different builders highlights a wide spread in pricing for the same job, and comparing them line by line, rather than by the total figure alone, reveals where the differences actually sit. Timing the work for autumn or winter, when builders have quieter diaries, often brings better rates than booking in peak spring and summer months.

Combining the roof, electrics and heating work into a single contract with one main tradesperson, rather than several separate suppliers, also tends to reduce overall cost and cuts down on coordination problems between trades. For a wider look at how conversion costs compare with building an extension from scratch, MyBuilder's single-storey extension cost guide sets out per-square-metre figures for new-build work, and the conservatory roof replacement cost guide breaks down roof-only pricing in more depth.

Posting the job with clear details of the existing conservatory's age, roof type and foundation depth helps builders quote accurately from the outset.

Post your job for free

Find an Extension Builder Near You on MyBuilder

An extension builder brings together the structural, roofing and finishing knowledge a conservatory conversion needs, rather than treating it as a simple like-for-like swap. This matters most on jobs where foundations are borderline, or where the new room needs to tie into the existing house's brickwork, roofline and services without an obvious seam.

All tradespeople on MyBuilder undergo checks at registration, such as ID documents, company details, certifications for regulated jobs and skill assessments, allowing you to hire with confidence.

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Frequently Asked Questions

Is converting a conservatory into an extension cheaper than building a new extension?

Yes, in most cases. Reusing the existing floor slab, frame and some glazing keeps costs lower than digging entirely new foundations for a fresh extension. A new single-storey rear extension of around 20m² typically costs £30,000 to £50,000, while converting an existing conservatory of similar size averages £15,000 to £30,000.

Do I need an architect to convert my conservatory?

Not always. Simple roof-only upgrades rarely need drawings, but a full structural conversion involving new foundations, load-bearing changes or a larger footprint benefits from proper plans. Posting the job on MyBuilder connects homeowners with an architectural designer who prepares the drawings and calculations building control asks for.

How long does a conservatory to extension conversion take?

A roof-only upgrade takes 1 to 2 weeks, while a full structural conversion with new walls, foundations and services takes 3 to 6 weeks from start to completion, depending on the size of the room and how much groundwork is involved.

Will my conservatory foundations need to be replaced?

It depends on how they were originally built. Many conservatories sit on a shallow concrete slab that carries lightweight glazing but not brick walls and a tiled roof, so a structural survey checks whether the base needs strengthening or full replacement before work begins.

Does converting a conservatory add value to my house?

A well-finished conversion that turns an underused conservatory into a genuine year-round room generally supports a higher property valuation than an unheated glass extension, particularly where the new space is used as a kitchen extension or family room rather than a rarely used sunroom.