Convert a Conservatory Into an Extension

Millions of UK homes have conservatories that are too hot in summer, too cold in winter, and used as storage rooms for most of the year. Converting a conservatory into a proper extension transforms dead space into a year-round living room - and it costs a fraction of building from scratch.

Here's how to do it, what it costs, and what regulations apply.

Three Levels of Conversion

Level 1: Solid Roof Only (£4,000-£8,000)

The simplest and most popular upgrade. Replace the glazed or polycarbonate roof with an insulated solid roof while keeping the existing walls, windows, and separating door.

What's involved:

• Remove existing glazed/polycarbonate roof
• Install a lightweight insulated roof system (Guardian, Supalite, Leka)
• Internal plastered ceiling
• New guttering to match

What stays:

• Existing dwarf walls and window frames
• The separating wall and door between house and conservatory
• Existing floor

Building Regulations: Required for the roof change (structural loading and thermal performance).

Result: A much more comfortable room - 10-15 degrees cooler in summer, dramatically warmer in winter. But still separated from the house by the existing wall and door.

Level 2: Full Conversion (£10,000-£25,000)

A comprehensive upgrade that turns the conservatory into a properly insulated room integrated with the house.

What's involved:

• Solid roof (as Level 1)
• Insulate existing walls (internal PIR boards + plasterboard)
• Replace old windows/doors with thermally efficient units
• Remove the separating wall between conservatory and house (structural beam required)
• Upgrade or insulate the floor
• Extend electrics and heating into the new space
• Full plastering and decoration

Building Regulations: Required - full compliance with Part L, Part A, and Part B. Apply via your council or an LABC Approved Inspector.

Result: A seamless extension of your living space that feels like a proper room, not a conservatory. This is the sweet spot for most homeowners.

Level 3: Demolish and Rebuild (£25,000-£50,000)

Remove the conservatory entirely and build a new extension in its place. Essentially a standard single-storey extension project.

When to choose this:

• The conservatory base is cracked or settling
• The structure (frames, walls) is beyond repair
• You want to change the size, shape, or position
• You want to build to a higher standard than conversion allows

Building Regulations: Yes - treated as a new extension.

Planning: Usually permitted development if the new build stays within the same footprint and PD limits.

Cost Breakdown: Level 2 Full Conversion (15m2)

Add 25-35% for London and the South East. Use our free calculator for a location-specific estimate.

The Separating Wall Decision

This is the single biggest decision in a conservatory conversion.

Keep the Wall (Simpler, Cheaper)

If you keep the existing external wall and door between the house and conservatory:

• The conservatory can retain some Building Regulations exemptions
• You still have the option to close off the space
• Lower conversion cost (no structural beam needed)
• Less disruption during the work

Remove the Wall (Better Result, More Complex)

If you remove the separating wall to create open-plan flow:

• The entire conservatory must comply with full Building Regulations
• A structural beam replaces the wall (£2,000-£4,000 including engineer)
• The result is dramatically better - a true extension of the living space
• Heating, insulation, and ventilation must meet current standards throughout

Most homeowners who invest in a conversion choose to remove the wall. Keeping it defeats much of the purpose - you still have a separated room that feels like a conservatory.

Solid Roof Systems

The roof is the biggest single upgrade. Three main systems dominate the UK market:

All systems are designed to fit existing conservatory frames without strengthening the base - they're significantly lighter than a tiled roof, which would overload most conservatory foundations.

Important: The roof must be installed by an approved installer for the warranty to be valid. Each manufacturer maintains a network of accredited installers. Check their credentials through TrustMark.

Roof Options

A solid roof with a roof lantern is the most popular choice - it solves the overheating problem while maintaining the light that made the conservatory attractive in the first place.

Insulating the Walls

Existing conservatory walls need upgrading to meet Building Regulations Part L:

Dwarf Walls (Below Window Level)

Most conservatories have brick or block dwarf walls (300-600mm high). These often have no insulation. Options:

• Internal insulated plasterboard (50-75mm PIR bonded to plasterboard): £30-£50/m2
• External insulation (if rendering over): £60-£100/m2

Full-Height Walls

If the conservatory has full-height glazing that you want to replace with insulated walls:

• Build new insulated stud wall inside existing frame: £60-£100/m2
• Replace glazing with insulated panels: £50-£80/m2

Windows and Doors

Old conservatory windows are typically single-glazed or early double-glazed with poor U-values (2.0-3.0+). Replace with:

• Current Part L compliant windows (U-value 1.6 or better)
• FENSA-registered installer for self-certification
• Consider Crittall-style or aluminium bifolds for the garden-facing elevation

See our window replacement guide for detailed pricing.

Floor Insulation

Conservatory floors often have minimal or no insulation. If removing the separating wall, the floor must meet Part L standards (U-value 0.22 or better):

If converting, try to match the floor level with the main house for a seamless transition. A step between rooms is acceptable under Building Regulations but less desirable.

Heating the Converted Space

Once insulated and integrated, the conservatory needs proper heating:

Check your boiler has enough capacity before extending the radiator circuit. A 15m2 room adds roughly 1.5-2kW of heating demand.

Common Mistakes

1. Cheap solid roof without Building Regulations - an uncertified roof conversion may not be insured and will be flagged when selling
2. Removing the wall without a structural engineer - the wall may be load-bearing or supporting the floor above. Always get an engineer to check.
3. Not upgrading the floor - a cold floor in a warm room feels terrible and wastes heating energy
4. Keeping old windows - old glazing undermines the entire conversion. New efficient windows are essential.
5. Forgetting ventilation - enclosed rooms need adequate ventilation. Include trickle vents in new windows and consider an extract fan.

Next Steps

1. Assess your conservatory - is the base sound? Are the frames in good condition?
2. Decide your level - roof only, full conversion, or demolish and rebuild?
3. Get a structural engineer if removing the separating wall
4. Apply for Building Regulations approval
5. Get 3 quotes - from solid roof installers and builders. Find TrustMark registered contractors.
6. Get a cost estimate - use our free calculator for conversion and extension costs
7. Compare with alternatives - is conversion the best option, or would a new extension be better?