Quick answer: Conservatory insulation costs £2,000–£8,000 and suits homeowners with a structurally sound conservatory that’s simply too hot or cold. Garden rooms (£10,250–£35,000) work best for standalone, flexible space that doesn’t touch your existing footprint. Full extensions cost the most and take the longest, but add integrated living space and typically the strongest resale value. Your choice depends on budget, timeline, and whether you need a fix or a rebuild.
Your conservatory feels unusable half the year. Or maybe you’ve outgrown your current floor plan and need to decide whether to insulate, build a garden room, or commit to a full extension. Each option solves a different problem, at a different price, with a different level of disruption to your daily life.
Choosing wrong is expensive. Overspend on an extension when insulation would have solved the problem, and you’ve tied up tens of thousands of pounds you didn’t need to spend. Underspend on insulation when your conservatory really needs replacing, and you’ll be back to square one within a few years.
This guide breaks down the real costs, planning requirements, and resale implications of all three options — so you can match your investment to your actual needs.
How do conservatory insulation, garden rooms, and extensions compare?
Here’s how the three options stack up on cost, time, and disruption:
| Option | Typical Cost | Installation Time | Disruption Level |
|---|---|---|---|
| Internal conservatory roof insulation | £2,000–£4,500 (9m²) | 1–2 days | Low |
| New insulated conservatory roof | £5,000–£8,000 | 3–5 days | Low–Medium |
| Garden room (conservatory-style) | £10,250–£16,750 | Several weeks | Medium |
| Garden room (orangery-style) | £30,000–£35,000 | Several weeks | Medium |
| House extension | From £2,500–£3,500+ per m² | Several months | High |
Costs and timelines vary based on size, materials, and site access, so Checkatrade’s house extension cost guide is worth checking for a figure closer to your specific project.
When does each option make the most sense?
Conservatory insulation suits you if your existing conservatory is structurally sound but uncomfortable — too hot in summer, freezing in winter, or noisy when it rains. You’re not adding floor space; you’re making the space you already have usable year-round.
A garden room fits when you want a self-contained space — a home office, gym, or creative studio — without touching your house’s existing structure. It’s a good middle ground if you need more room but don’t want the disruption of a connected build.
An extension makes sense when you need genuinely integrated living space: a bigger kitchen, an extra bedroom, or a family room that flows directly from your existing layout. It’s the biggest commitment, but it delivers the most flexible, long-term outcome.
What will each option actually cost you — and how disruptive is it?
Cost and disruption tend to move together. Conservatory insulation is the cheapest and fastest route: internal roof insulation typically costs £2,000–£4,500 for a standard 9m² conservatory, and installation takes just one to two days. If your existing roof needs full replacement rather than an internal upgrade, budget £5,000–£8,000 and three to five days of work.
Garden rooms sit in the middle. A conservatory-style garden room typically costs £10,250–£16,750, while an orangery-style version runs £30,000–£35,000. Because they’re usually standalone structures, they don’t disrupt your existing house during the build — a real advantage if you’re living in the property throughout.
Extensions cost the most and take the longest, often stretching across several months rather than days or weeks. You’ll also want to budget for hidden extras: structural surveys, party wall agreements, and building control fees can all add to the final bill. Before committing, it’s worth reading RICS’ guidance on home extensions and improvements, which sets out how to budget realistically and avoid common pitfalls.
How complex is the planning process for each option?
Planning complexity scales with the size of the project.
- Conservatory insulation rarely needs planning permission. Building regulations may apply if you’re replacing the roof entirely, but internal insulation on a structurally sound conservatory is usually straightforward. Conservatories are often exempt from building regulations when they’re single storey, under 30m², separated from the house by external-quality doors or windows, and fitted with an independent heating system. Any new structural opening between the conservatory and your house, though, will need approval.
- Garden rooms are usually treated as outbuildings under permitted development rules, meaning you often won’t need planning permission. Restrictions do apply, though — outbuildings must generally stay single storey, keep eaves height under 2.5 metres, and avoid covering more than half the land around your original house. If you’re near a boundary or in a conservation area, check with your local planning authority first.
- Extensions almost always require building regulations approval, and larger projects may need full planning permission too. You may also need to follow the Party Wall Act if you’re building near a boundary. This is the option where professional advice pays for itself — an RICS member can guide you through compliance and help you avoid a costly enforcement notice.
Which option adds the most value to your property?
Resale impact varies more than most homeowners expect.
A poorly insulated, dated conservatory can actually reduce your asking price — estate agents report knocking off as much as £15,000 for an outdated glass box that buyers see as a demolition job waiting to happen. A well-insulated, properly finished conservatory, on the other hand, can add around 5% to your property’s value. The difference isn’t the conservatory itself — it’s whether it’s usable.
Garden rooms tend to add value in the region of 5–10%, particularly when they’re finished to a high standard and marketed as flexible space (home office, guest room, studio). Because they don’t touch your existing house structure, they’re also lower-risk from a buyer’s perspective — there’s nothing to unpick if a new owner doesn’t want it.
Extensions generally carry the strongest resale potential because they add genuine, integrated square footage. The value depends heavily on quality of build and how well it matches your local market’s expectations, but a well-executed extension is rarely wasted money.
Which option is right for you? A quick decision guide
Ask yourself these three questions:
- Is your current conservatory structurally sound but uncomfortable? Choose insulation. It’s the fastest, cheapest fix, and you’ll notice the difference within days.
- Do you need extra space that doesn’t have to connect to your house? Choose a garden room. You get flexible, standalone square footage without the disruption of a connected build.
- Do you need permanently integrated living space and plan to stay long-term? Choose an extension. It costs more and takes longer, but it delivers the biggest boost to daily living space and resale value.
What is the difference between an insulated conservatory and an extension?
An insulated conservatory keeps its existing lightweight structure — typically a glass or polycarbonate roof and frame — and adds internal insulation to improve comfort. An extension is a solid, brick-built addition that’s fully integrated into your home’s structure, heating system, and building fabric. The insulated conservatory is a comfort upgrade to an existing space; the extension is new, permanent living space built to the same standard as the rest of your house.
Conservatory insulation vs a full extension: the real trade-off
The choice often comes down to what “usable” means to you. An insulated conservatory can genuinely transform a room you’ve been avoiding into a space you use daily — for a fraction of an extension’s cost and with almost none of the disruption. If your main complaint is temperature, noise, or condensation, insulation solves that problem directly.
But insulation won’t add floor space, and it won’t fix a conservatory that’s structurally failing or badly designed for your home. If you’re outgrowing your house rather than just avoiding one room, an extension solves a different problem entirely. It’s a bigger investment, but it’s the option that grows with your family and holds up best at resale.
Neither choice needs to be overwhelming. Start by being honest about which problem you’re actually solving — comfort, space, or long-term value — and the right option becomes much clearer.
Speak to us before choosing a major rebuild
Getting this decision right saves you from overspending on a rebuild you didn’t need, or underspending on a fix that won’t last. Before you commit to any option, get a professional assessment of your existing conservatory or extension plans. We’ll help you work out whether insulation, a garden room, or a full extension makes the most sense for your home, your budget, and your timeline.
Frequently Asked Questions
How much does conservatory roof insulation cost in the UK?
Internal conservatory roof insulation typically costs £2,000–£4,500 for a standard 9m² conservatory. A full insulated roof replacement costs more, usually £5,000–£8,000.
How long does it take to insulate a conservatory compared to building an extension?
Conservatory insulation takes one to two days for internal upgrades, or three to five days for a full roof replacement. Extensions typically take several months from planning to completion.
Do I need planning permission for a garden room?
Most garden rooms fall under permitted development and don’t need planning permission, provided they meet height and coverage limits. Check with your local planning authority if you’re near a boundary or in a conservation area.
Will an extension add more value than a garden room?
Extensions generally add more value because they create permanently integrated living space. Garden rooms typically add 5–10% to property value, while a well-built extension can add more, depending on quality and local market demand.
What’s the biggest risk of choosing the wrong option?
Overspending on an extension when insulation would solve the problem, or underspending on a temporary fix when your conservatory needs full replacement. Both mistakes cost more in the long run than getting professional advice upfront.