Question 1

How much does a house extension cost in London?

Accepted Answer

Extension costs in London depend on the type of extension. Typical project investment, including VAT, is £60,000 – £120,000+ for a rear extension, £55,000 – £100,000+ for a side return and £80,000 – £160,000+ for a wraparound. Final costs depend on size, design complexity, property type, and your chosen specifications. Use our calculator above for an estimate tailored to your project.

Question 2

How much does a 30m² extension cost?

Accepted Answer

A mid-sized rear extension in London is typically £60,000 – £120,000+ including VAT, depending on finish level and site conditions. More complex wraparound or double-storey schemes sit higher. Our calculator gives you a personalised estimate in seconds.

Question 3

How accurate are these estimates?

Accepted Answer

Our estimates come from current Trovix build rates for London projects and are returned as indicative ranges rather than fixed quotations. They provide a reliable starting point for budgeting, but final costs depend on site conditions, specifications, and finishes chosen. We recommend booking a free survey for a precise quote.

Question 4

What's included in the price?

Accepted Answer

Our estimates include all standard building works, plumbing and electrical installation, glazing (windows and doors), external doors, and VAT. Kitchen and bathroom fittings, flooring, and decorating are typically additional based on your specifications.

Question 5

How long does an extension take to build?

Accepted Answer

A typical rear extension takes 10–14 weeks from start to completion. Side return extensions are usually 8–12 weeks, while wraparound extensions can take 14–18 weeks. Double-storey extensions typically take 16–22 weeks. These timelines assume planning and building control approvals are in place.

Question 6

Do I need planning permission for an extension?

Accepted Answer

Many single-storey rear extensions fall under Permitted Development (PD) rights, meaning no planning application is needed — provided they meet size and position limits. Side extensions, wraparound extensions, and double-storey extensions usually require full planning permission. Properties in conservation areas or flats have additional restrictions. We handle all planning submissions as part of our service.

Question 7

How much does a loft conversion cost?

Accepted Answer

Loft conversion costs in London vary by type: a rear dormer is typically £60,000 – £100,000, a hip-to-gable £80,000 – £130,000 and a mansard £85,000 – £150,000+, all including VAT. The final price depends on the size of the loft, structural requirements, and the level of finish. Use our calculator to get an estimate for your specific loft type.

Question 8

How long does a loft conversion take?

Accepted Answer

Most loft conversions take 8–12 weeks to complete. Simpler rooflight conversions may be faster (6–8 weeks), while complex mansard or L-shaped dormers can take 12–16 weeks. You can usually remain in your home throughout the project.

Question 9

Do I need planning permission for a loft conversion?

Accepted Answer

Many loft conversions fall under Permitted Development rights, meaning no planning application is needed. However, mansard conversions, properties in conservation areas, and flats typically require full planning permission. We'll advise on your specific situation during your consultation.

Question 10

What are the most common mistakes to avoid when building an extension?

Accepted Answer

The biggest mistakes homeowners make include: underestimating the budget (always add a 10–15% contingency), not checking planning requirements before starting, choosing the cheapest quote over quality and reliability, skipping a structural survey, not planning the interior layout early enough, and failing to notify neighbours under the Party Wall Act. Working with an experienced design-and-build firm like Trovix helps you avoid all of these.

Question 11

Do you handle all planning and building control?

Accepted Answer

Yes. We manage the entire planning process including permitted development certificates, full planning applications, building regulations submissions, and liaison with building control inspectors. You won't need to deal with the council directly.

Question 12

Can I live in my house during the build?

Accepted Answer

Yes, most clients stay in their home throughout the build. We use dust barriers, maintain clean access routes, and keep disruption to a minimum. For extensions, your existing kitchen and living spaces remain usable until the final connection stage. For loft conversions, the main disruption is staircase installation, which typically takes just a few days.

Question 13

Will an extension add value to my London home?

Accepted Answer

Yes. A well-designed extension in London typically adds around 1.5 times its cost to your property value. Adding an extra bedroom, expanding the kitchen, or creating open-plan living space are among the most effective ways to increase value. In high-demand London boroughs, the return can be even higher.

Question 14

Is a double-storey extension worth it?

Accepted Answer

A double-storey extension is one of the best value home improvements. You get twice the floor space for roughly 50–60% more than a single-storey build, because you share the same foundations and roof. It is ideal for adding bedrooms above a kitchen or living extension. Value impact varies by location, property type, design, specification and market conditions.

Project Type	Typical Cost
Rear extension	£60,000 – £120,000+
Side return extension	£55,000 – £100,000+
Wraparound extension	£80,000 – £160,000+
Double-storey extension	£100,000 – £190,000+
Rooflight loft conversion	£50,000 – £85,000
Rear dormer loft conversion	£60,000 – £100,000
Hip-to-gable loft conversion	£80,000 – £130,000
L-shaped loft conversion	£75,000 – £125,000
Mansard loft conversion	£85,000 – £150,000+

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