lean to gazebo in Greater London (281)

Planning a loft conversion, garage makeover or full house extension in London? You’re in the right place. Whether you’re adding space for a growing family, upgrading your layout or increasing your home’s value, we can help you find the right tradesperson for the job.

Find extension and conversion builders in London

Every builder on Checkatrade passes up to 12 checks before they appear in your search. You can read verified reviews, compare services, and even post your job to get quotes straight to your inbox, all in a few clicks. That’s how we help homeowners like you get a job done right.

What to expect from hiring an extension or conversion builder in London

Our checked tradespeople in London cover a wide range of projects, including:

• Single or double-storey house extensions

• Kitchen and diner extensions

• Loft, attic, garage or basement conversions

• Garden room extensions

• Utility room extensions

• Over-garage extensions and side returns

Costs to expect

Costs of extensions and conversions vary depending on size, structure and spec, but here's a rough guide:

Single - storey extensions: £21,000 - £65,000

Double - storey extensions: £55,000 - £95,000

Loft conversions: £35,000 - £65,000

Garage conversions: £8,000 - £20,000

What to check before you hire:

• Are drawings or planning permissions needed?
• Are they familiar with building regs?
• Is the quote fixed or flexible?
• Does it cover materials and project management?

Most builders will include prep, construction, electrics, plumbing and final finishes in their quote, but always double-check. Timelines range from a few weeks for simple jobs to several months for bigger builds.

Extension and conversion builders in London: Homeowners vs renters

Homeowners:

You’re in charge of the project. That means hiring the builder, securing permissions, and paying for the work. You may need:

• Planning permission (especially for double-storey builds or changes near boundaries)

• Drawings from an architect or structural engineer

• Building regs approval

If you’re not sure where to start, speak to a local builder or post your job to get help with the process.

Renters:

You’ll usually need your landlord’s approval to make any big changes. In most cases, your landlord will be the one arranging and paying for structural changes like loft conversions or extensions. That said, it’s worth flagging ideas if you think they’ll improve the property, especially if it means longer tenancies or fewer repairs.

Emergency extension or conversion help in London

Extensions and conversions are big projects, but sometimes, things go wrong and need sorting fast. Common urgent issues include:

• Leaks in newly converted lofts

• Structural cracks or shifting

• Faulty electrics or plumbing in newly added rooms

• Incomplete work by previous builders

Facing an emergency in London? Enter your postcode or post a job to find emergency services in your area.

Find the right extension or conversion specialist in London

Looking for a builder to help with:

• Rear house extensions
• Kitchen extensions
• Garage conversions
• Loft or attic conversions
• Garden room builds
• Basement or cellar conversions
• Conservatory roof upgrades
• Utility or porch extensions