Choosing the Right Contractor for Your House Extension

1. Planning the build

Getting plans off the ground is the first step toward extending or renovating. Before pretty much anything, you’ll need plans that address Permitted Development, Planning Permission and Building Regulations. There are two main options:

• Obtain plans from a professional architect or drawings provider: While some people might immediately assume they need an architect to extend, obtaining designs from a professional drawings service provides a flexible route towards tendering for contractors. While very complex projects might need an architect and possibly even a project manager, the vast majority of projects can be handled by companies like Fast Plans. 
• Work directly with the builder: Many builders provide various in-house services that manage the entire end-to-end project, from creating plans to building the extension. This seems like a simple option, but it limits your choices of contractor. In addition, once your plans are drawn up by the contractor in-house, switching to another contractor could be tough. 

If you need to obtain Planning Permission and/or a Party Wall Agreement, your architect/drawing service/builder can help you here. They’ll recommend a surveyor if necessary.


Fast Plans can manage planning applications on your behalf and will help you determine whether your plans fall under Permitted Development or whether you need Planning Permission.

2. Shortlisting builders

Once your detailed plans are in hand, together with engineer’s calculations, Planning Permission, and Party Wall Agreements (if applicable), it’s time to look for builders. 

When you search for builders in your local area, Google will provide a list with reviews and links to websites. Another option is My Builder, which lists builders with reviews, contact details, other useful information, etc. In some situations, you might need to search for specialist builders that handle highly bespoke projects or specialists in certain extensions like loft conversions or side-return extensions. 

Look for proven expertise and a solid track record of recent projects. You’ll also want to feel like you get on with your builder - and they should be enthusiastic about the work. Building extensions requires establishing trust and rapport, and the homeowner must hold the builder to account to ensure the project stays on track.

3. Looking for accreditations

Builders in the UK typically hold one or more accreditations from the following organisations: 

• Federation of Master Builders (FMB): A trade association that only accepts those deemed to meet the standards of the body. Some builders are part of Build Assure and offer an insurance-backed work guarantee option. Some builders might offer this anyway. 
• Guild of Builders and Contractors: Becoming a member of this body requires three years of trading with customer references. Members must abide by a code of conduct, including writing proper contracts and providing robust payment plans. 
• Guild of Master Craftsmen: Supports the tradespeople and artisans involved in the building project, e.g. for bespoke projects that include services outside the scope of the building service itself. 
• National Federation of Builders: Another well-known body that requires members to provide various references and hold valid public liability insurance. 

It’s worth mentioning that membership in these bodies is common, so it’s more of a “must-have” than something that differentiates builders from each other. Look at memberships in combination with reviews and portfolios. There’s no substitute for a solid portfolio of recent work. 

4. Get quotes from your shortlist

If you have your plans and calculations in hand, tendering for like-for-like quotes will be straightforward. 

In addition to your extension plans, you’ll need to create an itemised list of extras you want. Experienced contractors will have a list of extras that you’ll need to consider. It’s best to ensure the list is as comprehensive as possible to avoid surprises. 

When comparing quotes, it’s almost certain that you’ll notice substantial variations. But don’t be taken off guard by a cheaper-than-average quote that misses extra costs that need to be added to the bill later. 

If you have designs and engineer’s calculations in hand, obtaining comparable quotes will be much simpler. Fast Plans house extensions plans provide homeowners with everything they need to begin tendering for contractors. 

5. Payment plans

Most extensions are paid in stages. A good contractor will work with you to itemise your quote and map each stage to a time period and payment. 

You’ll pay some upfront, then when the groundwork is completed, walls are erected, the roof is finished, etc. 

It’s standard practice to reserve some of the payment until the entire job is finished - typically 2% to 5%. This enables homeowners to ensure everything is completed. The final payment is typically released once Building Control approval has been granted. 

Aim to establish a strong, mutually agreed payment plan that makes sense for all parties. This will keep the build on-track and avoid time-consuming disputes. 

6. Check-ins 

Many reputable contractors are happy to check up on the build after it’s finished, up to around six months after completion. 

This enables homeowners to pass on any small unfinished details and suggestions. Further, contractors may sort smaller issues out without payment. 

Ask if your contractor is willing to come and check up on the finished project some months after completion. 

Summary: Choosing a contractor

Choosing an extension or home renovation contractor is a pretty tricky task. It’s always worth shopping around rather than opting for the first quote you receive. 

Obtaining quality plans puts homeowners in a flexible position. With your plans in hand already, it’s simple for different contractors to provide you with detailed quotes that you can use to compare different options. 

Fast Plans provides a professional drawing and design service which equips you with everything you need to shop around for the best contractor.