Builder or Extension Builder: Who Should You Hire for a House Extension?

For a house extension, an extension builder is usually the strongest first choice, while a general builder can also be suitable if extensions are a genuine part of their experience and services.

The label matters less than the contractor's ability to manage the whole sequence of an extension, not just one construction stage.

What an extension builder should be able to coordinate

An extension builder may need to coordinate work involving:

• site preparation and groundworks;
• foundations and drainage;
• brickwork or blockwork;
• structural openings and supporting work;
• roof construction and covering;
• windows and external doors;
• plumbing and heating alterations;
• electrical work;
• insulation and internal build-up;
• plastering;
• flooring and finishes;
• making good where the new extension joins the existing house.

Not every business performs every trade directly. The important thing is that responsibility is clear.

When a general builder may be just as suitable

A builder can be an excellent choice when their real project history includes similar extensions.

Ask whether they regularly take on:

• single-storey rear extensions;
• side extensions;
• kitchen extensions;
• structural alterations connected with extensions;
• full shell-to-finish projects;
• coordination of the associated trades.

A business that mainly handles small repairs is not automatically the right fit simply because it uses the word “builder”. Equally, a capable general builder does not become unsuitable because their category is broader.

Compare experience with your type of project

A small utility-room extension is different from a large open-plan rear extension involving major structural changes and a new kitchen.

Useful questions include:

• Have you completed similar extensions recently?
• Who normally manages the project day to day?
• Which trades are employed directly and which are subcontracted?
• Who arranges scaffolding, skips and deliveries?
• Who coordinates building-control inspections where required?
• What part of the work is excluded?
• Who is responsible for final making good?

The aim is not to interrogate the builder. It is to make sure both sides are pricing the same project.

Get the project information organised before comparing quotes

A builder cannot price a moving target accurately.

Before asking several firms for quotes, gather whatever design information already exists, such as:

• drawings;
• dimensions;
• structural information where applicable;
• window and door positions;
• roof design;
• proposed internal layout;
• kitchen or bathroom requirements;
• electrical and plumbing changes;
• finishes you expect to be included.

If some of those decisions are still open, say so clearly.

Planning and building-control questions should be separated from the builder choice

Do not assume that finding a builder automatically settles every permission or technical-approval issue.

Depending on the project, planning, building regulations, structural design, party-wall matters or other approvals may need to be dealt with separately. Confirm what is already in place and what the contractor expects you or your designer to provide.

Avoid asking different builders to make different assumptions about approvals and then comparing the totals as though they are like-for-like.

Which other TradeKind categories can be involved?

Extensions commonly overlap with several categories already represented on TradeKind.

Depending on scope, you may need:

• groundworkers for excavation, drainage and external preparation;
• roofers for the roof covering;
• window and door fitters for new openings and external units;
• electricians for fixed electrical work;
• plumbers for water and waste changes;
• plasterers for internal finishes.

One extension business may coordinate all of these. Another may expect you to contract some separately. Ask before accepting the quote.

What should be included in the first enquiry?

Tell the builder:

• your Sussex town;
• the property type;
• where the extension will be built;
• approximate size if known;
• whether drawings exist;
• whether any approvals have already been obtained;
• what rooms the extension will create;
• whether the existing kitchen, bathroom or heating system is affected;
• whether the property will remain occupied;
• access for materials and waste;
• any known constraints;
• your preferred broad timing, if there is one.

Photos of the existing house and access route are also useful.

Do not compare extension quotes by the bottom-line number alone

Two quotes can appear to cover the same extension while including different work.

Check whether each one includes or excludes:

• demolition and site clearance;
• groundworks;
• structural work;
• roof covering;
• windows and doors;
• electrics;
• plumbing;
• plastering;
• flooring;
• decorating;
• waste removal;
• scaffolding;
• supply of major materials;
• final external works.

A clear scope is more useful than a cheap-looking total with large gaps.

The best first choice

Start with an extension builder, or a general builder with genuine extension experience, and compare them on relevant completed work, project responsibility and clarity of scope.

Browse Sussex extension builders, browse builders or post your extension project.