What’s included in shell extension costs?

Question

I'm considering doing the internal work myself with some of my extended family to keep costs down. We're at early stages here, but around 15 to 20 square metres. What should we expect the shell extension to cost and what would be included? Is this also something that builders are happy to do, or will they just not bother quoting for a partial job?

Michael · Answer

Just the shell would be £20ooo to £25000 depending on acess

Simon · Answer

Yes a lot of builders will consider just doing the shell build if an extension, I would include all Groundworks and brick and blockwork that is required to take it to roof level. Then fully roofed. Depending on the customer also supply and fit the windows and doors so the extension is watertight. Hope this helps
Simon

Ricky · Answer

A shell job will include everything up to decorating.
Drainage, foundations, walls.
Roof on.
1st fix electrics and plumbing.
Plastering.
2nd fix electrics and plumbing.
Skirting and architraves.

Renoext would be happy to assist.

Othmani · Answer

Shell extension is only building walls , roof and floor foundation. It is usually cheaper if the owners knows how to finish the rest of the work

Simon · Answer

Works to a shell finish are limited to the entire structure elements and wind and weather proof . In my experience of timber frame construction the cost , depending on specification is in the region of £80 per sqft or £860 per m2.

Paul · Answer

Hi, most builders would be happy to take on a shell only contract. at that size for footings sub floor and brick and block walls and a flat roof with felt and a set of french doors you would be in the region of £20,000 this would include insulation in the floor and cavity but would not include plasterboard and ceiling insulation electrical and plumbing. works i hope this helps. 

kind regards 

Paul Willson

Durga · Answer

A shell extension usually covers everything needed to make the new space structurally complete and weather-tight, but not the internal finishes. You should expect it to include:

Foundations and all groundwork

External walls (brickwork or blockwork)

Damp-proofing

Structural steels or lintels if required

Roof structure and roof covering

Basic insulation to walls and roof

External windows and doors (often included, but always confirm)

Rainwater drainage and making the extension watertight

Once finished, the extension is fully enclosed and protected from the weather, ready for you to complete the inside.

What isn’t included?

Shell extensions normally exclude:

Internal plastering

Electrics and plumbing

Flooring

Decorating

Kitchens, bathrooms and heating

This is what allows you to save money by doing the internal work yourself or with family.

How much should a 15–20 m² shell extension cost?

As a rough guide in the UK, you should expect:

Around £8,000 to £18,000 for a shell-only extension of this size

The exact price depends on:

Ground conditions

Type of roof (flat or pitched)

Whether windows and doors are included

Access to the property

A site visit will always give the most accurate figure.

Will builders quote for a shell-only job?

Yes, many builders are happy to quote for shell extensions. It’s a well-defined scope of work and suits homeowners who want to manage the internal fit-out themselves. Some builders prefer full builds, but plenty are comfortable doing shell-only projects.

Best advice before getting quotes

Be very clear when you contact builders and say:

You want a shell-only extension

Internal works will be done separately

Ask for a written breakdown of what is and isn’t included

That avoids confusion and keeps costs under control.

Doug · Answer

To be honest if you have started a build most builders probably won’t be interested as they could not guarantee the work that’s been done is up to building standards 
You might be lucky with a local bricky that would work to un recorded work

What’s included in shell extension costs?

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