Commercial building work covers office fit-outs, retail units, restaurants and mixed-use premises across London, where downtime is expensive and every week on site has a direct cost to your business. In 2026, a London office fit-out typically costs £45 to £150 per square foot depending on specification, while a full Cat A to Cat B refurbishment of a larger floor can run considerably higher.

At a glance

Basic fit-out: £45 to £85 per square foot, functional finishes and essential power
Mid-range fit-out: £85 to £150 per square foot, branded finishes and upgraded meeting room technology
Premium fit-out: £150 to £200+ per square foot, bespoke joinery and full AV integration
Cat A shell: £35 to £80 per square foot, the landlord’s base fit-out before tenant works
Typical programme: 8 to 14 weeks on site for spaces up to 10,000 square feet

Cat A and Cat B, and why the difference matters

Cat A refers to the base landlord fit-out: raised floors, suspended ceilings, basic lighting and mechanical services, ready to lease but not ready to occupy. Cat B is the tenant fit-out layered on top: partitions, meeting rooms, branded finishes, kitchen facilities and furniture. Understanding which category your project falls into, and who is contractually responsible for it, determines both the specification and who ultimately pays.

What a commercial fit-out costs in London

For a 5,000 square foot office at mid-range specification, budget roughly £425,000 to £675,000 all-in, covering construction, partitioning, mechanical and electrical work, joinery, lighting and Building Regulations compliance. This figure typically excludes loose furniture, which adds a further £12 to £35 per square foot, along with AV and IT infrastructure, branding and professional fees.

Retail and restaurant fit-outs carry their own specific costs on top of a standard office rate, particularly restaurant kitchens, which require specialist extraction and services, and any works affecting a shopfront, which typically need landlord licence-to-alter approval before starting.

Retail and restaurant fit-outs

Retail units generally combine a shorter, more compressed programme with strict landlord conditions on shopfront alterations, trading hours during works, and dilapidations at the end of the lease. Restaurant fit-outs add commercial kitchen extraction, grease trap installation and enhanced fire safety and ventilation requirements, all of which need coordinating with the base building’s existing services before work starts.

Minimising disruption to your business

Commercial clients rarely have the luxury of an empty building to work in, whether that means phasing a retail fit-out around trading hours, coordinating an office fit-out around a phased staff move, or working around live kitchen operations in a restaurant. We plan every commercial project around your operational constraints from the outset, not as an afterthought once a fixed programme has already been agreed.

Our commercial building process

We survey the existing space, including mechanical and electrical infrastructure, structural condition and any landlord requirements, before quoting. From there we manage licence-to-alter applications where needed, coordinate specialist trades such as commercial kitchen installers or data cabling contractors, and deliver the fit-out to a fixed programme agreed with your business in mind.

Why choose Alpha London Builders for commercial building work

We apply the same fixed-price, single point of contact approach to commercial projects as we do to residential work, with the added discipline that commercial clients need: a realistic programme that respects your trading calendar, and a site manager who understands that time genuinely is money on a live commercial unit.

Frequently asked questions

Can you work around our trading hours

Yes, we regularly phase commercial work around live trading, whether that means working overnight, on weekends, or in sectioned-off areas of a larger unit while the rest remains open.

Do you handle landlord licence-to-alter applications

Yes, we manage this process alongside your lease requirements, ensuring the specification submitted matches what is actually agreed to be built.

How long does a typical office fit-out take

Most fit-outs up to 10,000 square feet take 8 to 14 weeks on site. Larger or more complex projects, particularly those involving significant mechanical and electrical works, can extend to several months.

Do you handle dilapidations at the end of a lease

Yes, we carry out dilapidations and reinstatement works, returning a unit to its base building condition in line with your lease obligations.

Fit-Outs Built Around Your Business