More businesses are looking at the warehouse or industrial unit they already occupy and asking a simple question: can we just build an office in here instead of leasing separate space across town?
It’s a fair question. Rents are up, commuting between sites eats into the working day, and most warehouses have more headroom than they know what to do with. But before you start sketching out partition walls or ordering steel for a mezzanine, there’s a planning question to answer first.
Why This Isn’t Just an Internal Matter
Your industrial unit almost certainly sits under Use Class B8 (storage and distribution) or B2 (general industrial). Office space, since the 2020 reforms, falls under Class E, the same broad commercial category that also covers shops, gyms and clinics.
Moving part of your building from B8 or B2 into E is a change of use between different planning classes. That’s not something you can just decide to do because it’s your building and your money. Local planning authorities treat it as a material change, and depending on the scale and specifics, it may need a formal planning application or prior approval before work starts.
Ancillary Office Space vs a Genuine Change of Use
Not every desk and filing cabinet triggers a planning application. A small site office used to run the warehouse floor, coordinate deliveries or manage staff is generally treated as ancillary to the main B8/B2 use, and won’t usually need separate permission.
The picture changes once office space becomes a meaningful part of the building rather than a support function for it. Convert a large chunk of your unit into open-plan office floors, and you’re moving into change-of-use territory, which does need sign-off from the local planning authority.
There’s no fixed percentage that decides this automatically. It comes down to how the space functions and how the local authority reads your specific proposal, which is exactly why early conversations with your planning department, or a pre-application enquiry, are worth the modest fee.
Building Regulations Sit Alongside Planning, Not Instead of It
Getting planning permission sorted, if you need it, is only half the job. Building regulations apply separately and cover how the space is actually built.
This matters most if you’re adding a mezzanine floor to create the extra office space, which is the most common way businesses carve office space out of warehouse height.
Fire safety is the big one. Escape routes need to be clearly marked and accessible, wall and ceiling materials need to resist flame spread, and fire-resistant barriers are often required between floors. Mezzanines over 400 square metres, or those covering more than half of the room below, can trigger extra measures such as sprinklers or additional fire walls.
You’ll also need:
- Structural sign-off confirming the floor can carry the load of people, furniture and equipment
- Compliant staircases, handrails and guardrails around any open edges
- Adequate ventilation, heating, lighting and welfare facilities such as toilets and washing facilities, since the space is now somewhere people work, not just store goods
Building control will inspect the finished work and issue a completion certificate. Skip this step and you’re left with a space you can’t legally occupy as an office, whatever your planning permission says.
Common Mistakes We See Businesses Make
Assuming internal work doesn’t need permission because nothing changes outside the building. Planning permission is about use, not appearance. A building can look identical from the car park and still need a change-of-use application.
Checking the lease after the design is finished. Most industrial leases restrict how the space can be used and may require landlord consent for structural alterations like a mezzanine. Get this confirmed before you commit to a layout.
Underestimating fire safety requirements for mezzanines. This is the area most likely to cause delays, because it’s often addressed too late in the design process rather than built in from the start.
Treating the office as an afterthought. A warehouse office still needs proper acoustic separation, decent lighting and sensible M&E provision. Bolting on a basic partitioned box rarely serves the team using it, or the image you want to present to clients who visit.
What This Tends to Cost
Every project is different, and the honest answer is that cost depends heavily on the specifics of your building and your brief. A few things consistently make the biggest difference:
Structural complexity of any mezzanine. Span, loading requirements and site access all affect the steelwork involved, and no two warehouses are quite the same shape.
Condition of the existing building. Older industrial units often need M&E upgrades, such as power distribution, heating and ventilation, that a newer building wouldn’t. This is frequently the difference between projects that come in on budget and ones that don’t.
Specification level of the office fit-out itself. A functional, no-frills space costs a fraction of one with bespoke joinery, premium finishes and feature areas. Get clear early on what the space actually needs to do.
Whether planning permission is required. A straightforward fit-out with no change-of-use application can move much faster than one that needs a formal application, which adds the local authority’s determination period on top of design and build time.
Because of this range of variables, it’s worth getting a proper site assessment before budgeting, rather than working from a rule of thumb that may not reflect your building.
Getting It Right From the Start
Adding office space to an industrial unit can be a genuinely good use of space you already pay for, but it needs the planning and regulatory groundwork done properly first. Get that sequence wrong and you risk a design you can’t legally use, a landlord dispute, or work that has to be redone to meet fire safety requirements.
The Planning Portal’s guidance on use classes is a useful starting point if you want to understand where your building currently sits.
If you’re weighing up whether your industrial unit could support an office fit-out, SJP Interiors can help you work through the planning, design and build side together. Get in touch to talk through your space and what’s realistic for it.
