Designing the data hall: white space
White space is the part of a data centre that earns its keep — the floor where the racks live. How you lay it out, contain the airflow and plan for density decides how many usable, coolable, powered rack positions you actually get from a room, and how easily it grows. This is a design-led guide to getting white space right, with an interactive planner to size a hall as you go.
White Space vs Grey Space
Every data centre divides into two worlds. White space is the IT floor — the raised-floor or slab area where racks, cabling and in-row infrastructure live; the part that does the computing. Grey space is everything that supports it: UPS, switchgear, generators, chillers and air handlers. White space is where capacity is sold and filled, so the entire purpose of its design is to fit the most usable, powered, coolable rack positions into the room — with the headroom to grow.
White space = the IT floor
Racks, rows, aisles, containment, structured cabling and in-row power. The revenue-generating area — measured in rack positions and kW delivered, not just square metres.
Grey space = the support
The M&E plant that powers and cools the white space. Essential, but back-of-house — and not the subject of this guide; here we focus on the IT floor itself.
Usable, not just big
A large room badly laid out yields fewer real rack positions than a smaller one designed well. Aisles, containment, pathways and clearances all eat floor — planning is what turns area into capacity.
Density changed the game
White space used to be planned by the square metre. Now a single rack can draw what a whole row once did, so it’s power and cooling per rack — not floor area — that sets the real limit.
The Building Blocks of a Data Hall
A well-designed hall is a repeating pattern: rows of racks arranged front-to-front and back-to-back, so cool air and hot exhaust never mix. Around that sit the floor, the containment and the pathways that feed power and connectivity to every cabinet. Here’s the cross-section.
The rack & the row
The 42U/48U cabinet is the unit; rows of them, arranged front-to-front, create the alternating cold and hot aisles that make airflow management possible.
Raised floor vs slab
The classic raised floor is a cold-air plenum and cable route. High-density halls increasingly go slab-on-grade with overhead distribution — heavy racks and liquid loops don’t love a void.
Pathways: over or under
Power (busway) and data (cable basket) run overhead or underfloor. Overhead is now the default — it keeps the floor clear, eases changes and suits high density.
Power to the rack
Busway overhead, rack PDUs in the cabinet, A+B feeds for resilience — sized for the density and metered so capacity can actually be managed.
Size a Hall, Live
Floor area, power, cooling and rack count are all linked — change one and the rest move. Set a rack count and a density below and watch the white space size itself: the IT load, the floor area it needs, the layout, and the cooling strategy that density demands.
Drag the rack count, pick a density. The floor fills, and the numbers size the hall.
Indicative only — real layouts depend on rack footprint, aisle widths, clearances, the cooling approach and code. The point the planner makes is the relationship: as density rises, the same compute fits in less floor but demands more from power and cooling — which is why modern white space is designed around kW, not m².
Containment & Airflow Management
The biggest, cheapest win in white space is simple: don’t let cold supply air and hot exhaust mix. Every degree of cold air that sneaks into a hot aisle, or hot air that recirculates to a rack inlet, is cooling you paid for and wasted. Containment and good airflow housekeeping are what let a hall run warmer, denser and far more efficiently.
Cold-aisle containment
Enclose the cold aisle so supply air is delivered only to rack inlets. Simple and effective; the rest of the room runs warm.
Hot-aisle containment
Enclose the hot aisle and duct exhaust straight back to the cooling. Often preferred for high density — the working space stays cool.
Blanking & sealing
Blanking panels in empty U-space, brush grommets on cable cut-outs, sealed floor edges. Cheap parts that stop the bypass and recirculation that wreck efficiency.
Bypass & recirculation
The two enemies: cold air that returns unused (bypass) and hot air that loops back to an inlet (recirculation). Both create hot spots and force you to over-cool the whole room.
Get containment right and you can raise supply temperatures into the upper end of the ASHRAE band, run economisers more of the year, and push PUE down — without risking inlet temperatures. It’s the highest-return discipline in the white space, and it’s mostly about rigour, not capital.
Designing for Density, Growth & Change
White space is never “finished” — it fills, densifies and gets re-laid-out over a decade. The best designs anticipate that: modular, headroom-aware, and able to take a mix of densities (and one day a liquid loop) without ripping the room apart.
Design in pods
Repeatable rack/row/containment modules let you fit out in phases, keep cost aligned to demand, and standardise the install — rather than building the whole hall on day one.
Plan for mixed density
Not every rack is 80kW. A good layout zones the room so low- and high-density kit each get the right power and cooling, instead of designing everything for the worst case.
Headroom, deliberately
Power, cooling and pathway capacity planned with spare — so the next deployment is a patch and a PDU, not a redesign. Stranded capacity is waste; no headroom is a wall.
Liquid-ready
Even an air hall today should consider the route for water tomorrow — floor loading, pathways and space for CDUs — so going liquid later is an upgrade, not a rebuild.
Pathways for change
Generous, accessible cable and power routes so moves, adds and changes are quick and safe — congested pathways turn every change into a risk.
Documented & managed
An accurate floor plan, labelling and capacity records (DCIM) — so decisions about what goes where are made on real data, not guesswork.
Part of the bigger picture
White space is where several of our other guides meet: the structured cabling that feeds it, the AI/GPU density that's reshaping it, the operations that run it, and the facility you choose to put it in.
Designed in Our Whitespace Builder
We don’t sketch white space in PowerPoint. We model it in Whitespace Builder — our own design tool — where a single scene model drives the 3D view, the 2D drawings and the rack, power and cabling counts, all at once. Change the model and every output updates together. The hall below is a real (anonymised) design built in it — live in your browser, not a render. Drag to orbit, scroll to zoom.
One model, every output
A single source of truth: the 3D, the floor-plan drawings and the quantities all come from the same model — so they can never drift out of sync.
Counts straight off the model
Rack positions, power per row, containment runs and cabling counts are read directly from the design — which is how we cost a fit-out in under 48 hours.
What you see is what we build
Tender-stage models that become the build. The design you sign off — layout, densities, containment — is the one our engineers install.
How Optronix Helps
White-space design and fit-out is at the heart of what we do. We take a room — or a drawing — and turn it into a working data hall: layout, containment, power distribution, pathways and the structured cabling that ties it together, for hyperscale, colocation and enterprise clients across the UK, EMEA and worldwide. Our own engineers, end to end.
Model-derived design, fast
We turn a client drawing into a costed, model-derived white-space design — rack layout, densities, containment, power and cabling counts — in under 48 hours. The counts come straight off the model, so what you approve is what we build.
Designed for what’s next
Halls planned in pods, for mixed density and with the headroom — and liquid-readiness — to grow. So the white space you fit out today still works when the kit going into it changes.
Design & model
Layout, density zoning, containment strategy, power and pathway design — modelled and costed from your drawing, fast.
Fit-out & install
Racks, containment, busway and power distribution, overhead pathways and the structured cabling plant — installed cleanly by our own engineers.
Commission & certify
Airflow and containment verified, cabling tested and certified, documentation delivered — so the hall performs from day one.
Operate & evolve
Ongoing moves, adds and changes, capacity management and phased expansion as the hall fills and densifies.
Fitting out a hall, or rethinking one?
Send us the space and your target densities, and we’ll come back with a costed, model-derived white-space design — layout, containment, power and cabling — built to scale.
Sources & notes
- ASHRAE TC 9.9 thermal guidelines — recommended inlet-temperature band (18–27°C) and airflow management practice
- Uptime Institute and common industry practice for white-space layout, containment, raised floor vs slab, and capacity planning
- White-space area per rack (~2.5–4 m² including aisles & access) is a planning rule of thumb; actual figures depend on rack footprint, aisle widths and clearances
- Cabling per TIA-942 / ISO 11801 and high-density / liquid considerations per our structured cabling and AI/GPU guides
General guidance, not a design specification. Area, load, layout and energy figures from the planner are indicative and rounded; real designs depend on rack footprint, aisle and clearance requirements, the cooling approach, redundancy and local code. Energy uses a representative PUE for the density and a £0.20/kWh illustration. Confirm against an engineered design.