Before you start
This guide describes general good practice. It is not engineering advice for your site, and it is not a substitute for a qualified professional.
Power, cooling, fire suppression and structural work are regulated. Design and installation must be carried out by appropriately licensed engineers and contractors, and remain subject to local statutory approval and inspection. Requirements differ by jurisdiction and by building. Nothing here overrides them.
MDCS accepts no liability for decisions taken on the basis of this guide.
01 · Choosing the room
The room is usually chosen before anyone technical is asked, and it is the constraint everything else inherits. Five things decide whether a candidate room is viable.
Look up before you look around. What runs above the ceiling disqualifies more candidate rooms than anything at floor level.
| Check | Why it matters | Rules a room out when |
|---|---|---|
| What is above | Water services, plant rooms, toilets or kitchens overhead are the most common cause of a catastrophic loss in a small room. | Wet services cannot be diverted or fully isolated. |
| Floor loading | A fully populated rack is concentrated point loading, not spread weight. Upper floors and older buildings are frequently unsuitable. | The structural engineer will not sign it off. |
| Clear height | Rack height plus containment plus airflow plus containment above. Ducts and beams intrude more than plans suggest. | There is no path for return air. |
| Access route | Racks and UPS units arrive on pallets. Doors, corridors, lift capacity and turning circles all constrain what can physically reach the room. | Equipment cannot be delivered without dismantling it. |
| Power availability | The building’s incoming capacity and spare distribution board capacity, not the room’s current sockets. | Upgrading the incoming supply is not viable. |
Ask what the room was before
Basements flood. Rooms below plant rooms take vibration and leaks. Rooms on an external wall with windows take solar gain and are a physical security problem. Rooms that used to be a store cupboard often have no cable route to anywhere.
02 · Floor, ceiling and structure
- Floor loading is a question for a structural engineer, not an estimate. Provide the intended rack count, position and fully loaded weight and ask for a written answer.
- Raised floors are not required at this scale and are often the wrong choice. They add cost, height and a maintenance burden, and modern small rooms usually run overhead containment instead.
- Seal the room. Penetrations for cable, pipe and duct should be sealed to their required fire rating after installation — this is routinely left undone and it invalidates the compartmentation the building relies on.
- No suspended ceiling voids shared with the rest of the floor where avoidable. They defeat both fire compartmentation and physical security.
03 · Power
Power is the constraint that binds first in most small rooms, and it is the one people discover last.
Size from the load, not the rack count
Work out the actual draw of the equipment going in, add headroom for growth, and add the cooling load that heat creates. A room specified on rack count alone is usually specified wrong in both directions — over-provisioned on floor space and under-provisioned on supply.
- Two distribution paths to every rack, so dual-corded equipment is actually dual-fed. Two cords into one strip achieves nothing.
- UPS runtime is a decision. Long enough for a generator to start and stabilise, or long enough for an orderly shutdown if there is no generator. Those are very different sizes and the choice should be explicit.
- Earthing and bonding to the standard applicable in your jurisdiction, designed and certified by the electrical engineer. Poor earthing produces intermittent faults that are extremely difficult to diagnose later.
- Isolation and labelling. Somebody must be able to safely isolate a rack, or the room, without guessing.
- Generator, if the business case supports it. Fuel supply, testing regime and start-up time all belong in the design, not in a later conversation.
All of the above is designed and installed by licensed electrical engineers and contractors and is subject to inspection and certification. The role of an infrastructure designer is to state the load, the redundancy requirement and the layout — not to design the electrical installation.
04 · Cooling
The arrangement matters more than the capacity. A well-arranged room with adequate cooling outperforms a badly arranged room with more.
- Racks face each other. Cold aisle between fronts, hot aisle between backs. Everything else follows from this and it costs nothing to get right at layout stage.
- Contain one aisle. Usually the cold one at this scale. Containment is the single highest-return item in a small room, and it is very difficult to retrofit once racks are populated.
- Blank the empty U spaces. Unblanked gaps let hot air recirculate to the front of the equipment, which defeats the aisle arrangement entirely. Blanking plates cost very little and are skipped constantly.
- Redundancy is N+1 at minimum, so a unit can fail or be serviced without a thermal problem. One unit sized exactly to the load is one failure from a shutdown.
- Consider what happens on power loss. Cooling on the UPS or not is a real decision — a room with no cooling reaches critical temperature far faster than most people expect.
Humidity, and the condensate path
Cooling produces water. The condensate route, its fall, and what happens if it blocks belong in the design. A blocked condensate tray above a rack is the same event as a leak from the floor above.
05 · Fire
Detection, suppression and compartmentation are regulated, jurisdiction-specific, and designed by a fire engineer. What follows is what to raise, not what to specify.
- Early detection is more valuable than suppression in a small room. Aspirating detection responds far earlier than standard point detectors.
- Suppression choice has consequences for the equipment. Water-based systems and gas systems fail very differently, and the decision is a business one about what is being protected.
- Compartmentation is only as good as the sealing of every penetration made during installation. See the note in section two.
- Interlocks. What the fire system does to power and cooling on activation should be understood, agreed and tested, not assumed.
- Statutory approval and periodic inspection apply throughout, and the regime differs by jurisdiction and building class.
06 · Physical security
All the network segmentation in the previous guide is defeated by an unlocked door.
- Controlled access with an audit record — who entered and when. A key that three people share is not an access control system.
- No windows where avoidable. Where unavoidable, treat as a perimeter to be secured.
- Camera covering the door and the rack rows, retained long enough to be useful after a delayed discovery.
- Racks lock, and someone owns the keys.
- Contractor access is supervised. Most physical incidents in small rooms are accidental and caused by someone doing legitimate work.
07 · Containment and routes
- Separate containment for power and data, at separation appropriate to your standard. Running them together produces interference and makes both harder to work on.
- Overhead rather than under-floor at this scale, in most cases. Visible, accessible, and it does not obstruct airflow.
- Size containment for twice what you install. It is the cheapest thing to over-provision and among the most disruptive to extend.
- Two diverse entry routes into the room for external fibre or copper where availability matters. A single entry point is a single cause of total loss.
- Label at both ends, always.
08 · Environmental monitoring
A small room is usually unattended, which makes monitoring the difference between an alert and a discovery.
| Monitor | Placement | Catches |
|---|---|---|
| Temperature | Top, middle and bottom of the cold aisle, and in the hot aisle. | Cooling failure, and recirculation the aisle arrangement should have prevented. |
| Humidity | Cold aisle. | Condensation risk and static conditions. |
| Water | Under cooling units, at the lowest floor point, near any pipe route. | A leak, while it is still small. |
| Door state | Every door. | A door propped open — which defeats cooling and security simultaneously. |
| Power | At the PDU, per phase. | Phase imbalance and approaching capacity limits. |
These feed the same monitoring platform as everything else. The Zabbix, Grafana and Prometheus guide covers collection and alert thresholds.
What goes wrong
The recurring ones, in rough order of how expensive they are to correct afterwards.
| Problem | Cost of fixing it later |
|---|---|
| Room chosen with wet services above | Relocation, or permanent accepted risk. |
| No aisle containment | Very difficult once racks are populated and running. |
| Single power path | Rewiring a live room, or planned outages forever. |
| Cooling with no redundancy | A second unit, plus the pipework and power it needed from the start. |
| Containment sized to the initial install | Recabling, or an untidy and unsupportable room. |
| No environmental monitoring | Cheap to add. The cost is the incident that was not detected. |
| Unblanked rack U spaces | Trivial to fix, routinely never done. |
Survey checklist
Worth walking a candidate room with this before any commitment is made.
| Item | Record |
|---|---|
| Dimensions and clear height | Including beams, ducts and any intrusion into the volume. |
| What is directly above | Room use, and any wet services. |
| Floor construction and level | For the structural loading question. |
| Delivery route | Door widths, corridor turns, lift capacity, thresholds. |
| Incoming power and spare board capacity | Building level, not room level. |
| Existing cooling and its condition | And whether it can be extended. |
| Fire detection and suppression present | And the compartmentation of the room. |
| Cable entry points | How many, and whether diverse. |
| Doors, windows, and existing access control | Photograph everything. |
Take photographs of everything, including the ceiling
Every subsequent conversation with an engineer, a contractor or a supplier will go faster for having them, and the detail that turns out to matter is rarely the one anyone thought to measure.