Home data center guide: advice, opinions and trends
Building a server room on your own premises is feasible, often cheaper than expected to buy, and almost always dearer than expected to run. This guide says both.
Estimate my cost →The essentials, if you read nothing else #
- A four-rack room costs €40,000 to €110,000 to buy — and €45,000 to €70,000 a year to run. In under two years, running it exceeds everything you bought. The electricity drawn by cooling decides, not the price of the racks.
- Three questions can kill the project before the first quote: will your floor carry a tonne and a half on four feet, will your landlord authorise the work, and how long until your site can be connected to fibre. None of them is solved with money.
- The items people forget outweigh the ones they list: cooling, UPS, fire and access control together exceed all the rest of the budget.
- Below five racks, have colocation costed alongside. Fixed costs do not divide, and they crush a small installation. We say so even though our tool exists to help you build.
Build on your own site, or rent from a provider: the table that settles it #
We repeat below that under five racks colocation deserves to be costed. We may as well put the criteria side by side straight away.
| The criterion | On your site | With a provider |
|---|---|---|
| What you pay up front | €40,000 to €110,000 at once | Nothing, or setup fees |
| What you pay every year | €45,000 to €70,000, electricity included | A rent, power included or rebilled |
| Who answers at night | You, or nobody | An on-call team, contractually |
| Who carries the liability | You, fire and access included | The provider, within the contract |
| If you grow by half | Building works, perhaps a move | One more rack, within weeks |
| If you relocate | Part of the investment stays on the wall | You terminate at the end of the term |
| What you keep | Full control and physical proximity | Time, and someone accountable |
⚠️ There is no general right answer, there is a right answer for your acceptable downtime. If your business can absorb a day of outage, a room of your own may well be enough and will cost you less in constraints. If it cannot absorb two hours, you are buying on-call cover you will not actually have.
What this guide calls a home data center #
A server room installed in your own premises: between one and about thirty racks, in a building that was never designed for it. That is the case of a small company, a local authority, a practice, an industrial site keeping its data in house.
It is not a data center in the professional sense: no site redundancy, no on-call team, no certification. That is not an insult — many companies need nothing more. The mistake would be to believe you build one by buying the components of the other.
Everything below is costed by our sizing tool, which applies the French NF C 15-100 method to the assumptions you enter. The figures quoted here are orders of magnitude: some are market references, others are estimates, and the tool says which.
Our advice before you buy anything #
Three questions decide the project, and none of them is solved with money. Ask them before you request the first quote.
- Will your floor carry the load? A full rack weighs up to 1.3 tonnes, and it does not rest flat: everything goes through four feet, about 340 kg on each. ⚠️ That figure cannot be compared with an office floor rating: the latter is expressed in kilos spread over a square metre, whereas a rack punches through four points. Only a structural engineer can say whether your slab takes it, by looking at its thickness, its screed and its punching shear resistance. Have it done before ordering the first rack: this is the leading real reason a server room on an upper floor is refused, and it is not negotiable with anyone.
- Do you own the building, or lease it? Under a lease you may drill and run your entries: a lease does not say “forbidden”, it says “authorised in writing, and you hand the premises back as you found them”. That is not a refusal, it is an exit cost to provision from the first quote.
- Is your site eligible for fibre, and within what lead time? This is not a budget line, it is a calendar line. A site that is not eligible takes months to connect, and it is the one item money does not speed up. Start the carrier study first.
⚠️ And one piece of advice that costs almost nothing: drilling through a fire-rated wall means sealing it again immediately, back to its rating, with a certified system. Not when the tenant leaves: as soon as the cables are pulled. While the hole is open, the building's fire compartmentation is breached, and that is the path smoke takes.
The real budget: what you buy once, and what comes back every year #
Here is a four-rack room at 3 kW, under lease, with overhead cable tray. Figures are low and high brackets, excluding tax.
| Line item | To buy | Price status |
|---|---|---|
| 4 empty 42 U racks | €3,200 – 10,000 | market reference |
| Power strips, 2 per rack | €720 – 2,400 | estimated |
| Protected feeds from the board | €1,600 – 6,000 | estimated |
| Overhead cable tray, 15 m | €225 – 600 | estimated |
| Copper and optical patching | €2,600 – 9,600 | estimated |
| Precision cooling | €14,400 – 30,000 | market reference |
| UPS and batteries | €9,480 – 12,480 | market reference |
| Fire detection and suppression | €5,000 – 20,000 | market reference |
| Access control and video | €3,000 – 10,000 | market reference |
| Mesh earthing, blanking panels, entries | €1,150 – 4,280 | estimated |
| Total to buy | €41,600 – 111,300 | |
| And every year | €45,200 – 69,300/yr | electricity and maintenance |
Read the last line twice. In under two years, running the room will have cost more than everything bought for it. A 12 kW IT room on comfort air conditioning runs at an energy ratio of 2.0 to 2.5: it can therefore draw up to 28 kW at the meter. ⚠️ That is an upper bound: cooling does not run at full load all year, and a unit sized for a heatwave draws less in February. Keep the order of magnitude, not the decimal.
That is the figure missing from almost every comparison, and it is the one that decides.
The five questions a managing director asks, and that the engineering does not answer #
This guide was first written from the point of view of whoever installs the room. An outside review reminded us that this is not the point of view of whoever decides. Here is what was missing.
- Does your insurance cover this room? Putting servers into premises insured as offices changes things. Tell your insurer BEFORE the work starts: it is often the insurer, not the regulations, that requires fire detection — and a claim in an undeclared room is a very hard conversation.
- Who enters the room, and how do you prove it? If you process personal data, physical security is part of your obligations. An access log, including contractors, is not a gadget: it is what you will be asked for.
- What happens when the outage lasts? A UPS holds for minutes, not hours. ⚠️ Without a generator your room stops after a quarter of an hour — and that is a decision, not an oversight. Reckon €250 to €400 per kVA, plus €5,000 to €15,000 of civil works and transfer switch. ⚠️ That ratio holds for sizeable units. On a small installation — 12 to 20 kVA — the chassis, the acoustic canopy and the control electronics are fixed costs that do not scale down: the real installed price per kVA can be twice as high. Get a quote before building your plan. And a generator never tested UNDER LOAD proves nothing.
- One fibre, one digger. Two subscriptions with two carriers are not two routes if they share the same duct. Ask for the PHYSICAL PATH, not the supplier name.
- And if you move in three years? A raised floor cannot be dismantled; an overhead tray can. At comparable price, prefer what can be taken with you: that is the difference between an investment and a sunk cost.
- How long can you afford to be down? This is the question that comes before all the others, and it is not a technical one. Until you have written down, in hours, the interruption your business can absorb, you cannot know what to buy — nor whether a room of your own makes any sense against a hosting provider.
- Your cooling commits you beyond its price. Cooling machines contain regulated refrigerants: an annual leak test by a certified body is mandatory, and it is paid every year. Ask what the maintenance contract covers BEFORE signing.
- Dust is a quiet killer. A server room in an ordinary office building suffers the neighbours' building works. Dust destroys disks and trips servers into protection long after the works that caused it. At the very least, plan for serious filtration on the cooling, and require the neighbouring works to be sealed off. ⚠️ Someone may advise putting the room under slight positive pressure: it works, but it requires a fresh-air handling unit — heavy equipment, and rare on a room of a few racks.
Our opinion on the line items everyone forgets #
In the budget above, the four bold lines — cooling, UPS, fire, security — weigh more than all the rest combined. They are not options: they are the items that never appear on a list written from memory.
- Cooling commands everything else. Without sized cooling, your racks stay capped at 5 kW whatever you buy elsewhere. And the comfort ranges so common in small companies do work, but they are not built for a permanent load: that is exactly what drives the bill up.
- Blanking panels are the cheapest item with the biggest effect on the budget. A few tens of euros per rack. Without them hot air recirculates through the empty U, the rack's thermal ceiling collapses, and you have to buy more racks.
- Mesh earthing is not optional. Every rack is bonded individually to the building earth through a dedicated bar — never daisy chained from rack to rack. Reckon on 16 mm². It is personal safety, and it is also what makes a screened cable worth anything: a floating screen protects nothing.
- UPS batteries are replaced every four to six years, for a quarter to a third of the UPS price. This is not a one-off purchase.
Maximum power per rack is not chosen, it is imposed #
A rack's capacity follows the weakest-link rule: the cooling available, the cable feeding it, or your electricity contract. Delivering 22 kW to a rack achieves nothing if your cooling only removes 5: the rack will overheat within minutes.
This is the costliest misunderstanding in small-company sizing, and here are the three ceilings in detail.
| Ceiling | What it is worth | Who sets it |
|---|---|---|
| Thermal | 5 kW open air · 10 kW contained aisles · 40 kW liquid | your cooling |
| Electrical | 16 A 1-ph ≈ 3.7 kVA · 32 A 1-ph ≈ 7.4 kVA · 16 A 3-ph ≈ 11.1 kVA · 32 A 3-ph ≈ 22.2 kVA. ⚠️ A strip is rated in kVA, heat is counted in kW: with the power factor of modern servers, 22.2 kVA yield only about 21 kW usable. | your power strip |
| Contractual | what your meter allows, across all uses | the network operator |
⚠️ The trap: buying a 32 A three-phase strip and believing you can load 22 kW into the rack, when the real ceiling is 5 kW, that of comfort air conditioning. A power strip does not create cooling.
Our advice: cold aisle containment takes a rack from 5 to 10 kW, and therefore halves the number of racks needed. It is not weighed as a comfort, it is weighed against buying more racks.
Where the cables run: six cases, and only one to refuse #
Routing is not an installation detail. Do not overlook the route of the power cables: packed together or exposed to heat, they risk overheating. Your electrician will then have to install thicker — and considerably dearer — cables to meet the safety rules. Decide the route before costing the cables, or you pay twice.
| Solution | Indicative price | Our opinion |
|---|---|---|
| Wire mesh tray, overhead | €15 – 40/m | The default for a small company: fast, reversible, no building work |
| Perforated tray, overhead | €30 – 70/m | When loads must be carried or dust kept out |
| Trunking or skirting, surface mounted | €5 – 20/m | One or two racks, no more: grouping crushes the factors |
| Raised floor | €70 – 350/m² | Dedicated room. Under lease: feasible, conditionally |
| Mixed, power and data separated | €40 – 90/m | What actually happens once the site grows |
| Cables on the floor | — | Refuse it. Trodden on, torn out, impossible to rework |
On a 20 m² room with a 15 m run, overhead costs about €225 and a raised floor at least €1,400 — a factor of six, and up to eighteen in data center class. A small company does not need a raised floor; it needs to be told why.
⚠️ Your power cables and your network cables must run on separate routes, or you invite interference and intermittent faults. Formally forbid your contractor from mixing them in the same tray — that is a line for the tender, not a clearance for you to check yourself.
For the record, and for your installer: 200 mm between an unscreened power cable and an unscreened data cable, 50 mm if a steel divider separates them, crossing at 90°. Optical fibre escapes those distances — but not crushing.
Our opinion on structured cabling: when it starts paying #
Structured cabling is not a luxury you treat yourself to as you grow. It is an investment that pays once a link repeats often enough — and below that, it costs more than it returns. Saying so is as useful as recommending it.
| Size | What you need | Pre-terminated trunks (MPO) |
|---|---|---|
| 1 to 2 racks | Direct patching, wall box for the carrier | No. There is nothing to prefabricate |
| 3 to 10 racks | One distributor in a dedicated rack | Useful: removes on-site termination |
| 11 to 30 racks | Main distributor plus zone distributors | Recommended |
| Over 30 racks | Distribution zones, redundant main distributor | Structural: it becomes a lead-time question |
Do not go into the detail of optical fibre standards: leave that choice to your project manager. Copying terms you do not master into a tender means being steered by the first contractor who walks in.
Two contractual clauses are enough, and they protect you better than borrowed vocabulary:
⚠️ “Cabling guaranteed 20 years by the manufacturer” — that warranty only exists if the installer is approved by them, which rules out improvised work from the start.
⚠️ “Test report for every link handed over before the final payment” — the only clause that guarantees what was installed was actually measured, link by link.
Finally, a rule no specification ever writes: your carrier's engineer must never cross the server room to reach their equipment. Otherwise every visit becomes an escorted access, and in practice an unescorted one.
What your measurement is really worth, and why your PUE has no second decimal #
Do not steer your room by its energy ratio: entry-level meters show up to 40 % error at low load. That is all you need to take away; what follows explains it for those interested in measurement.
A ratio is never more precise than the two meters that build it.
- A computer room distribution unit measures to 2–5 % at the minimum level, 1–2 % with a proper meter, 1 % at the state of the art.
- A UPS, at system level, measures to 3–5 % at minimum and 1–3 % at the state of the art.
- A manual reading at the service entrance nonetheless uses a good meter: it is the collection that is imprecise, not the instrument.
- And a rack power strip typically claims 5 % of full scale.
⚠️ That last line is the costliest trap in this whole guide. “5 % of full scale” is not “5 % of the reading”. On a 32 A strip it means ±1.6 A whatever the load. A rack drawing 13 A is therefore measured to ±12 %. A rack drawing 4 A, to ±40 %. The relative error explodes when the rack is lightly loaded — which is exactly the small-company case.
This is not a defect of the strip: most of its current sensors are low-cost components designed to protect the circuit against overload, not to measure. “Metered” does not mean “well measured”.
The direct consequence: with a main meter at 3 % and IT counted at 5 %, a displayed ratio of 1.6 actually sits between 1.5 and 1.7. Announcing 1.58 suggests a precision the instruments do not have, and the gap between 1.58 and 1.64 may be nothing but instrument noise. Our advice: never display more decimals than your meters support, and start by instrumenting the weakest link — a measurement chain is never better than its worst instrument.
Trends: what is actually moving, and what is not for you #
Three subjects come up at every conference and on every blog in the sector. Here is what they are worth for a room of a few racks.
- Direct current distribution. The idea is sound: a conventional AC chain crosses six conversion stages, a 380 V DC chain only three. The gain is real. ⚠️ But the equipment is less common, the skills rarer and the spares less standard. Below a few hundred kilowatts the question does not arise: AC remains the reasonable choice, and that is not conservatism.
- Liquid cooling. It takes a rack from 5 to 40 kW, and it is the only way beyond that. For a room at 3 kW per rack, it answers a question you are not asking yet.
- The questioning of PUE itself. The metric has a known flaw: running server fans at full speed improves PUE while consuming more, since the energy shifts to the IT side. A PUE that improves with no change to the cooling deserves a check of absolute consumption.
Our opinion, and it runs against our own tool: below five racks, building a room is rarely the right call. The fixed items — fire, security, UPS, cooling — do not divide, and they crush a small installation's budget. Colocation deserves at least to be costed alongside. Our tool computes both, and it does sometimes conclude you should not build.
What this guide does not cover #
It replaces neither an electrical contractor's study nor the verification of an approved body. Our tool's calculations apply the NF C 15-100 method to the assumptions you enter; they are provided for information and do not constitute a calculation note.
It also does not cover backup, disaster recovery, or application architecture. A perfect room protects nothing if the data exists in only one place.
Finally, several prices quoted here are estimates, with no verified source: they give an order of magnitude so nothing is forgotten, not a budget. Replace them with your own quotes.
FAQ #
Between €41,600 and €111,300 to buy, and €45,200 to €69,300 a year to run. In under two years, running it costs more than everything bought for it. The item that decides is the electricity consumed by cooling, not the price of the racks.
Yes. A lease does not forbid drilling: it requires written authorisation from the landlord, then reinstatement when you leave. That is not a refusal, it is an exit cost to provision from the first quote — and a reason to prefer, at equal price, what can be dismantled.
The lowest of three ceilings: what your cooling removes (5 kW open air, 10 in contained aisles, 40 in liquid), what your power strip carries (3.7 to 22 kVA depending on rating), and what your meter allows across all uses. A power strip does not create cooling.
Rarely, for a small company. On a 20 m² room, an overhead tray costs about €225 against at least €1,400 for a raised floor. And beyond 0.91 m of void, fire suppression under the floor generally becomes mandatory — an extra cost that never appears on the floor quote.
No. Allow 200 mm between an unscreened power cable and an unscreened data cable, 50 mm if a steel divider separates them, and cross them at 90° where they must cross. Optical fibre, immune to electromagnetic interference, escapes that distance — but not crushing.
Not necessarily. Most current sensors in a power strip are low-cost components designed to protect the circuit against overload, not to measure. Their typical accuracy is 5 % of full scale: on a 32 A strip that is ±1.6 A whatever the load, or ±40 % on a rack drawing only 4 A.
As many as your meters support, and not one more. With a main meter at 3 % and IT counted at 5 %, a PUE of 1.6 sits between 1.5 and 1.7: displaying 1.58 suggests a precision that does not exist, and rules out any serious comparison with another site.
No, at that scale. The gain is real — three conversion stages instead of six — but the equipment is less common, the skills rarer and the spares less standard. Below a few hundred kilowatts, AC remains the reasonable choice.
Twelve trades are involved: rack distributor, qualified electrician, generator manufacturer, UPS supplier, transfer switch supplier, cooling installer, fire installer, access control installer, cable tray contractor, structured cabling contractor, fibre carrier and electricity supplier. Our tool names the market players for each — and above all what to ask them for in the quote.
No, and that is deliberate. Below five racks the fixed items — fire, security, UPS, cooling — do not divide and crush the budget. Our tool costs colocation alongside, and it does sometimes conclude you should not build.
Written on 17 September 2026.
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