How a Prefab Home Is Actually Built

The factory half is the part everybody photographs. The site half is the part that decides whether it works.

How a Prefab Home Is Actually Built — practical guidance from the team running Prefab homes in South Africa on the Garden Route. Here is the actual sequence, what happens in parallel, and the points where a prefab programme goes wrong.

What ‘prefab’ covers

Prefabrication is a spectrum, not a product. At the light end, roof trusses are prefabricated — which means almost every conventional house in South Africa is already partly prefab and nobody calls it that. In the middle sits panelised construction: walls, floors and roof cassettes manufactured flat in a factory and assembled on site. At the far end sits volumetric modular, where whole rooms are built and fitted out in a factory and craned into place.

This page is about the middle: panelised prefab, which is what most South African prefab suppliers actually deliver for houses. Modular is covered separately because the logistics are genuinely different.

The panels themselves vary — timber frame, light steel frame, structural insulated panels, precast concrete. The construction sequence below is broadly the same whichever it is.

Design freeze: the step that has no equivalent in a normal build

On a conventional site you can move a door in week six. It costs a morning and a bag of cement. On a prefab build you cannot, because by week six that wall has been cut, drilled for services, and is on a truck.

So a prefab project front-loads all the decisions. Layout, window and door positions and sizes, every socket and light point, plumbing runs, where the geyser goes, where anything heavy will hang. All of it has to be settled before production starts, because the openings and the noggins are cut into the panels in the factory.

This is the single biggest cultural difference for a client coming from a conventional build, and it is where most prefab programmes slip. The factory cannot start until the design is frozen, and every week the client spends still deciding is a week the programme does not get back. Handled well, it is also the reason prefab is fast: nothing is being figured out on site.

It is worth being blunt about the trade-off. You buy speed and price certainty with decisions made early. If you are the kind of client who likes to walk the slab and change your mind, panelised prefab will frustrate you and a conventional build will suit you better.

Two programmes running at once

Once the design is frozen, the factory starts and the site starts, and they run in parallel. That parallelism is where the time saving comes from — not from the panels going up quickly, although they do.

On site: set out, excavate, trial holes confirmed, foundation cast, cure, services brought to the slab, and the platform made ready and level. Level matters more here than on a masonry build. A brick wall can absorb a few millimetres of tolerance course by course. A panel cannot — it is a fixed dimension, and an out-of-level slab shows up as a gap at the top of every wall.

In the factory: panels cut, framed, sheathed, openings formed, service chases and noggins built in, and in some systems insulation and even windows fitted before delivery.

The critical dependency is the slab. It has to be finished, cured and dimensionally correct before the truck is booked, because a delivered panel set with nowhere to go is an expensive thing to store and a magnet for damage.

Delivery, erection and closing in

Panels arrive in erection sequence and go up fast — a modest house shell can be standing in a few days. Access is the constraint nobody checks early enough: the truck has to reach the site and there has to be room to offload and, on many systems, to get a crane or telehandler in.

On a tight Garden Route erf with a steep driveway and overhead cables, that is a real planning item, and it is worth walking the access route with the supplier before the order is placed rather than discovering it on delivery day.

Once panels are up and braced, the roof structure goes on and the building is closed in — roof covering, breather membrane, external cladding or finish, windows and doors. Getting watertight quickly is a genuine advantage of the method, particularly if you are building through a Southern Cape winter.

The joints between panels are the detail to watch. Every panelised system lives or dies on how the vertical joints are sealed and how the wall meets the slab and the roof. Ask to see the standard details, and ask to see a five-year-old building rather than a new one.

First fix, second fix and the finishes

From closing in onwards a prefab build looks like any other build. Electrical and plumbing first fix through the chases that were formed in the factory, insulation topped up where the system does not include it, internal linings, ceilings, then second fix, joinery, floor finishes, paint.

This back half is not faster than conventional, and it is usually more than half the total programme. That is worth knowing, because the marketing tends to quote the erection time and let you assume the rest follows at the same pace. It does not. A house that is standing in four days is not a house you can move into in three weeks.

It is also where scope tends to be excluded. Check whether the quote includes internal linings, ceilings, floor coverings, kitchen and bathroom fittings, the electrical certificate of compliance, and the connection to municipal services or the septic system.

Where prefab genuinely wins, and where it does not

It wins on programme, on price certainty, and on quality consistency in the shell — a panel built on a jig under a roof is straighter and drier than the same wall framed in the rain. It wins hard on remote and difficult-access sites, where the alternative is housing a wet trade team a long way from anywhere for months. It wins on repetition: five similar units are much cheaper per unit than one.

It does not win on a complex one-off architectural design with few repeating elements — the factory setup cost gets amortised over nothing. It does not win where the site access will not take a delivery truck. And it does not win where the client cannot commit to a frozen design, because every post-freeze change is a factory variation rather than a site instruction.

It also does not remove the need for the conventional parts. Plans, engineering, NHBRC, foundations, services and the municipal process are all exactly the same as they would be for a brick house.

Frequently asked questions

How long does a prefab house take to build?

The shell goes up in days and the whole project usually runs a good deal shorter than the equivalent masonry build, but the saving comes from running the factory and the site in parallel, not from the erection itself. The realistic view is that design and approvals take as long as they always do, the foundation takes as long as it always does, and the finishes take as long as they always do. What you compress is the middle.

Is a prefab house cheaper than brick?

Often, but the margin is smaller than the headline suggests and it depends heavily on repetition and access. One-off houses on an easy urban site show the smallest saving. Multiple similar units, or a single unit somewhere hard to reach, show the largest. Foundations, services, roof and finishes cost much the same either way.

Will a bank grant a bond on a prefab house?

It is possible and it is more difficult than for masonry. Lenders look for approved plans, NHBRC enrolment, a conventional designed foundation, and an Agrément certificate on the building system where one exists. Speak to the bank before you commit to a system, because the answer varies by lender and by system.

Do prefab houses need approved plans?

Yes. A dwelling requires council-approved plans and has to satisfy the National Building Regulations regardless of how the walls are manufactured. The factory drawings are not plans. Any supplier suggesting otherwise is not somebody to build a house with.

Can the design be changed once production starts?

Only at a cost, and sometimes not at all. Openings and service chases are cut into the panels in the factory, so a moved window after production is a remanufactured panel. This is the main discipline prefab asks of a client and it is why the design freeze matters so much.

Does a prefab house last as long as a brick one?

A properly designed and maintained one does. Durability comes from the foundation, the structural design, keeping water out of the frame, and maintaining the external finish. None of those are functions of where the wall was assembled. Where prefab buildings fail early, it is almost always a joint or a flashing detail rather than the panel.

Thinking about a prefab build?

We will look at the site access, the ground and the design before anything is ordered, and tell you honestly whether prefab is the right method for your project or whether it is not.

See our prefab builds

Book a site visit