Rewiring a Landed House: Decide Before the Walls Close

There is a moment on every landed project when the shell is up, the blockwork is done, and the house is about to be plastered. It looks like progress and it feels like the hard part is over.

It is also the last cheap moment to decide almost everything electrical. After the walls close, every change becomes a chase cut into finished work, a patch, a repaint, and an argument about who pays. The electrical package is the trade where "we can decide that later" costs the most, because all of it is buried and none of it is visible when the decisions are being deferred.

This is what has to be settled before the walls close, in roughly the order the site forces it, and what to ask about each.

Rewiring is not one decision, it is four

Owners tend to say "we're rewiring" and mean "new sockets". In an older house it usually means four separate things, and they carry different costs and different lead times.

The incoming supply. What the house is fed with, which was sized for how a house was used decades ago. If the load is going up materially, this involves the utility rather than the builder, and it is the item with the longest lead time on the whole M&E package.

The distribution board. How many ways, how the circuits are split, and what protection is on them. Older boards commonly have too few circuits, everything on rewireable fuses, and no residual current protection at all.

The cabling. The actual wiring in the walls. In genuinely old houses this can be perished, undersized for what is plugged into it now, and installed without an earth at every point.

The earthing arrangement. The least visible and the most important, and the one nobody asks about.

A quotation that says "rewiring" without saying which of these four it covers is a quotation you cannot compare with another one. That is the same problem as allowances generally — provisional sums and PC sums covers how to read a quotation with lines like that in it.

Who is actually allowed to do it

Electrical work of this kind is the province of a licensed electrical worker, and the supply arrangements with the utility are signed off by that licensed person, not by the builder. That is worth understanding early, because it sets who you are actually relying on for the certification at the end and who has to be appointed in time to design the installation rather than just install it.

A builder's job here is coordination: getting the LEW involved at design stage rather than at first fix, making sure the electrical layout matches the structure that is actually being built, and holding the sequence so that conduits go in before the things that would have to be broken to install them.

Wong Lye Pte Ltd is a licensed builder holding a BCA General Builder Class 2 (GB2) licence. What we take on is set out on the A&A works page.

Load is the decision that has to be made first

This is where modern landed houses catch people out, because the house being built is not the house that was originally there.

Count what is now normal: an aircon unit in every bedroom plus the living areas, an induction hob, an oven, instantaneous water heaters in several bathrooms, a booster pump, possibly a home lift, possibly pool or water-feature equipment, and increasingly an EV charger in the car porch. Each is modest. Together they are a different house from the one the original supply was sized for.

The reason it has to be decided first, rather than tidily at the end, is lead time. If the supply has to change, that is not a site decision — it involves the utility, it has its own process, and it does not compress because the plasterers are booked. Establishing early whether the existing supply is adequate is one of the cheapest things you can do on the whole job, and one of the most commonly skipped.

The two deadlines that are not the same

People think of "before the walls close" as a single deadline. On site there are two, and the earlier one is much harder.

Before the concrete. Anything cast into a slab or passing through a beam has to be in place, sleeved, and in the right position before the pour. Getting this wrong is not a patching job later — coring through a structural element after the fact is a structural question, not a convenience, and the answer is sometimes no. Conduit drops in cast walls, sleeves for services crossing beams, and anything serving a lift pit or a roof plant area belong to this deadline.

Before the plaster. Conduits, back boxes, and every switch and socket position. This is the one owners think of, and it is genuinely the last cheap moment for layout — but it is already too late for anything in the first list.

If your project is large enough that these two are weeks apart, ask which one each item is against. It is a question good site teams answer immediately.

Do the walk-through with tape, on site

The single most useful hour an owner can spend on a landed build is walking the shell before first fix with masking tape and a marker, sticking a piece of tape where every switch and socket is going to be.

A drawing does not tell you that the bedroom switch will end up behind the door swing, that the bedside socket lands where the headboard sits, that there is nothing on the wall the study desk was always going to go against, or that the kitchen has no socket where the kettle actually lives. Standing in the room does. Every builder has watched an owner discover four of these in twenty minutes.

Three things worth taping specifically, because they are the ones most often missed: sockets outside, at the porch, the yard and wherever the pressure washer or the Christmas lights will be plugged in; the position of the DB, which has to be reachable and is often shoved somewhere awkward at the last minute; and a socket near the front door for whatever the household ends up charging there.

Lighting: decide the control, not the fittings

The fittings can be chosen late. The control cannot, because it is wiring.

Which switch operates which group, whether the staircase and the long corridor are two-way or three-way, whether anything is to be dimmed, and whether anything is on a sensor — all of that is decided at first fix and is expensive to change afterwards. Dimming in particular is a wiring and compatibility question, not a fitting you swap in later.

Where a project includes a loft, a void or a double-height space, the lighting and its switching need to be resolved with the structure rather than after it — see internal lofts and mezzanines and light wells and voids, where access for changing a lamp is itself a design decision.

Data, and why wifi struggles in a landed house

A landed house is three or four storeys of concrete slabs and, often, some solid walls. That is close to the worst case for a single wireless router, and no amount of buying a better one fixes a floor slab.

The fix is boring and cheap at first fix: conduit from a sensible central point to at least one position on each floor, so that a wired access point can go where it is needed. Doing it now costs conduit. Doing it later means surface trunking down a finished stairwell, which nobody is ever happy with.

Where M&E and structure argue

Three fights recur on landed jobs, and all three are cheaper to settle on paper.

Aircon. Where the condensers go, whether the ledge or the flat roof can take them and be reached for servicing, how the refrigerant pipes and condensate runs get there, and whether the condensate has continuous fall the whole way. A drain run with a dip in it is a permanent maintenance problem, and it is created in a single careless afternoon at first fix.

Water. A tall house usually needs a booster arrangement for the upper storeys, which needs a location, power, and enough space around it to be serviced. It also needs somewhere that a leak would not be a disaster.

Anything on the roof. If solar is even a possibility later, the time to run a conduit route and leave space in the board is now, not after the roof is finished — making a landed roof solar-ready goes through the structural and waterproofing side of the same decision. The same logic applies to a home lift, where the shaft, pit and approvals carry a power and drainage requirement that has to be in the design rather than added to it.

EV charging: the cheapest thing you will ever not need

Whether or not there is an electric car today, the argument for provision now is one-sided.

Leaving a spare way in the board, a conduit route to the car porch and a draw wire in it is a small cost while the walls are open. Retrofitting the same run afterwards means chasing finished walls, lifting finished driveway, or surface trunking across the front of the house. Owners who skipped it rarely regret the money; they regret the route.

Then get the paperwork that makes it maintainable

At the end, three things are worth more than they look.

A labelled distribution board schedule, describing circuits in the language of the house — "kitchen sockets", "master bathroom heater" — rather than numbers only. Every future electrician and every future owner depends on it.

The certification from the licensed electrical worker, filed with the rest of the completion documents rather than loose.

A marked-up plan showing where things actually run. Not the design drawing — the as-built. It is what stops somebody drilling into a cable in five years, and it is worth asking for while the walls are still open and someone can still photograph them. Photographs of every wall before plastering, room by room, cost nothing and are the single most useful record of a build.

These belong with the rest of the handover documents, and it is worth checking they are actually there — the room-by-room handover inspection is the moment to notice a missing certificate, not two years later.

The short version

Establish the incoming supply and the total load early, because that item has the longest lead time and involves the utility. Get the licensed electrical worker in at design stage, not at first fix. Know which items are against the concrete deadline and which are against the plaster deadline. Walk the shell with masking tape before first fix and mark every switch and socket standing in the room. Decide lighting control rather than lighting fittings. Run conduit for data and for EV charging whether or not you need them yet. And insist on the labelled board schedule, the certification and an as-built markup at the end.

Every one of those is cheap while the walls are open, and expensive in exactly the same order once they are not. Deciding late is also how a project accumulates variations, which have their own cost — what variation orders really cost is worth reading before the plastering starts rather than after.

Planning the M&E on a landed A&A? WhatsApp us on 9107 2601 — tell us the house type, what stage the project is at, and whether an EV charger, lift, pool or solar is anywhere in the plan, and we will tell you which decisions are already urgent and which can genuinely wait.