You inherit the previous owner's decisions, including the ones that were never approved. Investigation comes before design.
The honest version: a resale flat cannot be accurately quoted from a floor plan alone.
Unapproved works become your problem, not the seller's
This is the part that catches people. If a previous owner hacked a wall, enclosed a balcony or rewired without a permit, the obligation to put it right transfers with the flat — HDB can require reinstatement, and the cost lands on the current owner. It is worth identifying this before you buy if you still can, and before you design if you cannot. We look for the tell-tales during the site assessment: fresh plaster on a structural line, a socket in an improbable place, a floor level that steps for no reason.
The electrical system is the most commonly underestimated item
A flat built in the 1980s was wired for a household with a fraction of today's connected load, and forty-year-old wiring, an undersized distribution board and a shortage of socket outlets are all common. Rewiring is disruptive because it means chasing walls and therefore redoing finishes, so it is far cheaper done now than in three years. Electrical work must be carried out by a Licensed Electrical Worker — this is a licensing requirement, not a preference, and it is worth asking to see the licence.
One month, not three
Renovation in an existing block must be completed within one month of the permit being granted, against three months for a newly completed block. That is a real constraint on a project that also involves hacking, disposal and rectifying whatever is found behind the tiles. It needs to shape the programme from the start rather than being discovered halfway through.
A contingency is not pessimism, it is arithmetic
In an older flat, some things genuinely cannot be known until a wall or a floor is opened: water damage behind a wet-area wall, screed that has failed, a pipe run that is not where the drawing says. A sensible allowance for hidden conditions, agreed openly at the start, is what stops the project stalling over a mid-build argument. We would rather show you that allowance than quote a lower number and find it later.
Keeping things is often the smart move
Not everything needs to go. Windows, flooring in good condition and sometimes kitchen carcasses can be retained and are a legitimate way to protect the budget for the work that matters. The test we apply is whether the item will still be serviceable in five years — because replacing it later means disturbing the finished work around it.
Approvals & rules
Who approves the work.
Approving bodyHDB
The renovation permit is applied for by a contractor listed in HDB's Directory of Renovation Contractors.
Works must be completed within one month of the permit being granted for an existing block.
Hacking, wet-area alterations, rewiring and window replacement all require HDB approval.
General renovation is allowed 9am–6pm on weekdays and Saturdays, never on Sundays or public holidays.
Noisy works are restricted to 9am–5pm on weekdays only, for a maximum of three consecutive days.
Your contractor must give immediate neighbours written notice at least three days before works begin.
Unapproved alterations by a previous owner may have to be reinstated at the current owner's cost.
Rules and timeframes change. These were checked against the linked official pages on the date shown — please confirm anything critical with the relevant authority.
What drives the cost
Where the money actually goes.
Listed roughly largest first, for this property type specifically. A reliable figure still needs a site assessment — this is what to expect it to be made of.
We do not quote a fixed package price, because two homes of the same size rarely need the same works.
01
Extent of hacking, and the disposal that goes with it — frequently underquoted
02
Condition of the electrical system, and whether rewiring is needed
03
Wet areas: waterproofing and full bathroom replacement are major items
04
Carpentry, particularly where existing walls are out of square
05
Rectifying inherited or unapproved work
06
The hidden-conditions allowance, which is real money and should be visible
Common mistakes on this property type
Accepting a firm price before anyone has opened up a wet area
Quotations that omit hacking, disposal, protection and post-works cleaning
Assuming the existing waterproofing is sound because there is no visible stain
Unpermitted alterations left undeclared, which become your liability
Very old flats: any suspected asbestos-containing material must be handled under the proper process, never by a general crew
How long it takes
Timeline, honestly.
Typically around 10 to 16 weeks on site. Hacking, disposal and rectification of whatever is found add both time and sequence dependency compared with a BTO.
Delays most often come from late material selections or changes requested mid-build, not from the site work itself.
Questions worth asking
What we'll ask you first.
01
How old is the flat, and has it been renovated before?
02
Has the electrical system been assessed by a licensed electrical worker?
03
Are there alterations by a previous owner that may not have been approved?
04
Which areas can realistically be retained?
05
What hidden-condition allowance are you comfortable carrying?
Not sure of the answers yet? That is fine — working them out is part of the first conversation. For the wider picture, the renovation guide covers permits, hours, materials and costs in detail.
Start with clarity
Ready to talk through your resale hdb renovation?
Tell us your property type, timeline and the work you have in mind. We'll help you decide the next practical step.
