Basement Construction

We can't point you to a current independent price for building a basement or repairing a leaking one, so here's what makes one job bigger than another. A deeper dig needs a taller retaining wall and, below the water table, puts more water pressure on the floor and walls. Digging under a house you're keeping means holding up its foundations while the ground beneath is removed, which a rebuild avoids. A neighbour close to the boundary means a stiffer retaining wall and closer monitoring, and BCA and URA's Be Good Neighbours guide tells owners planning a basement to factor in the cost of the retaining system, its design submission to BCA and repairing any damage the dig causes. High groundwater means pumping during the dig, and a basement that needs a pumped drainage system afterwards goes on costing power and servicing for it. For a leak, sealing one joint or crack is a smaller job than lining whole walls or adding a drainage system, and reaching the outside face means digging. Our basement construction cost article explains what has to be investigated before a price can be relied on.

URA allows basements under landed houses within set limits, so in principle yes, but adding one under a house you're keeping is a harder job than building one into a rebuild. The house's foundations have to be held up while the ground beneath is dug out, in a tight space and a set order; a rebuild or major extension opens other options. Under URA's envelope control guidelines, a basement that sticks out above ground can't come closer to the road than URA's road buffer, or closer to your other boundaries than the building setback. A fully underground one can come closer. The road reserve is land to be handed to the State for the road, and the road reserve line on the Road Line Plan is where that land meets your plot; a fully underground basement can go right up to that line if the part under the green buffer is at least 2 m down, and up to your site boundary if there are no technical requirements such as sewerage or drainage, no adverse impact on the adjoining property and no openings into the next site. Terrace and semi-detached houses also need the part under the 2 m planting verge at least 2 m down, and in a Good Class Bungalow Area it's set back 2 m from the boundary. On sloping ground, URA may consider an exposed protrusion that stays within the envelope height. Between terrace or semi-detached neighbours, URA and BCA's Be Good Neighbours guide says a basement can be allowed, but the owner should weigh the risk to the party walls and take measures against damage.

Yes. Only a Qualified Person who is a registered Professional Engineer in the civil or structural discipline can apply for BCA's structural plan approval, and once the plans are approved, structural work can't start until a permit is issued. The permit is applied for jointly by the developer (under the Building Control Act, the person the building works are carried out for), the QP and the builder who will do the work. Plans can be approved in phases, and BCA's own example includes a basement stage; a material change to the approved plans needs approval before it's built. The structural plan application includes URA's planning permission or lodgement receipt, so the design also has to sit within URA's basement limits. PUB's drainage code says a new house or a rebuild has to meet its Minimum Platform Level, while A&A works to an existing building with no link to underground special facilities such as rapid transit systems need not, though PUB says the QP should still recommend that level to reduce flood risk; the QP confirms which applies.

It can, which is why a survey before the dig is a legal requirement and monitoring during it is part of URA and BCA's guidance, though none of this guarantees no damage. BCA's guide to pre-construction surveys says Regulation 32 of the Building Control Regulations requires a survey recording the condition of buildings close to the site before any excavation, piling, foundation or demolition work starts, and failing to carry it out is an offence. The builder should carry it out in consultation with the QP, who decides how far it needs to go; as a guide, BCA's minimum zone for excavation is 15 m from the site boundary. Each nearby owner must get a copy of the report on their house before construction starts, which helps show later whether a crack was already there. URA and BCA's Be Good Neighbours guide says the engineer should also assess the dig's impact, and where neighbours could be affected, the owner must make sure the builder monitors those houses closely so work can be halted if damage starts to show.

We can't give you a number of weeks until the ground is investigated and the design is drawn, because the dig, the structure and the waterproofing depend on what the investigation finds. The time figures we can point to are BCA's processing targets. Under CORENET X, which BCA says is mandatory for all new projects by 1 October 2026, structural plans go in as part of a joint cross-agency submission that BCA aims to process within 20 working days, and the structural works permit within 7 working days of complete documents. Those targets apply to complete applications that meet the requirements first time.

Yes, but an inside lining keeps water out of the room, not out of the wall. Sika says internal systems, applied to the inside face, do not prevent damage to the structure from water ingress and are only recommended for refurbishment where the outside surfaces can't be reached. On an existing basement the outside face can only be reached by digging down beside it, so an inside repair ranges from sealing one leaking joint or crack, to lining whole walls, to a system that collects the water and pumps it away, which needs power, servicing and a plan for blocked drains and pump failures. Waterproof paint over a damp patch doesn't tell you which of these the leak needs. Sort out the water before choosing a floor; the basement buying guide explains choosing flooring for a dry, assessed floor.

Not on every site. On sites in low-lying landed housing areas, URA's envelope control guidelines for terrace, semi-detached and detached houses require any building structures or living areas below the Minimum Platform Level, which PUB sets, to be fully sealed with no external openings. If external openings are proposed, PUB's additional requirements apply: the internal finished floor at least 300 mm above the adjacent road, only driveways, bin centres, turfed compound areas, car porches or other areas PUB approves below that level, and bedrooms and M&E installations above it. PUB's drainage code also requires a crest level, a minimum height for the bottom of every entrance, exit and opening into a basement, ventilation openings included. An open light well lets rain straight in, and that water has to be drained or pumped away. A room people use also needs fresh air and equipment that can be serviced, which our article on basement ventilation and plant access covers.

It may be possible, provided the lift is chosen before the basement design is fixed. Pit, shaft and headroom needs depend on the lift system, and any pit sits below the basement floor, so it becomes part of the structure and the waterproofing. Our guide to home lift shaft dimensions explains what a shaft needs, and the home lift service page covers the lift itself.