How BTO Floor Plans Are Structured
Build-to-Order (BTO) flats are designed by HDB architects who work within a standardised module system. Each flat type — 2-room Flexi, 3-room, 4-room, 5-room, and Executive — occupies a defined structural bay width and depth. Within this bay, HDB places the wet areas (bathrooms, kitchen, service yard) in fixed positions determined by the building's vertical plumbing stacks, which run continuously from the ground to the highest floor. These stacks cannot be relocated, and the positions of wet areas are therefore permanent constraints regardless of the renovation approach.
Flat buyers receive a set of floor plan drawings when they collect their keys. These drawings indicate room dimensions, door swing directions, power point locations, and — critically — which walls are RC (reinforced concrete) versus partition (lightweight internal dividers). First-time homeowners often overlook this distinction, which can lead to renovation plans that assume a wall can be removed when it structurally cannot.
Load-Bearing vs Partition Walls
Reinforced Concrete (RC) Walls
RC walls in HDB flats perform two roles: they carry vertical loads from the floors above, and they provide lateral stability for the entire block. These walls are distinguishable on floor plan drawings by a solid fill pattern and are typically 150–200mm thick. You can knock on an RC wall and hear a solid, dense sound rather than a hollow one, though this acoustic test is not reliable enough to make renovation decisions — the floor plan drawings or an inspection by the renovation contractor should be the definitive reference.
RC walls may not be hacked, cut through, or have conduits embedded in them without PE-stamped drawings. This restriction applies even to small penetrations for electrical conduits or plumbing. A licensed professional engineer must certify that any penetration through an RC element does not compromise the structural system. In practice, most interior designers and contractors avoid proposing work on RC walls precisely because of the additional approval cost and time.
Partition Walls
Partition walls in BTO flats are typically built with lightweight concrete blocks (AAC blocks, 100mm thickness) or, in older HDB construction, with calcium silicate boards. These are non-structural and can be hacked or re-erected with a renovation permit from HDB. They do not carry floor loads — their only structural function is to provide lateral bracing between RC elements, and HDB renovation guidelines account for this when approving partition wall changes.
Common renovation work involving partition walls includes opening up the living room and a bedroom to create a larger combined space, widening doorways, or removing a small dry kitchen partition to extend the counter area. Each of these requires a permit, and the replacement partition (if any) must be built with materials from HDB's approved list.
The 3-Room Configuration
A standard 3-room BTO flat has a floor area of approximately 65–68 sqm and contains two bedrooms, one common bathroom, one attached bathroom in the master bedroom in newer launches, a kitchen, a living and dining area, and a service yard. The bedrooms are separated from the living area by partition walls in most configurations, though some newer 3-room types use RC walls between bedrooms to improve acoustic performance.
The tight footprint of a 3-room flat makes layout planning particularly consequential. The most common change is removing the bedroom-to-living partition to create an open-plan layout, which works structurally in most BTO builds but must be weighed against the reduction in privacy and the loss of a defined sleeping space if the flat is occupied by multiple family members.
The 4-Room Configuration
At roughly 90–93 sqm, a 4-room BTO flat has three bedrooms plus the standard wet areas. The additional bedroom is typically a smaller second common room, often used as a study, a child's room, or a home office. The kitchen in the 4-room type is usually slightly larger than in the 3-room, though still constrained by the position of the exhaust duct and the plumbing stack.
For couples or small families buying a 4-room BTO flat, the most frequent layout question involves the third bedroom. Removing the partition between the third bedroom and the living or dining area is a common approach to gaining open-plan space. This is structurally viable in most configurations. The alternative — converting the third bedroom into a walk-in wardrobe for the master bedroom — requires a door opening to be cut through a partition wall, which is a permitted work under a renovation permit.
The 5-Room Configuration
At 110–113 sqm, a 5-room BTO flat is the largest standard type in current launches. It has three bedrooms plus a utility room, two bathrooms, and a more spacious kitchen-service yard arrangement. The utility room is a particular planning variable — it is commonly used for storage, as a helper's room, as an additional bathroom (converted from dry to wet with HDB approval), or as a study.
Converting the utility room to an en-suite wet bathroom involves repositioning a floor trap or adding one where none exists, which requires waterproofing works and a permit. The floor-to-floor height in HDB blocks is approximately 2.8 metres, leaving sufficient clearance for dropped ceilings, concealed plumbing, and false beams — all common in 5-room renovation schemes targeting a more residential feel.
Planning sequence: Identify all RC walls on your floor plan → determine wet area constraints from vertical plumbing stack positions → map your must-have layout changes → check each change against HDB's permitted works list → engage a registered contractor to apply for the permit before any hacking begins.
Floor-to-Floor Height and Ceiling Works
BTO flats delivered with keys have a raw ceiling at slab level — typically around 2.6 metres of clear height after screed but before any ceiling finishes. Most homeowners install a dropped ceiling of gypsum board or timber battens to conceal electrical conduits and create a finished look. The minimum clear height after any ceiling works is 2.4 metres, as specified in HDB guidelines. This constraint affects the choice of lighting fixtures, air conditioning units, and the routing of ventilation ducting for kitchen hoods.
Official Resources
Floor plan drawings for current BTO launches are available through the HDB Flat Portal. Homeowners who have already collected keys can access their specific unit's as-built drawings through My HDBPage. The Urban Redevelopment Authority's ura.gov.sg provides context on broader residential design standards.