FAQs & Contact Us

FAQs

For structural works on HDB properties, the Qualified Person (QP) must ensure full compliance of his design according to the current Code of Practice and local regulatory/ statutory requirements.

Contact us

You can contact us if you have any queries. Here are the following contact details for commercial renovation matters:

  • Telephone: 1800-866-3073 (Weekdays: 8:30am to 5:00pm)
  • Fax service: 6397-2477 or 6397-2478
  • Email: plgmail@mailbox.hdb.gov.sg
  • Address: HDB Hub,  480 Lorong 6 Toa Payoh, Atrium 3rd storey, Singapore 310480 (Weekdays: 8:30am – 5:00pm and Saturdays: 8:30am – 1:00pm)

1. What is the concrete grade that can be considered for design?

Type of Structures

Minimum Concrete Grade

Substructures, superstructures, precast reinforced concrete piles, pile caps, and building precast concrete components

40

Bored piles

35

Grease trap, inspection chamber, and screen chamber

30

 

2. What is the concrete cover that can be considered for design?

Structure and Location

Minimum Concrete Cover (mm)

Remarks

Slab

Top

20

-

Bottom

30

-

Beam

Top, bottom, and sides

35

-

Column

60

To main reinforcement bars

Wall

35

To vertical bars

Water Tank

Inner face in contact with water

40

-

Pile cap

Top and sides

75

-

Bottom

50

From pile head

Footing

Top, bottom, and sides

75

-

 

3. What are the types of foundation systems that can be considered for design?

Most types of pile foundations (bored piles, steel H-piles, micropiles, jack-in steel pipe piles, jack-in steel H-piles, and precast reinforced concrete piles) are acceptable except for timber piles. All pile foundations have to be designed with a minimum safety factor of 2.5 times the nominal working load.

For the design of footing, the bearing capacity of the soil must be based on borelog results. If no soil information is available, the bearing capacity of the soil must be limited to 50kN/m2 at 1.5m below ground level.

4. What are the requirements for designing slopes and earth-retaining structures?

The QP must submit the slope stability and design calculations for proposed slopes greater than 2.5m in height. Slope-protection measures must be in place to stabilise any slopes that fail to satisfy the required factor of safety. A minimum factor of safety of 1.5 is required for slope stability. 

For the earth-retaining wall, the following factors of safety have to be considered:

Condition

Factor of Safety

Overturning and sliding

2

Allowable bearing pressures

3

Overall stability or slip circle failure

1.5

In addition to the factor of safety stated, the following requirements must to be adopted:

  • Take into account the full water table height at ground level when considering the water pressure acting on the wall
  • Take into account the surcharge of minimum 10kN/m2 or other incidental loads, whichever is higher
  • Consider a minimum unplanned excavation depth of 0.5m or 10% of the total height of earth retained, whichever is deeper
  • Net pressure analysis method is not acceptable

 

5. What are the requirements for designing new column?

The new column must be designed as a short column and founded for independent structures.

Columns or walls that are next to driveways must be checked and designed for vehicular impact load. Tie beams must be provided for columns at the ground floor and roof.

No opening can be made through the columns. 

6. What are the requirements for designing a new strong room or mezzanine floor within the existing structure?

The proposed structure must be independently supported. For cases where the soil information is not available, the QP must consider the safe bearing capacity to be limited to 50kPa with a minimum founding depth of 1.5m.

7. What are the requirements for designing a new cold/ chiller room?

A minimum air gap of 150mm must be provided between the cold/ chiller room and existing structure. The existing floor slab needs to be topped up with approved insulation material. Construction of the cold/ chiller room is only allowed on the first storey.

8. What are the requirements for designing new steel structures and claddings?

S275 steel sections must be used for general structural steel members. 

Drilling is not allowed if a steel hollow section is used. Only steel plates, angels, or cleats can be used and they must be welded to secure the cladding or metal roofing sheets. 

If roofing sheets or claddings are designed by a specialist, the QP must check and ensure that the design complies with current safety, stability, and durability requirements. 

The appropriate separator must be used at the contact between 2 different metals to prevent galvanic corrosion.

9. What are the requirements for designing new grease traps, inspection chambers and screen chambers?

All grease traps, inspection chambers, and screen chambers must be subjected to a design-imposed load of 5kN/m2. They do not have to be subjected to a vehicular load.

The total operating weight (with full content weight) must be considered in the design.

10. What are the requirements for erecting new walls within the existing structure?

New walls can be erected as long as the maximum thickness of the brick or hollow blocks does not exceed:

  • 100mm for the first storey
  • 63mm for subsequent storeys

11. What are the requirements for installing a cantilever awning onto the existing structure?

A lightweight awning can be mounted onto the existing structural member as long as it is not a cantilever beam.

Awnings that span more than 2.4m and are supported directly by reinforced concrete columns or peripheral beams must be propped up.

12. What are the requirements for the proposed Outdoor Refreshment Area?

Adjacent to buildings taller than 4 storeys

For an Outdoor Refreshment Area adjacent to buildings taller than 4 storeys (high-rise), its structure must be supported on independent foundation. The roofing material has to be non-combustible and be composed of:

  • Reinforced concrete with a minimum thickness of 125mm
  • Sandwiched panels with a minimum thickness of 50mm or a precast ferrocement roof with a minimum thickness of 40mm

If the composition of the proposed sandwiched panel deviates from the reference above or if other (non-combustible) roofing material is to be used, the structural professional engineer must conduct an impact load test with an accredited laboratory and submit the test report to us. The report must justify that the material is able to withstand the impact load of a 6-kg flower pot falling from the height of 45m, assuming that the impact contact time is 0.1 sec.

A precast ferrocement roof must have:

  • A minimum strength of 40N/mm2
  • A minimum thickness of 40mm
  • A layer of square wire mesh (with a minimum thickness of 6mm at 100mm spacing) sandwiched between 4 layers of square wire mesh (with a minimum thickness of 1.5mm at 25mm spacing)
  • Wires galvanised with zinc coating with a minimum weight of 65g/m2 with a minimum proof stress of 300N/mm2

Adjacent to buildings 4 storeys or shorter

Outdoor Refreshment Area adjacent to buildings that are 4 storeys or shorter require:

  • An umbrella-type Outdoor Refreshment Area (area greater than 4m × 4m = 16m2) has to be supported on independent foundation
  • A Structural QP for design and supervision works