10.1.4Garage floors

Garage floors shall transmit all loads to either the foundations or the ground safely and without undue movement. Issues to be taken into account include:

  1. bearing capacity of the ground
  2. resistance of the floor to moisture from the ground
  3. thickness of floor slabs
  4. floor drainage
  5. structural topping.

Garage floors will be acceptable where they are in accordance with:

  • Chapter 5.1 ‘Substructure and ground-bearing floors’
  • Chapter 5.2 ‘Suspended ground floors’
  • the guidance given in this chapter.

Unless ventilation is specifically required, the void beneath a garage floor which is suspended precast concrete may be unventilated where:

  • the floor has adequate durability
  • the ground beneath is well drained
  • there is unlikely to be a build-up of soil gases.

Bearing capacity of the ground

Where the depth of fill exceeds 600mm, concrete floors should be in accordance with Chapter 5.2 ‘Suspended ground floors’ and BS 8103-1.

Supporting fill should comply with the requirements in Chapter 5.1 ‘Substructure and ground-bearing floors’.

Where protection is needed to prevent attack by sulfates in either the ground, ground water or fill below the slab, an impervious isolating membrane should be provided between the concrete and the ground.

Resistance of the floor to moisture from the ground

Generally, a DPM is unnecessary, except where:

  • it is needed to prevent dampness entering the home, or
  • the floor has to be protected against chemical attack from the ground.

Where no DPM is provided, the floor may show signs of dampness.

Where the floor is below ground level, precautions should be taken to prevent the entry of ground water, and tanking may be required.

Thickness of floor slabs

Ground-bearing floors, where provided, should not be less than 100mm thick, including a float finish.

Floor drainage

When practicable, garage floors should to be laid to falls to ensure that water or spillage is directed out of the garage via the vehicle doorway.

Structural topping

Where reinforced screeds are to be incorporated as structural topping, they should be designed by an engineer in accordance with Technical Requirement R5.