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Building Regulations

 Ground Preparation

Part C of the Building Regulations (Site Preparation and Resistance to moisture) states that the ground to be covered should be reasonably free from vegetable matter and that a suspended concrete floor should incorporate:

  • Damp proof membrane (to be provided if the ground below the floor has been excavated below the lowest level of the surrounding ground and will not be effectively drained)
  • Ventilated air space -in those situations where there is a risk of an accumulation of harmful gases.
  • Where ventilation (referred to above) is provided, two opposing external walls should have ventilation openings placed so that the flow of air will have a free path under the floor.
  • Where there is a likelihood of upward ground movement (e.g. clay heave), adequate space should be provided to accommodate the movement.

 Thermal Insulation

The thermal transmission (U value) of a floor depends upon the type of floor finish, floor size and insulation employed. The simplest and most effective way of providing the necessary insulation to prestressed concrete floors is to place it above the structural floor and below the finishes.

To calculate the heat loss through a precast ground floor slab, see Thermal Properties Datasheets.

When used at upper floor levels, concrete floors act as a thermal store, especially when under-floor-heating systems are used, this can reduce heating costs.

Milbank Hollowcore Planks used at ground floor level can be supplied with polystyrene insulation bonded to the underside of the slab. Alternatively the necessary insulation can be placed on top of the structural floor below the finishes.

 Sound Insulation

The basic Building Regulation requirements for a precast concrete floor base remains unchanged since 1992 when the minimum mass for separating floors in dwellings was increased to 300kg/m².

Prior to July 2003, the Building Regulations did not require any measurable performance criteria for a precast concrete floor base; - there were only specified forms of floor construction, that were "Deemed to Satisfy" the Regulations.

The government recognised that these Deemed to Satisfy forms of construction had not always delivered an acceptable degree of sound reduction; so in Part E of the Building Regulations 2000 (England and Wales), specific sound reduction values were set for Sound Insulation between Dwellings and Rooms for Residential Purposes (E1), and for the first time there is a requirement for Internal Sound Insulation in Houses (E2).

To achieve the new performance criteria, careful attention needs to be given to the detailing and on site workmanship when applying the floor and ceiling finishes.

 E1 - Sound Insulation between Dwellings and Rooms for Residential Purposes
Attention is drawn to the following extract from The Building Regulations 2000 (as amended by SI 2002/2871). Interpretation (Regulation 2): “room for residential purposes” means a room, or suite of rooms, which is not a dwelling-house or flat and which is used by one or more persons to live and sleep in, including rooms in hotels, hostels, boarding houses, halls of residence and residential homes but not including rooms in hospitals, or other similar establishments, used for patient accommodation.

The performance criteria for this category are:

Airborne Sound Insulation DnT,w + Ctr - 45dB (Minimum)
Impact Sound Insulation L'nT,w + Cl - 62dB (Maximum)

The Builder / Developer must demonstrate compliance with these performance criteria on every site by having on site "Pre Completion Tests" (PCT) carried out by an independently accredited acoustic engineer.

These tests measure the performance of the floor zone as a whole, not the individual components.

Floor Finishes
Whole Floor Zone
Structural Precast Concrete Floor Base (Minimum Mass 300 kg/m²)
Ceiling Finishes

 Good Practice Notes for Part E1

  • The precast floors (300kg/m² Minimum) should be built into separating walls.
  • All voids between the floor units and supporting walls should be filled.
  • The floor should be properly grouted to prevent air paths.
  • External Walls: If the cavity is not completely filled with mineral wool or expanded polystyrene bead, a flexible closer should be placed in the cavity to stop sound passage up or down the cavity.
  • The first joint in the floor parallel to a Separating wall should be a minimum of 300mm from the cavity face of the inner leaf.
  • Internal Cavity Walls: A flexible closer should be placed in the cavity to stop sound passage up or down the cavity.
  • Solid Separating Walls: A flexible closer should be placed between the units so that the floor is not continuous through the separating wall.
  • Service Penetrations: Service penetrations should be wrapped in mineral wool quilt, adequately boxed and sealed with tape or sealant.
  • All screeds and / or floating floor treatment should be laid in accordance with the manufacturer’s instructions.
  • Resilient flanking strips should be placed in accordance with the manufacturer’s instructions.
  • The ceiling finishes should be fixed in accordance with manufacturer’s instructions.

 Robust Details
As an alternative to Pre Completion Tests, a series of "Robust Details" have been developed which give sound insulation values that are superior to the requirements of Part E1.

Airborne Sound Insulation DnT,w + Ctr - 50dB Mean 47dB Minimum
Impact Sound Insulation L'nT,w + Cl - 57dB Mean 60dB Minimum

For precast concrete floors, these Robust Details take into account the whole flooring system which includes the Floor finishes, Precast floor and Ceiling Finishes.

To qualify as a Robust Detail, the combination of the Floor finishes, the Precast Concrete Floor Base and the Ceiling finishes must be tested on site and consistently achieve higher sound insulation values than that required by Part E1. (These tests must be carried out on at least 30 pairs of rooms, not more that 8 pairs on any given site.)

A handbook "Robust details Part E - Resistance to the passage of sound", published by Robust Details Ltd (www.robustdetails.com) provides further information on separating wall and floor construction.

It should be noted that even if a Robust Detail is used, Local Building Control Inspectors can still require Pre Completion Testing.

Currently the only Robust Detail available for Precast Concrete Floors uses a 150mm (minimum) deep Hollowcore plank floor with a minimum mass of 300kg/m².

 Milbank Range for part E1
Milbank offer the following Hollowcore Plank floors for use in Separating Floors:

Unit Ref: Depth Self Weight
PS-150H 150mm 301 kg/m²
PS-200 200mm 303 kg/m²
PS-250 250mm 352 kg/m²

Note:
There is no requirement, either in the Regulations or in Robust Details, to fill the hollow cores at the bearing ends of the planks; indeed test results have demonstrated that solid ends have no significant effect on the reduction of sound transmission.
(Milbank are unable to offer a cost effective solution for Beam and Block Floors to meet the requirements of Part E1.)

 E2 - Internal Sound Insulation in Houses
The performance criteria for this category are:

Airborne Sound Insulation Rw - 40dB (Minimum)
Impact Sound Insulation No values given

Compliance with these performance criteria can be demonstrated by laboratory tests on various types of floor construction.

 Laboratory Tests
Tests on both Beam and Block and Hollowcore plank floors yielded the following results:

Floor Type Floor Depth Self Weight Sand or cement screed Ceiling finishes Rw(dB)
Beam & Block 150mm 186 kg/m² - Single layer plasterboard (8.0 kg/m²) fixed to 50 x 50 timber battens at 1.2m centres 40
Beam & Block 150mm 186 kg/m² 40mm Single layer plasterboard (8.0 kg/m²) fixed to 50 x 50 timber battens at 1.2m centres 49
Hollowcore Plank 150mm 236 kg/m² - - 53

 Milbank Range for part E2
Milbank offer the following Precast Floors for use in housing:

Beam and Block:

Beam Type Beam Depth Beam Centers Block Density Self Weight Floor
T150 150mm 525mm 1350 kg/m³ 179 kg/m²
T150 150mm 525mm 1900 kg/m³ 227 kg/m²
D225 225mm 540mm 1350 kg/m³ 240 kg/m²
D225 225mm 540mm 1900 kg/m³ 280 kg/m²

Hollowcore Plank:

Unit Ref: Depth Plank Width Self Weight
PS-150L 150mm 1200mm 252 kg/m²
PS-150H 150mm 1200mm 301 kg/m²
PS-200 200mm 1200mm 303 kg/m²