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:
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.
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.
Whole Floor Zone
Structural Precast Concrete Floor Base (Minimum Mass 300 kg/m²)
Good Practice Notes for Part E1
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|
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.
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|
|Unit Ref:||Depth||Plank Width||Self Weight|