A separating floor is defined as a floor that separates adjoining dwelling houses, flats or rooms used for residential purposes.

Section E1 of the Approved Document E (ADE Section 4) introduces performance criteria for separating floors. The minimum value for airborne sound insulation is

Airborne Sound D_nTw + C_tr=43 dB (or greater)

Impact Sound L_nTw =64 dB (or less)

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Section E1 of Part E document deals with the protection against sound from other parts of the building and adjoining buildings; Dwelling houses, flats and rooms for residential purposes shall be designed and constructed in such a way that they provide reasonable resistance to sound from other parts of the building and from adjoining buildings.

The Part E requirement for separating floors is subject to both airborne and impact sound regulations.

Work to existing construction
New floor treatments will impose additional loads on the existing structure. The existing structure therefore should be assessed to ensure that the additional loading can be carried safely, with appropriate strengthening applied where necessary.

Before a new floor treatment is applied, appropriate remedial work to the existing construction should be undertaken:
.  If the existing floor is timber, then any gaps in floor boarding should be sealed by overlaying with hardboard or filled with sealant
. Where floor boards are to be replaced, boarding should have a minimum thickness of 12mm, and 100mm minimum Rockwool Roll or Flexi should be laid between the joists in the floor cavity.
. If the existing floor is concrete and the mass per unit area of the concrete floor is less than 300Kg/m², or is unknown, then the mass of the floor should be increased to at least 300Kg/m. Any air gaps through a concrete floor should be sealed. A regulating screed may also be required.
. If there is an existing lath and plaster ceiling, it should be retained as long as it satisfies Building Regulation Part B – Fire Safety.
. Where the existing ceiling is not lath and plaster, it should be upgraded as necessary to provide at least two layers of plasterboard with joints staggered, total mass per unit area 20Kg/m2.

Flanking Sound
A major cause of reduced acoustic performance in separating floors is due to flanking paths via the surrounding structure rather than a direct path through the floor. Good practice detailing at the design stage, especially at key junctions, together with good workmanship will minimise this effect and optimise performance levels. Guidelines of good practice detailing at key junctions are provided throughout the new Approved document E.

Junctions with floor penetrations
Pipes and ducts that penetrate a floor separating habitable rooms in different flats should be enclosed for their full height in each flat.

The enclosure should be constructed of material having a mass per unit area of at least 15Kg/m² (eg 2 x 12.5mm standard plasterboard)
. Either line the enclosure with 50mm Rockwool Flexi, or wrap the duct or pipe within the enclosure with 25mm Rockwool Techtube.
. The enclosure may go down to the floor base if isolated from the floating layer.
. Penetrations through a separating floor by ducts and pipes should have fire protection to satisfy Building Regulation Part B – Fire Safety. Fire stopping should be flexible and also prevent rigid contact between the pipe and floor. Rockwool Insulated Fire Sleeve meets these requirements.