Acoustic Flooring in London Flats and Terraces: Impact Noise, Airborne Sound, and Specification

SOUND TRANSMISSION BETWEEN FLOORS IN LONDON RESIDENTIAL BUILDINGS OCCURS IN TWO DISTINCT PATHWAYS — IMPACT AND AIRBORNE — AND THE TREATMENT REQUIRED FOR EACH IS DIFFERENT.

IMPACT NOISE (STRUCTURE-BORNE SOUND): IMPACT NOISE IS GENERATED WHEN AN OBJECT STRIKES THE FLOOR SURFACE — FOOTSTEPS (THE DOMINANT SOURCE IN LONDON FLAT CONVERSIONS), DROPPED OBJECTS, CHILDREN RUNNING, CHAIR SCRAPING. THE IMPACT ENERGY IS TRANSFERRED DIRECTLY INTO THE FLOOR STRUCTURE AND RADIATES AS SOUND INTO THE ROOM BELOW. IMPACT NOISE IS MEASURED AS THE NORMALISED IMPACT SOUND PRESSURE LEVEL (L'NT) — A LOWER L'NT VALUE MEANS LESS IMPACT NOISE TRANSMISSION (BETTER PERFORMANCE). PART E REQUIREMENT FOR CONVERSIONS (EXISTING BUILDINGS): L'NT,W + CI ≤ 61 DB (MAXIMUM WEIGHTED IMPACT SOUND PRESSURE LEVEL). FOR NEW BUILD FLOORS: L'NT,W ≤ 62 DB.

AIRBORNE SOUND (SOUND WAVES TRANSMITTED THROUGH THE AIR THEN INTO THE STRUCTURE): AIRBORNE SOUND IS GENERATED BY VOICES, TV, MUSIC, AND ANY OTHER SOURCE THAT CREATES SOUND WAVES IN THE AIR. THESE WAVES CAUSE THE FLOOR/CEILING CONSTRUCTION TO VIBRATE, AND THE VIBRATION IS RE-RADIATED AS SOUND ON THE OTHER SIDE. AIRBORNE SOUND IS MEASURED AS THE WEIGHTED SOUND REDUCTION INDEX (RW) OR MEASURED IN SITU AS DNT,W. PART E REQUIREMENT FOR FLOORS IN CONVERSIONS: DNT,W + CTR ≥ 43 DB. FOR NEW BUILDS: DW ≥ 45 DB.

WHY VICTORIAN TIMBER FLOORS FAIL BOTH CRITERIA: ORIGINAL VICTORIAN TIMBER FLOOR CONSTRUCTION (38MM T&G FLOORBOARDS ON 225MM X 50MM JOISTS AT 400MM CENTRES, LATH AND PLASTER CEILING BELOW) TYPICALLY ACHIEVES: IMPACT: L'NT ≈ 75 TO 85 DB (SIGNIFICANTLY ABOVE THE 61 DB TARGET — VERY HIGH IMPACT NOISE TRANSMISSION). AIRBORNE: DW ≈ 35 TO 45 DB (OFTEN BELOW THE 43 DB TARGET — SIGNIFICANT AIRBORNE SOUND TRANSMISSION). THE ORIGINAL VICTORIAN FLOOR CONSTRUCTION IN LONDON PROPERTIES REQUIRES SUBSTANTIAL ACOUSTIC TREATMENT TO MEET PART E.

PART E OF THE BUILDING REGULATIONS (RESISTANCE TO THE PASSAGE OF SOUND) APPLIES TO NEW DWELLINGS, MATERIAL CHANGE OF USE (INCLUDING CONVERSION OF A HOUSE INTO FLATS — THE MOST COMMON SCENARIO IN LONDON), AND MATERIAL ALTERATIONS.

KEY PART E TRIGGERS IN LONDON RENOVATION: CONVERSION OF A VICTORIAN TERRACE INTO FLATS: THE FLOOR BETWEEN THE CONVERTED FLATS MUST MEET PART E PERFORMANCE TARGETS. THIS IS THE MOST FREQUENTLY TRIGGERED PART E REQUIREMENT IN LONDON RENOVATION. ALL FLOOR/CEILING SEPARATING ELEMENTS BETWEEN DIFFERENT DWELLINGS (EVEN IF THE HOUSE IS BEING CONVERTED TO ONLY TWO FLATS — GROUND FLOOR AND UPPER FLOORS) MUST BE TESTED AND CERTIFIED. NEW ROOM ABOVE EXISTING HABITABLE ROOM (LOFT CONVERSION — WHEN ADDING A NEW HABITABLE ROOM ABOVE AN EXISTING BEDROOM OR LIVING ROOM): THE NEW FLOOR BETWEEN THE LOFT AND THE ROOMS BELOW IS A SEPARATING FLOOR AND MUST MEET PART E TARGETS. TESTING: PART E COMPLIANCE MUST BE DEMONSTRATED EITHER BY FOLLOWING A ROBUST STANDARD DETAIL (PRE-APPROVED CONSTRUCTION TYPE FROM THE PART E APPROVED DOCUMENT) OR BY COMMISSIONING AN ACOUSTIC TEST (SOUND INSULATION TEST BY AN ACCREDITED ACOUSTIC CONSULTANT — COST £400 TO £900 PER TEST).

ROBUST STANDARD DETAILS (RSDs): THE PART E APPROVED DOCUMENT INCLUDES APPROVED CONSTRUCTION DETAILS (ROBUST STANDARD DETAILS) FOR FLOORS. IF THE FLOOR IS BUILT EXACTLY TO ONE OF THESE DETAILS, AN ACOUSTIC TEST IS NOT REQUIRED — COMPLIANCE IS ASSUMED. THE RSD APPROACH IS WIDELY USED IN LONDON FLAT CONVERSIONS TO AVOID THE COST AND PROGRAMME RISK OF PRE-COMPLETION TESTING.

THE ACOUSTIC TREATMENT APPROACH FOR A LONDON VICTORIAN TIMBER FLOOR DEPENDS ON WHETHER WORKS ARE BEING DONE FROM ABOVE (FLOOR TREATMENT) OR FROM BELOW (CEILING TREATMENT) OR BOTH.

FLOOR TREATMENT (FROM ABOVE): THE MOST EFFECTIVE APPROACH FOR IMPACT NOISE IS TO ADD A RESILIENT LAYER BETWEEN THE FLOOR FINISH AND THE STRUCTURAL FLOOR DECK — DECOUPLING THE SURFACE FROM THE STRUCTURE.

REGUPOL ACOUSTIC 4515 (ONE OF THE MOST WIDELY SPECIFIED RESILIENT UNDERLAYS FOR LONDON FLAT CONVERSION ACOUSTIC FLOORS): REGUPOL 4515 IS A 15MM THICK RECYCLED RUBBER RESILIENT LAYER (MADE FROM RECYCLED TYRES) LAID ACROSS THE ENTIRE FLOOR SURFACE BELOW THE STRUCTURAL OVERLAY DECK. THE OVERLAY DECK (22MM TONGUE-AND-GROOVE CHIPBOARD OR PLYWOOD) IS LAID ON TOP OF THE REGUPOL AND ACTS AS THE STRUCTURAL BASE FOR THE FINAL FLOOR FINISH. THE REGUPOL 4515 PROVIDES IMPACT SOUND REDUCTION OF APPROXIMATELY 17 TO 22 DB (ΔLW) — THE SINGLE BIGGEST IMPACT NOISE REDUCTION FROM A SINGLE PRODUCT.

FERMACELL ACOUSTIC FLOOR SYSTEM (GYPSUM FIBRE BOARDS ON FERMACELL ACOUSTIC ELEMENTS): FERMACELL ACOUSTIC FLOOR ELEMENT IS A GYPSUM FIBRE BOARD WITH AN INTEGRAL RESILIENT POLYSTYRENE UNDERLAY — LAID OVER EXISTING FLOORBOARDS OR PLYWOOD SUBFLOOR. THE SYSTEM PROVIDES BOTH IMPACT AND AIRBORNE SOUND REDUCTION AND IS SUITABLE AS A DRY FLOOR ACOUSTIC TREATMENT WITHOUT SCREED. FERMACELL FLOOR ELEMENT 22MM (2E12) ON FERMACELL ACOUSTIC ELEMENT PROVIDES ΔLWT 17 TO 21 DB IMPACT SOUND REDUCTION.

FLOATING SCREED ON RESILIENT LAYER: A SAND-CEMENT OR ANHYDRITE SCREED (65MM MINIMUM) LAID ON A RESILIENT LAYER (ISOVER ACOUSTIC FLOOR SLAB OR REGUPOL RESILIENT LAYER) IS THE MOST EFFECTIVE SINGLE MEASURE FOR BOTH AIRBORNE AND IMPACT SOUND REDUCTION IN A LONDON FLAT CONVERSION FLOOR. THE MASS OF THE SCREED (APPROXIMATELY 130 KG/M² FOR 65MM SAND-CEMENT SCREED) SIGNIFICANTLY REDUCES AIRBORNE SOUND TRANSMISSION. THE RESILIENT LAYER DECOUPLES THE SCREED FROM THE STRUCTURAL FLOOR, REDUCING IMPACT SOUND TRANSMISSION.

CEILING TREATMENT (FROM BELOW) IS USED WHERE FLOOR TREATMENT FROM ABOVE IS NOT POSSIBLE OR NOT SUFFICIENT — AND IS PARTICULARLY RELEVANT FOR LONDON FLAT CONVERSIONS WHERE THE UPPER FLAT IS ALREADY OCCUPIED AND THE WORKS MUST BE DONE FROM THE FLAT BELOW.

INDEPENDENT CEILING (THE MOST EFFECTIVE CEILING TREATMENT FOR LONDON FLAT CONVERSIONS): AN INDEPENDENT CEILING IS CONSTRUCTED ENTIRELY SEPARATELY FROM THE EXISTING FLOOR STRUCTURE — TYPICALLY USING A NEW SET OF CEILING JOISTS (C24 47MM X 70MM OR 47MM X 95MM) FIXED TO THE WALLS BELOW THE EXISTING FLOOR JOISTS, WITH MINERAL WOOL ACOUSTIC QUILT (KNAUF ACOUSTIC QUILT 50MM OR ROCKWOOL FLEXI SLAB 75MM) DRAPED BETWEEN THE CEILING JOISTS, AND 12.5MM + 12.5MM DOUBLE LAYER PLASTERBOARD FIXED TO THE CEILING JOISTS. THE CRITICAL FEATURE IS THAT THE INDEPENDENT CEILING JOISTS MUST NOT TOUCH THE EXISTING FLOOR JOISTS ABOVE — ANY DIRECT CONTACT (EVEN AT WALL PLATES) CREATES A FLANKING PATH THAT BYPASSES THE ACOUSTIC ISOLATION.

RESILIENT BAR CEILING (LESS EFFECTIVE THAN INDEPENDENT CEILING BUT EASIER TO CONSTRUCT IN TIGHT SPACES): WHERE THERE IS INSUFFICIENT ROOM TO FIT AN INDEPENDENT CEILING (E.G. WHERE CEILING HEIGHT IS ALREADY LOW IN A VICTORIAN GROUND-FLOOR FLAT), RESILIENT METAL FURRING CHANNELS (BRITISH GYPSUM RESILIENT BAR OR SINIAT WAB RESILIENT CHANNEL) ARE FIXED AT 400MM CENTRES ACROSS THE EXISTING CEILING JOISTS WITH 12.5MM + 12.5MM DOUBLE PLASTERBOARD. THE RESILIENT BARS PROVIDE A DEGREE OF VIBRATION ISOLATION BETWEEN THE FLOOR STRUCTURE AND THE NEW PLASTERBOARD CEILING. LESS EFFECTIVE THAN AN INDEPENDENT CEILING FOR IMPACT SOUND BUT SIGNIFICANTLY BETTER THAN DIRECT-FIX DOUBLE PLASTERBOARD.

FOR A TYPICAL LONDON VICTORIAN TERRACE FLAT CONVERSION (CONVERTING A 3-STOREY VICTORIAN HOUSE INTO 2 OR 3 FLATS), THE COMBINED FLOOR AND CEILING TREATMENT APPROACH IS NORMALLY REQUIRED TO RELIABLY MEET PART E TARGETS.

TYPICAL COMBINED SPECIFICATION (MEETING PART E ROBUST STANDARD DETAILS FOR EXISTING TIMBER FLOOR): FROM ABOVE (UPPER FLAT): LIFT EXISTING FLOORBOARDS. INFILL JOIST BAYS WITH 100MM ROCKWOOL SOUND INSULATION BATTS (RESTING ON TOP OF EXISTING CEILING PLASTERBOARD BELOW — NOT COMPRESSING IT). RELAY 22MM T&G CHIPBOARD OR PLYWOOD OVERLAY ON REGUPOL 4515 RESILIENT LAYER (LAY REGUPOL FIRST, THEN OVERLAY — CHIPBOARD OR PLY MUST FLOAT ON REGUPOL, NOT FIXED TO JOISTS). FINAL FLOOR FINISH (ENGINEERED TIMBER, LVT, OR CARPET WITH PREMIUM UNDERLAY) OVER CHIPBOARD.

FROM BELOW (LOWER FLAT CEILING): INDEPENDENT CEILING FRAME (47MM X 70MM C24 JOISTS AT 400MM CENTRES ON WALL-MOUNTED NOGGINS — NOT TOUCHING EXISTING FLOOR JOISTS). ROCKWOOL ACOUSTIC QUILT 50MM OR KNAUF ACOUSTIC QUILT DRAPED BETWEEN INDEPENDENT CEILING JOISTS. DOUBLE LAYER BRITISH GYPSUM WALLBOARD 12.5MM + BRITISH GYPSUM SOUNDBLOC 12.5MM (TWO LAYERS, STAGGERED JOINTS).

ACHIEVED PERFORMANCE (TYPICAL): COMBINED SYSTEM ABOVE TYPICALLY ACHIEVES: DW (AIRBORNE): 52 TO 58 DB — WELL ABOVE PART E 43 DB MINIMUM. L'NT (IMPACT): 48 TO 58 DB — BELOW (BETTER THAN) PART E 61 DB MAXIMUM.

ACOUSTIC FLOOR AND CEILING TREATMENT COSTS IN LONDON DEPEND ON SYSTEM TYPE, FLOOR AREA, AND WHETHER WORKS ARE DONE FROM ABOVE, BELOW, OR BOTH.

FLOOR TREATMENT FROM ABOVE (REGUPOL 4515 + 22MM CHIPBOARD OVERLAY, MATERIALS SUPPLY PER M²): REGUPOL 4515 15MM RESILIENT LAYER: £12 TO £18 PER M² SUPPLY. 22MM T&G CHIPBOARD: £8 TO £12 PER M² SUPPLY. TOTAL MATERIALS: £20 TO £30 PER M². INSTALLATION (LIFT EXISTING BOARDS, LAY ROCKWOOL INFILL, LAY REGUPOL AND CHIPBOARD OVERLAY): £25 TO £45 PER M².

CEILING TREATMENT (INDEPENDENT CEILING — MATERIALS AND INSTALL PER M²): INDEPENDENT CEILING JOISTS, ROCKWOOL QUILT, DOUBLE PLASTERBOARD, PLASTER SKIM, REDECORATION: £60 TO £100 PER M² INSTALLED.

COMBINED FLOOR AND CEILING TREATMENT (FULL ACOUSTIC PACKAGE — SUPPLY AND INSTALL BOTH): £100 TO £180 PER M² FOR THE COMBINED SYSTEM.

TYPICAL LONDON FLAT CONVERSION SEPARATING FLOOR (60 M² FLOOR AREA): FLOOR TREATMENT FROM ABOVE: £2,700 TO £4,500. INDEPENDENT CEILING BELOW: £3,600 TO £6,000. TOTAL COMBINED: £6,300 TO £10,500 FOR ONE SEPARATING FLOOR. ACOUSTIC TEST (TO DEMONSTRATE PART E COMPLIANCE): £400 TO £900 PER TEST. TESTING IS REQUIRED WHERE THE CONSTRUCTION IS NOT A LISTED ROBUST STANDARD DETAIL.