Acoustic Insulation and Soundproofing for London Victorian Homes: Impact Noise, Airborne Noise, and Party Wall Solutions

ACOUSTIC PERFORMANCE IN BUILDINGS IS MEASURED IN TWO DISTINCT WAYS THAT ADDRESS DIFFERENT PATHS OF SOUND TRANSMISSION.

AIRBORNE SOUND (RW — WEIGHTED SOUND REDUCTION INDEX): AIRBORNE SOUND IS PRODUCED BY A VIBRATING AIR COLUMN — SPEECH, MUSIC, TELEVISION, TRAFFIC. IT TRAVELS THROUGH THE AIR AND IS TRANSMITTED THROUGH WALLS AND FLOORS BY CAUSING THE STRUCTURE TO VIBRATE. THE RW (OR DnT,W IN FIELD MEASUREMENT TERMS — STANDARDISED LEVEL DIFFERENCE) IS THE METRIC USED TO QUANTIFY HOW MUCH AIRBORNE SOUND A PARTITION REDUCES. A HIGHER RW VALUE MEANS BETTER SOUND ATTENUATION. BUILDING REGULATIONS PART E REQUIRES A MINIMUM AIRBORNE PERFORMANCE OF RW 45 DB (WALLS) AND RW 43 DB (FLOORS BETWEEN FLATS IN A CONVERSION) FOR SEPARATING ELEMENTS IN CONVERTED DWELLINGS.

IMPACT SOUND (LN,W — WEIGHTED NORMALISED IMPACT SOUND PRESSURE LEVEL): IMPACT SOUND IS CAUSED BY DIRECT PHYSICAL CONTACT WITH THE STRUCTURE — FOOTSTEPS, DROPPED OBJECTS, CHAIR MOVEMENT. IMPACT SOUND TRAVELS THROUGH THE STRUCTURE ITSELF (STRUCTURE-BORNE SOUND) RATHER THAN THROUGH THE AIR. THE LN,W (OR L'NT,W IN FIELD MEASUREMENT) IS THE METRIC FOR IMPACT PERFORMANCE — UNLIKE AIRBORNE SOUND, A LOWER LN,W VALUE MEANS BETTER PERFORMANCE (LESS IMPACT NOISE TRANSMITTED). BUILDING REGULATIONS PART E REQUIRES A MAXIMUM IMPACT NOISE LEVEL OF LN,W 62 DB FOR FLOORS BETWEEN FLATS IN A CONVERSION.

IN PRACTICE: LONDON PARTY WALLS (TYPICALLY 225MM SOLID BRICK OR 275MM CAVITY BRICK) HAVE INHERENT AIRBORNE SOUND PERFORMANCE WELL ABOVE THE RW 45 DB PART E MINIMUM FOR WALLS (TYPICALLY RW 50 TO 55 DB) — THE MASS OF THE SOLID BRICK PROVIDES GOOD AIRBORNE ATTENUATION. THE PROBLEM IS LOW-FREQUENCY TRANSMISSION AND FLANKING PATHS (SOUND TRAVELLING VIA THE FLOOR STRUCTURE OR CEILING RATHER THAN DIRECTLY THROUGH THE WALL). FOR FLOORS, VICTORIAN TIMBER JOIST CONSTRUCTION (75X200MM JOISTS AT 400MM CENTRES WITH FLOORBOARDS ABOVE AND LATH-AND-PLASTER CEILING BELOW) TYPICALLY HAS AN AIRBORNE PERFORMANCE OF RW 35 TO 40 DB AND IMPACT PERFORMANCE OF LN,W 80 TO 90 DB — SIGNIFICANTLY BELOW THE PART E REQUIREMENTS FOR A CONVERSION.

THE MOST EFFECTIVE WAY TO IMPROVE BOTH AIRBORNE AND IMPACT SOUND PERFORMANCE OF AN EXISTING TIMBER JOIST FLOOR IS TO COMBINE A FLOATING FLOOR SYSTEM ABOVE THE STRUCTURE WITH AN INDEPENDENTLY SUSPENDED CEILING BELOW.

FLOATING FLOOR SYSTEMS (IMPACT SOUND TREATMENT FROM ABOVE): A FLOATING FLOOR SYSTEM DECOUPLES THE WALKING SURFACE FROM THE STRUCTURAL FLOOR, REDUCING IMPACT TRANSMISSION. THE MAIN SYSTEM TYPES ARE:

DRY FLOATING FLOOR (REGUPOL 4515 OR ACOUSTILAY 28DB): REGUPOL 4515 IS A 15MM THICK COMPOSITE RESILIENT LAYER (RECYCLED RUBBER GRANULES + PUR BINDER) THAT IS LAID OVER THE EXISTING STRUCTURAL FLOOR BOARDING, WITH 18MM OR 22MM TONGUE-AND-GROOVE CHIPBOARD (OR 18MM CABERDEK FLOORING) LAID ON TOP AND GLUED AT ALL JOINTS. THE REGUPOL LAYER PROVIDES ISOLATION FOR FOOTSTEP VIBRATIONS — IMPACT IMPROVEMENT APPROXIMATELY DELTA LW OF 22 TO 28 DB. ACOUSTILAY 28DB (RECYCLED RUBBER 5MM + EVA FOAM 5MM COMPOSITE) IS A THINNER ALTERNATIVE WHERE FLOOR HEIGHT LOSS IS CRITICAL.

WET FLOATING SCREED SYSTEM: HIGHER PERFORMANCE AND BETTER MASS FOR AIRBORNE ATTENUATION. ISOVER APR 1200 ACOUSTIC FLOOR SLAB (50MM THICKNESS, 30KG/M' RIGID MINERAL WOOL) OR ROCKWOOL FLEXI (50MM, 40KG/M') LAID OVER THE STRUCTURAL FLOOR DECK, COVERED WITH 75MM SAND-CEMENT SCREED (MINIMUM) ON A DPM (DAMP-PROOF MEMBRANE). THE SCREED MUST BE CUT FREE FROM THE WALLS ON ALL SIDES (ACOUSTIC QUILT PERIMETER UPSTAND TO PREVENT FLANKING) AND FROM THE STRUCTURAL FLOOR BELOW. COMBINED WITH A CEILING TREATMENT, A WET FLOATING SCREED SYSTEM CAN ACHIEVE PART E COMPLIANCE IN MOST LONDON FLAT CONVERSIONS.

INDEPENDENT CEILING (RESILIENT BAR CEILING): THE MOST EFFECTIVE CEILING TREATMENT FOR AIRBORNE AND IMPACT SOUND IS AN INDEPENDENTLY SUSPENDED CEILING ON RESILIENT BARS. RESIBAR (KNAUF), ACOUSTIC HANGER (ISOVER), OR GENIE CLIP (NOISESTOP SYSTEMS) METAL BARS ARE SPRING-MOUNTED AND FIXED TO THE UNDERSIDE OF THE STRUCTURAL JOISTS. 25MM ROCKWOOL RWA45 OR ISOVER APR 1200 ACOUSTIC MINERAL WOOL IS LAID BETWEEN THE JOISTS IN THE VOID. TWO LAYERS OF 12.5MM BRITISH GYPSUM SOUNDBLOC PLASTERBOARD (TOTAL 25MM) ARE SCREWED TO THE RESILIENT BARS. THE SPRING-MOUNT DECOUPLING PREVENTS STRUCTURAL VIBRATIONS FROM BEING DIRECTLY TRANSMITTED TO THE CEILING PLASTERBOARD.

WHERE AIRBORNE SOUND THROUGH A PARTY WALL IS AN ISSUE (NEIGHBOURS' TELEVISION, MUSIC, CONVERSATION), A WALL LINING SYSTEM ON THE INNER FACE OF THE PARTY WALL CAN IMPROVE PERFORMANCE — BUT MUST BE DONE CORRECTLY TO BE EFFECTIVE.

CEMENT-BASED ACOUSTIC SYSTEMS ARE INEFFECTIVE AT LOW FREQUENCIES. MASS ALONE DOES NOT ADDRESS LOW-FREQUENCY TRANSMISSION — WHILE ADDING MASS (EXTRA PLASTERBOARD LAYERS) IMPROVES AIRBORNE PERFORMANCE AT HIGHER FREQUENCIES (ABOVE 500 HZ), IT HAS MINIMAL EFFECT ON LOW BASS FREQUENCIES BELOW 125 HZ WHERE THE PARTY WALL COINCIDES WITH A RESONANT FREQUENCY.

RESILIENT WALL LINING APPROACH (NOISESTOP, QUIETZONE, ISOVER): THE EFFECTIVE WAY TO IMPROVE PARTY WALL AIRBORNE PERFORMANCE IS TO DECOUPLE THE WALL LINING FROM THE PARTY WALL STRUCTURE. THIS IS ACHIEVED USING:

METHOD 1 — INDEPENDENT STUD WALL: A NEW STEEL STUD FRAME (50X50MM CW STUD AT 600MM CENTRES) IS ERECTED 25 TO 50MM AWAY FROM THE PARTY WALL FACE (NOT TOUCHING THE WALL). ROCKWOOL RWA45 (100MM BATT) IS PLACED IN THE CAVITY BETWEEN THE PARTY WALL AND THE STUD. 2 LAYERS OF 12.5MM SOUNDBLOC PLASTERBOARD ARE FIXED TO THE STUD, AND THE PERIMETER IS SEALED WITH ACOUSTIC SEALANT (TREMCO ACOUSTICAL SEALANT, ISOVER ACOUSTIC SEALANT, OR SIKAFLEX 11FC+) AT ALL JUNCTIONS WITH ADJACENT SURFACES. THIS SYSTEM PROVIDES AN IMPROVEMENT OF APPROXIMATELY RW +10 TO +15 DB COMPARED TO THE BARE PARTY WALL — HIGHLY EFFECTIVE BUT LOSES 75 TO 100MM OF ROOM DEPTH.

METHOD 2 — RESILIENT ACOUSTIC FRAME (INDEPENDENT LEAF WITH MINERAL WOOL CAVITY): NOISESTOP S20 SYSTEM — A PROPRIETARY RESILIENT METAL FRAME SYSTEM THAT CREATES A DECOUPLED LEAF WITH A 100MM ROCKWOOL RWA45 ACOUSTIC FILL AND DOUBLE SOUNDBLOC PLASTERBOARD FINISH AT ONLY 75MM TOTAL DEPTH. TEST PERFORMANCE DnT,W = 55 DB (AIRBORNE) FROM A 225MM SOLID BRICK PARTY WALL BASE.

WARNING: DIRECT FIXING OF PLASTERBOARD TO THE PARTY WALL SURFACE (ACOUSTIC DOT-AND-DAB) WITH MINERAL WOOL ACOUSTIC QUILT SIMPLY LAID BEHIND IS NOT AN EFFECTIVE ACOUSTIC TREATMENT — IT PROVIDES MINIMAL SOUND REDUCTION AND WASTES THE COST OF THE MINERAL WOOL. THE DECOUPLING PRINCIPLE IS THE CRITICAL PERFORMANCE FACTOR.

THE TWO MAIN ACOUSTIC MINERAL WOOL PRODUCTS USED IN UK RESIDENTIAL ACOUSTIC SYSTEMS ARE ROCKWOOL RWA45 AND ISOVER APR 1200.

ROCKWOOL RWA45 (ROCK MINERAL WOOL, 45KG/M' DENSITY): THE UK MARKET STANDARD FOR ACOUSTIC CAVITY FILL IN WALL AND FLOOR SYSTEMS. AVAILABLE IN 50MM AND 100MM BATTS IN STANDARD WIDTH OF 600MM (TO FIT 600MM STUD CENTRES) AND 1200MM. THE 45KG/M' DENSITY GIVES GOOD FLOW RESISTANCE (WHICH DETERMINES ACOUSTIC ABSORPTION PERFORMANCE) — LOWER DENSITY MINERAL WOOL (15KG/M' STANDARD GLASS WOOL FOR THERMAL INSULATION) HAS INSUFFICIENT FLOW RESISTANCE FOR EFFECTIVE ACOUSTIC USE. KEY SPECIFICATION: ALWAYS USE ACOUSTIC-SPECIFIC MINERAL WOOL (MINIMUM 45KG/M' FOR WALLS; MINIMUM 60KG/M' FOR FLOORS) AND NOT STANDARD THERMAL INSULATION PRODUCTS.

ISOVER APR 1200 (GLASS MINERAL WOOL, 12KG/M' DENSITY, SPECIFICALLY DESIGNED FOR ACOUSTIC APPLICATIONS): APR 1200 IS A HIGH-PERFORMANCE GLASS MINERAL WOOL DESIGNED SPECIFICALLY FOR ACOUSTIC APPLICATIONS, WITH A UNIQUE FINE-FIBRE STRUCTURE THAT PROVIDES VERY HIGH FLOW RESISTANCE AT RELATIVELY LOW DENSITY. ISOVER APR 1200 HAS A FLOW RESISTANCE RATING (SIGMA IN NS/M') COMPARABLE TO MUCH DENSER ROCKWOOL PRODUCTS. APR 1200 IS AVAILABLE IN 50MM AND 100MM SLABS AND IS THE PREFERRED PRODUCT FOR LIGHTWEIGHT PARTITION ACOUSTIC SYSTEMS.

PRACTICAL GUIDANCE: FOR WALL LININGS AND PARTITIONS — ROCKWOOL RWA45 100MM OR ISOVER APR 1200 100MM ARE BOTH APPROPRIATE. FOR FLOOR VOIDS (BETWEEN JOISTS) — ROCKWOOL RWA45 50MM IS THE STANDARD SPECIFICATION TO IMPROVE AIRBORNE SOUND PERFORMANCE WITHOUT ADDING EXCESSIVE WEIGHT TO AN ALREADY-LOADED TIMBER JOIST FLOOR. FOR SCREED FLOATING FLOOR SYSTEMS — ISOVER APR 1200 OR ROCKWOOL FLEXI 50MM IS USED AS THE ISOLATION LAYER BENEATH THE SCREED.

BUILDING REGULATIONS APPROVED DOCUMENT E (RESISTANCE TO THE PASSAGE OF SOUND) APPLIES TO ALL DWELLINGS IN ENGLAND AND WALES. FOR MATERIAL CHANGES OF USE (E.G., CONVERTING A HOUSE INTO FLATS) AND CONVERSIONS, PART E REQUIRES THAT ALL NEW SEPARATING ELEMENTS (WALLS AND FLOORS BETWEEN DWELLINGS) ACHIEVE MINIMUM ACOUSTIC PERFORMANCE.

PART E MINIMUM STANDARDS FOR CONVERSIONS (MATERIAL CHANGES OF USE):

SEPARATING WALLS (DnT,W + CTR IN FIELD TEST): MINIMUM DnT,W + CTR = 43 DB. NOTE: THE CTR CORRECTION TERM IS A SPECTRUM ADAPTATION TERM FOR LOW-FREQUENCY NOISE — WHERE MUSIC AND BASS IS A CONCERN, THE +CTR VERSION OF THE STANDARD IS MORE DEMANDING THAN THE HEADLINE DnT,W FIGURE.

SEPARATING FLOORS — AIRBORNE (DnT,W + CTR): MINIMUM DnT,W + CTR = 43 DB.

SEPARATING FLOORS — IMPACT (L'NT,W): MAXIMUM L'NT,W = 64 DB.

ACOUSTIC PRE-COMPLETION TESTING: UNLIKE THERMAL (SAP) TESTING WHERE AN APPROVED DOCUMENT CALCULATION SHOWS COMPLIANCE, PART E PERFORMANCE MUST BE DEMONSTRATED BY IN-SITU ACOUSTIC FIELD TESTS ON COMPLETION OF THE WORKS. AN ACCREDITED ACOUSTIC TESTER (MEMBER OF THE ASSOCIATION OF NOISE CONSULTANTS — ANC, OR USING UKAS ACCREDITED TEST EQUIPMENT) CARRIES OUT THE TESTS WITH A CALIBRATED LOUDSPEAKER AND MICROPHONE ARRAY. IF THE TESTS FAIL, THE WORKS MUST BE IMPROVED AND RE-TESTED. BUILDING CONTROL WILL NOT ISSUE A COMPLETION CERTIFICATE FOR A CONVERSION WITHOUT PASSING ACOUSTIC FIELD TEST RESULTS.

ACOUSTIC INSULATION COSTS IN LONDON DEPEND SIGNIFICANTLY ON THE SYSTEM SELECTED, THE ACCESS CONDITIONS, AND WHETHER WORKS ARE PART OF A WIDER RENOVATION OR A STANDALONE ACOUSTIC UPGRADE.

FLOOR ACOUSTIC SYSTEM (FLOATING FLOOR — REGUPOL 4515 + 22MM T&G CHIPBOARD, EXISTING FLOOR BOARDED SURFACE AS SUBSTRATE, PER M'): £45 TO £75 PER M' SUPPLY AND FIT. FOR A TYPICAL LONDON TERRACE BEDROOM (15M'): £675 TO £1,125.

FLOOR ACOUSTIC SYSTEM (FLOATING SCREED — ISOVER APR 1200 50MM + 75MM SAND-CEMENT SCREED, PER M'): £85 TO £130 PER M' SUPPLY AND FIT, EXCLUDING DEMOLITION OF EXISTING FLOOR FINISH. FOR A 15M' ROOM: £1,275 TO £1,950.

RESILIENT BAR CEILING SYSTEM (KNAUF RESIBAR + ROCKWOOL RWA45 IN VOID + DOUBLE SOUNDBLOC, PER M'): £55 TO £90 PER M' SUPPLY AND FIT. FOR A 15M' CEILING: £825 TO £1,350.

INDEPENDENT STUD PARTY WALL LINING (50MM CW STUD + ROCKWOOL RWA45 100MM + DOUBLE SOUNDBLOC, INCLUDING STRIPPING EXISTING PLASTER, PER LINEAR METRE OF WALL AT 2.4M CEILING HEIGHT): £120 TO £200 PER LINEAR METRE OF WALL. FOR A 5M WIDE ROOM: £600 TO £1,000.

ACOUSTIC PRE-COMPLETION TESTING (FIELD TEST BY ANC-ACCREDITED TESTER, AIRBORNE AND IMPACT): £300 TO £600 FOR A STANDARD FLAT CONVERSION WITH TWO TEST JUNCTIONS.