Will lagging make the pipe silent?

No, but the reduction is large. The general figure from lagging practice is around 10 to 15 dB for a properly fitted and sealed wool-plus-MLV system. A realistic target is turning a rush that wakes you into a faint sound that does not.

Can I wrap MLV straight onto the pipe without wool?

You can, but it performs far worse, because the sheet vibrates with the pipe. The 25 to 50 mm wool layer between pipe and sheet is what makes the system work, and it is available at any builders’ merchant.

Is foam or wool on its own enough?

No. Foam and wool are light and cannot block sound; their job here is to decouple the sheet from the pipe. The layer that blocks the sound is the MLV, at about 5 kg/m².

The noise is the flush from the unit above. Can I fix it from mine?

You can treat the length of stack that runs through your shaft, which is usually most of the problem. Noise from the toilet, the flush valve or water hammer in the supply has to be dealt with at source, upstairs.

How many rolls do I need?

A 110 mm pipe with 50 mm wool takes about 0.72 m of sheet width per metre of pipe, so one 5 m² roll lags about 6 m — one or two stacks in a typical shaft. To test first, the 1 m² trial piece lags about 1 m.

Yes, in Bangkok. If you collect, it is ready within 1 working day of cleared payment. If we deliver, you will typically have it in 3–5 working days.

Soundproofing drain pipes and ducts: lagging with mass loaded vinyl

Why the pipe is loud

In most Thai condominiums the soil and waste stacks are thin-wall uPVC, run vertically inside a boxed shaft closed with a single layer of plasterboard or fibre-cement, and the shaft is very often against the bedroom. Water dropping down the stack sets the pipe wall vibrating and it radiates sound; a thin, unsealed shaft board passes nearly all of it into the room. The result is the familiar rush every time the unit above uses the bathroom.

The energy sits mostly in the middle frequencies, roughly 250 to 2,000 Hz, which is exactly where adding mass to a radiating surface works well. Compared with footfall or a subwoofer through a party wall, this is one of the more tractable noise problems in a condominium and one of the cheaper ones to fix.

What you hear, the likely source, and what actually fixes it
Symptom	Source	Fix
Rushing water along the shaft whenever the unit above drains	Pipe wall radiating	Lag the pipe, or line the inside of the shaft board
A thump when a tap closes or after a flush	Water hammer in the supply, or the flush valve	Plumbing at source; lagging helps only marginally
Louder at the edge of the shaft panel and around the floor penetration	Unsealed gaps and sleeves	Seal first with a flexible acoustic sealant
Vibration you can feel in the wall or floor	Rigid pipe clamps to the structure	Resilient (rubber-lined) clamps; lagging will not help
Air rush from a duct above the ceiling	Duct wall breakout	Lag the first 3 to 5 m from the fan unit

The two-layer principle

Wrapping MLV directly onto the pipe underperforms, because the sheet simply vibrates with the pipe. The system that works is two layers: a soft, resilient inner layer of 25 to 50 mm glass or mineral wool that decouples the sheet from the pipe and absorbs sound in the gap, and a heavy, limp outer layer of MLV that provides the mass. Mass on a spring, with the pipe as the source.

As a general figure from lagging practice — not a manufacturer value — a properly fitted and sealed wool-plus-MLV lagging reduces radiated pipe noise by around 10 to 15 dB, which is the difference between a rush that wakes you and a faint sound you have to listen for. On site, the result depends mainly on how well the ends and penetrations are sealed.

The lagging system and where each part comes from
Layer	Material	Function	Source
Inner	25–50 mm glass or mineral wool, roll form	Decouples the sheet, absorbs in the gap	Any builders’ merchant
Outer	BlastBlock BB830 MLV, nominally 5 kg/m² at about 3 mm	Mass barrier	IAC Acoustics (Thailand)
Seams	Aluminium foil tape, 50 mm or wider	Closes the longitudinal seam	Any builders’ merchant
Fixing	Cable ties or wire, every 300 mm	Holds the sheet tight	Any builders’ merchant
Ends and penetrations	BA890 acoustic sealant	Seals the lagging ends and the sleeves	IAC Acoustics (Thailand)

How much MLV you need

BB830 is supplied in rolls 1 m wide and 5 m long, 5 m² per roll. Measure the circumference of the pipe after the wool is on, add a 50 mm overlap, and that is the width of sheet per metre of pipe. The table below is worked for the common sizes with 50 mm wool.

Pipe length lagged per roll of MLV (50 mm wool, 50 mm overlap)
Pipe	Sheet width per metre of pipe	Per 5 m² roll	Per 1 m² trial piece
110 mm uPVC	about 0.72 m	about 6 m	about 1 m
160 mm uPVC	about 0.87 m	about 5 m	about 1 m
300 × 300 mm duct	about 1.65 m	about 3 m	not enough

A stack inside one unit’s shaft is typically 2.5 to 3 m per floor, so one roll covers one or two stacks. If you want proof before ordering rolls, the 1 m² trial piece lags about 1 m of the loudest section — enough to hear the difference.

Method

Open the shaft panel and confirm the pipe wall is the source, not a rigid clamp or an open sleeve, using the table above.
Pack and seal every sleeve where the pipe passes through floor and ceiling with BA890 before anything else.
Wrap 25 to 50 mm wool snugly around the pipe without compressing it; hold with wire or ties.
Cut the MLV to the width in the table, wrap it firmly over the wool with a 50 mm longitudinal overlap, and put the seam on the side facing the wall, not the room.
Tape the longitudinal seam with aluminium foil tape. Overlap successive pieces along the pipe by 50 mm and tape those too.
Fix with cable ties every 300 mm and at every sheet end.
Seal the top and bottom ends of the lagging with BA890, carrying the MLV to the slab and soffit where access allows.
Replace the shaft panel and seal its perimeter with BA890 before making good.

Ducts

Duct noise comes in two forms and they need different fixes. Breakout — sound radiating from the duct wall into the room or ceiling void — is treated like a pipe: wool plus MLV lagging, concentrated on the first 3 to 5 m from the fan unit where the duct is loudest. Duct-borne noise — fan noise travelling with the air and emerging at the grille — is not touched by external lagging at all; it needs an in-line attenuator, which is a project design question.

Thin rectangular duct drums easily, and lagging it also reduces condensation. Keep flanges and access panels clear so the system can be inspected.

A worked budget

For 6 m of 110 mm stack in a shaft. Prices include 7% VAT and cover acoustic materials only; wool, tape, ties and the labour to open and close the shaft are extra.

Acoustic materials for 6 m of 110 mm pipe, THB including 7% VAT
Item	Quantity	Total incl. VAT
BB830 MLV, 5 m² roll	1 roll	5,612
BA890 acoustic sealant	2 cartridges	894
Total acoustic materials		about 6,500

That basket is below the free-delivery threshold, so delivery is THB 500 in Bangkok and the surrounding provinces or THB 900 upcountry; collection from the warehouse is free. The 1 m² trial piece is THB 1,122 including VAT.

Cautions

MLV is not a firestop. The existing fire seal where the stack passes between floors must stay in place. Where the building imposes a fire requirement inside the shaft, use BB830FR, which carries an independent laboratory report.
Hot-water or flue pipes above about 90 °C are not suitable: the manufacturer’s heat tolerance for BB830 is 93 °C.
The shaft is usually common property. Tell the juristic person before opening it.
Do not lag over a clean-out; make that section removable.
Noise from the toilet itself or the flush valve upstairs cannot be fixed from your unit. That is a source problem.