The complaint, and what is behind it
The enquiry almost always arrives the same way. An owner or tenant reports a rush of water in the bedroom wall every time somebody upstairs uses the bathroom, the shaft is on the other side of that wall, and the building has to decide what to do about it. The complaint names a wall, but the wall is rarely the thing to treat.
What is making the noise is the stack itself. The soil and waste pipes in most Thai buildings are thin-wall uPVC. Water dropping down the stack sets the pipe wall vibrating, and the pipe wall radiates sound into the shaft; the shaft is then closed with a single layer of plasterboard or fibre-cement, usually unsealed at its perimeter, which passes most of that sound into the room. uPVC radiates more from its side wall than the cast iron the same detail was designed around, which is why buildings that were quiet twenty years ago are not quiet now.
The energy sits mostly in the middle frequencies, which is where adding mass to a radiating surface works well. Set against the other complaints a building manager handles — footfall through a slab, bass through a party wall — this is one of the more tractable ones, and one of the few that can be scoped and priced from a drawing.
What can be done, in the order that decides the result
- Open the shaft at the complaining unit and listen with the stack running. Confirm the pipe wall is the source rather than a rigid bracket or an open sleeve. This is one access visit and it decides everything that follows.
- Seal the sleeves where the stack passes through floor and soffit, and the perimeter of the shaft board. An open sleeve lets sound out before any lagging matters. Never pack rigid mortar hard against the pipe — it makes a solid bridge into the structure.
- Change any bracket that clamps the stack rigidly to a party wall or a bedroom wall for a resilient one. Do this before lagging, not after, because it is the same access visit.
- Lag the length of stack that runs past the affected units, continuously, carried to slab and soffit wherever access allows.
- Close the shaft and seal the board perimeter before making good. A lagged stack behind an unsealed board gives back a large part of what was paid for.
Scope it by complaint, not by building. A stack is 2.5 to 3 m a floor. Treating the floors where complaints have actually been raised, plus one floor above and one below, is normally where the money does its work; lagging twenty floors because two of them complained is twenty floors of access cost for two floors of benefit.
Check this before ordering: does the shaft carry a fire requirement
This is the question to settle first, and it is the commonest reason a product is rejected after it has been installed. A services riser is a vertical shaft passing between compartments, and in a great many buildings it is covered by a fire specification — the building’s own, the project specification, or a condition the approving authority attached. If that is the case here, BB850 is not the material: it carries no laboratory fire classification at all, and we will not supply it into a fire-specified shaft.
The grade for that case is BB830FR, which has been tested by an independent third party to AS/NZS 1530.3:1999 — SGS report AJFTS26000525R01_EN dated 3 February 2026, returning indices of 0/0/0/7 with none of the six specimens igniting. It is a mass loaded vinyl sheet, so it is used in the hand-built build-up described below rather than as a ready-made wrap. That is a material test result and not a certification of the shaft, the riser or the building, all of which remain matters for the project’s approving authority.
Two things that follow from this and are worth putting in writing before work starts. Lagging is not a firestop: the existing fire seal where the stack passes between floors stays in place, whatever is wrapped around the pipe. And if nobody in the building can say whether the shaft carries a fire requirement, treat the answer as yes until somebody can, and specify BB830FR. The cost difference is far smaller than stripping a completed installation out.
The two ways to lag it
BB850 BlastLag is the purpose-made answer where no fire requirement applies, and it is what we would put on a riser. It is a 5 kg/m² loaded-vinyl barrier laminated at the factory to 25 mm of open-cell polyether foam with a reinforced foil facing, 27 mm in total. The foam goes against the pipe, to decouple the pipe wall from the mass layer; the foil faces outward. It is supplied in whole rolls only, 1000 × 4000 mm, so 4 m² a roll, at THB 1,500 per m² including VAT (THB 1,402 excluding) — THB 6,001 a roll. In stock in Bangkok.
The case for it is construction and labour, not performance. It is one operation where the hand-built wrap is three, and the decoupling layer is already bonded to the mass layer, so it cannot be compressed flat while the sheet is pulled tight. That matters more on a riser than anywhere else: pulling the mass layer tight until the wool underneath goes flat is the commonest way these installations underperform, nothing afterwards shows that it has happened, and on a riser the only way to find out is to open the shaft again. We make no claim that BB850 blocks more sound than a well-built hand wrap, because we hold no test that would support one. What it is, is easier to fit and more consistent once fitted.
The hand-built alternative remains on the table and is the right answer in two cases: where the shaft carries a fire requirement, and where the clearance around the stack is under 27 mm. It is 25 to 50 mm of mineral wool against the pipe, then BB830 wrapped over it with a 50 mm overlap, the longitudinal seam closed with aluminium foil tape, ties every 300 mm, and the ends sealed with BA890. BB830 is nominally 5 kg/m² at about 3 mm according to the manufacturer’s datasheet, reference BB830/20/v2, and BB830 is rated STC 32 (ASTM E413) per that same datasheet — a laboratory value for BB830, and a figure that belongs to BB830 alone. One 5 m² roll is about 25 kg and lags about 6 m of 110 mm pipe. For a fire-specified shaft the same build-up is made up in BB830FR instead of BB830.
Prices
| What it is for | Material | Price |
|---|---|---|
| Lagging a riser where no fire requirement applies | BB850 BlastLag | 1,500 /m² (1,402) |
| BB850, whole roll | 4 m² roll | 6,001 /roll (5,608) |
| A shaft with a fire specification — the hand-built build-up | BB830FR | 1,288 /m² (1,204) |
| The hand-built build-up where no fire requirement applies | BB830 | 1,122 /m² (1,049) |
| BB830, whole roll | 5 m² roll, about 25 kg | 5,612 /roll (5,245) |
| Sealing the floor sleeves and the ends of the lagging | BA890 sealant | 447 /cartridge (418) |
| Lining the back of the shaft board where the pipe cannot be wrapped | BA990 adhesive | 546 /cartridge (510) |
The mineral wool, the aluminium foil tape and the ties for the hand-built build-up are ordinary builders’ merchant items and are not sold here. Delivery is free nationwide over THB 20,000 excluding VAT; below that it is THB 500 in Bangkok and the surrounding provinces or THB 900 upcountry, excluding VAT, and collection from the warehouse is free. The minimum online order is THB 5,000 including VAT, which a riser of any length comfortably exceeds.
A worked example: one stack, five floors
A 160 mm main soil stack in a boxed shaft, treated over the five floors around the complaints, at about 3 m a floor — 15 m of pipe. Sheet is worked out from the circumference of the wrapped pipe plus a 50 mm overlap, and whole cross-pieces are cut across the roll length, so for 160 mm pipe a 4 m² roll of BB850 yields about 5 m of lagged pipe. Fifteen metres therefore needs three rolls.
| Item | Quantity | Total |
|---|---|---|
| BB850 BlastLag, 4 m² roll, about 5 m of 160 mm pipe a roll | 3 rolls, 12 m² | 18,003 (16,824) |
| BA890 sealant, for the floor sleeves and the lagging ends | 4 cartridges | 1,788 (1,672) |
| Acoustic materials, total | 19,791 (18,496) |
That is about THB 1,200 a metre of lagged pipe, with nothing further to buy. At THB 18,496 excluding VAT the basket sits just under the THB 20,000 free-delivery threshold, so add THB 500 in Bangkok or THB 900 upcountry, excluding VAT, unless the material is collected.
Where the shaft carries a fire specification, the same 15 m is built by hand in BB830FR. Over 50 mm wool a 160 mm stack takes about 0.87 m of sheet width a metre of pipe, so about 13 m², ordered as three whole 5 m² rolls — 15 m². At THB 1,288 per m² that is THB 19,320 including VAT, about THB 1,288 a metre of pipe, plus the wool, the foil tape and the ties bought separately, and three operations on site instead of one. Neither figure includes labour or access, and that is the part worth reading twice.
What this does not fix
- Vibration felt in a wall or a floor, rather than heard. That is the brackets feeding the structure, and it is corrected with resilient brackets at the fixings. No lagging reaches it.
- A thump when a tap closes, or immediately after a flush. That is water hammer in the supply or the flush valve, and it is a plumbing fault at source.
- Noise from the fitting itself in the unit above — the pan, the cistern, the flush valve. It cannot be reached from the shaft below.
- Footfall and impact from the unit above. It travels through the slab, has nothing to do with the riser, and belongs on the residential page.
- A hot-water or flue pipe with a surface above about 90 °C. The manufacturer’s stated heat tolerance for BB830 is 93 °C, so neither the mass layer nor a foam-faced laminate belongs there.
- A fire-stopping deficiency. If the seal where the stack crosses a floor is missing or has been cut through, that is a fire issue to be put right on its own terms, and no acoustic material substitutes for it.
- A clean-out or an inspection eye. Do not lag over one; make that short section removable, and expect it to be slightly louder than the rest.