Updated 16 Oct 2026floor trap8 min read
What is a floor trap?
Quick answer
A floor trap is the grated drain in a bathroom, kitchen or service yard floor that holds a pool of water, at least 50mm deep under PUB's Code, so sewer gas and insects cannot come up the pipe. Sinks, basins, showers, washing machines and floor wastes all drain into it, and it drains into the building's discharge pipe.
What is under the grating
Lift the grating with gloves on and shine a torch down. From the top, you are looking at four parts.
- 1Grating. The removable cover, flush with the tiles. It keeps out hair clumps, bottle caps and feet.
- 2Riser. The short vertical pipe from the floor surface down to the trap. Side pipes from the sink, basin or floor waste join here, below the grating and above the water.
- 3Water seal. The standing water a short way down. It sits in a U-shaped bend, so gas from the pipe beyond would have to push through water to reach your room.
- 4Outlet. Past the bend, the pipe runs to the stack in a flat, or to an inspection chamber outside on the ground floor of a landed house.
In words, the water path is: in through the grating or a side pipe, down the riser, through the water seal, up and over the lip of the bend, then out. The water that stays behind in the bend is the seal.
Most of the time a floor trap fails at the seal, not the grating. It dries out, or hair and soap fill the bend. Both are covered in our floor trap vs floor waste guide and the floor trap choke guide.
What PUB's Code requires
Floor traps in Singapore are built to PUB's Code of Practice on Sewerage and Sanitary Works. The 2025 edition sets two kinds.
| Floor trap | Shallow floor trap | |
|---|---|---|
| Water seal | At least 50mm | At least 50mm, in a built-in compartment |
| Outlet | At least 100mm across | At least 75mm across |
| Riser | Same diameter as the trap, up to finished floor level | Embedded in the slab, nothing sticking out below |
| Grating | To SS 213 dimensions | To SS 213 dimensions |
| Can take | Sink, basin, bathtub, shower, floor waste, washing machine, dishwasher | Not a kitchen sink or dishwasher |
| Other | Must have a way to stop mosquitoes breeding | If it has a service plug, a permanent label must say to put it back after cleaning |
A few more rules from the same section explain things you may notice at home. One floor trap cannot serve two units or two rooms. It cannot sit in an open area that catches rain. A kitchen sink must not drain into a floor trap in a toilet. In food shops, the cover has to be bolted or screwed down.
SS 213 is the standard PUB lists for uPVC sanitary pipes and fittings in section 4.8. Tying gratings to it means a grating is sized to fit a standard pipe, which is what makes off-the-shelf replacements possible.
Where you find one
| Room | What drains into it | What chokes it |
|---|---|---|
| Bathroom | Shower, often the basin, sometimes a floor waste in the shower area | Hair and soap |
| Kitchen | Kitchen sink, dishwasher. Often hidden inside the sink cabinet | Grease and food |
| Service yard | Washing machine hose, floor washing | Lint and detergent |
A smaller grating near the shower with no standing water under it is usually a floor waste, which drains into the floor trap. Our floor trap vs floor waste guide shows how to tell them apart.
The kitchen or service yard one is often called a gully. Norika, a Singapore grating supplier, sells a "Casting Floor/Gully Trap Grating" as one product. What a gully trap is covers the other meanings.
Floor trap covers and gratings sold in Singapore
This is what people usually mean when they search for a floor trap cover. Prices below are from Singapore retailer pages, checked October 2026.
| Type | What it does | Example sizes and prices |
|---|---|---|
| Plain stainless square grating | Straight swap for a rusty or cracked grating | A Plus Hardware: 304 stainless square, $40. Norika: 304L or 316L, product codes for 100 and 150 sizes |
| Round cover in a square frame | Same job, round centre plate on pins | Norika: 100 and 150 sizes |
| No-hole or locking grating | Solid top, or locked so it cannot be lifted easily | Norika: 150 size, heavy-duty versions |
| Tile-insert or linear drain | A tile sits in the top so the drain almost disappears | PH Bathroom (Lavastone): $85 to $179 on sale |
| Designer floor trap with anti-odour filter | Grating plus an internal filter to keep out insects and smell | Smart Home: 100x100 or 110x110mm $19, 150x150mm $29 |
| Anti-mosquito insert with filter | Sits under the grating to stop mosquitoes and insects getting in | Norika: ABS plastic insert for its 213 grating |
| One-way valve insert | A valve opens when water flows and closes after | Initial Green Drain for 90 to 100mm pipes, listed at $53.90 to $64.90 |
Smart Home says its design is up to 90% more efficient than a traditional floor trap. That is the seller's figure; we have not seen a test behind it.
A cover is not a substitute for the water seal
PUB's Code relies on the 50mm water seal, not on a flap. A valve or filter sits right where hair and lint arrive, so clean it whenever you clean the trap. If a valve sticks open, you are back to relying on the water under it.
Measuring for a replacement grating
- 1Lift the old grating and measure its outer frame, edge to edge. Square gratings are commonly sold as 100mm, 110mm and 150mm.
- 2Measure the inside of the riser, the pipe the grating sits in. A full floor trap's riser is at least 100mm across under PUB's Code. A much smaller hole is more likely a floor waste or a shallow floor trap.
- 3Note how the old one fits: sitting loose in a recess, on pins, or screwed down.
- 4Take a photo with a ruler across it and bring it, or the old grating, to the shop.
If the frame is set into the tiles and only the centre plate is broken, buy a matching plate rather than a whole new frame. A new frame means cutting tiles.
If you are re-tiling, HDB's renovation guidelines ask for a UPVC floor trap grating with a long collar. Ask the shop for it by that name. We did not find one priced on a Singapore retailer page, so get a quote.
The designer floor trap catch
Some anti-odour floor traps are not just a grating. Smart Home's installation note says the old one is cut out and the new one cemented in, at $90 a set for one set. That means cutting into the existing trap top.
In an HDB flat, that runs into a rule. HDB's building works guidelines say "No tampering of the floor trap is allowed" when tiles are laid over existing tiles, and HDB tells owners not to tamper with floor traps generally. A damaged trap can leak into the flat below, and a ceiling leak caused by renovation is the upper owner's bill.
What you can change freely: the grating, an anti-mosquito or anti-odour insert that sits on top, and a hair catcher. None of these needs a licence. Anything that cuts, moves or removes the trap body is not a homeowner job. The full do and do-not list is in our floor trap vs floor waste guide.
Before paying for a cut-out swap in an HDB flat, ask the seller in writing how they deal with HDB's rule and who pays if the flat below leaks.
When it needs a plumber
Water pooling around the grating, gurgling when the toilet flushes, or a smell that stays after you top up the water: these are chokes or seal problems, not cover problems. Clearing a floor trap does not need a PUB Licensed Plumber. Replacing damaged sanitary pipes does.
Typical prices for clearing a choked floor trap in Singapore are $50 to $120 for hair, soap or lint, $130 to $220 with a drain machine on the branch pipe, and $150 to $350 for renovation debris. See floor trap choke and the HDB floor trap page.
WhatsApp us a photo of the trap with the grating lifted, 24/7. We reply with the likely cause and a price range, and the price is agreed before any work starts.
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Frequently asked questions
What is the purpose of a floor trap?
To hold a pool of water, at least 50mm deep under PUB's Code, between your room and the sanitary pipes. Water can drain through it, but sewer gas, smells and insects cannot come back up. It also collects the waste water from sinks, basins, showers and the washing machine.
What is the difference between a floor trap and a gully trap?
In a Singapore home they are usually the same part; shops sell it as a floor trap or a gully trap, and the kitchen one is often called the gully. In PUB's Code, a cast iron gully trap is a heavier trap for markets, bin centres and car washing areas. See our gully trap guide.
What is the difference between a floor trap and a floor drain?
Floor drain is the general name for any grated outlet in the floor. A floor trap is a floor drain with its own water seal. A floor waste is a floor drain without one, which empties into a floor trap.
What is the meaning of floor trap?
A trap is any bend that holds water to block gas from a drain. A floor trap is that bend set into the floor, under a grating, so it can take water from the floor as well as from pipes.
What size floor trap cover do I need?
Measure the old grating's outer frame and the inside of the pipe it sits in. Square gratings in Singapore shops are commonly 100mm, 110mm and 150mm. Bring the old grating or a photo with a ruler across it to the shop.
Do anti-odour floor trap covers work?
They can help, especially in a trap that dries out because it is rarely used. They do not replace the water seal, and a valve or filter traps hair and lint, so it needs cleaning. If the smell comes with gurgling or slow draining, the problem is a choke, not the cover.
Get a price on WhatsApp
Send a photo or short video, your home type and postal code. We reply with a price range and the earliest slot.
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