The odor crisis in the bathroom: the inherent flaw of the traditional drainage system
In old apartments or luxury buildings in the greater Taipei area, homeowners often encounter a stubborn hygiene problem: even if they clean the toilet every day and use fragrance, a faint sewage swamp smell often wafts out of the bathroom floor drain holes. Even during the rainy season or late at night, cockroaches, mosquitoes or moths (moth gnats) will crawl into the room along the pipes. Many people will replace the anti-odor drain head, but the effect is often limited. In fact, this odor backflow phenomenon is caused by the structural defects of "multiple water seals and diverted drainage" in the traditional Taiwan hydropower configuration. In foreign countries, especially in modern buildings in Japan and Europe, the "Gully Trap" construction method has been widely used in bathrooms to completely block odors and germs from the physical source.
Core science: traditional multiple water seals vs. collective water traps
To understand the physical differences between these two construction methods, we can compare them from the management methods of water seals:
Traditional configuration: The bathroom under the washbasin, shower room floor drain, and bathtub drain outlet are each equipped with independent water traps. This diversion design has two main disadvantages:
1. If the bathtub or guest bathroom floor drain does not use water for a long time, the water in the trap will be lost due to air evaporation (the water seal disappears), and the methane and pests between the pipes will escape into the room without any hindrance.
2. When a large amount of water is discharged from the washbasin, the negative pressure generated by the drainage will act like an exhaust fan and "suck away" the water in the trap of the floor drain next door, resulting in insufficient height of the floor drain water seal and loss of anti-odor function.
Main Trap (Collected Drainage): The drainage branch pipes of the washbasin, shower area, and bathtub in the bathroom are all collected into the same large-volume "drainage manifold box (i.e., the main trap)" under the floor of the bathroom. This manifold box is then uniformly connected to the main drainage pipe of the building. Its advantages include:
1. Because the sink is a place where water is used frequently every day. The water discharged from the sink will continuously flow into the main water trap, automatically and continuously replenishing water, ensuring that the main water seal is always full and eliminating odor.
2. The main trap box is equipped with a patented cage filter. Once a blockage occurs (such as hair accumulation), the homeowner only needs to lift the floor drain cover in his bathroom and directly take out the filter for cleaning. There is no need to go downstairs and knock water pipes from the neighbor's ceiling like traditional construction methods, which can effectively avoid neighbor disputes.
Construction methods and limitations of installing a main trap in the renovation of old houses
If you want to introduce this advanced drainage system when renovating an old apartment in Taipei, there are the following points that must be paid attention to in the water and electricity project:
1. Assessment of drainage space on the same floor: The drainage manifold box (main trap) is large and must be buried under the floor. This means there must be a physical depth of approximately 15cm+ below your bathroom floor. After the tiles are removed and the floor is bottomed out, in an old apartment, if the structural floor does not have a "recessed floor", the "raised floor" construction method must be adopted to raise the bathroom floor by 10 to 15 centimeters. This will create a height difference, and anti-skid and anti-sill anti-seepage designs must be made in advance.
2. Double water sealing is strictly prohibited (Qi blockage pain points):If an S-type or P-type trap is installed under the sink and is subsequently connected to the main trap, a "double water seal" will be formed. The double water seal will cause the air between the two traps to be locked, preventing the water from flowing down. Every time the washbasin is drained, there will be a "gurgling" air blocking sound and the water will drain very slowly. Therefore, the end of the appliance branch pipe connected to the main trap must not be equipped with a trap.
Shuanbei Water and Electricity Budget for Main Trap Renovation
When renovating the entire bathroom in Taipei and New Taipei, the cost of retrofitting the collective drainage system is estimated as follows:
* The cost of the equipment itself is approximately NT$ 3,500 to NT$ 6,500.
* The plumber needs to carefully lay out the wiring, plan the drainage slope of each branch pipe, and connect the junction box with a high-airtight PVC pipe (such as Nanya Dachang). The cost of professional water, electricity and materials for this part is approximately NT$ 15,000 to NT$ 25,000 (this price does not include the initial tile removal and mud repair).
Although this construction method will increase the water and electricity piping budget by about more than 10,000 yuan, the anti-odor, anti-insect and convenience of on-site maintenance it brings can solve the biggest drainage pain point of the old house once and for all.
Commercial acquisition and businessman’s asset valuation perspective: the long-term financial benefits of neighbor-damage-free design
For commercial investment businessmen who specialize in buying apartments in Shuangbei for renovation, rent collection or resale, The most common property maintenance expenses (OpEx) for rental suites are water damage caused by tenants' hair clogging the floor drain, or tenants canceling the lease due to smelly bathrooms. With traditional construction methods, as long as the pipes are blocked or leaking, the landlord must negotiate with the neighbors downstairs to open the door or remove the ceiling, which is time-consuming, labor-intensive and full of conflicts. Adopting the drainage design of the main trap on the same floor, the landlord's property manager can complete the dredging within 10 minutes without drilling, reducing the legal liability for vacant rental losses and neighbor damage to zero. This modern drainage structure with "extremely low maintenance resistance and high tenant satisfaction" is a hidden trump card in real estate asset management to improve property value preservation and buyer's willingness to take over.
The latest standards for catching leaks and regulatory responsibilities in Shuangbei collective housing (2025-2026 practice)
According to Article 10 of the "Apartment Building Management Regulations" of the Ministry of the Interior and the trend of civil water leakage judgments in Shuangbei District Court in recent years, most water leakage disputes in old collective housing focus on the identification and definition of "exclusive parts" and "common parts". The roof platform and the public pipes are jointly owned by all separate owners, and the repair costs should be shared by public funds or all residents in proportion to their shares according to law; if the water supply and drainage pipes inside the floor slabs on the upper and lower floors are damaged, the pipes will be borne exclusively by the users or shared by the upper and lower floors.
At the engineering and technical level, modern professional leak detection has fully introduced non-destructive scientific testing, including "FLIR high-resolution infrared thermal imaging camera" (locating temperature difference leakage paths), "high frequency moisture meter" (measuring the moisture content of deep structures) and "pipeline air pressure and water pressure pressure test" (determining whether hot and cold water pipes are leaking). During construction, do not directly apply elastic cement or oil-based paint on the wet cement layer to seal it. Otherwise, the thermal expansion of internal water vapor will quickly cause the coating to blister and peel off, resulting in more serious powdery wall cancer. The standard construction method must first completely eliminate the water source, wait until the moisture content of the cement structure drops below 8%, and then apply the negative pressure resistant silicic acid permeability crystallized waterproof layer.
Recommendations on independent certificate storage and compensation process for water leakage repair
- Take photos and videos as evidence immediately: Use rulers to record the leakage range, frequency of water discharge, direction of water mark diffusion, and keep time stamps.
- Written notification and coordination survey: Officially notify the neighbors through the management committee or a certified letter, and agree on a professional third-party leak detection and appraisal unit recognized by both parties to conduct an on-site survey.
- The contract states the warranty terms: When signing the contract for the project, be sure to clearly specify the waterproofing warranty period (usually 1 year for partial repairs, and 2 to 5 years for the whole room or roof re-construction), and specify the water test acceptance criteria (such as a 48-hour water storage test in the bathroom shower area) to protect your own asset rights.
