[Bathroom Decoration Drainage Construction Method] Decorating caisson vs. floor elevation construction method when renovating bathroom layout! Calculation of drainage slope, exhaust between pipes and leak-proof cost of bathrooms in antique houses in Taipei

Challenges of double-north bathroom renovation: shifting and reshaping of drainage pattern

In the renovation of medieval houses and renovation of old houses in the greater Taipei area, homeowners often hope to enlarge the originally small and dark bathroom, or to realign the positions of the toilet and washbasin to achieve dry and wet separation or even a dual bathroom layout. However, the bathroom is the area with the highest water supply, drainage and waterproofing requirements in the whole family. When changing the layout of the bathroom, the core problem is: "How to extend the drainage pipeline? Is the drainage slope between the toilet and the floor drain steep enough? Does the bathroom floor need to be raised?" If the construction method is improperly selected or the drainage slope is insufficient, after moving in, you will face huge disputes such as frequent blockage of the toilet, extremely slow drainage of the floor drain, and even water on the floor seeping into the ceiling of the neighbor downstairs.

Construction method competition: lowered caisson construction method vs. floor elevating construction method

When reconfiguring the bathroom drainage pipeline, there are mainly two construction methods:

1. Sunken Slab System

The caisson construction method refers to lowering the entire structural floor of the bathroom area downwards by 35 to 50 centimeters during construction to form a sunken "caisson space." All water supply and drainage pipelines (toilet septic pipes, floor drains, bathtub drainage) are piped inside the caisson. After the pipes are completed, they are filled with light materials (such as ceramsite) and laid with waterproof layers and cement mortar floor tiles.

• Advantages: The drainage pipeline is extremely elastic, and the toilet and floor drain can be moved freely; the drainage noise is blocked by the caisson and ceramsite, and the noise prevention effect is excellent; and the bathroom floor can remain "completely flat (barrier-free flat floor)" with the indoor living room.
• Disadvantages: Only suitable for new construction or specific buildings with caisson design. The old apartments in Shuangbei that are more than 30 years old have no caisson structure at all, and it is impossible to directly drill the structural floor (it is strictly prohibited to penetrate the structural floor, otherwise it will destroy the structural safety of the building).

2. Raised Floor Drainage System

For traditional old apartments in Taipei without caissons, when the bathroom toilet or drain hole needs to be moved a large distance, the only and most common solution is to "raise the entire bathroom floor (raise the floor 10 to 20 cm)".

• Advantages: There is no need to penetrate the structural floor, and the elevated space is used to allow the fecal pipes and drainage pipes to extend horizontally and connect to the main pipes.
• Construction Core (Drainage Slope): Horizontal drainage pipes must maintain a drainage slope of at least 1/100 to 1/50 (that is, for every 1 meter of extension of the pipe, the height needs to decrease by 1 to 2 cm). If the displacement distance is up to 2 meters, the floor must be elevated by at least 15 centimeters to ensure that feces and water flow are smoothly discharged under the action of gravity without siltation.
• Disadvantages: There will be a first-order threshold (height difference) at the bathroom door, so attention must be paid to anti-slip and entry and exit safety.

The key to odor prevention and ventilation: exhaust between the trap and independent pipes

When renovating the bathroom layout, in addition to smooth drainage, odor prevention is also a top priority:

1. Anti-odor water trap: An anti-odor water trap with a water seal height (50 to 100mm) must be installed under each floor drain and washbasin, or a deep-pressure anti-odor floor drain door must be installed. Use the trapped water seal to completely block the methane and cockroaches and mosquitoes coming from the shared pipes in the building.
2. Independent exhaust on the same floor (Ventilation Upgrade): Old-style bathrooms in old apartments in Taipei often insert the exhaust pipe of the exhaust fan directly into the building's shared pipes, causing the odor of smoking and cooking downstairs to flow back into the bathroom through the pipes. During modification, an eccentric pipe should be used to extend the exhaust pipe to the exterior wall, implement "independent exhaust on the same floor" and install a check valve to completely eliminate the backflow of odors.

Shuangbei Bathroom Renovation Waterproofing and Elevated CapEx Budget Planning

For owner-occupiers or real estate flip investors who want to renovate the bathroom layout, the renovation cost of a 1.5 square meter standard bathroom is as follows:

Conclusion: Use standard construction methods to create a dry and odorless bathroom space

Bathroom renovation is a delicate project, and the drainage slope and waterproofing quality must not be sacrificed for the sake of aesthetics. When renovating an old house in Shuangbei, the construction method of lowering or elevating the slabs is accurately selected based on the structural conditions, strict requirements include a 1/100 drainage slope and a 48-hour full water waterproof test, and upgrading the independent exhaust of the floor. Only in this way can we create a high-quality bathroom asset that is beautiful, dry and never leaks.

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

1. 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.
2. 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.
3. 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.