The old house in Taipei was renovated to separate dry and wet areas and it keeps leaking? Construction of water-stop piers, embedding of thresholds and drainage slope of glass sliding doors

Separating wet and dry areas is not just a matter of installing a sliding glass door

In the renovation of medieval houses in Taipei and New Taipei, transforming traditional integrated bathrooms into wet and dry separation is a highly inquired project. However, a few months after completion and move-in, many homeowners discovered that water was leaking from the gaps in the floor tiles in the dry area, the wooden floors were blackened by moisture, and even the residents downstairs reported water leakage from the bathroom ceiling. The root cause of the problem is often not that the sliding glass door is not closed properly, but that the key "water-stop pier" construction method is omitted during the muddying stage, or the threshold is only superficially adhered to the tiles, causing bath water to underflow to the dry area along the pores of the adhesive layer of the tiles.

Why can’t silicone on the surface of tiles stop water?

Although the tiles themselves have low water absorption, the caulking agent between the tiles is microporous, and the cement mortar underneath is more capillary. When water accumulates in the shower area, the water can penetrate the gaps between the tiles and enter the screed. If there is no waterproof barrier wall between the shower area and the dry area that reaches directly to the structural floor, water will spread freely in the sand layer under the tiles. This is a typical "undercurrent seepage". Simply placing an artificial stone threshold on the finished surface and applying silicone on both sides will cause water to seep into the dry area continuously as long as the silicone ages or becomes moldy and degummed over time.

Construction of standard dry and wet separation threshold: Three steps of water-stop pier

1. Building pier with plain mud:After the bottom of the bathroom is dismantled (revealing the RC structural layer or base mortar), first use cement mortar to pour a concrete "water-stop pier" with a height of about 3 to 5 cm at the dry and wet junction.
2. Elastic cement waterproof coating: When applying elastic cement (water-based PU or polymer waterproof coating) to the entire room, the waterproof layer must be completely turned over both sides of the water stop pier and painted to the ground in the dry area to form a continuous "waterproof basin" structure. The waterproof layer should be painted in at least two to three coats, with each coat having a uniform thickness and crossing each other, and the corners should be reinforced with crack-resistant fiberglass mesh.
3. U-shaped threshold embedding or overlaying: Put the artificial stone or marble threshold upside down on the water stop pier, fill the interior thoroughly with cement mortar or special adhesive to ensure that there are no hollow gaps inside, and finally lay the tiles in the shower area and dry area. The tiles should be slightly below the top of the threshold, about 1 to 1.5 cm.

The golden ratio between the drainage slope and the configuration of the water head

According to Taiwanese construction engineering practices, it is recommended that the floor drainage slope inside the shower room be maintained at 1/50 to 1/100 (that is, for every 1 meter of advancement, the height decreases by 1 to 2 cm). If the slope is too gentle, it will easily accumulate water and scale in the corners. If the slope is too steep, it will cause discomfort when stepping on the floor or the height difference between the corners of the floor tiles (commonly known as scissors).

If you choose large-size floor tiles (such as 60x60cm or 30x60cm), the plaster master must accurately plan the eight-shaped cutting angle (diagonal cutting edge and slope); if you do not want to cut the tiles to damage the vision, it is recommended to use a long anti-odor drain head (invisible drainage channel), and make the entire shower area floor a one-way single slope design. The falling water head should be equipped with an insect-proof and odor-proof water seal or a gravity mechanical flap to prevent the backflow of odors from the building's public sewer pipes.

Purchasing shower sliding doors and safety and earthquake resistance

Taiwan is located in an earthquake zone, so the safety of glass in bathroom sliding doors cannot be ignored:

• Glass specifications:Be sure to use "fully tempered safety glass" of 8mm or above that has passed Taiwan's CNS national standard inspection, and the corners have been rounded and ground.
• In the event of self-explosion due to stress concentration or thermal expansion and contraction of the hardware, the fragments will stick firmly to the film to avoid instantaneous scattering and cuts to the human body.
• Hardware material: Taipei and New Taipei have a humid environment. Hardware hinges, tracks and pulleys must be made of SUS304 stainless steel or high-temperature anodized aluminum-magnesium alloy to prevent electroplated zinc alloy hardware from oxidizing, rusting and getting stuck within two years.
• Door opening movement lines: When the space is small, sliding doors (sliding doors) are more space-saving and safer than outward opening doors; if outward opening doors are used, the opening direction of the door must not block the active lines of the bathroom, and the shower area must be able to push the door easily to get out of trouble.

Acceptance test: 72-hour closed water test is essential

After the completion of the mud work and waterproofing work and before laying the tiles, a "48 to 72-hour water test" must be carried out. Properly seal the drainage hole in the shower area, and store the water to 1 cm below the top of the water stop. Observe whether the water level has dropped significantly, and work with the residents downstairs to check whether there are any traces of moisture around the ceiling pipes. Only after passing the closed water test can subsequent tile pasting and sliding door installation be carried out to protect dryness and peace of mind for decades to come.

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 a contract for a project, be sure to clearly specify the waterproofing warranty period (usually 1 year for partial repairs, and 2 to 5 years for complete 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.