[Structural Flatness Test] Are the walls crooked? The floor is sloped? Popular science on precision inspection of "laser level" and "gap gauge" and the dangers of tilting old houses

Dizzy living experience: Is your house really crooked?

In the greater Taipei area, many homeowners sometimes experience a strange physiological feeling after viewing a house or moving into a second-hand house or a newly built house: when staying in a corner of the living room, they will feel dizzy and lose their balance for no reason, or if a bottle of mineral water is placed on the floor, the bottle will automatically roll rapidly in the same direction. This is not a psychological effect or magnetic field problem, but a typical "floor tilt" or "wall skew" structural flaw. If the house is tilted, it may mean that wardrobes and bookcases cannot be placed against the wall, and wooden doors may automatically slide open or get stuck and cannot be opened. In severe cases, it may mean that the bearing capacity of the foundation is insufficient, or even improper pumping of large-scale construction projects nearby may cause foundation loss (such as the tilt incident of private houses in Taipei City). Therefore, during the house inspection stage, using a laser level to conduct accurate horizontal and vertical measurements is an important process for inspecting structural safety.

Popular science on measurement principles: the physical linkage between laser levels and gap gauges

In professional house inspections, checking flatness and verticality is not just a casual look with the naked eye or a level ruler, but the use of high-precision measuring instruments:
1. Laser level (datum plane projection): Equipped with a precision pendulum self-leveling system (or electronic induction gyroscope) inside, it can project perfect horizontal red/green laser light and vertical cross lines. The home inspector will set up a spirit level in the center of the room to project a horizontal baseline.
2. Digital laser range finder and steel tape measurement: The home inspector will measure the vertical height difference from the laser baseline to the ceiling or floor at different points on the wall or floor. For example, at point A, the laser line is 100cm from the ground, and at point B, which is 3 meters away, the distance is 101.5cm. This means that the floor has a vertical height tolerance of 1.5 centimeters within these 3 meters.
3. Feeler Gauge: Used to measure the slight unevenness of wall paint and tile splicing. Use a 2-meter straight gauge attached to the wall, insert metal gap gauges of different thicknesses into the gaps, and accurately read the flatness deviation value.

Taiwan's legal allowable tolerance standards for construction and house inspection

According to the "Construction Technical Rules" of the Republic of China and Taiwan's construction engineering management practices, due to the physical limitations of mud base and formwork assembly during house construction, extremely small tolerances are originally allowed, but exceeding the following red line is considered an unqualified defect:
1. The vertical deviation of each floor (height of about 3 meters) 0.5 cm). If the deviation is greater than 1 centimeter, it will appear visually skewed and it will be extremely difficult to place the cabinet against the wall.
2. For newly built houses, a single room has a height differenceat two points within 3 meters of each other. If the height difference of the entire living room (for example, 6 meters apart) reaches more than 1 cm, the human body will start to have a slight physiological sensation of tilt when walking barefoot on it. If it reaches more than 2 cm (about 1/150 slope rate), it is a serious deficiency, which may affect the safety of the foundation. The builder must perform floor grouting and leveling or structural reinforcement.
3. The "height difference" between the two tiles should not be greater than 0.5mm, otherwise it is easy to kick your toes and injure them.

Budget prices for Shuangbei floor leveling and old house tilt renovation projects

In the greater Taipei area, to correct floor tilt and horizontality deviations, the reasonable repair budget is as follows:
* Use high-fluidity, self-leveling, non-shrinkage cement mortar for floor leveling and primer. When the thickness is 1cm, the cost of continuous work and materials is about NT$ 3,500 to NT$ 5,500 / ping.
* Use the wood angles to adjust the level, and then lay the wooden floor. The cost including work and materials is about NT$ 6,000 to NT$ 9,500 / square meter.
* Involving professional structural civil engineering, it is necessary to drill holes in the foundation and grout (pouring epoxy resin or double liquid grout) to lift and straighten the foundation. Fees typically range from NT$ 200,000 to NT$ 600,000 and require certification by the Guild of Structural Technicians.

Commercial acquisitions and businessmen’s long-term asset thinking: Structural flatness is the CapEx watershed in the evaluation of medieval house renovations

For real estate businessmen who specialize in acquiring old apartments for renovation and resale (Flip) or boutique suites in Shuangbei, Older apartments are often slightly tilted due to age, earthquakes or nearby construction projects. If a businessman blindly buys a "mine tilt house" with a height difference of 3 centimeters without checking it with a laser level before signing a contract to buy it, during subsequent modifications, in order to solve the problem of automatic door sliding and furniture placement, he will have to spend more than hundreds of thousands of dollars on "self-leveling cement grouting throughout the room" or major woodwork height adjustment, which will directly burn the budget, extend the construction period by 2 weeks, and significantly reduce the IRR. On the contrary, if a businessman discovers a tilt before signing a contract, he can hold the inspection data and engage in a "destructive bargaining" with the seller, asking for a price reduction of 300,000 to 500,000 yuan. During the subsequent renovation, the house will be leveled with cost-effective self-leveling cement, repackaged as a "safe and beautiful house with a safe structure and compliance with flatness" and sold at a high premium. This is the high-end value-added mentality of real estate businessmen's actuarial CapEx.