Revealing the widespread existence and serious adverse health consequences of low-price rental housing in urban villages in Xiamen, China

The study addresses the surge of low-price rental housing (LPRH) due to rapid urbanization and large inflows of migrant workers whose housing needs are not fully met by government plans. Historically and globally, low-cost, rapidly constructed rental models often feature poor construction quality and substandard indoor environments, which can adversely affect health. Drawing on Sick Building Syndrome (SBS) literature, the authors note environmental and social factors influence SBS, with environmental conditions having more direct effects. In Xiamen, informal redevelopment of urban villages has produced partitioned rural rental houses (PRRHs), where owners expand and subdivide buildings into many small units to maximize rent. The study aims to answer: (RQ1) What is the stock status of PRRHs in Xiamen? (RQ2) What is the indoor environmental quality of these rentals? (RQ3) What are renters’ environmental experiences and health outcomes, and how are these related to the indoor environment?

Prior research documents that rapid urbanization often yields informal or low-quality rental housing with inadequate standards (e.g., back-to-back houses in the UK; backyard accommodations in South Africa; informal settlements in Brazil, Pakistan, Singapore). SBS encompasses non-specific symptoms (headache, mucosal irritation, lethargy, inability to concentrate, nausea, dizziness) linked to indoor environments, with evidence that environmental factors such as poor ventilation, temperature/humidity, and air pollutants are central determinants. Studies in Japan and South Korea link dampness, temperature/humidity issues, and poor ventilation design to higher SBS prevalence. Socio-demographic factors (gender, education, social status) also correlate with SBS, but environmental conditions exert stronger direct effects. Recent work shows renters often experience poorer air quality than homeowners and that ventilation improvements can reduce symptoms.

Design: Mixed-methods comprising web data crawling to characterize market stock, field measurements of indoor environmental quality, and a cross-sectional questionnaire with statistical analyses (non-parametric correlations and adjusted binary logistic regression). Rental information crawling: Data were scraped from 58.com (chosen for widest coverage) on 09/09/2021 using Octopus collector v8.2.2 (2014SR149170). Inclusion criteria: listings in Jimei, Haicang, Tongan, and Xiangan districts; owner-managed units to avoid duplicate agency posts. After manual deduplication and removal of non-residential posts, listings were classified by land type into PRRH units versus urban rental units. Indoor air quality (IAQ) measurements: Conducted in 20 one-bedroom PRRH units (Jimei and Tongan) on typical summer days (15–18 Sept 2020). Parameters: CO2, TVOC, PM2.5, PM10 following Chinese Indoor Air Quality Standards. For rooms <50 m², one measurement point at diagonal intersection, instruments at 1.1 m height. Instruments: TSI 7575 with probe 982 (CO/CO2), TSI 7575 with probe 986 (TVOC), DUSTTRAK DRX 8533 (PM2.5/PM10). Calibration performed. Testing times: morning (7:00–9:00), midday (12:00–14:00), evening (16:00–18:00), 45 min per test, each room monitored for two days. To reflect typical closed-up summer usage, doors/windows were closed for at least 12 h pre-test and remained closed during monitoring. Physical environment measurements: In 6 units, 48-hour continuous monitoring (14–16 Sept 2020). Parameters: air temperature, relative humidity, wind speed, illuminance per Standard of Testing Methods of Building Thermal Environment. Central measuring point at diagonal intersection; instruments at 1.1 m (except wind at 1.6 m). Instruments: Hengxin AZ8829 (temperature, humidity), TESTO 425 (air speed), Konica Minolta CL-200 (illuminance). Recording: temperature/humidity every 30 min automatically; illuminance hourly manual; wind speed 3-minute average hourly manual. For these tests, doors were closed and windows open; no active HVAC operation. Questionnaire survey: Cross-sectional survey (20–31 Aug 2020) in eight urban villages (two per district) across Jimei, Haicang, Tong'an, Xiang'an (Suncuo, Fenglin, Jinli, Jianmei, Wulv, Sikouzhen, Anbian, Nei'an). Instrument based on MM040EA SBS questionnaire. Four parts: (1) renter demographics (gender, age, occupation, education, smoking, health history, weekday time at home); (2) PRRH unit characteristics (rooms, building height/form, rental duration, post-move refurbishment, household size); (3) subjective indoor environment evaluation via 11 statements (5-level; “Somewhat agree” and above indicate a problem); (4) self-reported SBS symptoms (13 across five categories; 4-level; “Sometimes” and above indicate presence; any ≥1 symptom = SBS). Recall period: 3 months (summer). Sampling and data: 270 distributed, 248 valid. Eligibility: lived in PRRH ≥3 months. Administration in public village spaces by six trained investigators (three pairs). Analysis: Variables tested for normality; non-normal variables analyzed with non-parametric methods. Spearman correlations assessed associations between environmental evaluations and symptom categories. Binary logistic regression assessed multivariable associations after dichotomizing exposures and outcomes (present vs not) and adjusting for gender, age, education, smoking status, history of skin diseases, architectural form, building height, and number of rooms. Collinearity checks (VIF ~1) indicated no multicollinearity. Events-per-variable (EPV) values for models were all >10, indicating adequate power. Software: Excel 2016 and SPSS 19.0.

Market stock: 1,097 listings scraped; 40 removed (duplicates/non-residential). Final: 590 PRRH units and 467 urban rental units. PRRH building heights: 1–3 stories 18.6%, 4–6 stories 62.5%, 7–9 stories 16.8%, >10 stories 2.1%, suggesting lack of height/capacity controls. Unit size mix: 64.7% one-bedroom (vs 26.6% among urban units), 21.5% two-bedroom, 13.8% three-plus, indicating owners subdivide for profit. Spatially, PRRHs were widespread across the four non-central districts; rents per bedroom (RPB) increased toward the city center for both PRRH and urban rentals, but urban units had higher RPB by 65.3% (p<0.01). Indoor environment measurements: Nearly all parameters exceeded health-oriented standards, except relative humidity under some standards. Air quality exceedances (PE relative to national; international standards, respectively): TVOC 64.1%; 82.0%, CO2 38.7%; 50.4%, PM2.5 36.3%; 186.3%. PM10 also exceeded standards. Likely causes: low-quality materials/furnishings emitting VOCs, small per-capita volume, cooking in mixed-use spaces, and poor ventilation. Physical environment: Temperature and humidity generally high relative to standards; illuminance and wind speed frequently below limits (e.g., illuminance PoE 68.8% to 98.6% depending on standard; wind speed PoE 100%). Causes include dense construction, insufficient lighting and ventilation, and weak climate-adaptive design in a hot-humid climate. Subjective evaluations and health: Despite nearly half reporting overall satisfaction and 20.5% dissatisfaction, specific problems were frequent: >70% reported excessively high temperature and stuffy air; >40% reported poor ventilation and excessive humidity. SBS prevalence was high: only 17.7% reported no symptoms; psychological 66.5%, mucosal 55.2%, respiratory 42.7%, skin 40.3%, general 37.5%. Correlations (Spearman): significant associations between environmental problems and symptoms, e.g., general symptoms with poor ventilation (r=0.329**) and pungent odours (r=0.329**); total number of symptoms with poor ventilation (r=0.319**); noise showed no significant correlations. Adjusted logistic regression: poor air quality associated with general symptoms (AOR 3.341; 95% CI 1.683–6.634) and skin symptoms (AOR 2.13; 1.099–4.129); high temperature associated with mucosal symptoms (AOR 2.631; 1.316–5.260) and psychological symptoms (AOR 2.666; 1.354–5.248). EPV values for all models were ≥13.8, supporting robustness.

PRRHs have become a dominant segment of Xiamen’s rental supply due to low prices and accessible locations but exhibit significantly substandard indoor environmental conditions linked to elevated SBS symptoms among renters. The findings mirror patterns seen in other rapidly urbanizing contexts where informal or low-standard rental stock proliferates, bringing risks related to health, safety, and habitability. Policy implications include the need for anticipatory planning to meet low-cost rental demand, beyond limited-scale social housing. While Xiamen has housed 22,278 low-income families in social housing by end-2021, this is small relative to an inflow population of 2.715 million. Potential strategies include public–private partnerships to expand quality rental supply, incentivizing firms to relocate to suburbs to redistribute demand, and implementing regulations for future construction (e.g., Xiamen’s recent limits on floors/area). For the large existing stock, assessment, renovation subsidies, and, where appropriate, replacement or redevelopment are needed, as seen in examples from Mozambique, Kenya, and Guangzhou. The study also highlights renters’ relatively high overall satisfaction despite specific environmental problems, suggesting low expectations or awareness. Increasing the right-to-know (e.g., disclosing indoor environmental quality reports to renters) and targeted public education about healthy indoor environments are recommended.

PRRHs, a widespread form of low-price rental housing in Xiamen’s urban villages, constitute a major share of the rental market but suffer from poor indoor environmental quality. Objective measurements and renters’ subjective reports indicate multiple parameters exceed health-oriented standards. These adverse conditions are significantly associated with SBS-related symptoms among occupants, evidencing direct public health harms from disorderly housing construction. The study underscores the importance of governmental foresight and comprehensive intervention—from planning to regulation, renovation, and replacement—to ensure healthy, affordable rental housing and safeguard sustainable urban development. Public education on healthy indoor environments is also needed, given many occupants did not report overall dissatisfaction despite specific problems. Future research will examine indoor environment and health issues in Public Rental Housing (PRH) in Xiamen to compare with PRRHs and provide guidance on planning and constructing low-standard housing more responsibly.

Measurements and surveys focused on the summer season in a hot-summer, warm-winter climate; other seasons (transition and winter) were not covered due to research cycle and testing constraints. This seasonal focus, while capturing the harshest conditions for SBS symptoms, may limit generalizability across the full annual cycle.