title: Mechanical ventilation protects one-storey single-dwelling houses against increased air humidity, domestic mite allergens and indoor pollutants in a cold climatic region.
abstract: BACKGROUND
  Poor ventilation in modern, highly insulated housing is an important factor in promoting indoor humidity levels to exceed 7 g/kg in cold climatic regions.
  
  
  OBJECTIVE
  To investigate the ventilation rate in houses with different ventilation systems in relation to indoor air humidity, domestic mite allergen levels and volatile organic compounds (VOC).
  
  
  METHODS
  Measurements were performed regarding ventilation rate, indoor temperature, air humidity, mattress mite allergen concentrations using enzyme-linked immunosorbent assay and total indoor VOC in 59 similarly constructed one-storey single-dwelling houses. In 22 of the houses, a mechanical supply and exhaust ventilation were installed after construction.
  
  
  RESULTS
  In only five of the houses with mechanical supply and exhaust ventilation the air exchange rate per hour (ACH) was below 0. 5 compared with 24 of the 29 houses with natural ventilation (OR = 0. 06, CI 95% 0.01-0.2). None of the 23 houses with an ACH >/= 0.5 had an absolute indoor humidity (AIH) of 7 g/kg air or more, compared with 10 of the 36 houses with an ACH < 0.5 (P = 0.01 ). In none of the 23 houses with an ACH >/= 0.5 were concentrations of mite allergen exceeding 2 microg/g of dust found, compared with six of the 36 houses (17%) with an ACH below 0.5 (P = 0.04). Further, 10 of the 34 houses with a total VOC exceeding 200 microg/m3 had mite allergen in mattress dust exceeding 0.5 microg/g, compared with one of the 22 houses with VOC < 200 microg/m3 (P = 0.04).
  
  
  CONCLUSIONS
  The study shows that in modern, highly insulated, one-storey single-dwelling houses in cold temperate regions, mechanical ventilation increases the possibility of reaching an ACH of >/= 5 which protects against indoor humidity levels contributing to mite survival as well as high levels of indoor air pollutants in winter.
authors.affiliation: Department of Environmental Health, Stockholm County Council, Stockholm, Sweden; Institute of Environmental Medicine, Karolinska Institute, Stockholm, Sweden.
authors.forename: G
authors.initials: G
authors.lastname: Emenius
authors.forename: A
authors.initials: A
authors.lastname: Egmar
authors.forename: M
authors.initials: M
authors.lastname: Wickman
mesh_terms: D016902:Air Pollution, Indoor; D000485:Allergens; D000818:Animals; D003081:Cold Climate; D003627:Data Interpretation, Statistical; D004391:Dust; D004784:Environmental Monitoring; D005430:Floors and Floorcoverings; D006798:Housing; D006801:Humans; D006813:Humidity; D008925:Mites; D014691:Ventilation / Q000379:methods* / Q000592:standards
chemical_list: D000485:Allergens; D004391:Dust