CareHomeDeskCareHomeDeskMinimum extract rates, duct routing and the controls that prevent mould in care bedrooms.
Building Regulations Approved Document Part F (2021) sets the minimum extract ventilation for a bathroom containing a shower: 15 l/s continuous or 30 l/s intermittent. In care homes, the intermittent approach (fan on when shower is on, off when shower ends) is inadequate because the room continues to generate moisture after bathing through body heat, wet towels and resident respiration. Specify a continuous extract fan or heat recovery unit running 24 hours, with a boost mode triggered by humidity or occupancy.
A humidity-controlled fan (humidistat fan) is the most practical specification for care home wet rooms. The fan runs continuously at a low background rate (typically 8 l/s) and boosts to 30+ l/s when relative humidity rises above a set threshold (typically 65-70% RH). This avoids the common problem of care staff switching off bathroom fans to reduce noise, which leads to condensation and mould. Programme the fan so it cannot be switched off at the wall -- a pull-cord isolator switch is acceptable to allow maintenance access, but it should not be the primary control.
All extract ducts must discharge to external air -- not into roof voids, wall cavities or communal ceiling spaces. The duct must be as short and straight as possible, with a maximum of two bends before the external grille. Each bend reduces the effective extract rate significantly. Insulate the duct in unheated spaces to prevent condensation forming on the outside of the duct and dripping back into the ceiling. Use rigid duct (typically 100mm or 125mm diameter) rather than flexible duct in concealed locations -- flexible duct that kinks or sags reduces airflow and is harder to inspect.
In energy-sensitive developments or where planning requires consideration of heat loss, mechanical ventilation with heat recovery (MVHR) is increasingly used. An MVHR unit captures heat from the extract air before it leaves the building and uses it to warm incoming fresh air. For a single wet room, a room-level heat recovery unit (sometimes called a through-wall unit) is more practical than a whole-building MVHR system. CIBSE Guide B2 and HTM 03-01 provide detailed design guidance. In care homes, MVHR units must be specified with an appropriate filtration class to maintain air quality for residents with respiratory conditions.
CareHomeDesk gives you compliance checklists, maintenance logs, and contractor management tools built around exactly this kind of knowledge.