Understanding Building Regulations Part F – indoor air quality

Building regulations ensure the health and safety of people in and around buildings by specifying the functional requirements for their design and construction. They outline what types of building projects are subject to the regulations and what procedures to follow and therefore affect everyone within the building service industry whether it be architects, specifiers, developers, landlords or building owners.

It is generally accepted that inadequate ventilation has costs in terms of the health of occupants and in damages to the building fabric.  Part F of the Building Regulations document is concerned with indoor air quality and primarily associated with, but not limited to, domestic dwellings.   According to the Secretary of State buildings comply with Part F: “when a ventilation system is provided that under normal conditions is capable of limiting the accumulation of moisture which could lead to mould growth and pollutants originating within a building which would otherwise become hazardous to the health of the people in the building”.

In simple terms it is about removing the accumulation of moisture and pollutants – “stale air” – from within a building and replacing it with fresh air from the outside.  Providing outside air to breath, and assisting in the dilution and removal of pollutants as well as a reduction in humidity and condensation creates a more pleasant environment and relief for asthma and allergy sufferers whilst protecting the building fabric from damage

The importance of a suitable extract ventilation system should not be underestimated as it is thought that a typical family of four can produce around 50 litres of moisture a day simply by showering, cooking, doing the laundry and even breathing.  The Government’s commitment to reducing energy consumption and carbon emissions requires buildings to be more airtight and energy efficient than ever before.  (Air tightness is now measurable and covered within Part L of the building regulations).  In response to these government initiatives houses have become even more insulated through for example, the installation of double glazing, wall to wall carpets, and loft insulation, and it becomes more important to make provision for the removal of this stale air and water vapour before it condenses and becomes a problem.

Part F also considers that ventilation be both controllable and energy efficient so that reasonable indoor air quality is maintained whilst avoiding a waste of energy. The controls can be either manual (i.e. operated by the occupant) or automatic where sensors detect the level of occupancy, water vapour or other pollutants and adjust the ventilation rate accordingly in order to avoid over- ventilation and so reduce energy consumption.   With respect to energy efficiency Part F states that “Consideration should be given to mitigation of ventilation energy use, where applicable, by employing heat recovery devices, efficient types of fan motor and / or energy saving control devices in the ventilation system.”

The regulations specify the rate at which ventilation should occur and are detailed in table 1.1a and 1.1b of the document.  For example the minimum intermittent extract rate in a kitchen is 60l/s or 30l/s if adjacent to the hob and 15l/s in a bathroom, with table 1.1b providing continuous ventilation rates between 13 and 29l/s depending on number of bedrooms and occupancy levels.

There are a number of ways the required performance standards for ventilation can be met.  Suitable extract systems may be continuous or intermittent, localised in the rooms where most water vapour and or pollutants are released or whole building systems.  Typically whole building ventilation provides continuous air exchange whilst intermittent (purge) ventilation is required when there are high concentrations of water vapour or pollutants. The 4 suggested ventilation systems which have varying levels of control and energy efficiency capability and part F provides guidance on are:

  • Background ventilators and intermittent extract fans
  • Passive stack ventilation
  • Continuous mechanical extract, and
  • Continuous mechanical supply and extract with heat recovery

Each of these has their advantages and disadvantages and the decision regarding which one to implement will be based on a range of criteria.  The choice to some extent will be dependent upon whether it is a new build or existing build – this is explored more in the Draft 2010 Part F Building Regulations.  The preferred ventilation solution in new build properties is for a whole house solution coupled with heat source recovery technology.  However in existing housing stock, heat source recovery is difficult to implement partly because of their infrastructure but also because radiator sources would need to be 2-3 times larger to create the same level of warmth.

Another option is to use mechanical heat recovery ventilators which retain heat from extracted air and return pre-warmed fresh air.  But it is important to be aware that a high percentage of heat recovery (circa 80%) is claimed by some manufacturers as this is based on a high temperature differential between internal and external air.  In fact as these systems are designed to run continuously over the period of a year, the average heat recovery is likely to be closer to 40% due to the smaller heat differentials.  When using these types of systems, consideration must also be given to contamination issues because air is extracted continuously over a high surface area heat recovery membrane and therefore filters are required which would require regular maintenance to ensure the efficiency of the system.

Typically passive vents on their own are not considered sufficient and most certainly intermittent solutions are still valid. Where continuous extract ventilation is implemented then this will need to take into account the fire protection requirements associated with ducted systems.

In short it would seem that for existing properties the most efficient current method for ventilation is a smart controlled intermittent extractor system (sometimes used in conjunction with a continuous solution dependent upon the condition of the dwelling).   RHL offer a range of products across these areas and based on our years of expertise can recommend the right solution for you.

To view the Building regulations Part F in full please visit the Planning Portal website. If you have any queries or some guidance please drop us an email or call us on 0845 124 6066.