Fan Pressurisation Test

A fan or series of fans is connected to an external doorway which pressurises / de-pressurises the building. The test establishes the effectiveness of a building’s airtightness through measuring the extent to which air is lost through leaks in the building, in units of air changes per / hour at a test pressure of 50 pa. The current regulations require a maximum of 10 whereas the more demanding Passivhaus standard requires 0.6.


Indicates the risk of surface condensation, the lower the value, the greater the risk. The risk depends mainly on the surface energy balance and on the moisture content of the ambient air. Part C of the Building Regulations determines the minimum f-factor in a number of applications. 

Filter drain

A filter drain is a device that has a volume of permeable material below ground to store surface water. ‘Runoff’ flows to this storage area via a permeable surface.


The act of removing sediment or other particles from a fluid by passing it through a filter. Water filtration can be achieved in several ways including using Carbon filters, Ultraviolet (UV) filters, distillation, sand filters and ‘reverse osmosis’.

Flood routing

Refers to designing to channel water over land in a controlled fashion in the event of flooding and when the capacity of a drainage system has been exceeded.

Flow control device

Is one which controls the rate at which water is discharged to a surface water drain or watercourse.

Fly ash (PFA - Pulverised Fuel Ash)

Known as Pulverised Fuel Ash (PFA) in the UK, is a by-product from burning coal for the production of electricity. PFA is used as a cement substitute in the manufacture of concrete.

Fossil fuel

Coal, oil and gas.

Fresh water aquatic ecotoxicity

The impact of toxic substances emitted to freshwater aquatic ecosystems.