Ventilation

Correct ventilation is a vital element of any retrofit. Controlled ventilation helps to create a healthy internal environment whilst maintaining good energy efficiency. The building regulations dictate the levels of ventilation required in buildings. This can be found in the Approved Document Part F.

There are different ventilation strategies for properties, the choice of which has implications to other decisions like windows, heating type and service ducting, The main options are:

• Intermittent Extract Ventilation (IEV)

• Mechanical Extract Ventilation (de-centralised dMEV, or centralised cMEV)

• Demand Controlled Ventilation (DCV)

• Mechanical Heat Recovery Ventilation (MVHR)

• Positive Input Ventilation (PIV)

• Passive Stack Ventilation (PSV)

IEV is the most common and relies on extractors being switched on in wet rooms (kitchens, bathrooms etc). These tend to be controlled by the light switches or pull cords.

MEV are the common substitution for IEV and these run constantly in ‘trickle mode’ and then are controlled via relative humidity (RH) sensors. De-centralised systems run independent extractors in each wet room, whilst Centralised system have one fan and a series of vents and ducts that connect the wet rooms together.

DCV is less common, but probably the most cost effective as it balances the flow of incoming fresh air and extraction rates of moist stale air. It does this by monitoring key factors like relative humidity, temperature and CO2 levels and adjusting the ventilation system accordingly.

MVHR is used in high efficiency modern housing and works in a similar manner to DCV, but this uses a centralised heat recovery unit to transfer heat from the outgoing air to the incoming fresh air. These systems are expensive, require ducting and maintenance, but do save energy by the heat exchange process.

PIV is where fresh air (typically from the loft) is pumped into a property. This creates a positive pressure that then pushes stale air out of vents (typically trickle vents in windows). PIV is a pretty blunt instrument but have been used extensively in houses suffering from damp.

PSV or Natural Ventilation uses the natural differences in pressure between the outside and inside of a house to drive the ventilation. Whilst this does not require any energy it is not a well-controlled system of ventilation for properties.

Getting the strategy right for each property is vitally important. Getting the principles in place and a working system is a corner stone of modern retrofit.