Installing sustainable ventilation requires knowledge of the building and of the technological options available, as Cliff Jones explains.
New emissions targets are largely about airtightness, specifically air permeability levels of less than 5m³/hr/m² at 50Pa. This is a significant reduction from the 10m³ /hr/m² at 50 Pa stipulated in Part L of the previous edition of the Building Regulations.

Furthermore, this is a level of air tightness that can, without adequate ventilation, cause alarming levels of condensation, contaminants and staleness and lead to mould growth, damp and discomfort.

Mechanical extract ventilation (MEV) and mechanical ventilation with heat recovery (MVHR) systems can help alleviate this.

These enable contractors working on airtight buildings to meet new and future energy efficiency targets while providing occupants with improved air quality, superior comfort and reduced fuel bills.

However, early planning and best practice in installation are vital to the performance of any ventilation system.


About the building

The key things to know about the building from the outset are:

• How it's being built - the type of floors, walls and ceilings the dwelling will have will affect where and how you plan your duct routes.

• The layout of the rooms - bends in ducting create resistance to airflow, which increases the amount of energy the system will consume. Assess the layout of the building and plan your duct routes as efficiently as possible.

• Whether there will be a system cooker hood - if so, create a duct route from the hood to the ventilator. As the hood will remove moisture from the cooker, the kitchen valve can be positioned directly over the sink. Conversely, in kitchens without a system cooker hood, the valve should sit midway between the two main sources of moisture, i.e. the sink and the hob.

• If there are any solid fuel stoves or open fires - incorporate any wood burning stoves into your calculations, but don't connect them to a heat recovery unit. Stoves over 5 kW need dedicated ducts to the outside with a hit and miss grille. Always check the specification of any stove with the supplier before planning a ventilation system around it.

The recommended standard for ducting - and the type used in SAP Appendix Q tests - is the 204 mm by 60 mm rigid plastic type. This offers low resistance and is easy to install, especially in restricted spaces.

Avoid flexible ducting. It crushes easily in tight spaces, is difficult to support and creates double the resistance of rigid plastic. Also, badly connected flexible ducting can result in leaks, poor performance and failure to comply with Building Regulations.

Keep ducting out of harm's way: airing cupboards and lofts provide positions safe from accidental damage. Similarly, stay on the right side of the Building Regulations Part L1A - Conservation of Fuel and Power in new dwellings by insulating ducting in unheated areas with at least 25 mm of material with a thermal conductivity of 0.04 W/m.K. Insulate ductwork onsite, once installed.

It is important to allow plenty of space for the ventilation unit. MEV units, which can weigh as little as 3.5 kg and measure little more than a 300 mm³, can be mounted structurally or be suspended using nylon cord or strapping. MVHR systems are heavier, so must be mounted structurally. In both cases, the unit must be accessible for maintenance and an isolator switch must be positioned within a meter of the installation.

Once the installation is complete, the airflow rate must be tested in accordance with a procedure approved by the Secretary of State and the results submitted to the local authority within five days.