Keeping a healthy level of airflow in new homes

As new homes are required to be ever more energy efficient, Paul Croughan, national key account manager for EnviroVent, looks at how innovation is helping housebuilders to achieve the right balance between air tightness and adequate ventilation

It is almost nine years since Part F continuous ventilation became part of building regulations. Increasing requirements for air tightness and energy efficiency meant that ventilation guidance was essential in order to prevent dwellings becoming humid which could lead to condensation, damp and poor indoor air quality.

Updates to Part L1A in 2010 required a reduction in carbon emissions by 25 per cent compared to 2006 regulations using a variety of methods, including reducing the heat loss and improving the building fabric and services. Building regulations Part F updates introduced at this time meant that ventilation rates needed to be calculated by measuring how much a dwelling leaked air. Air leakage from a dwelling is measured through its surface area – in m3h of air and m2 of building area. Any property which was found to be leaking more than 5m3h/m2 needed no additional background ventilation requirements. For properties that were found to be below leakage of 5m3h/mw, there was a requirement to increase background ventilation.

It was at this time that ventilation equipment became part of the SAP calculation and Dwelling Emission Rates (DERs) were set to deliver the improvement over the previous regulations. The SAP Appendix Q website was also incorporated into the SAP software model and also meant that individual product performance could be assessed and taken into account as part of the property’s SAP calculations. As a result, housebuilders began specifying ventilation systems to reduce humidity levels in dwellings and improve their DERs.

Building regulations updates in 2010 placed greater importance on the effective design, installation and operation of ventilation systems, along with the introduction of the Domestic Ventilation Compliance Guide and BPEC Accreditation. These revisions to Part L and Part F have paved the way towards ventilation becoming more of a ‘controlled’ service, which focused on energy efficiency and correct installation to ensure that what is specified is fitted and works correctly. The aim of these updates was to maximise carbon reduction through correctly specified systems that are installed by competent engineers, therefore minimising energy losses.

The guidance also stated that instruction must be given to the homeowner as to how a ventilation system should be operated effectively.

Harmonising the requirements

Understandably concerns were raised by housebuilders about how to harmonise the apparently conflicting pieces of legislation of Part L and Part F – one requiring a more airtight building for greater energy efficiency and the other stipulating a need for greater airflow.

The options soon became apparent. To achieve Part F requirements, Positive Input Ventilation (PIV) has proven to be one of the most effective and least expensive options. PIV is the second most popular method of ventilating homes, after intermittent extract fans. PIV systems work by drawing in fresh, filtered, clean air from outside and gently ventilating the home from a central position – usually in the loft, above a landing in a house – or a central hallway in a flat or bungalow. It works by diluting moisture laden air, displacing it and replacing it to control humidity levels between 45 and 60 per cent.

The requirement for new dwellings to improve performance by an extra seven per cent to meet the 2013 edition of Part L1A (energy efficiency for new building), further reinforced the prominence of PIV, which may give savings on the DER of around five per cent. Where housebuilders are looking to achieve the higher code levels (4, 5 and 6), Mechanical Ventilation with Heat Recovery (MVHR) is often used as an option in order to gain points and lower their DER. A high performing MVHR system through SAP (Standard Assessment Procedure) may give a benefit in the best case of around seven – eight per cent lowering of the DER. Alternatively MVHR may be used if there was an acoustic condition that prohibited the opening of windows.

PIV however is much more affordable than Mechanical Ventilation with Heat Recovery (MVHR), plus it is easier to install. In some cases, PIV can also operate to draw cooler air directly from the atmosphere in warmer months (rather than the loft space). This means that it can offer all year round ventilation along with summer cooling.

Lowering the DER

Ventilation these days needs to be viewed very much as a service as well as a system and as such each installation and system gives a different reward through SAP, depending of course which methodology is used by way of lowering the DER by a certain percentage. It therefore offers the opportunity of not only meeting Part F, but also the opportunity of lowering the properties DER, thereby, as the saying goes, “Killing two birds with one stone”.

The online table – which can be viewed by visiting and entering the reference number 57361 – looks at two separate air permeabilities, comparing four house types built to current building regulations. What this shows is that using intermittent fans (System 1) means you may lower by 1.5 per cent the property’s DER. The cost of ventilation systems to meet Part F may cost as much as £500 per plot to use this methodology, given it also has very little impact through SAP by lowering the DER.
System 1 covers ventilation from each wet room by a locally situated intermittent extract fan. However, the cross ventilation requirement in meeting Part F does not have very much influence in reducing the DER, so has very limited value to housebuilders.

Housebuilders also need to take into account the cost of installing an extract fan in each room, in addition to the requirements to fit window trickle vents to satisfy Part F – usually between £7-15. If you were to look at a standard three- bedroom property, it could feasibly require a spend of £240 on window vents alone. This figure could be multiplied if there were acoustic issues.

The issue with an intermittent extract fan is that they can be perceived as noisy and may prove expensive at around £100 per room and also it is the case that a large proportion of these fans do not meet the requirements of the Domestic Building Services Compliance Guide.

System 2 (Passive Stack Ventilation) similarly gives little benefit to housebuilders in lowering the properties DER, although like System 1, it is energy neutral in SAP. System 3 covers Continuous Mechanical Extract Ventilation (MEV and DMEV) which may result in around a two per cent lowering of the DER, so sees a minor difference overall. System 4 is MVHR and what we have classed as System 5 is PIV, if accredited with a BBA certificate.

With MVHR, the cost could very well be around the £2,000-£3,000 mark to install in an average dwelling, and may offer a reduction of up to seven to eight per cent in SAP. PIV, on the other hand, can often be installed for around a quarter of that cost, which may provide a lowering of up to five to six per cent on the DER.

In addition, like MVHR, you don’t need background ventilation (window vents) if the air permeability is greater than three air changes per hour, along with negating the requirement for any extract fans – providing all wet rooms are off the central hallway and landing with openable windows.

When you compare PIV to other methods of meeting Part F, it is clearly a cost-effective way forward, given the benefit of not only meeting Part F along with the increased percentage in lowering the properties DER. In addition, given the requirements now for all installer’s of ventilation systems to be BPEC certified, with all flow results of all systems required now to be handed to Building Control, this is a much easier process with PIV. Housebuilders are increasingly taking the opportunity to use PIV or Multiple Input Ventilation (MIV) on a standard build, but to incorporate it with Air Source (PIVAS/ MIVAS), functionally or automatically alternating the source of air from either the loft space or directly from the atmosphere where there may be an acoustic condition to discharge. In the case of PIV the benefit is automatically calculated by SAP without the requirement of having to refer to the SAP Appendix Q database, which is used to validate individual product performances for systems 3 and 4, thereby allowing housebuilders to assess various different options and gain an understanding of how each accrues them points by way of lowering the DER.

In the future, on the road to zero carbon, it is likely that PIV will continue its rise in prominence as housebuilders recognise how it offers them a cost-effective option to reduce their DERs.