Part F Building Regulations Ventilation requirements for indoor air quality

The Building Regulations 2010 Part F: Ventilation puts the onus on builders and developers to improve indoor air quality and ensure that buildings have an adequate supply of fresh air. But what does it have to say about roof ventilation?

In recent years there has, rightly, been a significant focus on improving energy efficiency across all buildings. Measures to improve insulation and air tightness help to reduce our reliance on fossil fuels and combat climate change. In relation to dwellings, these regulations aim to ensure that homes are affordable to heat and require minimal energy. These are all essential for maintaining the wellbeing of occupants, helping them stay warm in the winter, mitigating fuel poverty and preventing excess winter deaths.

However, the emphasis on insulation and air tightness has led to a different problem: lack of ventilation and poor air quality. That’s why Approved Document F: Ventilation 2021 edition was published.

Energy efficiency vs indoor air quality

To understand the importance of the Part F update and its requirements around ventilation, we need to recognise how the drive towards increased energy efficiency has (but doesn’t have to) negatively affect indoor air quality.

Here’s what happens: a new building is designed and constructed to meet stringent energy efficiency standards. Currently, in England, that means Approved Document L Conservation of Fuel and Power (2021 edition incorporating 2023 amendments), and there are similar requirements in Scotland, Wales and Northern Ireland. Soon, there will also be the Future Homes Standard (FHS), which will require even higher levels of energy efficiency in homes.

The energy efficiency standards and regulations require high levels of insulation, low U-values and airtightness. That air-tight building prevents the unintended movement of air in and out of the building, reducing heat loss and improving energy efficiency's. Unfortunately, without enough ventilation, that warm air becomes stagnant, and moisture builds up. Viruses, bacteria, dust, mould, VOCs and other air-borne problems compromise the purity of the air, condensation occurs, and the dwelling becomes uncomfortable and stuffy. If occupants want fresh air, the only option is to throw the windows and doors wide open, letting all that precious heat escape.

And what about in the warmer months? As climate change becomes increasingly noticeable, those insulated and air-tight homes become seemingly impossible to keep cool on those hot summer days, meaning that overheating is also becoming a problem. Approved Document O: Overheating also went into effect in 2022 and aims to mitigate overheating in residential buildings.

Adequate ventilation is critical in preventing the various problems relating to poor air quality, condensation and, to some degree, overheating. But the key is to find the right balance between keeping warmth in, while also ensuring a constant flow of fresh air. That’s where Part F comes in.

The requirements of Part F Building Regulations

Part F of the Building Regulations addresses the issues of ventilation and air quality, while the associated Approved Document F provides valuable guidance on achieving compliance. As with Approved Document L, Document F is applicable in England, and there are similar documents in Scotland, Wales and Northern Ireland.

Part F1 (1) of the Building Regulations states: “There shall be adequate means of ventilation provided for people in the building.” To achieve this a building needs to have ventilation that meets the following requirements:

• It extracts water vapour and indoor air pollutants from areas where they are produced in significant amounts – such as kitchens, bathrooms and utility rooms.
• It supplies a certain level of fresh air.
• It quickly dilutes indoor air pollutants and disperses water vapour where necessary.
• It minimises the entry of external air pollutants.
• It produces low noise levels, offers easy access for maintenance and protects from cold draughts.

F1 (2) provides guidance on commissioning and testing ventilation systems, while regulations 39, 42 and 44 offer additional guidance on supplying information to building owners, as well as air flow rate testing and commissioning.

Approved Document F applies to new-build properties, as well as those undergoing work or alterations such as re-roofing, extensions and loft conversions. It is supplied in two volumes: volume one covers dwellings while volume two covers buildings other than dwellings.

The ventilation strategy set out in Approved Document F relies on a combination of extract ventilation, purge ventilation and whole-building ventilation. The ventilation can be delivered through natural or mechanical means or a combination of both. Although the focus of the guidance is the ventilation of habitable rooms, we must remember that the roof is a critical element in building design. Adequate roof ventilation plays a huge role in the wellbeing of the building occupants, as well as the long-term integrity of the building.

The role of roofs in ventilation and Building Regulations Part F

While the updated Approved Document F doesn’t say much about roof ventilation, Approved Document C: Site preparation and resistance to contaminants and moisture does. ‘Section 6: Roofs’ of the document provides guidance and technical solutions for dealing with moisture from outside, as well as interstitial condensation and surface condensation. And, as we know, these issues can lead to damp and mould, reducing air quality for building occupants.

Approved Document C may say more about roof ventilation than Part F does, but it still takes a somewhat minimalist approach, with less than two pages covering the topic. What it does do, however, is refer to BS 5250.

BS 5250: 2021 Managing Moisture in Buildings was significantly revised in 2021 to provide extensive guidance on mitigating issues such as condensation in roofs. It also offers clarification on the criteria for the ventilation of cold pitched roofs, which had previously been confusing – and some would say controversial – to interpret and apply in practice. For a complete breakdown of BS 5250, and its recommendations for pitched roofs, please see our blog post: What is BS 5250, and how does it relate to pitched roof design? 

With Approved Document L and the Future Homes Standard encouraging energy efficiency and the adoption of low-carbon technologies such as solar panels, it’s important to consider how solar installations could affect roof ventilation – particularly when using integrated solar panels, which act as a roof covering. Section 7.2.26.3 of the NHBC Standards 2025 states that arrays of integrated solar panels should be treated as air impermeable unless the panel manufacturer can demonstrate otherwise. As a result, the roof should be ventilated according to the guidance set out for roofs with nonbreathable membranes – typically, this means a combination of eaves and ridge ventilation to ensure adequate airflow.

The Marley SolarTile® is designed to be installed on top of the tiling batten, along with a 70mm internal upstand, this creates a cavity beneath the solar panel, promoting airflow. 

Complete roof systems for compliance with Part F and other Building Regulations and requirements

It’s safe to say that with so many regulations and standards to consider, there’s a lot to keep track of, and achieving compliance can be tricky. This is especially true when it comes to roofs, as there are so many different elements that must work together to create a finished structure that is both weather-tight and well-ventilated.

The Marley Complete Roofing System simplifies the process from design through to installation, giving specifiers, developers and housebuilders a reliable, single-source solution for building pitched roofs that are compliant with all building regulations and standards, as well as attractive and dependable. Our system includes everything from the roof trusses up, including:

• Vapour permeable and non-breathable underlays
• JB Red BS5534 Roof battens BBA accredited
• Concrete or clay roof tiles
• Timber shingles and shakes
• Ridge ventilation systems
• Eaves ventilation systems
• Roof vents
• Marley SolarTile®
• Fire protection

All elements are designed for mechanical fixing in accordance with BS 5534:2014+A2:2018, the British Standard code of practice for slating and tiling for pitched roofs and vertical cladding, and our systems are provided with a 15-year guarantee for peace of mind.

For more advice, or to discuss how Marley’s solutions can support your next project in meeting ventilation requirements, please contact us.